BSI Standards Publication Drain and sewe

BS EN 752:2017
BSI Standards Publication
Drain and sewer systems outside buildings
- Sewer system management
BRITISH STANDARD
BS EN 752:2017
National foreword
This British Standard is the UK implementation of EN 752:2017.
It supersedes BS EN 752:2008, which is withdrawn.
The UK committee draws users' attention to National Annex NA,
which provides further guidance to assist users in the application of
EN 752:2017 in the UK.
The UK participation in its preparation was entrusted to Technical
Committee B/505/22.
A list of organizations represented on this committee can be obtained on
request to its secretary.
This publication does not purport to include all the necessary provisions
of a contract. Users are responsible for its correct application.
© The British Standards Institution 2018
Published by BSI Standards Limited 2018
ISBN 978 0 580 86864 1
ICS 23.040.05; 93.030
Compliance with a British Standard cannot confer immunity from
legal obligations.
This British Standard was published under the authority of the
Standards Policy and Strategy Committee on 31 March 2018.
Amendments/corrigenda issued since publication
Date
Text affected
BS EN 752:2017
EUROPEAN STANDARD
EN 752
NORME EUROPÉENNE
EUROPÄ)SC(E NORM
)CS
.
.
;
April
.
Supersedes EN
:
English Version
Drain and sewer systems outside buildings - Sewer system
management
Réseaux d'évacuation et d'assainissement à l'extérieur
des bâtiments - Gestion du réseau d'assainissement
This European Standard was approved by CEN on
February
.
Entwässerungssysteme außerhalb von Gebäuden Kanalmanagement
CEN members are bound to comply with the CEN/CENELEC )nternal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions English, French, German . A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, (ungary, )celand, )reland, )taly, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMM)TTEE FOR STANDARD)ZAT)ON
COM)TÉ EUROPÉEN DE NORMAL)SAT)ON
EUROPÄ)SC(ES KOM)TEE FÜR NORMUNG
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
©
CEN
All rights of exploitation in any form and by any means reserved
worldwide for CEN national Members.
Ref. No. EN
:
E
BS EN 752:2017
EN 752:2017 (E)
Contents
Page
European foreword....................................................................................................................................................... 6
Introduction .................................................................................................................................................................... 8
1
Scope ................................................................................................................................................................. 10
2
Normative references ................................................................................................................................. 10
3
Terms and definitions ................................................................................................................................ 11
4
4.1
4.2
4.3
4.4
4.5
Objectives........................................................................................................................................................ 14
General ............................................................................................................................................................. 14
Public health and safety ............................................................................................................................. 15
Occupational health and safety ............................................................................................................... 15
Environmental protection ........................................................................................................................ 15
Sustainable development .......................................................................................................................... 16
5
5.1
5.1.1
5.1.2
5.1.3
5.1.4
5.1.5
5.1.6
5.1.7
5.1.8
5.1.9
5.1.10
5.1.11
5.1.12
5.1.13
5.1.14
5.2
5.2.1
5.2.2
5.2.3
5.2.4
5.2.5
5.3
5.3.1
5.3.2
5.3.3
5.3.4
5.3.5
Requirements ................................................................................................................................................ 16
Functional requirements........................................................................................................................... 16
Introduction ................................................................................................................................................... 16
Protection from sewer flooding .............................................................................................................. 18
Maintainability .............................................................................................................................................. 18
Protection of surface receiving water bodies .................................................................................... 18
Protection of groundwater ....................................................................................................................... 19
Prevention of odours and toxic, explosive and corrosive gases ................................................. 19
Prevention of noise and vibration ......................................................................................................... 19
Structural integrity and design working life ...................................................................................... 19
Watertightness .............................................................................................................................................. 19
Sustainable use of products and materials ......................................................................................... 19
Sustainable use of energy .......................................................................................................................... 19
Maintaining the flow ................................................................................................................................... 19
Not endangering adjacent structures and utility services ............................................................ 19
Inputs quality................................................................................................................................................. 19
Determination of performance requirements for the drain and sewer system ................... 20
Introduction ................................................................................................................................................... 20
Environmental performance requirements ....................................................................................... 22
Hydraulic performance requirements ................................................................................................. 23
Structural requirements............................................................................................................................ 24
Operational requirements ........................................................................................................................ 24
Design criteria ............................................................................................................................................... 24
Introduction ................................................................................................................................................... 24
Hydraulic design criteria........................................................................................................................... 25
Environmental design criteria ................................................................................................................ 27
Structural design criteria .......................................................................................................................... 28
Operational criteria..................................................................................................................................... 29
6
6.1
6.2
6.2.1
6.2.2
Integrated sewer system management ................................................................................................ 29
Introduction ................................................................................................................................................... 29
Investigation .................................................................................................................................................. 31
Introduction ................................................................................................................................................... 31
Purpose of investigation ............................................................................................................................ 33
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6.2.3
6.2.4
6.2.5
6.2.6
6.2.7
6.2.8
6.2.9
6.2.10
6.3
6.3.1
6.3.2
6.3.3
6.3.4
6.3.5
6.3.6
6.3.7
6.3.8
6.4
6.4.1
6.4.2
6.4.3
6.4.4
6.5
6.5.1
6.5.2
6.5.3
6.5.4
6.5.5
6.5.6
Review of performance information ..................................................................................................... 33
Determine the scope of the investigation ............................................................................................ 33
Review existing information .................................................................................................................... 33
Inventory update .......................................................................................................................................... 33
Hydraulic investigation .............................................................................................................................. 34
Environmental investigation .................................................................................................................... 34
Structural investigation ............................................................................................................................. 34
Operational investigation .......................................................................................................................... 34
Assessment...................................................................................................................................................... 35
Introduction.................................................................................................................................................... 35
Assessment of the hydraulic performance .......................................................................................... 35
Assessment of environmental impact ................................................................................................... 36
Assess structural condition....................................................................................................................... 36
Assess operational performance ............................................................................................................ 36
Compare with performance requirements ......................................................................................... 36
Identify unacceptable impacts ................................................................................................................. 36
Identify causes of performance deficiencies ...................................................................................... 36
Planning ........................................................................................................................................................... 37
Introduction.................................................................................................................................................... 37
Develop integrated solutions ................................................................................................................... 37
Assess solutions ............................................................................................................................................ 38
Prepare action plans.................................................................................................................................... 39
Implementation............................................................................................................................................. 43
Introduction.................................................................................................................................................... 43
Development of work programme ......................................................................................................... 44
Development of work specification ....................................................................................................... 45
Carrying out work......................................................................................................................................... 45
Measuring conformity................................................................................................................................. 45
Review performance requirements and update plan ..................................................................... 45
7
Health and safety .......................................................................................................................................... 45
8
8.1
8.2
8.3
8.3.1
8.3.2
8.4
8.4.1
8.4.2
8.4.3
8.4.4
8.5
8.5.1
8.5.2
8.5.3
8.5.4
8.5.5
8.5.6
8.5.7
8.6
8.6.1
8.6.2
Design ............................................................................................................................................................... 47
General ............................................................................................................................................................. 47
Types of system ............................................................................................................................................. 48
Physical layout ............................................................................................................................................... 49
Preliminary investigations........................................................................................................................ 49
Layout and profile ........................................................................................................................................ 49
Hydraulic design ........................................................................................................................................... 50
General ............................................................................................................................................................. 50
Foul drains and sewers ............................................................................................................................... 50
Surface water drain and sewer systems ............................................................................................... 50
Combined drain and sewer systems ...................................................................................................... 51
Environmental considerations ................................................................................................................ 52
General ............................................................................................................................................................. 52
Protection of surface receiving water bodies..................................................................................... 53
Protection of groundwater ........................................................................................................................ 53
Prevention of septicity ................................................................................................................................ 53
Combined sewer overflows and surface water treatment............................................................. 54
Surface water outfalls ................................................................................................................................. 55
Emergency overflows .................................................................................................................................. 55
Structural design........................................................................................................................................... 55
Introduction.................................................................................................................................................... 55
Structural design of pipelines .................................................................................................................. 56
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8.6.3
8.6.4
8.7
8.7.1
8.7.2
8.7.3
8.7.4
Structural design of other components................................................................................................ 56
Materials selection....................................................................................................................................... 56
Operational considerations ...................................................................................................................... 57
General ............................................................................................................................................................. 57
Control of inputs ........................................................................................................................................... 57
Self-cleansing conditions ........................................................................................................................... 57
Access to drains and sewers ..................................................................................................................... 58
9
9.1
9.2
9.3
9.4
Construction................................................................................................................................................... 58
General ............................................................................................................................................................. 58
Pipelines .......................................................................................................................................................... 58
Ancillaries ....................................................................................................................................................... 58
Testing.............................................................................................................................................................. 59
10
10.1
10.2
10.3
10.4
10.5
10.6
Operation and maintenance..................................................................................................................... 59
Introduction ................................................................................................................................................... 59
Monitoring ...................................................................................................................................................... 60
Data requirements....................................................................................................................................... 61
Investigation and analysis of operational problems ....................................................................... 61
Dealing with major incidents ................................................................................................................... 62
Techniques for operation and maintenance of components........................................................ 62
11
Qualifications and training ....................................................................................................................... 63
12
Sources of additional information ......................................................................................................... 63
Annex A (informative) Sources of additional information ........................................................................... 64
A.1
National Standards Bodies........................................................................................................................ 64
A.2
Austria .............................................................................................................................................................. 64
A.2.1 Regulatory Bodies ........................................................................................................................................ 64
A.2.2 Other organizations .................................................................................................................................... 64
A.3
Denmark .......................................................................................................................................................... 64
A.3.1 Regulatory Bodies ........................................................................................................................................ 64
A.3.2 Other organizations .................................................................................................................................... 65
A.4
Finland ............................................................................................................................................................. 66
A.4.1 Regulatory Bodies ........................................................................................................................................ 66
A.4.2 Other organizations .................................................................................................................................... 66
A.5
France ............................................................................................................................................................... 66
A.5.1 Regulatory Bodies ........................................................................................................................................ 66
A.5.2 Other organizations .................................................................................................................................... 67
A.6
Germany .......................................................................................................................................................... 67
A.6.1 Regulatory Bodies ........................................................................................................................................ 67
A.6.2 Other organizations .................................................................................................................................... 68
A.7
Ireland .............................................................................................................................................................. 68
A.7.1 Regulatory Bodies ........................................................................................................................................ 68
A.8
Italy.................................................................................................................................................................... 68
A.8.1 Regulatory Bodies ........................................................................................................................................ 68
A.8.2 Other organizations .................................................................................................................................... 68
A.9
The Netherlands ........................................................................................................................................... 69
A.9.1 Regulatory Bodies ........................................................................................................................................ 69
A.9.2 Other organizations .................................................................................................................................... 69
A.10 Norway ............................................................................................................................................................. 70
A.10.1 Regulatory Bodies ........................................................................................................................................ 70
A.10.2 Other organizations .................................................................................................................................... 70
A.11 Portugal ........................................................................................................................................................... 70
A.11.1 Regulatory Bodies ........................................................................................................................................ 70
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A.11.2
A.12
A.12.1
A.12.2
A.13
A.13.1
A.13.2
A.14
A.14.1
A.14.2
Other organizations ..................................................................................................................................... 70
Sweden.............................................................................................................................................................. 71
Regulatory Bodies ........................................................................................................................................ 71
Other organizations ..................................................................................................................................... 71
Switzerland ..................................................................................................................................................... 71
Regulatory Bodies ........................................................................................................................................ 71
Other organizations ..................................................................................................................................... 72
United Kingdom ............................................................................................................................................ 72
Regulatory Bodies ........................................................................................................................................ 72
Other organizations ..................................................................................................................................... 74
Annex B (informative) Rehabilitation approaches.......................................................................................... 75
Annex C (informative) Operation and maintenance techniques ................................................................ 77
C.1
Pipelines .......................................................................................................................................................... 77
C.1.1 General ............................................................................................................................................................. 77
C.1.2 Functional problems ................................................................................................................................... 77
C.1.3 Structural problems..................................................................................................................................... 77
C.2
Manholes and inspection chambers ...................................................................................................... 78
C.3
Combined sewer overflows ....................................................................................................................... 78
C.4
Detention tanks ............................................................................................................................................. 79
C.5
Separators, settling chambers and gullies........................................................................................... 79
C.6
Pumping installations ................................................................................................................................. 79
C.7
Inverted siphons ........................................................................................................................................... 79
C.8
Pest control ..................................................................................................................................................... 80
C.9
Making connections to existing drains and sewers.......................................................................... 80
C.10 Control of disused drains and sewers ................................................................................................... 80
C.11 Control of building over or adjacent to sewers.................................................................................. 80
Annex D (normative) Physical layout of the system ....................................................................................... 82
D.1
Preliminary investigations........................................................................................................................ 82
D.1.1 General ............................................................................................................................................................. 82
D.1.2 Topography..................................................................................................................................................... 82
D.1.3 Geotechnical survey..................................................................................................................................... 82
D.1.4 Groundwater .................................................................................................................................................. 83
D.1.5 Existing drainage services ......................................................................................................................... 83
D.1.6 Other existing utility services .................................................................................................................. 83
D.2
Layout and profile ........................................................................................................................................ 83
D.2.1 Introduction.................................................................................................................................................... 83
D.2.2 Layout ............................................................................................................................................................... 83
D.2.3 Accessibility .................................................................................................................................................... 84
D.2.4 Depth ................................................................................................................................................................. 85
D.2.5 Need for pumping ......................................................................................................................................... 85
D.2.6 Pumping installations ................................................................................................................................. 86
D.2.7 Drains and sewers near water abstraction areas ............................................................................. 86
D.3
Access to drains and sewers ..................................................................................................................... 86
Bibliography ................................................................................................................................................................. 88
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EN 752:2017 (E)
European foreword
This document (EN 752:2017) has been prepared by Technical Committee CEN/TC 165 “Waste water
engineering”, the secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by October 2017, and conflicting national standards shall
be withdrawn at the latest by October 2017.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent
rights.
This document supersedes EN 752:2008.
The principal changes in this revision are as follows:
a) the terminology has been aligned with EN 16323:2014;
b) all the text relating to the determination of performance requirements and design criteria has been
moved to Clause 5 as these are essentially part of this policy activity and not the design process;
c) Clause 5 has been updated to include references to show the links to the EU Water Framework
Directive (2000/60/EC) together with its daughter directives and the EU Floods Directive
(2007/60/EC);
d) Clause 6 has been updated to align with the latest revision of EN 13508-1 and some text that is
duplicated in EN 13508-1 has been deleted;
e) Clause 6 has been updated to align with EN 14654-2;
f)
contingency and emergency planning has been moved from the former Annex C to Clause 6 as it is
part of the integrated sewer system planning process;
g) some additional text from the former Annex D has been added to Clause 7, this has allowed the
former Annex D to be deleted as it largely duplicated Clause 7;
h) additional requirements have been added to Clause 8 on resilience of drain and sewer systems;
i)
all physical design requirements in the former Clause 9 have been moved to a new Annex D;
j)
all the hydraulic design requirements in the former Clause 9 have been moved to prEN 16933-2 to
provide a more coherent narrative;
k) former Clause 11 (now Clause 10) has been updated to include requirements on dealing with major
incidents;
l)
the text of the former Clause 12 has been integrated into 6.5.5, 10.4 (now 9.4) or 11.2 (now 10.2) as
appropriate;
m) the text from the former Annex A has been incorporated either in Clause 5 or Clause 7;
n) a new Annex B on rehabilitation approaches has been added;
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EN 752:2017 (E)
o) the text from the former Annex C has been incorporated into Clause 6 (for planning activities),
Clause 11 or the new Annex C;
p) the former Annex F has been deleted as this is superseded by the prEN 16932 series.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
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Introduction
Drain and sewer systems are part of the overall wastewater system that provides a service to the
community. This can be briefly described as:
— removal of wastewater from premises for public health and hygienic reasons;
— prevention of flooding in urbanized areas;
— protection of the environment.
The overall wastewater system has four successive functions:
— collection;
— transport;
— treatment;
— discharge.
Wastewater can, if necessary after treatment, be discharged to the environment or reused.
Collection and transport of wastewater is provided by drain and sewer systems.
Drain and sewer systems were installed because there was a need to remove the polluted water to
prevent diseases.
Traditionally, drain and sewer systems were constructed to collect and transport all types of
wastewater together irrespective of the initial source. This led to difficulties in handling the peak flows
in times of heavy rainfall and to the introduction of combined sewer overflows, which discharged
polluted water to surface receiving water bodies.
It was later recognized that separate systems, where foul wastewater was kept separate from runoff
derived from surface water, would be an improvement over such combined systems.
Although many drain and sewer systems started out as combined systems there are strong arguments
for considering the separation of foul wastewater and surface water. The pollutant effects are not the
same and the separation of effluents allows for the different treatment for each element of wastewater,
providing more environmentally friendly solutions.
This concept is included in the approach of integrated sewer management.
This European Standard provides a framework for the design, construction, maintenance operation and
rehabilitation of drain and sewer systems outside buildings. This is illustrated in the upper part of the
diagram in Figure 1. This European Standard is supported by more detailed standards for the
investigation, design, construction, organization and control of drain and sewer systems.
Investigation and assessment standards include:
— EN 13508 (all parts), Investigation and assessment of drain and sewer systems outside buildings.
Design and construction standards include:
— prEN 16932 (all parts), Drain and sewer systems outside buildings — Pumping systems,
— prEN 16933-2, Drain and sewer systems outside buildings — Design — Part 2: Hydraulic design,
— EN 1295 (all parts), Structural design of buried pipelines under various conditions of loading,
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EN 752:2017 (E)
— EN 1610, Construction and testing of drains and sewers,
— EN 12889, Trenchless construction and testing of drains and sewers,
— EN 15885, Classification and characteristics of techniques for renovation and repair of drains and
sewers.
Management and control standards include:
— EN 14654 (all parts), Management and control of operational activities in drain and sewer systems
outside buildings.
To support these detailed standards information comes from specifications produced by individual
organizations for their own use. Product standards should also take into account the functional
requirements in this European Standard through EN 476, EN 13380 and EN 14457.
Figure 1 — Pyramid diagram
The EU Public Procurement Directive (2014/25/EU) governs the procurement of goods and services by
public authorities. This includes procurement in relation to drain and sewer systems.
The Construction Products Regulation (No 305/2011) provides for uniform assessment methods of the
performance of construction products which are set out in harmonized European Standards.
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EN 752:2017 (E)
1 Scope
This European Standard specifies the objectives for drain and sewer systems outside buildings. It
specifies the functional requirements for achieving these objectives and the principles for strategic and
policy activities relating to planning, design, installation, operation, maintenance and rehabilitation.
It is applicable to drain and sewer systems from the point where wastewater leaves a building, roof
drainage system, or paved area, to the point where it is discharged into a wastewater treatment plant or
receiving water body.
Drains and sewers below buildings are included provided that they do not form part of the drainage
system for the building.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
EN 476, General requirements for components used in drains and sewers
EN 858-1, Separator systems for light liquids (e.g. oil and petrol) — Part 1: Principles of product design,
performance and testing, marking and quality control
EN 858-2, Separator systems for light liquids (e.g. oil and petrol) — Part 2: Selection of nominal size,
installation, operation and maintenance
EN 1295-1, Structural design of buried pipelines under various conditions of loading — Part 1: General
requirements
EN 1610, Construction and testing of drains and sewers
EN 1825-1, Grease separators — Part 1: Principles of design, performance and testing, marking and
quality control
EN 1825-2, Grease separators — Part 2: Selection of nominal size, installation, operation and
maintenance
EN 1990:2002, Eurocode — Basis of structural design
EN 12889, Trenchless construction and testing of drains and sewers
EN 13508-1, Investigation and assessment of drain and sewer systems outside buildings — Part 1: General
Requirements
EN 14654-1, Management and control of operational activities in drain and sewer systems outside
buildings — Part 1: Cleaning
EN 16323:2014, Glossary of wastewater engineering terms
prEN 16932 (all parts), Drain and sewer systems outside buildings — Pumping systems
prEN 16933-2, Drain and sewer systems outside buildings — Design — Part 2: Hydraulic design
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3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 16323:2014 and the following
apply.
Note 1 to entry: Certain key definitions from EN 16323:2014 have been repeated below for clarity. The
following additional terms used in this European Standard are defined in EN 16323:2014:
aerobic,
anaerobic,
backdrop manhole,
biochemical oxygen demand,
catchment area,
collection tank,
combined sewer overflow,
combined system,
confined space,
dam board,
detention tank,
domestic wastewater,
drain,
dry weather flow,
exfiltration,
extraneous flow,
foul wastewater,
gradient,
gravity system,
hydro-biological stress,
industrial wastewater,
infiltration (see Figure 2),
inspection chamber,
inverted syphon,
jetting,
maintenance,
manhole,
non-domestic wastewater
outfall,
pumping station,
ramp manhole,
receiving water body,
rehabilitation,
relevant authority,
renovation, repair,
replacement,
retention period,
rising main,
rodding,
runoff coefficient,
self-cleansing,
self-purifying capacity,
separate system,
septic wastewater,
sewer, sewer system,
surcharge,
tank sewer,
time of concentration,
time of flow,
wastewater,
wastewater treatment plant,
winching.
3.1
backwater level
elevation of the surface of the wastewater predicted or occurring in a drain and sewer system due to the
hydraulic conditions downstream
3.2
design working life
assumed period for which a structure or part of it is to be used for its intended purpose with anticipated
repair and maintenance but without renovation or replacement being necessary
[SOURCE: EN 1990:2002, modified to provide consistency with the terminology in EN 16323]
3.3
expected frequency
average rate of occurrence of an event
Note 1 to entry:
The expected frequency can be expressed as a return period (once in T years) or a probability
of occurrence in any one year (1/T) (see return period 3.11).
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3.4
flooding
condition where water overflows onto a surface or enters a building where it is not intended
3.5
flushing
use of a temporary substantially increased flow to facilitate removal of obstructions or sediments from
drains or sewers
3.6
integrated water policies
co-ordinated policies for the management of all bodies of water within a river basin including urban
drainage systems within it
3.7
operations
actions taken in the course of normal functioning of drain and sewer systems
EXAMPLE
Monitoring and regulation or diversion of wastewater.
3.8
pumping installation
pumping station together with any associated rising main(s)
3.9
rainfall intensity
depth of rain falling in unit time, or volume of rain falling in unit time per unit area
3.10
rainwater
water arising from atmospheric precipitation, which has not yet collected matter from the surface
Note 1 to entry:
See Figure 2.
[SOURCE: EN 16323:2014, 2.1.1.1]
3.11
return period
expression of the expected frequency of an event expressed as the average recurrence interval between
the events equalling or exceeding a specified magnitude (see expected frequency 3.3)
Note 1 to entry: The probability that an event of a certain return period being exceeded in any one year period
is the inverse of that return period measured in years.
3.12
runoff
water from precipitation that flows off a surface to reach a drain, sewer or receiving water
Note 1 to entry:
See Figure 2.
[SOURCE: EN 16323:2014, 2.1.1.2]
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EN 752:2017 (E)
3.13
sewer flooding
condition where wastewater escapes from or cannot enter a drain and sewer system and either lies on
the surface or enters buildings
3.14
structural condition
state of a drain and sewer in matters relating to the integrity of its fabric
3.15
surface receiving water body
receiving water body that is on the surface of the ground (e.g. river, lake or sea)
Note 1 to entry:
See Figure 2.
[SOURCE: EN 16323:2014, 2.1.3.7]
3.16
surface water
water from precipitation, which has not seeped into the ground and is discharged to the drain or sewer
system directly from the ground or from exterior building surfaces
Note 1 to entry:
See Figure 2.
[SOURCE: EN 16323:2014, 2.1.1.3]
3.17
urban drainage system
infrastructure for the management of wastewater and runoff in the built environment
3.18
drainage
<built environment> group of technologies techniques and actions to achieve satisfactory hygiene and
public health relating to wastewater, including both foul wastewater and surface water
3.19
wastewater
water composed of any combination of water discharged from domestic, industrial or commercial
premises, surface run-off and accidentally any sewer infiltration water
[SOURCE: EN 16323:2014, 2.3.10.65]
3.20
whole life cost
aggregate cost of a scheme over its design working life, being the sum of the construction, operating,
maintenance and end of life costs all calculated at the same time base
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Key
1 rain water
2 runoff
3 surface water
4 infiltration
5 surface receiving water body
Figure 2 — Terminology for flows derived from rain water [SOURCE: EN 16323:2014]
4 Objectives
4.1 General
The four objectives of drain and sewer systems are:
— public health and safety;
— occupational health and safety;
— environmental protection;
— sustainable development.
Objectives can be divided in objectives for the physical system and objectives for managing the
activities related to the physical system.
A number of European Union Directives (e.g. the EU Urban Wastewater Treatment Directive
(91/271/EEC)) make requirements for drain and sewer systems which relate to these objectives.
These objectives are the basis for the integrated sewer system management, including asset
management of the drain and sewer system.
The objectives are the basis for determining the functional requirements and the performance
requirements as illustrated in Figure 3.
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Figure 3 — Process for determining performance requirements from objectives
4.2 Public health and safety
Drain and sewer systems are provided in order to:
— prevent spread of disease by contact with faecal and other waterborne waste;
— protect drinking water sources from contamination by waterborne waste;
— manage rainwater and surface runoff while minimizing hazards to the public (including flooding
hazards).
Poorly designed, constructed or maintained systems can cause health or safety hazards to the public.
The objective is to design, construct, operate, maintain and rehabilitate the system in order to minimize
the health and safety risks associated with the conveyance of wastewater.
4.3 Occupational health and safety
All work associated with the installation, operation, maintenance and rehabilitation of drain and sewer
systems presents a range of occupational health and safety hazards.
The objective is to minimize the occupational health and safety risks likely to arise during installation,
operation, maintenance, and rehabilitation.
4.4 Environmental protection
The objective is to design, construct, operate and maintain the system to minimize the impact on the
environment. These include impacts on:
— water quality;
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— water ecology;
— local water balance.
The impact of drain and sewer systems on the receiving water bodies shall meet the requirements of
any national or local regulations or the relevant authority. Other environmental requirements specified
by any national or local regulations or the relevant authority shall also be met.
4.5 Sustainable development
The objective is to design, construct, operate, maintain and rehabilitate the system at the best
environmental, social and economical costs so that, in particular, it:
a) uses materials that minimize the depletion of finite resources;
b) can be operated with the minimum practicable use of energy; and
c) can be constructed, operated and, at the end of their life, decommissioned with the minimum
practicable impact on the environment.
5 Requirements
5.1 Functional requirements
5.1.1 Introduction
The function of the drain and sewer system is to collect and transport wastewater. Functional
requirements cover the drain and sewer systems, together with combined sewer overflows, pumping
installations and other components, including requirements from external constraints (e.g. effects on
surface receiving water bodies and wastewater treatment plants). The requirements shall be
considered in respect of the whole system to ensure that additions or modifications to the system do
not result in failure to meet the target standards.
Functional requirements shall be established to ensure that the objectives listed in Clause 4 are
achieved.
The functional requirements should include those listed in Table 1. Additional functional requirements
may be specified.
Each functional requirement can relate to more than one objective. An indication of the relationship
between the functional requirements and the objectives is shown in Table 1.
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Table 1 — Relationship between objectives and functional requirements
Clause No
Public health
and safety
Occupational
health and safety
Environmental
protection
Sustainable
development
Functional requirements relating to the system
5.1.2 Protection from
sewer flooding
XXX
XX
XXX
–
5.1.3 Maintainability
XX
XXX
XX
XX
5.1.4 Protection of
surface receiving water
bodies
XXX
X
XXX
XX
5.1.5 Protection of
groundwater
XXX
–
XXX
XXX
5.1.6 Prevention of
odours and toxic,
explosive and corrosive
gases
XXX
XXX
XXX
XXX
5.1.7 Prevention of
noise and vibration
XX
XXX
X
X
5.1.8 Structural
integrity and design
working life
XXX
XXX
XXX
XXX
5.1.9 Watertightness
XXX
X
XXX
XX
Functional requirements relating to the management of the system
5.1.10 Sustainable use
of products and
materials
–
–
XX
XXX
5.1.11 Sustainable use
of energy
–
–
XX
XXX
5.1.12 Maintaining the
flow
XXX
–
XXX
X
5.1.13 Not endangering
adjacent structures and
utility services
XXX
XXX
X
XX
5.1.14 Inputs quality
XX
XXX
XXX
XX
Key
XXX is High;
X is Low;
– is not related.
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5.1.2 Protection from sewer flooding
Flooding from drains and sewers can have an impact on the health of people affected. It can also cause
damage to buildings and urban infrastructure. The economic impact can be high and depends on the
type of location flooded.
Sewer flooding shall be limited to nationally or locally prescribed frequencies taking into account the:
— health and safety effects of the sewer flooding;
— costs arising from sewer flooding;
— extent to which any sewer flooding on the surface of the ground can be controlled without causing
damage;
— whether surcharge is likely to lead to sewer flooding of basements.
NOTE
In some jurisdictions it is the responsibility of the property owner to provide protection to prevent
sewer flooding of basements due to surcharge.
The hydraulic capacity shall limit sewer flooding to nationally or locally prescribed levels and
frequencies taking into account backwater levels. The hydraulic capacity shall allow for foreseeable
increases in flow over the design working life of the system.
Other forms of flooding can also impact on the drain and sewer system including:
a) river flooding – water from rivers and lakes which flows onto the land;
b) coastal flooding – water from the sea which flows onto the land;
c) surface water flooding – runoff that does not enter a drainage system;
d) groundwater flooding – water on land when the groundwater level rises above the ground level.
The effects of flows discharged into downstream sewers or receiving water bodies shall be considered.
Further details are included in Clause 8.
Where there are components in the system, which have a high risk of failure, measures should be taken
to avoid or minimize the risk of sewer flooding in the event of failure of those components.
5.1.3 Maintainability
The system shall be planned, designed, constructed and rehabilitated to allow appropriate maintenance
activities to be carried out safely and without risks to the health of personnel.
Adequate access and working space shall be provided for maintenance purposes.
5.1.4 Protection of surface receiving water bodies
Surface receiving water bodies shall be protected from pollution within nationally or locally prescribed
limits.
The impact of drain and sewer systems on the surface receiving water bodies shall meet the
requirements of any national or local regulations or the relevant authority. Other environmental
requirements specified by any national or local regulations or the relevant authority shall also be met.
The measures to achieve the standards required under EU Water Framework Directive (2000/60/EC)
are summarized in the water framework river basin plan.
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5.1.5 Protection of groundwater
Groundwater shall be protected from pollution within nationally or locally prescribed limits. The effect
of the drain and sewer system on the local recharge of aquifers shall be considered. Where infiltration
drainage systems are proposed, the effects of rainwater quality and quantity shall be considered.
The measures to achieve the standards required under the EU Water Framework Directive are
summarized in the river basin management plan produced in accordance with the water framework
river basin plan.
5.1.6 Prevention of odours and toxic, explosive and corrosive gases
Sewer systems shall be planned, designed, constructed, maintained, operated and rehabilitated as far as
practicable to avoid odour nuisance, or toxic, explosive or corrosive gases.
5.1.7 Prevention of noise and vibration
The system shall be planned, designed, constructed, maintained, operated and rehabilitated so that
noise and vibration are minimized.
5.1.8 Structural integrity and design working life
Drains, sewers and other components shall be planned, designed, constructed, maintained, operated
and rehabilitated to ensure structural integrity over the design working life.
5.1.9 Watertightness
New drains, sewers and ancillary structures, other than those specifically designed for infiltration
drainage, shall be watertight in accordance with the testing requirements of EN 1610. Existing drains,
sewers and ancillary structures shall be watertight in accordance with national or local testing
requirements.
5.1.10 Sustainable use of products and materials
Products, materials, and their construction methods shall be selected that minimize depletion of finite
resources having regard to the design working life of the component and the potential for re-use or
recycling, for example minimizing the volume of excavated material and the reuse of excavated
material.
5.1.11 Sustainable use of energy
The design and operation of the drain and sewer system shall, so far as is practical, minimize the use of
energy over the design working life of the system.
5.1.12 Maintaining the flow
The system shall be planned, designed, constructed, maintained, operated and rehabilitated to reliably
convey all permissible flows that can be discharged into the system to the point of discharge, ensuring
that the operation of the system is safe, environmentally acceptable and economically efficient.
5.1.13 Not endangering adjacent structures and utility services
The planning, design, construction, maintenance, operation and rehabilitation of drains and sewers
shall not endanger existing adjacent structures and utility services.
5.1.14 Inputs quality
The drain and sewer system can be designed to receive both domestic and non-domestic wastewater
inputs. The quality of the non-domestic wastewater inputs shall be controlled so that they do not
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compromise the integrity of the fabric of the system or its function or constitute a danger for the
environment. National or local regulations can give requirements for inputs quality.
5.2 Determination of performance requirements for the drain and sewer system
5.2.1 Introduction
In order to evaluate the performance of the system and to allow development of design standards,
measurable performance requirements shall be determined from each functional requirement. The
process for deriving performance requirements is illustrated in Figure 3.
Drain and sewer systems are part of the urban drainage system (see Figure 4). Urban drainage systems
comprise all infrastructures or the management of wastewater and rain water in the built environment.
The extent and role of the drain and sewer system within the urban drainage system depends on local
circumstances for each system.
Urban drainage systems are part of a wider system of water management (see Figure 4). The EU Water
Framework Directive (2000/60/EC) and the EU Floods Directive (2007/60/EC) provide the basis for
integrated management of the whole water management system through the river basin management
plans and flood risk management plans.
Integrated sewer system management is the coordinated management of the planning, design,
construction, rehabilitation, operation and maintenance of all drain and sewer systems in a catchment
area taking into account all aspects of their performance. It includes a consideration of the interactions
of the drain and sewer system with the urban drainage system as a whole, and the wider water
environment.
The performance requirements should take account of the role of the drain and sewer system which
should be determined within the context of the whole river basin catchment and the other elements of
the urban drainage system (see Figure 4). To determine this role account should be taken of integrated
water policies set by any national or local regulations or the relevant authority together with any
requirements of the integrated river basin management plan.
Integrated urban drainage management is the coordinated management of the planning, design,
construction, rehabilitation, operation and maintenance of all urban drainage systems in a catchment
area taking into account all aspects of their performance. Account should also be taken of any policies
resulting from integrated urban drainage management.
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Figure 4 — Drain and sewer systems in the river basin
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For each functional requirement there can be legal requirements, public expectations and financial
constraints which influence the performance requirements.
Examples of performance requirements in use in different countries can be obtained from the
organizations listed in Annex A.
Performance requirements shall be reviewed periodically and updated if necessary. The performance
requirements for the system should be updated after major extension, maintenance or rehabilitation.
In principle the performance requirements for a rehabilitated system shall be the same as those for a
new system.
5.2.2 Environmental performance requirements
The EU Water Framework Directive (2000/60/EC), together with its daughter directives including the
EU Bathing Waters Directive (2006/7/EC), the EU Shellfish Water Directive (2006/113/EC), the
EU Urban Wastewater Treatment Directive (91/271/EEC) and the EU Groundwater Directive
(2006/118/EC) provide a basis for setting performance requirements relating to the status of water
bodies including ground water, inland surface water bodies and coastal waters.
The EU Bathing Waters Directive (2006/7/EC) makes provisions for the monitoring and classification
of bathing water quality, the management of bathing water quality and the provision of information to
the public on bathing water quality. It specifies mandatory and guideline water quality standards. It
applies to surface water bodies where the competent authority expects a large number of people to
bathe and it has not imposed a permanent bathing prohibition, or issued permanent advice against
bathing.
The EU Shellfish Waters Directive (2006/113/EC) specifies mandatory and guideline water quality
standards for the quality of shellfish waters and applies to those coastal and brackish waters designated
by the Member States as needing protection or improvement in order to support shellfisheries.
The EU Urban Wastewater Treatment Directive (91/271/EEC) makes requirements for the collection,
treatment and discharge of wastewater. It requires the design, construction and maintenance of
wastewater collection systems have regard to the volume and characteristics of the wastewater, the
prevention of leaks and the limitation of pollution of receiving waters due to combined sewer
overflows. The directive contains the following advisory footnote: “Given that it is not possible in
practice to construct collecting systems and treatment plants in a way such that all waste water can be
treated during situations such as unusually heavy rainfall, Member States shall decide on measures to
limit pollution from storm water overflows 1). Such measures could be based on dilution rates or
capacity in relation to dry weather flow, or could specify a certain acceptable number of overflows per
year.”
The EU Groundwater Directive (2006/118/EC) establishes measures to prevent and control
groundwater pollution. These measures include criteria for the assessment of good groundwater
chemical status.
National or local regulations or the relevant authority can also specify performance requirements in
relation to the environmental performance of drain and sewer systems.
Environmental performance requirements for drain and sewer systems can be set in terms of emission
limits for discharges or in terms of the impact on the status of the receiving water body (including
groundwater, inland surface water bodies and coastal water bodies). The requirements should take into
account the impact of other emissions. The requirements should take account of the anticipated
1) In EN 752 the term "combined sewer overflows" has broadly the same meaning as the term "storm water
overflow" in the Directive.
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frequency of discharges, the physical (e.g. scour due to flow velocity), chemical, biochemical and other
relevant considerations.
Proposed controls on discharges from the drain and sewer systems shall take account of the water
environment in the river basin (see Figure 3) and in particular:
a) the current status of the receiving water bodies within the river basin including the chemical status,
the ecological status;
b) the objectives for the future status of the receiving water bodies;
c) any other proposed measures to improve or adversely affect the status of the receiving water
bodies;
d) any policies for achieving the objectives.
Emission limits can be also set in terms of the frequency, duration of the discharges as well as their
physical, chemical or biological composition. Environmental modelling can be necessary to establish
appropriate emission limits.
Alternatively standards can be set by specifying a method of treatment (e.g. screening or vegetative
treatment).
5.2.3 Hydraulic performance requirements
The EU Floods Directive (2007/60/EC) provides a framework for the management of flood risk from all
sources. However, the Directive permits member states to exclude sewer flooding from these
arrangements.
Performance requirements should be set taking into account the potential for damage and the hazards.
Separate requirements may be set for sewer flooding with surface water and sewer flooding with foul
or combined wastewater.
National or local regulations or the relevant authority can specify performance requirements in relation
to surcharge frequencies or sewer flooding frequencies.
There are two commonly used methods of setting hydraulic performance requirements within the drain
and sewer system:
— The expected frequency of sewer flooding in any year, or the return period of sewer flooding.
Different flood frequency requirements can be specified depending on the type of property
impacted and the extent of damage to people and property that would result from the sewer
flooding. In this way the requirements can reflect the sewer flood risk, taking account of both the
expected frequency of the sewer flooding (the expected frequency) and its impact (for example the
type of property flooded).
— The expected frequency of surcharge in drains or sewers can be specified depending on the type of
property impacted and the expected frequency that surcharge would result in sewer flooding (e.g.
the presence of basement properties).
The sensitivity of the surcharge or expected sewer flooding frequency to possible changes in rainfall
due to climate change should be considered.
Discharges of surface water or combined wastewater can impact on flood risk in surface receiving
water bodies. Performance requirements can also be set to limit the rate or volume of discharge from
drain and sewer systems in order to limit flood risk in the surface receiving water bodies.
Hydraulic performance requirements for drain and sewer systems shall therefore take account of the
wider river basin (see Figure 4) and in particular:
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a) the current flood risk in the drain and sewer system and in the river basin;
b) the objectives for future flood risk in the drain and sewer system and in the river basin;
c) any other proposed measures to improve or adversely affect the flood risk in the drain and sewer
system and in the river basin;
d) any policies for achieving the objectives for flood risk.
5.2.4 Structural requirements
The components of the system shall resist the foreseeable imposed loads throughout the design
working life without defects which can:
a) lead to unacceptable risk of loss of structural integrity;
b) impair the function of the system so that other performance requirements are not achieved.
5.2.5 Operational requirements
Operations should:
a) ensure that the entire system is operationally ready at all times and functions in accordance with
the other performance requirements;
b) ensure that the operation of the system is safe, environmentally acceptable, and economically
efficient;
c) ensure that as far as possible the failure of one part of a sewer system not adversely affects the
performance of other parts of the system.
5.3 Design criteria
5.3.1 Introduction
To ensure that the system achieves the performance requirements during its design working life, design
criteria should be set which usually exceed the performance requirements. The design criteria should
be set at a level which ensures that the system continues to meet the performance criteria taking
account of any foreseeable changes over the design working life of the system. Design criteria shall take
into account any changes expected over the design working life of the drain and sewer system if these
changes are not otherwise taken into account in the design.
The changes that should be taken into account can include:
a) increased flows due to new developments;
b) reduced flows due to changes in the development and changes in water use;
c) increased flows resulting from changes to existing developments;
d) reduced hydraulic capacity resulting from increased hydraulic pipeline roughness (e.g. due to
deterioration) in the drains or sewers or wear in pumps;
e) reduced hydraulic capacity due to build-up of sediments in sewers.
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5.3.2 Hydraulic design criteria
5.3.2.1 Introduction
Design criteria shall take into account any changes in flows expected over the design working life of the
drain and sewer system if these changes are not otherwise taken into account in the design. The
potential effects of climate change should be considered. This is to ensure that the sewer continues to
meet the performance criteria over the design working life of the system.
The frequency of an event can be expressed either as a return period or a probability of occurrence in
any one-year period.
Design criteria can be set for:
a) the expected frequency at which no surcharge occurs in the drain and sewer system;
b) the expected frequency at which a specified amount of surcharge occurs in the drain and sewers
system;
c) the expected frequency of sewer or surface water flooding (this can occur without surcharge); and
d) the impact of the flows from surface water outfalls on river flooding from surface receiving water
bodies or on groundwater flooding;
e) the impact of flows on the operation of the wastewater treatment plant.
The nature of design criteria depends on the type of design methods used.
In setting hydraulic design performance criteria for surface water sewers, allowance shall be made for
the design methods that are likely to be used. In all cases the scale of the consequences of sewer
flooding should be taken into account.
Where simple design methods are used, design criteria are typically expressed in terms of the
frequencies of design rainfall events that just fill the pipe without surcharge in the knowledge that this
generally provides protection against sewer flooding from more severe rainfall events. The degree of
flood protection depends on local factors (e.g. topography, sewer gradient).
Where more complex methods are used and it is possible to predict expected sewer flood frequencies,
sewer flooding design criteria should also be used.
Both the expected rainfall event frequency and the expected flood frequency can be expressed as a
return period, which is the average period in years between events, or a probability that an event will
be exceeded in any one year.
5.3.2.2 Full pipe design rainfall criteria
The design rainfall frequency is the rainfall intensity that causes the pipe to be just full without
surcharge. Different design criteria may be set for combined and separate systems.
National or local regulations or the relevant authority can specify design rainfall.
In setting design rainfall criteria for use when combined or surface water drains and sewers are
designed for full pipe flow the following points should be considered:
a) whether there are any connected basements not protected by anti-flooding devices, effluent lifting
stations or pumping stations;
b) whether the surcharge is likely to lead to sewer flooding of basements;
c) whether design criteria for flood frequency are also specified for the design.
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Examples of design rainfall frequency criteria are given in Table 2, however the criteria can vary widely
between countries.
Table 2 — Examples of design rainfall frequencies for pipes to run just full without surcharge
Location
Design rainfall frequencya
Return period
years
Probability of
exceeding
in any 1 year
Rural areas
1
100 %
Residential areas
2
50 %
City centres/industrial/commercial
areas
5
20 %
Underground railway/underpasses
10
10 %
a For the selected design rainfall event the pipe shall be no more than just full and shall
be without surcharge.
5.3.2.3 Sewer flooding design criteria
Design sewer flooding frequencies should be set in order to manage the risk of sewer flooding, having
regard to both the frequency and consequences of sewer flooding.
NOTE
The arrangement of the drain and sewer system together with the above ground space are considered
together to achieve these design criteria.
The effect of sewer flooding depends on the type of surface or building it affects. This depends on the
characteristics of the surface and the movement of the flood water across the surface. The impacts can
include damage to property and impacts on the health or safety of people.
Design criteria should take account of the following:
a) deep or fast flowing flood water presents an increased hazard to people;
b) flooding inside buildings can cause high economic damage and present a hazard to life and health;
c) depending on its extent, flooding that is confined to external surfaces such as roads often causes
more limited damage.
For locations with a high potential for damage or hazard, detailed investigations should be undertaken,
taking into account the movement of water and the effect of surface features (e.g. kerbs).
Different design criteria may be set for combined and separate sewer systems.
National or local regulations or the relevant authority can specify design sewer flooding frequencies.
Examples of design sewer flooding frequency criteria are given in Table 3, however the criteria can vary
widely between countries.
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Table 3 — Examples of design sewer flooding criteria for standing floodwater
Impact
Example locations
Examples of design sewer
flooding frequency
Return
period
years
Probability
of
exceeding
in any
1 year
Very low
Roads or open spaces away from buildings
1
100 %
Low
Agricultural land (depending on land use, e.g.
pasture, arable)
2
50 %
Low to medium
Open spaces used for public amenity
3
30 %
Medium
Roads or open spaces adjacent to buildings
5
20 %
Medium to high
Flooding in
basements
excluding
10
10 %
High
Deep flooding in occupied basements or road
underpasses
30
3%
Very high
Critical infrastructure
50
2%
occupied
buildings
Return period should be increased (probabilities reduced) where the floodwater is fast moving.
When undertaking rehabilitation of existing systems and where achieving the same design criteria for
a new system would entail excessive cost, a lower value may be considered.
5.3.2.4 Effect on downstream water bodies
Design criteria can be set for the impact of flows discharged from outfalls on the flood risk in receiving
water bodies. The criteria may be given in absolute terms or by reference to the current conditions.
Such criteria can include:
a) controls on the flow rates and volumes for discharges from the area drained; for example:
1) limiting the peak flow rate and volume of the discharge in prescribed rainfall conditions to
specified values;
2) ensuring there is no increase in the peak flow rate or volume in prescribed rainfall conditions;
b) criteria for the flood frequencies from the receiving water body; for example:
1) no increase in flood frequency from the receiving water body;
2) limiting the flood frequency from the receiving water body to prescribed values.
5.3.3 Environmental design criteria
There are several approaches for setting design criteria for the control of pollution from drain and
sewer systems including:
a) uniform emission limits can be set by national or local regulations or the relevant authority for
general use with each of the different types of discharge;
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b) site-specific emission limits can be set by any national or local regulations or the relevant authority
for individual points of discharge, to satisfy requirements for the quality and characteristics of the
receiving water body taking into account any environmental quality standards for the receiving
water body and the specific needs of the receiving water body;
c) specifying a method of treatment for the discharge, which in the opinion of the relevant authority
ensures that an adequate emission standard is achieved.
In many cases a combination of the two approaches should be considered.
Uniform emission limits are generally set in relation to what is technically feasible for the different
types of discharge. They form a baseline standard prior to the determination of site-specific limits
which do not put the self-purifying capacity of the receiving water body at risk. They are unlikely to be
applicable where discharge is to sensitive waters such as recreational areas, sources for water supply or
lakes. Generally in such cases, more stringent site-specific emission limits are necessary to satisfy the
receiving water quality requirements.
The site-specific emission limit approach is sensitive not just to the effects of an individual discharge,
but also to the combined effects of the whole range of discharges to receiving water bodies. These
discharges, including those from industry, treatment works and non-point sources can demand an
integrated approach to the identification of solutions.
The principal advantage of method based criteria is that there is no on-going cost of sampling. The
principal disadvantage is reduced confidence in the compliance. For this reason, method-based criteria
are generally only set for low risk discharges.
The relevant authority for environmental regulation can classify receiving water bodies according to
current or projected uses or interests, for example:
— abstraction for potable supply;
— fishery;
— bathing or other water contact activities;
— special ecosystem.
The emission limits or method based criteria can then be set by any national or local regulations or the
relevant authority using, where appropriate, water quality simulation models.
5.3.4 Structural design criteria
Structural design criteria should be set taking account of the actions on the structures in accordance
with the EN 1991 series taking account of the principles of structural design set out in EN 1990 or, for
buried pipelines, taking account of EN 1295-1. Design criteria can include:
a) prescribing a design working life for each component;
b) prescribing the loads that each component shall be able to withstand;
c) prescribing any special safety factors to be used;
d) limit states used for design.
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5.3.5 Operational criteria
Operational design criteria should be set to ensure:
a) the safety and welfare of operator personnel when carrying out operation of the system;
b) the reliable operation of the system (e.g. blockages or pump failures).
6 Integrated sewer system management
6.1 Introduction
Integrated sewer system management is the process of achieving an understanding of existing and
proposed drain and sewer systems, and using this information to develop measures to ensure that the
hydraulic, environmental, structural and operational performance meets the specified performance
requirements taking into account future conditions and economic efficiency. It incorporates the asset
management of the drain and sewer system.
Integrated sewer system management should be carried out in the framework of the management
principles of the wastewater utility. National or local regulations or the relevant authority can influence
these principles.
The principles can include:
a) technical principles to achieve compliance with the performance requirements. These incorporate
any legal requirement regarding the performance of the drain and sewer systems;
b) asset management principles;
c) economic principles;
d) risk management principles;
e) liabilities to third parties.
Economic principles can include:
— avoiding overall deterioration of the assets or making up for past deterioration;
— determination of the long-term financial requirements to achieve the defined performance through
the production of investment requirement plans;
— determination of optimal levels of financial resources taking account of the costs and benefits;
— prediction and balancing of future wastewater tariffs;
— phasing expenditure to produce a manageable expenditure profile throughout the period of the
plan;
— phasing with other works;
— phasing work to achieve a consistent work load to make best utilization of personnel and
equipment.
Risk management can include:
— risk identification;
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— risk analysis;
— risk assessment;
— risk treatment.
The integrated sewer system management process is illustrated in Figure 5.
The integrated sewer system management process has four principal activities:
— appropriate level of investigation of all aspects of the performance of the drain and sewers system;
— assessment of the performance by comparison with the performance requirements including
identification of the reasons for any observed performance failures;
— planning – developing the plan of measures to be taken;
— implementation of the plan.
Figure 5 — Integrated sewer system management process
The need for further investigation can become apparent either during the performance assessment or
the planning.
Integrated sewer system management forms the basis for the operation and rehabilitation of the drain
and sewer system. The information is regularly updated for the future management of the drain and
sewer system.
For large drain and sewer systems, for example where one serving a large city, an outline integrated
sewer system management plan may first be developed following an outline investigation of the whole
system. More detailed plans may then be developed for each sub-catchment within the context of the
outline plan (see Figure 6).
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The integrated sewer system management plan is further developed during the implementation phase
(see 6.5), by subsequent investigation, assessment and planning to develop work programmes and
individual projects to implement the plan.
Figure 6 — Increasing degree of detail in integrated sewer system planning
The boundary conditions with adjacent drain and sewer systems and with other urban drainage
systems or with river systems should be considered at all stages.
6.2 Investigation
6.2.1 Introduction
The investigation is the first stage in the integrated sewer system management as described in 6.1
(see Figure 5). The process for investigation is outlined in Figure 7.
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Figure 7 — Process for investigation
Damaged, defective or hydraulically overloaded drains and sewers represent a potential hazard
through sewer flooding and collapses, and through pollution of surface receiving water bodies,
groundwater and soil. The problems found in existing drain and sewer systems are frequently
interrelated and upgrading works are often designed to overcome a number of problems at the same
time. The investigation and planning of rehabilitation work should be carried out on defined catchment
areas in phases if appropriate, so that all problems and their causes can be considered together. The
procedures described in this European Standard can be applied in any drain and sewer system, but
detailed application should take account of the age, location and type of system, the materials used in its
construction, together with functional and climatic factors.
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6.2.2 Purpose of investigation
The investigation is carried out in order to make an assessment of the performance of the drain and
sewer system and its components. This can include:
— investigation aimed at strategic planning;
— investigation aimed at operational planning.
The purpose of the investigation influences the way in which it is carried out (e.g. choice of method,
degree of detail, desired accuracy) and the way in which the results are assessed.
The components of the drain and sewer system included in the investigation shall be those that are
necessary to fulfil the purpose of the investigation. The investigation shall be carried out in accordance
with EN 13508-1. Any coding of the results from visual inspections should be in accordance with
EN 13508-2.
6.2.3 Review of performance information
An indication of the type of performance problems, if any, on existing systems is likely to be known
through reports of incidents such as sewer collapses, sewer flooding or polluted watercourses and from
previous investigations. For details of performance monitoring see 10.2. Records of past incidents and
any other relevant information shall be brought together and analysed. This information should be used
to establish the scope of the investigations.
Where large numbers of complete or partial catchments are in need of investigation, the existing
information collected may also be used to assign priorities to the investigation of the perceived
problems in each catchment (for example by comparing the cost of the investigation with the benefit
that might be achieved). These can then be used to draw up a comprehensive programme so that the
catchments with the most serious problems are investigated first.
6.2.4 Determine the scope of the investigation
Following the review of the current performance information it is possible to decide whether to carry
out an investigation and whether the extent of the problems justifies an investigation of the entire
catchment area. The extent and detail of the subsequent investigation of the hydraulic, environmental,
structural and operational aspects shall be determined. Further guidance on the type of investigations
can be found in EN 13508-1.
6.2.5 Review existing information
The collection and review of all available relevant information about the drain and sewer system shall
be carried out and is the basis from which all other activities are subsequently planned.
A review should also be undertaken of the information required to manage the drain and sewer system.
This information should be assessed to determine what further information is required in order to
carry out the investigation (see EN 13508-1).
6.2.6 Inventory update
Where the inventory is incomplete it shall be updated so that a sufficient record of the drain and sewer
system is available to carry out the investigation.
NOTE
The update of the other information is included in the hydraulic, environmental, structural and
operational investigations.
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6.2.7 Hydraulic investigation
Testing and inspection procedures can be required in order to ensure an adequate evaluation of flows
(wet and dry weather, infiltration, flow through gaps in manhole tops (between the cover and frame),
exfiltration and wrong connections). Surveys can include precipitation and flow measurements,
identification of wrong connections and groundwater measurements.
In some cases it is not possible to understand the hydraulics of the system without using a hydraulic
model. This sewer flow simulation model should be based on an as-built report updated after onsite
investigation of the main works. However a model is not usually recommended where:
— there are no known hydraulic problems (particularly where the sewer system takes only foul
wastewater flows); and
— there are no combined sewer overflows; and
— no significant new developments are proposed within the system; and
— structural problems are to be solved using techniques which do not reduce the hydraulic capacity
of the sewer.
Information on the use of computer based sewer flow simulation programs is given in prEN 16933-2.
6.2.8 Environmental investigation
The environmental impact depends on the nature of the wastewater and its potential to escape from the
system.
The quality of surface receiving water bodies shall be ascertained to see whether they meet the
requirements and if not, whether the sewer system is a significant factor.
Consideration should be given to other environmental factors such as noise, odour, visual intrusion and
potential soil and groundwater contamination, taking into account the availability of the information.
6.2.9 Structural investigation
It is important to ensure that investigation of the system is selective in order to avoid duplication of
previous work. The structural investigations may include either a complete survey of the drain and
sewer system or a more selective approach. Consideration should be given to the age and location of
existing infrastructure, geotechnical data including the pipe bedding and surround, and the
vulnerability of existing buildings and other utility services, taking into account the availability of the
information.
Where appropriate, other qualitative and quantitative investigation techniques may be used. These
include sonar (for pipes that are filled with water) and ground probing radar or other geophysical
techniques (e.g. for detecting voids behind the wall of the sewer pipe) or mechanical techniques (e.g.
internal jacking to measure the stiffness of the side wall support). Investigation of the chemical
composition of the groundwater and the soil should be carried out where this can affect the structural
integrity.
The results of the structural investigations can also be relevant to the assessments of the hydraulic
performance and environmental impact.
6.2.10 Operational investigation
Existing operational procedures, inspection schedules and maintenance plans shall be identified and
documented.
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The frequency and location of recorded operational incidents (e.g. blockages, pumping station failures,
sewer collapses) shall be reviewed.
The impact of operational problems on the hydraulic, environmental and structural performance of the
system should be determined from incident records.
The causes of significant recurrent operational incidents shall be investigated.
To deal with operational problems in the most cost effective way, it is necessary to investigate and
understand the causes. Further information can be found in 10.4.
6.3 Assessment
6.3.1 Introduction
The performance of the system shall be assessed against the performance requirements (see 5.2). The
performance assessment shall include the evaluation of risks of failure to achieve the performance
requirements.
The assessment shall be carried out in accordance with EN 13508-1 (see Figure 8).
6.3.2 Assessment of the hydraulic performance
The results of the hydraulic surveys and/or the verified flow simulation model shall be used to assess
the hydraulic performance of the system for a range of rainfall conditions related to the performance
requirements (see 5.2.3).
Figure 8 — Process for assessment
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6.3.3 Assessment of environmental impact
The results of the investigations shall be considered together with information on the frequency,
duration volume and pollution load of discharges to receiving water bodies, determined using a verified
flow simulation model or flow and pollution load simulation model (see prEN 16933-2) where this is
available or from site measurements. This information shall then be used to assess the environmental
impact (including impact on soil and groundwater) of the drain and sewer system.
The results of the structural investigation (see 6.2.9), the industrial wastewater survey and other
relevant investigations shall be examined to identify:
— sources of hazardous effluents;
— exceedence of permissible concentrations and discharges;
— other deviations from permits.
6.3.4 Assess structural condition
Once the system has been inspected, the next stage is to examine the results to identify those areas
requiring action. A number of methods have been developed to assist in this process. Details of these
can be obtained from the organizations listed in Annex A.
6.3.5 Assess operational performance
The operational performance of the system as measured by the number of operational incidents or
failures should be assessed. This should be recorded in a data management system.
6.3.6 Compare with performance requirements
The results of the assessment of the hydraulic, environmental, structural and operational performance
should be brought together so that the performance of the system and its components can be compared
to the performance requirements (see 5.2).
Performance indicators are one method of comparing the performance of a system with performance
requirements. Any performance indicators used should be:
— clearly defined, concise and unambiguous;
— verifiable;
— simple and easy to use.
6.3.7 Identify unacceptable impacts
Details of those parts of the system where the hydraulic, environmental, structural or operational
performance of the system or its components does not meet the performance requirements should be
recorded.
6.3.8 Identify causes of performance deficiencies
Based upon the results of the hydraulic, environmental, structural and operational investigations, the
causes of performance deficiencies shall be determined. The relative impact of each cause should be
assessed in order to develop appropriate solutions and to set the priority for action.
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6.4 Planning
6.4.1 Introduction
The integrated sewer system management plan may take one of two forms.
a) The plan outlines the approach to be taken (e.g. a major new sewer to alleviate sewer flooding or
reduce discharges to surface receiving water bodies). Where an outline plan is produced further
detail can be included in detailed plans for parts of the catchment.
b) The plan describes the proposed activities and measures (e.g. a major new sewer or separation of
surface water to alleviate sewer flooding or reducing the discharges to surface receiving water
bodies) and specifies the resources and timescales.
Outline plans are likely to be more long term (e.g. 25 years) than medium term integrated sewer system
management plans (e.g. 5 years) or detailed work programmes (see 6.5).
The process of developing the plan to fulfil the performance requirements is outlined in Figure 9.
6.4.2 Develop integrated solutions
Integrated solutions shall be developed that fulfil the performance requirements, taking into account
future conditions. Different types and groups of solutions are listed in Table 4. Development of
solutions for rehabilitation of existing drain and sewer systems should be carried out in accordance
with EN 14654-2.
Figure 9 — Process for developing the plan
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Table 4 — Solution types and groups for rehabilitation
Type
Group
Hydraulic
Maximize use of existing flow capacity
Source control – reduce the hydraulic input to the sewer system
Attenuate peak flows
Increase sewer system flow capacity
Environmental
Reduce pollutant inputs to system
Decrease planned pollutant discharges to receiving water bodies
Decrease impact by relocation of points of discharge
Reduce exfiltration by rehabilitation measures
Structural
Protect fabric of sewer by provision of appropriate linings or internal coatings
Rehabilitate fabric of pipeline
Operational
Undertake planned inspection and cleaning of a drain or sewer (see EN 14654–1)
Optimize frequency of maintenance of pumps or pumping stations
Provide additional resilience in the event of future failure (e.g. provision of stand-by
equipment or emergency storage)
NOTE
This list is not exhaustive.
6.4.3 Assess solutions
Solutions shall be assessed and the optimal solution selected having regard to the basic performance
requirements (see Clause 5) and factors such as:
a) Safety in construction and operation - The minimization of risks to health and safety during
construction and subsequent operation of the system and during decommissioning at the end of its
design working life.
b) Social disruption - The disruption to local residents and other members of the public due to traffic
delays, dust, noise and other social factors shall be considered.
c) Sustainable use of resources - The use of energy and other finite resources in the construction
and operation of the system shall be taken into account. The ability to recycle materials used in the
upgrading works and any waste produced shall be considered.
d) Phasing of the works - The possibility of integrating the solution into a staged programme of
works shall be considered. This shall take into account the priorities of the works and the benefits
in terms of improved performance associated with each identified phase of the works, and the cost
savings associated with deferral of the later stages.
e) Relationship to other infrastructure works - The benefits of phasing the works with other
infrastructure works shall be considered.
f)
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Capacity and resource constraints - Account should be taken of the resource constraints (e.g.
personnel, supply chain and financial) in the selection and phasing of the options.
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g) Future maintenance liabilities - The cost of future maintenance works and other operational
costs of the system should be taken into account. The environmental impact of disposal of
maintenance residues (see 8.5.1) shall also be considered.
h) Economic appraisal - The costs and benefits shall be considered to determine whether the
additional benefits of one solution over another, for example increased asset life, are justified.
i)
Whole life cost - The whole life cost of a solution is the present value of all the costs over the life of
the solution including temporary works, diversion of other utility services and all design,
construction, investigation, maintenance and operational costs together with possible recycling
costs shall be taken into account as well as the indirect costs (e.g. cost of social disruption). When
comparing different options, the whole life cost shall be calculated over the same period for each
option.
6.4.4 Prepare action plans
6.4.4.1 Introduction
The selected integrated solution shall be documented to give a single plan for the drain and sewer
system. The documentation should include:
— detailed objectives;
— legal requirements and permits, including any timescales for improvement;
— performance criteria;
— priorities;
— proposed works including costs and phasing;
— relationship to other construction or planned development;
— consequences for operations and maintenance.
Four types of plan can be prepared:
— new development plan;
— operations and maintenance plan;
— rehabilitation plan;
— contingency and emergency plan.
6.4.4.2 New development plan
Where significant new development or redevelopment is proposed in the catchment, a new
development plan should be produced showing:
a) whether the foul and surface water from the new development should be drained by extension to
an existing drain and sewer system or by an independent system;
b) if the system is to be an extension of an existing system, the upgrading works to the existing system
to accommodate the additional flows should be described in the rehabilitation plan for that system;
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c) whether surface water should be managed by surface water drains and sewers, a system of open
channels or by an infiltration system;
d) the attenuation requirements for surface water management;
e) an outline of the main sewer systems to serve the development.
6.4.4.3 Operations and maintenance plan
The operations plan should include inspection schedules and operational procedures. The operations
plan shall indicate the approach to be taken in a particular drain and sewer system. The plan shall
include:
a) Inspection routines, including which assets are to be inspected and the inspection frequencies, shall
be established for the system, taking into consideration the requirements and importance of each
component. Routines shall include the inspection of:
1) pipelines including inspection chambers, manholes, pipe bridges, above ground pipelines and
outfalls, taking into account the gradient and/or velocity;
2) pumping installations, according to potential risk and type of equipment;
3) overflows and detention tanks, taking into account storm frequency;
4) inverted siphons, depending on risk of blockage and potential consequences;
5) separators, according to technical requirements;
6) grit chambers, gullies, etc., taking into account storm frequency, capacity and land use.
b) Procedures for the operation of the components of the system should include plans for:
1) operation of pumping stations;
2) operation of any special components (e.g. vacuum or pressure installations within the system);
3) setting dam boards, valves and weirs;
4) operation of detention tanks;
5) showing the assignment of responsibilities for carrying out procedures;
6) real time control systems.
The maintenance plan should include details of maintenance policies and schedules for each component
of the system. The maintenance plan can include a cleaning plan, which should be in accordance with
EN 14654-1, a pest control plan, and an electrical and mechanical equipment maintenance plan. The
maintenance plan shall include:
c) type of maintenance strategy to be used in each component of the system and the monitoring
requirements and frequencies. The strategies for maintaining drain and sewer systems are planned
or reactive maintenance, or a combination of both.
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1) Planned maintenance includes a programme of work to remedy the defects and problems
identified during inspection. It is particularly required to reduce the incidence of failure where
the consequences are severe.
2) Reactive maintenance involves responding to failures and problems as they are identified. It is
appropriate for those parts of the system that can function with little or no maintenance.
6.4.4.4 Rehabilitation plan
Rehabilitation includes a wide range of activities to restore or upgrade the performance of a drain and
sewer system including those examples shown in Table 5.
Table 5 — Scope of rehabilitation
Examples of system related
measures
Restore
— Remove extraneous flows
original
— …
performance
Examples of component related
measures
—
—
—
—
Cleaning
Repair
Renovation
Replacement (like for like)
Upgrade
— Maximize use of existing flow — Replacement (increased capacity)
original
capacity
performance — Reduce hydraulic input to the
drain and sewer system
— Attenuate peak flows
— …
The rehabilitation plan should include information on proposed rehabilitation works. The options to be
considered fall into one or more of the four categories: hydraulic, environmental, structural and
operational performance. The works necessary to upgrade an existing drain and sewer system to meet
the performance requirements should be incorporated into a rehabilitation plan. This should include:
a) details of the necessary upgrading works;
b) other options for upgrading the system;
c) any anticipated phasing of the work;
d) whether any of the items are conditional on any planned developments.
Rehabilitation includes a plan of work to remedy the defects and problems identified during
investigation (see 6.2).
One or more of the following possible approaches can be used to formulate the plan:
1) asset value approach;
2) area-related approach;
3) condition based approach;
4) multi-utility approach;
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5) functional related approach;
6) reactive approach.
The reactive rehabilitation approach should only be used where the risk of failure is considered
acceptable, taking into account both the probability of failure and the consequence.
Further details of these approaches can be found in Annex B.
6.4.4.5 Contingency and emergency plan
Contingency and emergency planning is the process of setting out procedures to be used in case of
crisis, e.g. breakdown of a part of the system. It should also include procedures for dealing with major
failures and other emergencies. Procedures can be required for a range of possible incidents including:
— accidental spillages of toxic, noxious or explosive substances;
— discharge of special substances used in fire fighting;
— failure of pumping installations or pre-treatment facilities;
— sewer flooding;
— the effect of other forms of flooding on the system;
— major sewer collapse.
Contingency and emergency plans shall include:
a) organization of the management of the crisis;
b) details of emergency services;
c) estimated times for response (in general terms);
d) lists of those to be notified;
e) location of available resources;
f)
procedures to be followed (including protection of receiving water bodies and wastewater
treatment plant).
The resource requirements need to be determined, including:
1) personnel;
2) vehicles;
3) equipment;
4) materials.
These resources sometimes need to be available at short notice. This can influence resourcing decisions
for normal operations and maintenance work.
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6.5 Implementation
6.5.1 Introduction
The integrated sewer system management plan does not generally contain the necessary detail to
proceed directly to the implementation of the work. To implement the work usually involves applying
the stages of investigation, assessment and planning (see Figure 10) to produce the following.
a) A work programme which outlines a series of projects, in line with the plan, to ensure that the drain
and sewer system meets the performance requirements. The outline for each project in the work
programme lists the objectives of the proposed project.
b) A work specification describes an individual project in sufficient detail to carry out the work.
Work programmes and specifications can be developed for work in connection with new development,
rehabilitation as well as operations or maintenance activities.
A typical implementation process can be summarized in Figure 10. Depending on the assignment of
tasks and the local conditions specific steps of this process may be omitted.
Further guidance on management and control of implementation work is given in EN 14654-1.
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Figure 10 — Process for implementation
6.5.2 Development of work programme
The development of the work programme involves further investigation and assessment in order to
define a series of projects which together implement the integrated sewer system management plan to
achieve the performance requirements (see Clause 5). In line with the plan, the programme can have
four aspects of new development, rehabilitation, operations and maintenance. For each project the
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programme should define the objectives and describe the work in sufficient detail to allow the project
specification to be developed. The programme should also describe any issues relating to the sequence
of the work or timing in relation to other developments.
The development of the programme typically includes the following stages:
— conception;
— preliminary topographical, geotechnical and other investigations (see 8.3);
— preliminary calculations to check the feasibility of the proposed approach.
6.5.3 Development of work specification
The project specification should contain all the necessary information to carry out the works outlined in
the programme. The development of the work specification usually involves further detailed
investigation and assessment of parts of the existing drain and sewer system or other constraints on the
proposed works. The development of the specification usually includes the following stages:
— confirmation of design criteria;
— refinement of the general concept;
— more detailed calculations;
— production of detailed drawings or specifications.
6.5.4 Carrying out work
Any new construction or rehabilitation works should be designed in accordance with Clause 8, the
prEN 16932 series and prEN 16933-2 and constructed in accordance with Clause 9.
Operations and maintenance activities should be carried out in accordance with Clause 10.
After completion of any work records (inventory) shall be updated as necessary including updating any
sewer flow simulation model.
6.5.5 Measuring conformity
It is important to monitor the effectiveness of solutions to ensure that the performance of the solutions
conforms to the required performance. The performance of the drain and sewer systems should also be
monitored during the operational life of the system (see 10.2). Examples of the tests and assessments
can be found in EN 1610 and EN 13508-1.
The effectiveness of maintenance should be assessed by comparing the performance of the drain and
sewer system with the functional requirements (see 5.1). In addition, for reactive maintenance, target
response times can be used as an assessment. This also forms the basis for future planning.
6.5.6 Review performance requirements and update plan
The performance requirements should be reviewed periodically and the whole planning process
repeated so that all the plans remain up to date.
7 Health and safety
The fundamental strategy for occupational health and safety is laid down in the EU Safety and Health
Framework Directive 89/391/EEC. This requires employers to avoid risks to health and safety, to
assess the risks which cannot be avoided and to use the results of that assessment to mitigate the
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residual risks through combating these risks at source in preference to the application of protective
measures and to ensure that preference is given to collective protective measures over those protecting
the individual only. These are the principles of prevention. The directive also requires that employees
are appropriately instructed in the risks to their health and safety.
The EU Temporary or Mobile Construction Sites Directive 92/57/EEC sets out requirements directed
towards all the parties to a project, including the owner, the designer and the constructor. With regard
to design, Directive 92/57/EEC requires that due account is taken of the principles of prevention set out
in the EU Safety and Health Framework Directive 89/391/EEC, in the design and preparation stages of
the project, that specific documentation regarding health and safety risk is drawn up and made
available to parties to the project and that workers are consulted over and informed of the risks to their
health and safety. Annex IV of Directive 92/57/EEC sets out a range of specific health, safety and
welfare requirements relating to work practices and to indoor and outdoor workplaces on site.
Accordingly drain and sewer systems shall be designed, constructed and operated so that the
occupational health and safety risks to personnel undertaking work associated with the drain and
sewer system are minimized. In addition welfare facilities shall be provided where appropriate.
Those who are responsible for work in drains and sewers, including the operator of the drain and sewer
system shall ensure that the work does not present a risk to the health or safety of any person carrying
out the work or any person who can be affected by their actions.
In addition it is the responsibility of employers to:
— provide safe systems of work including arrangements for safe access to and egress from the sewer
system, and sufficient working space while in the sewer system;
— ensure that their employees are properly instructed, trained and supervised in the work being
carried out and in the safe systems of work in use.
National or local regulations or the relevant authority can specify requirements regarding the health,
safety and welfare of the public and operator personnel. They can include more requirements than
indicated in this European Standard.
There are specific hazards that apply to work in drain and sewer systems including:
a) oxygen deficient and toxic atmospheres;
b) potentially explosive atmospheres;
c) proximity to moving traffic;
d) collapse of excavations;
e) contact with toxic, flammable or irritant materials;
f)
exposure to pathogenic organisms (e.g. leptospirosis, tetanus, hepatitis and poliomyelitis).
The EU Safety and Health Framework Directive (89/391/EEC) together with its daughter directives and
other relevant safety and health directives can apply including:
— EU Noise at Work Directive (2003/10/EC);
— EU Machinery Directive (2006/42/EC);
— EU Work Equipment Directive (2009/104/EC);
— EU Personal Protective Equipment Directive (89/656/EEC);
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— EU Manual Handling Directive (90/269/EEC);
— EU Display Screens Directive (1990/270/EEC);
— EU Asbestos at Work Directive (2009/148/EC);
— EU Temporary or Mobile Sites Directive (92/57/EEC);
— EU Working Time Directive (2003/88/EC);
— EU Explosive Atmospheres (ATEX) Directives (2014/34/EU and 1999/92/EC);
— EU Temporary Work at Height Directive (2001/45/EC);
— EU Physical Agents (Vibration) Directive (2002/44/EEC);
— EU Chemical Agents Directives (98/24/EC);
— EU Carcinogens or Mutagens at Work (2004/37/EC);
— EU Low Voltage Directive (2006/95/EC).
8 Design
8.1 General
Design is the process of defining the project in sufficient detail so that instructions can be given to
others for the system to be constructed or maintained.
Designers should take into account the practicability of safely constructing, operating and maintaining
the system (see Clause 7).
The design shall fulfil the objectives (see Clause 4) and meet the functional requirements (see Clause 5)
and the action plan (see 6.4.4). Specific requirements shall be considered in case of rehabilitation.
Together with the functional requirements (see Clause 5) the financial and economic aspects of the
various options shall also be considered before reaching a decision as to the preferred solution. The
above matters-shall be considered in terms of their implications on the whole life cost.
The consequences or likelihood of some hazards and threats can be mitigated by good design of
systems or of upgrading works. This shall be taken into account when designing new assets and when
upgrading existing system. The cost of any changes shall be balanced against the extent to which they
reduce the risks.
The extent to which risks are mitigated through enhanced design are influenced by the system
operator's or regulator's tolerance of risk.
Foreseeable hazards include:
a) failure of a component of the drain and sewer system;
b) excessive rainfall (see 8.4.3.3);
c) the impact of other foreseeable hazards (e.g. river flooding) on the drain and sewer system or any
of its components.
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8.2 Types of system
There are two types of wastewater to be collected and transported by the system; foul wastewater and
surface water. Two options are available as follows:
— combined system – where both types of wastewater are mixed;
— separate system – where each type of wastewater is collected and transported in a dedicated sewer
(surface water in a surface water sewer or open channel and foul wastewater in a foul sewer).
Variants of these basic systems are also possible.
The selection of a system mainly depends upon:
— national or local water management policies;
— type of system which presently exists and how it is expected to evolve;
— possible future changes in the catchment;
— capacity and quality of receiving water bodies;
— nature of influents to the system;
— need for prior treatment;
— topography;
— ground characteristics;
— treatment plant;
— economic considerations;
— other local conditions.
Adopting an integrated approach towards surface water drainage benefits both the quality and quantity
impacts on receiving water bodies. Where a new system is being proposed, surface water should be
kept separate from other wastewater as far practicable taking into account the levels of pollution in the
surface water. The discharge of surface water should, depending on the levels of pollutants in the
surface water and the availability of suitable discharge points, be in accordance with the following
hierarchy:
a) to an adequate infiltration drainage system;
b) directly to a surface receiving water body;
c) to a drain and sewer system discharging to a surface receiving water body;
d) to a drain and sewer systems discharging to a wastewater treatment plant.
Storage should be provided to limit the peak discharges to acceptable flow rates.
National or local regulations or the relevant authority can specify the type of system to be used.
Permissible influents to the system are:
— domestic wastewater;
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— authorized industrial wastewater. (In some cases pre-treatment of such industrial wastewater is
necessary before discharge to the system is permitted in order to achieve the quality required by
national or local regulations or the relevant authority);
— surface water and, where exceptionally permitted, groundwater.
The nature of the expected influents shall be assessed.
The design shall take into account the conveyance of wastewater, including industrial wastewater,
which neither damages the system and/or the wastewater treatment plant, nor impair their operation.
8.3 Physical layout
8.3.1 Preliminary investigations
Preliminary investigations should be undertaken to enable the evaluation of the route and construction
options. These investigations should be from records or surveys and should include:
a) topographical investigations;
b) geotechnical investigations;
c) groundwater investigations;
d) investigations of existing drainage and other utility services.
As the project develops further, more detailed investigations should be carried out where necessary.
8.3.2 Layout and profile
The design of the system shall ensure that the layout and profile meets all relevant functional
requirements including:
— maintainability (see 5.1.3);
— protection of occupational health and safety (see 4.3);
— not endangering adjacent structures and utility services (see 5.1.13).
The layout and profile is influenced by topography, the character of developments served, existing and
future flows from the catchment, the suitability of receiving water bodies or receiving wastewater
treatment plant and the adequacy of any existing system to accept the design flow.
Economical design is usually achieved when drains and sewers follow the natural falls of the ground.
Where practicable they should be laid at such gradients as to prevent excessive accumulation of solid
matter in the invert. The route shall be selected so as not to impair the stability of structures.
Manholes and inspection chambers should be sited in locations where they can be reached by operator
personnel and equipment. Information on operations and maintenance techniques can be found in
Annex C. Access should also be provided for excavation to repair or replace a sewer, if this were to be
necessary.
Circumstances can make the pumping of wastewater either necessary or advisable and should be
considered alongside the long-term energy commitments and the whole life costs involved. Detailed
design of pumping installations should be carried out in accordance with the prEN 16932 series.
Positive and negative pressure systems are relatively independent of gradient and the depth of cover. In
certain circumstances they are alternatives to, or can form part of, systems operating essentially under
gravity. Long-term energy commitments and whole life costs including maintenance shall be considered
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for each option. Positive pressure systems should be designed in accordance with as above. Vacuum
sewer systems should be designed in accordance with as above.
Where an appropriate sewer is not available and cannot immediately be provided, provision for local
treatment of wastewater shall be provided.
The levels of the receiving water bodies at the outfalls shall be taken into account in the planning of the
sewer system.
Detailed design of layout and profile is described in Annex D.
8.4 Hydraulic design
8.4.1 General
The hydraulic design of the system shall ensure that the design meets all relevant functional
requirements including:
— protection from sewer flooding (see 5.1.2);
— maintainability (see 5.1.3);
— maintaining the flow (see 5.1.12).
8.4.2 Foul drains and sewers
The design flows for drains and sewers comprise:
— domestic wastewater flows;
— authorized industrial wastewater flows.
Extraneous water flows may be included in the calculation where these flows cannot be avoided.
Design flows should be calculated in accordance with prEN 16933-2.
The hydraulic capacity of the pipelines shall be calculated in accordance with prEN 16933-2.
Surcharging is undesirable in foul gravity drain and sewer systems. Foul drains and sewers should
therefore be designed to run at less than pipe full conditions.
Rising mains shall be designed to carry the required design flows in self-cleansing conditions without
using excessive energy (see the prEN 16932 series). The retention time should also be limited so that
septicity does not occur.
Detailed design of the hydraulic design of foul drains and sewers is described in prEN 16933-2.
8.4.3 Surface water drain and sewer systems
8.4.3.1 General
Surface water drain and sewer systems collect and transport runoff generated within a catchment area
during rainfall, for safe discharge into a receiving water body or treatment plant. The magnitude of peak
flows depends on the intensity and duration of rainfall, the size and configuration of impermeable areas
and measures taken to reduce surface water. The topography, soil type and its permeability have also to
be considered when estimating the flows emanating from other areas.
Surface water drain and sewer systems are dimensioned in order to limit sewer flooding. It is usually
impracticable to avoid sewer flooding from very severe storms. A balance shall therefore be drawn
between cost and the political choice of the level of protection provided.
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The level of protection should be based on a risk assessment of the impact of sewer flooding to persons
and property. The level of protection should be specified in performance criteria for sewer flooding
frequencies or design rainfall events used in calculation.
The hydraulic capacity of surface water drains and sewers shall limit surcharge to nationally or locally
prescribed levels and frequencies taking into account backwater levels.
Surface water drain and sewer systems shall be designed taking reasonable measures to minimize the
impact to persons and property from any sewer flooding caused by rainfall in excess of the nationally or
locally prescribed sewer flooding frequencies.
Storage should be provided (e.g. by use of detention tanks and ponds) to minimize the hydraulic impact
on receiving water bodies.
Other techniques can be used to reduce the runoff entering the drain and sewer system either in
addition to or as a substitute to the use of drains and sewers. These techniques are based on one or
more of the following principles:
— infiltration systems;
— minimizing the area of impermeable surfaces connected to the drain and sewer system;
— time lag and attenuation of the flow.
For surface water drains and sewers, design flows for the surface water pipelines are runoff. No
allowance shall be made for any other wastewater component.
8.4.3.2 Surface water inlets
Surface water inlets shall be designed in order to ensure an adequate transfer of runoff from
impermeable areas into the surface water drains and sewers.
8.4.3.3 Surface water drains and sewers
The designer shall assess risk of sewer flooding in events that exceed the design sewer flood frequency,
taking into account both the consequences of the sewer flooding and the frequency. Flow routes for
excess flows should be investigated to determine the consequences and where possible, the design
should be changed to minimize the impact. Where the risk of sewer flooding cannot be reduced by these
means the design frequency should be decreased.
In simple design methods the pipes are usually designed to run just full, without surcharge, for
relatively frequent storms in the knowledge that this provides protection against sewer flooding from
much larger storms.
For larger developments and for schemes particularly where risks to public health or the environment
are significant, time-varying design rainfall and computer based flow simulation models shall be used.
Any model used shall be chosen in cooperation with the relevant authority. For any application it is
necessary to select a method where the appropriate balance between cost complexity and required
accuracy is achieved. Guidance on when they should be used and the type of method to select is given in
prEN 16933-2.
In these cases design should be undertaken to limit frequency of surcharge following which the design
should be checked to ensure that the design meets the design flood frequency criteria at specific
sensitive locations. These design checks are particularly important on steeply sloping catchment areas.
8.4.4 Combined drain and sewer systems
The hydraulic design of combined drain and sewers shall be undertaken in the same way as surface
water drains and sewers with the design flows increased to include the dry weather flow. Since the dry
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weather flow is generally only a small proportion of the capacity of the sewer, less allowance is
necessary for the peak dry weather flow rate.
Detailed design of the hydraulic design of combined drains and sewers is described in prEN 16933-2.
For combined drains and sewers, the design flowrate is made up of runoff, which is by far the
predominant component, plus an allowance for foul wastewater flows. The runoff component should
therefore be estimated using the methods outlined in prEN 16933-2. The foul wastewater component is
estimated as described in prEN 16933-2. As the foul wastewater flows are usually considerably lower
than the design flow rates, particular consideration should be given to self-cleansing velocities during
dry weather conditions.
8.5 Environmental considerations
8.5.1 General
The environmental design of the system shall ensure that the design meets all relevant functional
requirements including:
— Protection of surface receiving water bodies (see 5.1.4);
— Protection of groundwater (see 5.1.5);
— Prevention of odours and toxic, explosive and corrosive gases (see 5.1.6);
— Prevention of noise and vibration (see 5.1.7);
— Minimizing the use of finite resources (see 5.1.10 and 5.1.11).
Control of the sources of pollution from drain and sewer systems shall be considered as it can limit the
environmental impact to levels acceptable to the relevant authority.
Consideration of impacts shall pay due regard both to short-term effects and to cumulative long-term
effects.
Short-term effects can include fall in the concentration of dissolved oxygen, acute toxicity and hydrobiological stress. Cumulative long-term effects can include the build-up, in aquatic biota and sediments,
of persistent pollutants such as heavy metals and certain organic compounds.
Sources of environmental impact include:
— outfalls;
— combined sewer overflows;
— emergency overflows, for example from pumping installations or detention tanks;
— exfiltration to groundwater;
— infiltration of groundwater;
— untreatable non-domestic wastewater;
— disposal of residues produced during sewer cleaning (see EN 14654-1).
Any untreatable non-domestic wastewater can have an impact when subsequently discharged from a
combined sewer overflow or the wastewater treatment plant.
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Infiltration can also affect the frequency and volume of discharges from combined sewer overflows and
the quality of discharges from wastewater treatment plants.
Surface water can contain pollutants deposited on impervious surfaces including organic matter,
deposits derived from road vehicles, grit or sand from deterioration of the road surface, or adjacent soil.
Consideration shall be given to the risk of spills of noxious substances within the catchment area,
particularly on surface water systems. Where there is significant risk of spillage or discharge of
significant quantities of fire fighting water containing harmful substances, appropriate measures shall
be taken to avoid entry into or exit from the sewer system of these substances by, for example, the
provision of separators (see 8.7.2) or retention tanks.
Pipelines shall be designed to avoid leakage that might cause pollution of groundwater.
To minimize odour nuisance gravity drains and sewers shall be sufficiently ventilated to atmosphere by
allowing a free passage of air through the system. In very cold areas special precautions can be
required.
Disused drains and sewers shall be removed or, where this is impracticable, they shall be filled with
suitable material to prevent for example, structural deterioration, unauthorized use, ingress of
groundwater and infestation by rodents.
Care should be taken in the design of systems to minimize the accumulation of deposits as residues
from sewer cleaning activities can cause pollution.
8.5.2 Protection of surface receiving water bodies
The quality, quantity and frequency of any discharge to a surface receiving water body from any sewer
including a surface water sewer, combined sewer overflow, pumping installation or treatment works
shall meet the requirements of any national or local regulations or the relevant authority. Design shall
be such that the surface receiving water body is protected against overloading of its self-purifying
capacity. It shall take account of physical, chemical, biochemical, bacteriological, aesthetic and any other
relevant considerations.
8.5.3 Protection of groundwater
In order to protect groundwater, the national or local regulations or the relevant authority can require
stringent performance and testing in high-risk areas such as drinking water abstraction or aquifer
protection zones and areas with high groundwater levels. In such areas a number of zones with
different levels of protection can be specified by any national or local regulations or the relevant
authority, depending on risk.
8.5.4 Prevention of septicity
Septicity caused by the prolonged retention of wastewater under anaerobic conditions is undesirable
and should be avoided by limiting the time of retention in rising mains, sewers/detention tanks and
siphons and by the provision of self-cleansing conditions in sewers to achieve aerobic conditions within
the liquid. Where this is not possible or effective, intervention can be necessary by using, for example,
chemical oxidation and/or precipitation. Where chemicals are used, the choice of chemicals shall take
account of their potential environmental impact.
Septic wastewater can produce lethal or explosive gases, particularly hydrogen sulphide (H2S) and
methane (CH4) and lead to offensive odours, chemical attack, difficulties in wastewater treatment
processes, safety hazards and danger to life.
Septicity within a drain and sewer system is undesirable and therefore shall be minimized. It affects the
wastewater treatment process and can lead to the production of hydrogen sulphide (H2S) and
mercaptans. Hydrogen sulphide is malodorous, toxic and potentially lethal even in small concentrations.
Depending on its concentration and local conditions it can be oxidized to sulphuric acid, it tends to
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attack some materials in pipelines, treatment works and pumping installations. Parameters on which
the concentration of hydrogen sulphide depend, and which shall be taken into account include:
wastewater temperature, biochemical oxygen demand (BOD), sulphate availability, retention time, flow
velocity, turbulence, pH, ventilation, existence of rising mains or particular industrial wastewater
discharges upstream of the gravity sewer.
Predictive formulae can be applied in order to quantify sulphide formation both in pressure and gravity
sewers.
The following other gases can also be produced from normal wastewater in anaerobic conditions:
a) Methane has little odour and while it is a simple asphixiant by displacing oxygen, its main property
is that it produces an explosive mixture with air over a wide range of concentrations. A particular
vehicle for methane production is leachate from landfill sites which has been allowed to enter the
drain and sewer system. Such leachates could need to be treated at source.
b) Ammonia has a distinct and strong odour which gives good warning characteristics before reaching
toxic levels, which are themselves unlikely to be generated from normal wastewater.
c) Carbon dioxide has no odour and acts as an asphixiant by displacing oxygen.
d) Carbon monoxide is also odourless and is highly toxic and lethal after only limited exposure.
Production of all these gases can be limited by the application of strategies to reduce septicity.
Other gases can be produced under anaerobic conditions where particular industrial wastewater has
been allowed to enter the drain and sewer system.
Methods to control the effects of anaerobic conditions can be used, considering the potential
distribution of gases and their odours, including:
— natural or forced ventilation;
— natural or forced entrainment of air in the flow;
— addition of reagents to the flow.
8.5.5 Combined sewer overflows and surface water treatment
Combined sewer overflows are usually necessary devices in combined sewer systems to limit the flows
in the drain and sewer system and into wastewater treatment plants during rainfall events due to the
limitations on the hydraulic capacity as well as process-related restrictions.
Combined sewer overflow structures shall be designed to limit the impact of any discharges on the
environment to meet the performance requirements.
Various methods such as source-based surface water management, flow detention, sedimentation in
detention basins or vortex separators within the drainage system or increased capacity of wastewater
treatment plants can be used to assist in limiting pollution inputs from combined sewer overflows to
receiving waters. The pollution discharges to receiving water bodies from combined sewer overflows
and treatment works shall be considered together.
Factors to be considered include:
— flow rates;
— volume, duration and frequency of discharges;
— pollution concentrations and loads;
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— hydro-biological stress;
— aesthetic impacts, e.g. floating solids, oil films or bank-side litter.
8.5.6 Surface water outfalls
Depending on its origin and the use of drained surface areas, runoff can carry considerable amounts of
pollutants requiring some sort of retention and/or treatment before discharged to receiving water
bodies. This especially holds true for runoff from highly frequented traffic areas.
Outfall structures shall be designed and located to limit the impact of any discharges on the
environment to meet the performance requirements.
Various methods can be used to assist in limiting pollution inputs to receiving water bodies including:
a) source-based surface water management;
b) flow detention and sedimentation in detention basins;
c) vegetative treatment systems;
d) vortex separators within the drainage system;
e) filtration systems.
8.5.7 Emergency overflows
Emergency overflows can be installed immediately upstream of wastewater treatment plants, at
pumping stations and at other critical parts of the system for use under exceptional circumstances.
The environmental impact of such overflows shall be considered.
8.6 Structural design
8.6.1 Introduction
The structural design of the system shall ensure that the design meets all relevant functional
requirements including:
— prevention of noise and vibration (see 5.1.7);
— structural integrity and design working life (see 5.1.8);
— sustainable use of products and materials (see 5.1.10);
— not endangering adjacent structures and utility services (see 5.1.13).
The structural design of drain and sewer systems shall take account of:
— structural integrity taking into account the loads;
— watertightness of the drain and sewer system (see EN 1610);
— prevention of floatation;
— bearing capacity of the soil;
— chemical nature of the soil has an effect on the materials used;
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— effect of aggressive, corrosive and/or erosive wastewater on the materials used;
— possible differential settlement between structures and all drains and sewers and outgoing rising
mains and other services;
— any requirements of national or local regulations or the relevant authority.
Where buildings are near to drains or sewers or where a building is proposed near a drain or sewer the
design should consider the potential:
— effect on the sewer of the building; and;
— effect of any failure of the sewer on the building.
8.6.2 Structural design of pipelines
The structural design of buried pipelines shall be carried out in accordance with one of the methods
described in EN 1295-1 or otherwise designed in accordance with EN 1990.
In the case of renovation, a partial structural contribution of the existing pipe may be taken into account
only if the soil and pipe fabric is stable and when this contribution can be quantified.
Where common trenches for drains or sewers and other utility services are used care shall be taken to
ensure the stability of the pipes.
Where a pipeline is to be laid close to foundations of a structure, the potential effects of the structure on
a pipeline shall be considered. Care shall be taken to ensure that the foundations are not undermined or
damaged.
8.6.3 Structural design of other components
The structural design of other components of drain and sewers systems shall be designed in accordance
with EN 1990, or otherwise in accordance with relevant product standards.
8.6.4 Materials selection
The selection of an appropriate material is an important part of the design of the structure. The
durability of materials used in the construction of components of drain and sewer systems can be
affected by the chemical action of groundwater and the wastewater. In some conditions the material
can also be affected by the physical and chemical action of sediments contained in the wastewater.
In selecting materials designers shall consider:
— chemical content of the wastewater;
— possible presence of hydrogen sulphide (see 8.5.4);
— abrasive nature of any sediments carried in the wastewater;
— corrosive properties of any sediments and the effect of chemicals they could generate;
— chemical content of the ground and groundwater;
— physical properties of the soil;
— environmental impact of chemicals released during installation.
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8.7 Operational considerations
8.7.1 General
The operational considerations of the design shall ensure that the design meets all relevant functional
requirements including:
— protection from sewer flooding (see 5.1.2);
— maintainability (see 5.1.3);
— prevention of odours and toxic, explosive and corrosive gases (see 5.1.6);
— prevention of noise and vibration (see 5.1.7).
Planning, design, construction and rehabilitation shall take into account the operation and maintenance
requirements.
The system shall be designed to minimize the risks to the health and safety of operator personnel.
The cost of maintenance of the system shall also be considered. When balancing the construction costs
with future maintenance costs, the whole life cost should be minimized.
8.7.2 Control of inputs
Where appropriate, separators or other means of control shall be provided on or near inlets to exclude
or minimize the entry of solids or other materials that could impair the operation of the drain and
sewer system. These can include:
— grit separators to limit entry of sediments which could accumulate in the system restricting the
flow;
— grease separators to limit the entry of fats and grease which could be deposited in the system
restricting the flow;
— light liquid separators to limit the entry of flammable liquids which could cause a hazard in the
drain and sewer system.
National or local regulations can require the control of inputs.
The hydraulic design of the means of control is described in prEN 16933-2.
8.7.3 Self-cleansing conditions
Wastewater is likely to contain a variety of materials that can accumulate in drains and sewers or cause
blockage.
Drains and sewers shall be designed to minimize the risk of blockage from any material permitted in
wastewater.
The build-up of permanent deposits of solids in drains or sewers can significantly increase the risk of
sewer flooding and pollution. Drains and sewers shall be designed to provide sufficient shear stress to
limit the build-up of solids to levels which do not significantly increase this risk.
Special maintenance provisions can be required to ensure frequent sewer cleaning on sewers where it
had not been possible to provide self-cleansing conditions.
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8.7.4 Access to drains and sewers
Safe access shall be provided at reasonable intervals to allow for inspection and maintenance. Manholes
shall be designed to facilitate safe entry and egress by operator personnel and to provide sufficient
working space.
Wherever possible, provisions should be made for work to be carried out from surface level. National or
local regulations or the relevant authority can specify requirements for the access. Requirements for the
design of the access, taking account of the operational considerations, can be found in Annex D.
9 Construction
9.1 General
Drain and sewer systems shall be constructed in accordance with the design. Unless explicitly specified
the requirements in this Clause apply both for new construction and rehabilitation. During construction
the following issues should be taken into account:
a) health, safety and welfare of construction personnel and other people;
b) optimum sequence of construction particularly with regard to maintaining the operation of existing
drain and sewer systems which could be affected by the work;
c) methods of dealing with existing flows in part completed systems or when carrying out
rehabilitation of existing flows;
d) protection of the environment.
9.2 Pipelines
In the case of new construction, pipelines shall be constructed in accordance with EN 1610 or
EN 12889 as appropriate.
In case of rehabilitation, pipelines shall be constructed according to the relevant installation manual
(referring to the corresponding system standards when existing).
In any case the following points should notably be accounted for:
— pipeline geometry;
— flow performance;
— watertightness;
— proper load transfer from soil to pipeline through embedment;
— proper structural embedment.
Where common trenches for sewers or drains and other utility services are used, care shall be taken to
ensure the stability of the pipes.
Testing shall be carried out to verify that the work has been constructed in accordance with the design.
9.3 Ancillaries
Ancillaries, such as inspection chambers and manholes, should be constructed in order to ensure
correct junctions with the pipes (pipelines).
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Special care should be granted to differential displacements.
In any case the following points should notably be accounted for:
— geometry;
— flow performance;
— water tightness;
— proper structural embedment.
For ancillaries the performance requirements specified in relevant European product standards should
be taken into account. Grease separators to EN 1825-1 shall be installed in accordance with EN 1825-2.
Separator systems for light liquids to EN 858-1 shall be installed in accordance with EN 858-2.
9.4 Testing
It is necessary to test and assess the performance of the drain and sewer systems during construction
and at the completion of the construction stage.
Examples of tests and assessments are:
a) watertightness test with water;
b) watertightness test with air;
c) infiltration test;
d) visual inspection.
The tests to be undertaken to determine the performance being achieved by the drain and sewer
system depend on whether it is a new system, a rehabilitated system, or an existing system being tested.
Requirements for testing of new pipelines can be found in EN 1610.
10 Operation and maintenance
10.1 Introduction
The purpose of operation and maintenance is to ensure that the drain and sewer system perform in
accordance with the functional requirements defined in Clause 5 and in accordance with any operations
and maintenance plan (see 6.4.4.3).
Operations include:
— starting or stopping pumps;
— inserting dam boards;
— regulating valves and weirs;
— using detention tanks;
— acting in accordance with contingency and emergency plans;
— monitoring wastewater quality;
— inspecting periodically;
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— pest control (see C.8);
— making connections to existing drains and sewers (see C.9);
— control of disused drains and sewers (see C.10);
— control of building activities over or adjacent to sewers (see C.11).
Urgent interventions that are generally intended to be temporary are included in operations.
Maintenance includes:
— local repair or local replacement of damaged pipes or other structures in order to maintain the
functioning;
— cleaning and removal of sediments, obstructions, etc. to restore hydraulic capacity;
— maintenance of mechanical plant (e.g. pumps).
Effective operation and maintenance of the drain and sewer system depends on, for example:
— planning;
— rights of access;
— sufficient number of competent personnel;
— clear assignment of responsibilities;
— suitable equipment;
— knowledge of the system, its operational components and the users connected;
— adequate records and analysis.
There can also be requirements relating to the resolution of performance deficiencies, for example to
remedy failures and problems within acceptable timescales.
10.2 Monitoring
It is necessary to test and assess the performance of the drain and sewer systems during construction,
at the completion of the construction stage and also during the operational life of the system.
Monitoring can include:
a) inspection of the condition of the system;
b) recording incidents and performance failures of the system (e.g. flooding, blockages, collapses);
c) monitoring of inputs to the system;
d) monitoring within the system for toxic and/or explosive gas mixtures;
e) monitoring effluent quality, quantity and frequency at point of discharge to receiving water body;
f)
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The effectiveness of maintenance should be assessed by comparing the performance of the drain and
sewer system with the functional requirements (see 5.1). In addition, for reactive maintenance, target
response times can be used as an assessment.
10.3 Data requirements
Data shall be collected:
— for management purposes;
— for regulatory reporting purposes (e.g. properties at risk of sewer flooding);
— meet statutory requirements (e.g. maintaining plans showing the location of the public sewers).
It is possible to store a wide range of data on drain and sewer systems. However, collection, validation,
storage and updating the data can be expensive. The amount of data collected depends on the reasons
listed above.
The information can include:
— inventory of the system including records of drains, sewers, manholes, pumping installations,
combined sewer overflows, detention tanks, etc.;
— details of permits for influents into the system (industrial wastewater, hazardous materials, etc.);
— details of permits to discharge from the system into receiving water bodies (combined sewer
overflows, pumping installations, etc.);
— records of inspections of the system (e.g. closed circuit television (CCTV) survey reports);
— records of incidents such as blockages, collapses, pumping station failures, rising main failures and
sewer flooding incidents;
— information on rainfall;
— records of planned maintenance work carried out;
— actual response times for dealing with emergencies;
— information on the cost of incidents and maintenance activities to allow budgetary control and
performance review;
— information about the hydraulic capacity; and
— records of system performance (see 6.2.3).
Computer based geographical information systems (GIS) are a powerful tool for storage retrieval and
analysis of information on sewer systems.
10.4 Investigation and analysis of operational problems
To deal with operational problems in the most cost effective way, it is necessary to investigate and
understand their causes and effects. Investigations can be required to determine:
— route of a pipeline;
— cause and location of the sediment, blockage or collapse;
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— cause and location of a surface depression;
— location, source, quality of making of a connection;
— quality of a repair;
— condition of a pipe;
— extent of scale or grease build up;
— effectiveness of sewer cleaning and associated work;
— origin, quality and composition of influent;
— quantity and composition of the wastewater;
— presence of hazardous gasses;
— watertightness.
Operational investigation techniques available include:
— dye tracing;
— electronic location (using radio-transmitters and a directional receiver);
— closed circuit television (CCTV);
— walking through sewers;
— mirrors;
— flow measurement;
— sampling and analysis;
— in situ measurement of the composition of influent;
— watertightness tests (see EN 1610).
Operational problems concern the various components of the drain and sewer system. The techniques
available to resolve them are described in 10.6 and Annex C.
10.5 Dealing with major incidents
Where an incident occurs which cannot be managed by usual operating procedures emergency
procedures should be activated and the contingency and emergency plan (see 6.4.4.5) shall be used
accordingly. The extent to which an incident cannot be managed by ususal operating procedures
depends on the nature of the incident and the size of the organization.
National or local regulations or the relevant authority can have requirements regarding the
management of major incidents.
10.6 Techniques for operation and maintenance of components
Cleaning activities in drains and sewers shall be carried out in accordance with EN 14654-1.
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Separator systems for light liquids to EN 858-1 shall be operated and maintained in accordance with
EN 858-2. Grease separators to EN 1825-1 shall be operated and maintained in accordance with
EN 1825-2.
Guidance on operation and maintenance of pumping systems can be found in the prEN 16932 series.
Information on techniques for operation and maintenance are given in Annex C.
11 Qualifications and training
Personnel at all levels shall have appropriate training to allow them to carry out their work safely and
competently. This on-going training shall introduce and explain relevant legislation and techniques.
Training shall be repeated periodically when required and should cover safety, technical and legal
topics where appropriate.
The owners of construction works (procuring entity for public work or private agent for a private
contract, or their designer) shall request a proof that the enterprise carrying out the work is sufficiently
qualified for the specific work.
12 Sources of additional information
Various national organizations provide supplementary detail and guidance on the planning, design,
construction and maintenance of drain and sewer systems outside buildings.
Examples of the sources of relevant information include:
— Complementary National Standards;
— European, national or local regulations;
— Guidance issued by professional or trade associations;
— Guidance documents issued by national or local government organizations;
— Suppliers of technical software.
A list of organizations that produce relevant supplementary guidance is given in Annex A.
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Annex A
(informative)
Sources of additional information
A.1 National Standards Bodies
Details of national standards bodies that are CEN members and affiliates can be obtained from CEN.
CEN Management Centre
www.cen.eu
17, Avenue Marnix
B-1000 Brussels
A.2 Austria
A.2.1 Regulatory Bodies
Bundesministerium für Land- und Forstwirtschaft, www.lebensministerium.at
Umwelt, und Wasserwirtschaft. (Federal Ministry
for Agriculture, Forestry, Environment and Water
Management)
Stubenring 1
A-1012 Wien
Österreich
A.2.2 Other organizations
ÖWAV - Österreichischer Wasser - und
Abfallwirtschafts Verband.
(Austrian Water and Waste Management
Association)
www.oewav.at
Marc-Aurel-Strasse 5
A-1010 Wien
Österreich
A.3 Denmark
A.3.1 Regulatory Bodies
Miljøstyrelsen
(Danish Environmental Protection Agency)
www.miljoestyrelsen.dk
Strandgade 29
1401 København K
Erhvervs- og Byggestyrelsen
64
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(National Agency for Enterprise and Construction)
Dahlerups Pakhus,
Langelinie Allé 17
DK-2100 Copenhagen Ø
Arbejdstilsynet
www.arbejdstilsynet.dk
(The Danish Working Environment Authority
(WEA))
Landskronagade 33
DK-2100 København Ø
Vejdirektoratet
(Danish Road Directorate)
www.vejdirektoratet.dk
Niels Juels Gade 13
Postbox 9018
1022 Copenhagen K
A.3.2 Other organizations
Dansk Vand. Og Spildevandsforening
www.danva.dk
(Danish Water and Wastewater Association
(DWWA))
Vandhuset
Danmarksvej 26
8660 Skanderborg
Ingeniørforeningen i Danmark (IDA)
www.ida.dk
(The Water Pollution Committee of the Society Of
Danish Engineers)
Kalvebod Brygge 31–33
DK-1780 Copenhagen V
Denmark
DHI Institut for vand and miljø
(Danish Hydraulic Institute)
www.dhi.dk
Agern Allé 5
DK-2970 Hørsholm
Denmark
Teknologisk Institut
(The Danish Technological Institute)
www.teknologisk.dk/
Gregersensvej 1
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DK – 2630 Taastrup
A.4 Finland
A.4.1 Regulatory Bodies
Maa- ja metsätalousministeriö
(Ministry of Agriculture and Forestry)
www.mmm.fi
PL 30,
00023 Valtioneuvosto
Sosiaali- ja terveysministeriö
(Ministry of Social Affairs and Health)
www.stm.fi
PL 33,
00023 Valtioneuvosto
Ympäristöministeriö
(Ministry of the Environment)
www.ym.fi
PL 35,
00023 Valtioneuvosto
A.4.2 Other organizations
Suomen Vesilaitosyhdistys ry
(Finnish Water Utilities Association (FIWA))
www.vvy.fi
Ratamestarinkatu 7 B
FIN-00520 Helsinki
Työterveyslaitos
(Finnish Institute of Occupational Health)
www.ttl.fi
PL 40
00251 Helsinki
A.5 France
A.5.1 Regulatory Bodies
Ministère de l’Ecologie et du Développement
Durable
www.environnement.gouv.fr
(Ministry
for
Ecology
and
Sustainable
Development)
Tour Pascal A et B
Tour Sequoia
92055 La Défense CEDEX
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A.5.2 Other organizations
Comité Français pour les travaux sans tranchée www.fstt.org
(FSTT)
French Society for Trenchless Technology
4, rue des Beaumonts
94120 FONTENAY SOUS BOIS
A.6 Germany
A.6.1 Regulatory Bodies
The following Ministries for the Environment of the States (Länder)
Baden-Württemberg:
www.um.baden-wuerttemberg.de
Bayern:
(Bavaria)
www.stmuv.bayern.de
Berlin:
www.berlin.de/umwelt/behoerden
Brandenburg:
www.mlul.brandenburg.de
Bremen:
www.bauumwelt.bremen.de
Hamburg:
www.hamburg.de/bue
Hessen:
www.umweltministerium.hessen.de
Mecklenburg-Vorpommern:
www.lu.regierung-mv.de
Niedersachsen:
www.umwelt.niedersachsen.de
Nordrhein-Westfalen:
(North Rhein Westfalia)
www.umwelt.nrw.de
Rheinland-Pfalz:
www.mulewf.rlp.de
Saarland:
www.saarland.de/ministerium_umwelt_verbraucherschutz.htm
Sachsen:
(Saxony)
www.smul.sachsen.de
Sachsen-Anhalt:
(Lower Saxony)
www.mlu.sachsen-anhalt.de
Schleswig-Holstein:
Thüringen:
(Thuringia)
www.schleswigholstein.de/DE/Landesregierung/V/v_node.html
www.thueringen.de/th8/tmuen
Bundesministerium für Umwelt, www.bmub.bund.de
Naturschutz,
Bau
und
Reaktorsicherheit (BMUB)
Ministry
for
the
Federal
Environment, Nature Conservation,
Building and Nuclear Safety
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Bonn Office:
Robert-Schuman-Platz 3
D - 53175 Bonn
Berlin Office:
Stresemannstr. 128 - 130
D - 10117 Berlin
The Ministries of the relevant states.
A.6.2 Other organizations
Deutsche Vereinigung für Wasserwirtschaft, www.dwa.de
Abwasser und Abfall (DWA)
(German Association for Water, Wastewater and
Waste)
Theodor-Heuss-Allee 17
D-53773 Hennef
Germany
A.7 Ireland
A.7.1 Regulatory Bodies
Department of the Environment, Heritage and
http://www.housing.gov.ie/
Local Government
Custom House,
Dublin 1
Ireland
A.8 Italy
A.8.1 Regulatory Bodies
Ente Nazionale Italiano Di Unificazione - Uni
www.uni.com
Via Sannio, 2
20137 MILANO
A.8.2 Other organizations
ASPI – Associazione nazionale manutenzione e
www.associazioneaspi.it
spurgo di reti fognarie e idriche
Via S. Caboto, 2
33170 PORDENONE
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A.9 The Netherlands
A.9.1 Regulatory Bodies
Ministerie van Infrastructuur en Milieu (I&M)
www.government.nl/ministries/ministry-of(Ministry of Infrastructure and the Environment infrastructure-and-the-environment
(I&M))
Plesmanweg 1–6
2597 JG The Hague
P.O. Box 20901
2500 EX The Hague
Directorate-General for Public Works and Water
Management
Koningskade 4
2596 AA The Hague
P.O. Box 20906
2500 EX The Hague
A.9.2 Other organizations
Stichting RIONED (RIONED Foundation)
(national centre of expertise in sewer
management and urban drainage)
http://www.stichtingrioned.nl
Galvanistraat 1
6716 AE Ede
P.O. Box 133
6710 BC Ede
Koninklijk Nederlands Waternetwerk (KNW)
www.waternetwerk.nl
Binckhorstlaan 36-M420
2516 BE The Hague
Unie van Waterschappen UvW
(Association of Water Bodies)
www.dutchwaterauthorities.com
www.uvw.nl
Koningskade 40
2596 AA Den Haag
P.O Box 93218
2509 AE The Hague
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A.10 Norway
A.10.1 Regulatory Bodies
Norwegian Building Authority
http://www.dibk.no/
PO Box 8742 Youngstorget
NO 0028 Oslo
Norway
Norwegian Environment agency
www.miljodirektoratet.no
PO Box 5672 Sluppen
N-7485 Trondheim
Norway
A.10.2 Other organizations
Norwegian Water BA
http://www.norskvann.no/
Vangsvegen 143
NO 2317 HAMAR
Norway
A.11 Portugal
A.11.1 Regulatory Bodies
Ministério da Economia
Rua Horta Seca 15, 3° -s 318 1200–221 Lisboa
Ministério do Ambiente,
Território e Energia
Ordenamento
do
Rua de «O Século», 51
1200–433 Lisboa
Entidade Reguladora de Águas e Resíduos
www.ersar.pt
(ERSAR)
Centro Empresarial Torres de Lisboa
Rua Tomás da Fonseca, Torre G - 8°
1600–209 LISBOA
A.11.2 Other organizations
Laboratório Nacional de Engenharia Civil (LNEC)
Av. do Brasil, 101,
1700–066 Lisboa
70
http://www.lnec.pt/
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A.12 Sweden
A.12.1 Regulatory Bodies
Boverket
(The Swedish National Board of Housing, Building www.boverket.se
and Planning)
Naturvårdsverket
(Swedish Environmental Protection Agency)
http://www.naturvardsverket.se
Arbetsmiljöverket
(The Swedish Work Environment Authority)
www.av.se
Havs- och vattenmyndigheten
(The Swedish agency for Marine and Water www.havochvatten.se
Management)
A.12.2 Other organizations
Svenskt Vatten
(Swedish Water and Wastewater Association)
www.svensktvatten.se
Box 14057
SE-167 14 Bromma
Sweden
A.13 Switzerland
A.13.1 Regulatory Bodies
D: Bundesamt für Umwelt (BAFU)
F: Office fédéral de l'environnement (OFEV)
http://www.bafu.ch
http://www.ofev.ch
Postfach, 3003 Bern
Gewässerschutz-Fachstellen der einzelnen Kanton
www.kvu.ch
(Fachstellen von 26 Kantonen)
Die Post- und Internet-Adressen können über
www.kvu.ch erfragt werden.
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A.13.2 Other organizations
D: VSA, Verband Schweizer Abwasser- und
Gewässerschutzfachleute
F: VSA, Association suisse des professionnels de la www.vsa.ch
protection des eaux
E: VSA, Swiss Water Pollution Control Association
Europastrasse 3,
Postfach
CH-8152 Glattbrugg
A.14 United Kingdom
A.14.1 Regulatory Bodies
A.14.1.1 General
Health and Safety Executive
www.hse.gov.uk
Rose Court
2 Southwark Bridge
London
SE1 9HS
A.14.1.2 England
The Department for Communities and Local
www.gov.uk
Government (Building Regulations)
Fry Building,
2 Marsham Street,
London,
SW1P 4DF
Department of the Environment, Food and Rural
www.defra.gov.uk
Affairs
Nobel House
17 Smith Square
London
SW1P 3JR
The Environment Agency
Horizon House
Deanery Road
Bristol
BS1 5AH
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A.14.1.3 Wales
Welsh Government (Building Regulations)
www.wales.gov.uk
Housing and Regeneration Directorate
Welsh Government
Rhydycar
Merthyr Tydfil
CF48 1UZ.
Welsh Government (Water and Sewerage)
www.wales.gov.uk
Environment - protection and quality
Cathays Park
Cardiff
CF10 3NQ
Natural Resources Wales
www.naturalresourceswales.gov.uk
Tŷ Cambria
29 Newport Road
Cardiff
CF24 0TP
A.14.1.4 Scotland
Scottish Building Standards Division (BSD).
http://www.gov.scot/Topics/BuiltEnvironment/Building/Building-standards
Denholm House
Almondvale Business Park
Livingston
EH54 6GA
Scottish Environmental Protection Agency (SEPA)
www.sepa.org.uk
SEPA Corporate Office
Erskine Court
Castle Business Park
STIRLING
FK9 4TR
A.14.1.5 Northern Ireland
Department of Finance and Personnel (Building
http://www.dfpni.gov.uk/
Regulations)
Building Regulations Unit
Office estates and Building standards Division
10th Floor
River House
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48 High Street
Belfast,
BT1 2AW
The Environment and Heritage Service
http://www.ehsni.gov.uk/
Environmental Protection
Calvert House
23 Castle Place
Belfast
County Antrim
Northern Ireland
BT1 1FY
A.14.2 Other organizations
Water UK
www.water.org.uk
3rd Floor
36 Broadway
Westminster
London
SW1H 0BH
Water Research Centre (WRc)
www.wrcplc.co.uk
Frankland Road
Blagrove
Swindon
Wiltshire
SN5 8YF
Foundation for Water Research (FWR)
Allen House
The Listons
Liston Road
Marlow
Bucks
SL7 1FD
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Annex B
(informative)
Rehabilitation approaches
One or a combination of the following possible approaches can be used to formulate the rehabilitation
plan:
a) Asset value approach - A financial based approach that is used to ensure that rehabilitation is
carried at a rate that ensures that the value of the system at the end of a specified period does not
fall below a specified threshold.
b) Area-related approach - One part of the network is selected having common characteristics,
requirements and properties, for example: a pumping station catchment area, a groundwater
protection zone, a residential or commercial area or the whole of a specific street.
c) Condition based approach - All drains and sewers are inspected and those drains or sewers that do
not meet some specified threshold condition are rehabilitated.
d) Multi-utility approach - The rehabilitation of wastewater systems is carried out jointly with
rehabilitation of other utility services in the same location in one construction activity.
e) Functional related approach - This is built around the need for changes to improve the performance
of the system (e.g. the need to reduce or eliminate discharges to receiving water) and takes the
opportunity to do other rehabilitation work where this can be done more efficiently at the same
time.
f)
Reactive approach - This involves responding to failures and problems as they are identified.
Examples can include: restoring structural integrity following a collapse, removing a complete or
partial blockage in order to restore the flow, or increasing hydraulic capacity following a sewer
flooding incident.
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Table B.1 —Advantages and disadvantages of different rehabilitation approaches
Approach
Asset
approach
Area-related
approach
Condition
approach
Advantages
Disadvantages
value • The changes in asset value of the
system can be made transparent.
• Suitable for determining a fixedrate budget.
• It is easy to get a clearer view of
the work and the benefits.
• It is possible to carry out the work
in a defined period.
• Concentration of work in one area
can be financially efficient.
• Part
of
the
system
is
comprehensively rehabilitated.
based • Reduction in need for reactive
rehabilitation.
• The complete drain and sewer
system is maintained to a defined
standard.
• It is solely financially driven.
• Needs
to
be
used
in
combination
with
other
approaches.
• A detailed cost estimate can
only be made after detailed
investigation of the area.
• Problems remain in other areas
of the system for a longer period.
need
for
• Increased
coordination with other projects.
• Problems with a lower priority
remain in the system for a longer
period.
• Loss of efficiency by the
possible need to carry out further
works in the same parts of the
system at a later time.
Multi-utility
approach
• Reduced costs through economies • Less control through need to
of scale by working with other utilities. carry out works in cooperation with
• Improved acceptance by the public. other utilities.
need
for
• Increased
coordination.
• Problems remain in other areas
of the system for a longer period.
• Costs arise before they are
necessary in order to achieve
coordination.
Performancerelated approach
• Future-oriented planning creates • Cannot be applied as sole
capacity, alleviating problems before approach.
they occur.
Reactive approach
• Can be cost effective
consequence of failure is low.
where • Cannot
occurring.
prevent
failures
The reactive rehabilitation approach should only be used where the risk of failure is considered
acceptable, taking into account both the probability of failure and the consequence.
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Annex C
(informative)
Operation and maintenance techniques
C.1 Pipelines
C.1.1 General
The common problems associated with drains and sewers (man-entry and non man-entry) can be
divided into two types, functional problems and structural problems.
C.1.2 Functional problems
Functional problems can include:
— blockage - this usually occurs when sediments/debris are deposited within the sewer system,
forming obstructions and a reduced pipe capacity;
— sedimentation - this can also lead to blockages;
— encrustation - build up of mineral deposits on the wall of the pipeline;
— grease - deposited on the wall of the pipeline;
— intrusion of tree roots;
— infiltration or exfiltration caused by structural problems (see C.1.3);
— failure of air entry and release valves and other protection systems (for rising mains).
EN 14654-1 specifies requirements for cleaning activities in drains and sewers.
C.1.3 Structural problems
Structural problems can include:
— collapse;
— cracking or fracturing of the pipe;
— chemical attack or corrosion;
— ground erosion outside the wall of the pipe - usually caused by infiltration of soil into the pipe;
— defective connections;
— pipe deformation;
— open or displaced joints between pipes.
The following methods can be used to deal with the problems described above:
— repair;
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— renovation;
— replacement.
Where problems are widespread or a significant length of sewer is involved an integrated sewer system
study (see Clause 6) of the whole catchment area or part of it should be considered.
C.2 Manholes and inspection chambers
Manholes and inspection chambers are needed for access to sewers and drains for maintenance and
operations. The problems include:
— defective covers - these include covers which are broken, cracked, ill-fitting or are not flush with
the ground level;
— problems with access - e.g. inadequately sized access shaft, or defective steps or ladders;
— structural problems with the fabric of the chamber including chemical attack and infiltration;
— sediment in the invert;
— odours or gas/oxygen deficiency.
These can be solved by works such as: cleaning; replacement and resetting of the covers; repair,
renovation or replacement of the fabric of the chamber; reconstruction of access; replacement of steps
or ladders; efficient ventilation.
C.3 Combined sewer overflows
The purpose of combined sewer overflows is to spill excess flows from a system to surface receiving
water body (see 8.5 and prEN 16933-2).
Problems associated with combined sewer overflows include:
— blockages;
— siltation of the chamber;
— fouling of screens;
— structural problems.
Blockages can be caused by restrictions in size of the downstream sewer resulting in low flow velocity
upstream leading to silting and general build-up of silt/debris in the chamber.
Siltation can be minimized by high pressure water jets to clean the chamber, high volume suction units
to remove debris or flushing of the chamber.
Planned maintenance can be necessary in order to limit the environmental impact to satisfy the
requirements of national or local regulations or the relevant authority. The problem can be solved using
planned maintenance procedures, which includes inspection and reporting. From the report, work can
be given a priority and inspection frequencies determined.
Screens, where fitted, can require cleaning following heavy storms.
Structural problems arising may be dealt with in a similar fashion to structural problems in manholes.
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C.4 Detention tanks
The role of the detention tank is to reduce peak flows by the temporary storage of wastewater within
the system. They are often used to reduce flooding and to reduce discharge and pollution load from
combined sewer overflows. The problems include:
— blockage of flow control devices;
— removal of sediment.
Methods of optimizing the removal of sediments are:
— modifications to the structure of the tank e.g. by use of low friction coatings (these shall not be used
on areas required for access as it can be a hazard to operatives);
— modification of inlet design to increase scour;
— modification to the benching or installation of dry weather flow channels;
— use of mechanical plant in the tank to periodically remove sediments.
Where a blockage has occurred and wastewater has been detained for some time, clearing the blockage
suddenly can have an unacceptable impact on the wastewater treatment plant. Consideration should be
given to the gradual emptying or removal of effluents from the tanks.
C.5 Separators, settling chambers and gullies
Separators are used to intercept light liquids e.g. oil, hydrocarbons, etc., grease or solids. Planned
maintenance of separators is required if they are to function efficiently.
Grit separators, settling chambers and gullies are often used to prevent sand and gravel from entering
the system.
Separators, settling chambers and gullies should be emptied periodically to prevent blockage, especially
after spillages and, where appropriate, severe storms.
EN 858-2 specifies requirements for the operation and maintenance of separators for light liquids.
EN 1825-2 specifies requirements for the operation and maintenance of grease separators.
C.6 Pumping installations
Guidance on operation and maintenance of pumping systems can be found in the prEN 16932 series.
C.7 Inverted siphons
The main problem associated with inverted siphons is sedimentation and blockage of the pipe. Planned
inspection and maintenance should be carried out to ensure that inverted siphons continue to operate
efficiently.
Inspection can include:
— checking that washout valves and pumps can be operated;
— checking for surcharging at the upstream end of each pipe, which can be a sign of partial blockage;
— visual inspection of pipelines.
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Cleaning methods can include high pressure water jets, high volume suction units to remove debris,
flushing of the inverted siphon.
C.8 Pest control
The principal pest problem in sewers is related to rats, though in some areas especially where there is
insufficient ventilation, or deposits of faecal sediments, insects such as cockroaches or mosquitoes can
also be a problem.
Since the sewer network can be a refuge for rats, control of rodents is needed to minimize health risks
(including Leptospirosis and Salmonella) and to prevent structural damage caused by burrowing.
Treatment programmes should be carried out in accordance with the requirements of national or local
regulations or the relevant authority, to control the infestation. To ensure maximum effectiveness
treatment programmes for sewers and drains should be carried out on a catchment wide basis and
should be coordinated with the treatment of surface infestations.
Areas for treatment should be identified, in collaboration with national or local regulations or the
relevant authority and by reference to records of sightings of rodents. Areas may also be categorized
according to the risks to public health. The treatment programmes should be recorded and the
effectiveness measured so that records can be used to plan future programmes.
C.9 Making connections to existing drains and sewers
A large proportion of structural problems on drains and sewers are associated with poorly made lateral
connections. Problems are particularly common where manholes, inspection chambers or pre-formed
junctions are not used.
The control of new connections shall be undertaken to ensure that:
— fabric of the drain or sewer is not weakened or damaged by the connection;
— no operational problems are caused by the connection;
— sewer is inspected at the point of connection before and after construction;
— system is watertight at the point of connection;
— connections are made to the correct sewer, where there are separate sewer systems.
Connections other than at manholes or inspection chambers should be made using pre-formed
junctions.
New connections to brick sewers should be avoided, however if one is necessary, a thorough inspection
of the sewer shall be made beforehand.
C.10 Control of disused drains and sewers
Disused drains and sewers shall be removed or, where this is impracticable, they shall be filled with
suitable material to prevent, for example, structural deterioration, unauthorized use, ingress of
groundwater or infestation by rodents.
C.11 Control of building over or adjacent to sewers
Construction work in close proximity to drains and sewers should be controlled in order that the
operation and maintenance of the sewer system is not impaired by:
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a) excessive loading leading to structural failure of part of the drain and sewer system;
b) prevention of access by maintenance personnel or equipment to manholes or inspection chambers,
wastewater pumping stations, or other ancillary structures;
c) prevention of access by maintenance personnel or equipment for excavation to repair a defect on a
pipeline;
d) creating an undue risk of failure of the building in the event of a structural failure of the drain or
sewer;
e) obstructing an overland flow path leading to an excessive risk of sewer flooding in the building.
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Annex D
(normative)
Physical layout of the system
D.1 Preliminary investigations
D.1.1 General
Attention needs to be paid to both the topographical features present in the localities concerned and to
the geological nature of the underlying strata.
D.1.2 Topography
Surface reconnaissance and examination of contour maps and aerial photographs enable preliminary
lines for drains, sewers and rising mains to be established so that the general feasibility of the proposals
can be determined before detailed layouts and longitudinal sections are prepared. It is important to use
any available geological survey data in conjunction with contour maps when deep open-cut and trenchless options have to be considered.
D.1.3 Geotechnical survey
At the conception stage of the design an understanding of the ground conditions to be encountered
during the construction of the scheme is essential in order to be able to evaluate fully all the route and
construction options.
The aim in this initial geotechnical survey is to gain broad information in the most cost effective
manner. As the project develops, more intensive investigations are necessary.
Geological maps are, even with their limitations, a source of general information. Where these are
inadequate, a preliminary ground investigation should be undertaken.
The data gathered in a geotechnical survey should, as appropriate, be sufficient to be able to assess:
a) ground loadings on the pipes/structures;
b) landslide conditions;
c) subsidence conditions;
d) fine particle movement;
e) any likely swelling of clay strata;
f)
groundwater levels and movement;
g) aquifer recharge potential;
h) loadings from adjacent structures and highways;
i)
previous land use (including mining);
j)
alternative construction methods;
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k) options in pipe type choice;
l)
pipe bedding options;
m) aggressive soil or groundwater conditions.
Soil and rock samples should be retained especially where tunnelling or other trench-less methods are
contemplated.
D.1.4 Groundwater
Where appropriate, groundwater levels including seasonal variations shall be determined during
representative periods of time. Investigations shall be carried out to identify conditions which can be
detrimental to the integrity of the pipeline and its surroundings.
D.1.5 Existing drainage services
The lines, levels, hydraulic adequacy and structural condition of all relevant existing features (e.g.
drains, sewers, ditches, land drains and watercourses) shall be ascertained. When designing a
rehabilitation project the existing pipe shall be assessed in accordance with 6.3.
D.1.6 Other existing utility services
The positions of other existing relevant utility services shall be ascertained as accurately as possible.
D.2 Layout and profile
D.2.1 Introduction
The principles for the physical design of drain and sewer systems are specified in 8.1.
D.2.2 Layout
The layout is influenced by factors such as:
a) site conditions, environmental considerations, retained features and existing utility services;
b) protection of water abstraction areas;
c) availability of suitable sewers or outfalls;
d) layout of buildings, disposition of drainage systems inside buildings, appliances located on levels
necessitating direct connections to drains;
e) use of buildings served;
f)
planning and coordination of utility services;
g) social disruption during construction and its cost implications;
h) practical aspects of construction methods, working space, adequate protection and support;
i)
stability of building during and following construction of the drains and sewers;
j)
existing, planned and future development;
k) connections to or from existing drains and sewers which are to be retained;
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l)
provision for phased construction and occupation;
m) available gradients and depths of construction;
n) possibility of real-time control;
o) levels of receiving water bodies;
p) effects of tides, waves and currents;
q) groundwater levels;
r)
access for inspection and maintenance;
s)
overland flood flow paths;
t)
obstacles from other infrastructure (e.g. utility services, railways, waterways, major roads);
u) land ownership;
v) proximity of trees and other vegetation.
The routing of drains and sewers to take into account such factors can have major consequences: e.g.
excessive depths or length, need of pumping or inverted siphons.
D.2.3 Accessibility
D.2.3.1 General
Manholes and inspection chambers should be in locations where they can be accessed by all those who
could have need to use them, having regard to the need for access in an emergency.
Where frequent access is required (e.g. pumping stations or combined sewer overflows with screens) or
access by special plant can be required (e.g. tanks, pumping stations or washout valve chambers) this
should be taken into account (see also D.3).
Sewers serving more than one property should be at locations where the access for repair is possible.
D.2.3.2 Location of manholes and inspection chambers
The principles for provision of access are described in 8.7.4.
The maximum spacing between access points should take account of the maintenance equipment and
practices likely to be used.
In the case of drains, access shall be provided where practicable, at every change of alignment or
gradient by means of manholes, inspection chambers and rodding points (a small non-man access
connection that facilitates cleaning or inspection). Where this is not practicable, provision for access
shall ensure that changes of alignment or gradient can be reached.
In the case of non man-entry sewers, access shall be provided, where practicable, at every change of
alignment or gradient, at the head of all sewers, at every junction of two or more sewers, wherever
there is a change in the size of a sewer and in addition at reasonable intervals for inspection and
maintenance. In general, access should be provided through manholes. Inspection chambers may be
used within the system.
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In the case of man-entry sewers, access shall be provided at reasonable intervals to allow for inspection
and maintenance, having regard to the nature of the work to be undertaken and the proposed safe
systems of working.
National or local regulations can specify requirements for the:
— location and spacing of access points on drains and sewers;
— positioning or the maximum spacing of manholes or inspections chambers;
D.2.4 Depth
The approximate depth is determined during the conceptual design and finalized during the detailed
design.
Depth has a significant effect on the cost of construction and maintenance. In deciding the method of
construction, the depth of drains and sewers shall be considered, in conjunction with other factors such
as:
— protection against sewer flooding;
— nature of the ground;
— presence of groundwater;
— proximity of foundations;
— proximity of utility services;
— proximity of trees or heavy root growth;
— protection against frost;
— minimum cover.
D.2.5 Need for pumping
Circumstances which can make the pumping of wastewater either necessary or advisable include the
following:
a) avoidance of excessive depths of sewer;
b) drainage of low lying or other parts of the catchment area susceptible to sewer flooding;
c) development of areas not capable of gravitational discharge to an adjoining drain and sewer
system, a wastewater treatment plant or an outfall;
d) overcoming an obstacle, e.g. a ridge, a watercourse, a railway or for avoiding the use of an inverted
siphon;
e) correction of difficulties in a drain and sewer system resulting from mining subsidence;
f)
provision of sufficient head for operation at a wastewater treatment plant;
g) centralization of wastewater treatment;
h) raising wastewater to detention tanks.
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Where part of a system cannot be effectively drained using a gravity system then consideration should
be given to the use of one or more pumping installations. The optimum number of installations shall
first be determined having regard to the whole life cost.
D.2.6 Pumping installations
Where pumping installations are provided the design shall take into account:
a) whole life cost;
b) energy usage;
c) operations and maintenance requirements;
d) risk and consequences of failure;
e) health and safety of public and operating staff;
f)
environmental impact;
g) nature of wastewater which can:
1) be aggressive, corrosive and/or erosive;
2) have a high solid content increasing the potential for blockage;
3) be toxic;
4) lead to potentially explosive conditions.
The design of the pumping station and the rising main shall take into account the interaction between
them.
Where the wastewater is pumped consideration shall be given to the effects of the pump discharge
rates on the downstream parts of the system. Detailed design of pumping installations shall be designed
in accordance with the prEN 16932 series.
D.2.7 Drains and sewers near water abstraction areas
Installation of drains and sewers can be restricted in areas where water is to be abstracted for human
consumption. If in such areas drain and sewer systems are unavoidable, the designer shall take
measures to ensure permanent control and to prevent pollution of the ground and/or groundwater.
Such measures can include:
— installation of an additional equally watertight surrounding pipe;
— installation of alarm systems for leakage and breakage;
— installation of house connections directly to manholes and not to the sewer;
— special requirements for system components and method of construction.
D.3 Access to drains and sewers
Manholes and inspection chambers should be designed and installed so as to avoid any acute changes in
direction of flow from branch drains.
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National or local regulations can specify requirements for the dimensions of manholes or inspection
chambers.
The dimensions for manholes and inspection chambers shall not be less than the minimum dimensions
given in EN 476.
EN 476 contains requirements for three types of chamber as follows:
a) manhole with access for cleaning and inspection by personnel;
b) manhole with access for cleaning and inspection by personnel in only exceptional circumstances;
c) inspection or connection chamber.
National or local regulations or the relevant authority can prohibit entry of personnel into chambers
below a certain size.
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Bibliography
[1]
CEN/TR 1295-2, Structural design of buried pipelines under various conditions of loading —
Part 2: Summary of nationally established methods of design
[2]
CEN/TR 1295-3, Structural design of buried pipelines under various conditions of loading —
Part 3: Common method
[3]
CEN/TR 1295-4, Structural design of buried pipelines under various conditions of loading —
Part 4: Parameters for reliability of the design
[4]
EN 1991 (all parts), Eurocode 1: Actions on structures
[5]
EN 13380, General requirements for components used for renovation and repair of drain and sewer
systems outside buildings
[6]
EN 13508-2, Investigation and assessment of drain and sewer systems outside buildings — Part 2:
Visual inspection coding system
[7]
EN 14457, General requirements for components specifically designed for use in trenchless
construction of drains and sewers
[8]
EN 14654-2, Management and control of operational activities in drain and sewer systems outside
buildings — Part 2: Rehabilitation
[9]
EN 15885, Classification and characteristics of techniques for renovation and repair of drains and
sewers
[10]
Council Directive 91/271/EEC of 21 May 1991 concerning urban waste-water treatment
[11]
Regulation (EU) No 305/2011 of the European Parliament and of the Council of 9 March 2011
laying down harmonised conditions for the marketing of construction products and repealing
Council Directive 89/106/EEC
[12]
Council Directive 89/391/EEC of 12 June 1989 on the introduction of measures to encourage
improvements in the safety and health of workers at work
[13]
Council Directive 89/656/EEC of 30 November 1989 on the minimum health and safety
requirements for the use by workers of personal protective equipment at the workplace (third
individual directive within the meaning of Article 16 (1) of Directive 89/391/EEC)
[14]
Council Directive of 29 May 1990 on the minimum health and safety requirements for the
manual handling of loads where there is a risk particularly of back injury to workers (fourth
individual Directive within the meaning of Article 16 (1) of Directive 89/391/EEC)
(90/269/EEC)
[15]
Council Directive 90/270/EEC of 29 May 1990 on the minimum safety and health requirements
for work with display screen equipment (fifth individual Directive within the meaning of Article
16 (1) of Directive 89/391/EEC)
88
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EN 752:2017 (E)
[16]
Council Directive 92/57/EEC of 24 June 1992 on the implementation of minimum safety and
health requirements at temporary or mobile construction sites (eighth individual Directive
within the meaning of Article 16 (1) of Directive 89/391/EEC
[17]
Council Directive 98/24/EC of 7 April 1998 on the protection of the health and safety of workers
from the risks related to chemical agents at work (fourteenth individual Directive within the
meaning of Article 16(1) of Directive 89/391/EEC)
[18]
Directive 1999/92/EC of the European Parliament and of the Council of 16 December 1999 on
minimum requirements for improving the safety and health protection of workers potentially at
risk from explosive atmospheres (15th individual Directive within the meaning of Article 16(1)
of Directive 89/391/EEC)
[19]
Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000
establishing a framework for Community action in the field of water policy
[20]
Directive 2001/45/EC of the European Parliament and of the Council of 27 June 2001 amending
Council Directive 89/655/EEC concerning the minimum safety and health requirements for the
use of work equipment by workers at work (second individual Directive within the meaning of
Article 16(1) of Directive 89/391/EEC)
[21]
Directive 2002/44/EC of the European Parliament and of the Council of 25 June 2002 on the
minimum health and safety requirements regarding the exposure of workers to the risks arising
from physical agents (vibration) (sixteenth individual Directive within the meaning of Article
16(1) of Directive 89/391/EEC) - Joint Statement by the European Parliament and the Council
[22]
Directive 2003/10/EC of the European Parliament and of the Council of 6 February 2003 on the
minimum health and safety requirements regarding the exposure of workers to the risks arising
from physical agents (noise) (Seventeenth individual Directive within the meaning of Article
16(1) of Directive 89/391/EEC)
[23]
Directive 2003/88/EC of the European Parliament and of the Council of 4 November 2003
concerning certain aspects of the organisation of working time
[24]
Directive 2004/37/EC of the European Parliament and the Council of 29 April 2004 on the
protection of workers from the risks related to exposure to carcinogens or mutagens at work
(Sixth individual Directive within the meaning of Article 16(1) of Council Directive 89/391/EEC)
[25]
Directive 2006/7/EC of the European Parliament and of the Council of 15 February 2006
concerning the management of bathing water quality and repealing Directive 76/160/EEC
[26]
Directive 2006/42/EC of the European Parliament and of the Council of 17 May 2006 on
machinery, and amending Directive 95/16/EC (recast)
[27]
Directive 2006/95/EC of the European Parliament and of the Council of 12 December 2006 on
the harmonisation of the laws of Member States relating to electrical equipment designed for use
within certain voltage limits (codified version)
[28]
Directive 2006/113/EC of the European Parliament and of the Council of 12 December 2006 on
the quality required of shellfish waters
[29]
Directive 2006/118/EC of the European Parliament and of the Council of 12 December 2006 on
the protection of groundwater against pollution and deterioration
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[30]
Directive 2007/60/EC of the European Parliament and of the Council of 23 October 2007 on the
assessment and management of flood risks
[31]
Directive 2009/104/EC of the European Parliament and of the Council of 16 September 2009
concerning the minimum safety and health requirements for the use of work equipment by
workers at work (second individual Directive within the meaning of Article 16(1) of Directive
89/391/EEC)
[32]
Directive 2009/148/EC of the European Parliament and of the Council of 30 November 2009 on
the protection of workers from the risks related to exposure to asbestos at work
[33]
Directive 2014/25/EU of the European Parliament and of the Council of 26 February 2014 on
procurement by entities operating in the water, energy, transport and postal services sectors
and repealing Directive 2004/17/EC
[34]
Directive 2014/34/EU of the European Parliament and of the Council of 26 February 2014 on
the harmonisation of the laws of the Member States relating to equipment and protective
systems intended for use in potentially explosive atmospheres (recast)
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National annex NA
(informative)
Guidance for the use of BS EN 752:2017 in the UK
NA.1 Introduction
This National Annex gives additional information about practice to assist users in the application of
EN 752 in the United Kingdom. The numbers in brackets after the headings are the corresponding
clause or sub-clause numbers in the text of the European Standard.
Further information on the requirements of Sewerage Undertakers for sewers and lateral drains
that are to be adopted can be found in Sewers for Adoption [1], Sewers for Scotland [2] or Sewers for
Adoption for Northern Ireland [3], as appropriate.
For other drains and sewers, Building Regulations will apply. Information on the requirements of
Building Regulations can be found in Approved Document H for England [4] and for Wales [5], the
Technical Handbooks to the Building Standards (Scotland) Regulations [6] [7] (in Scotland) or the
Technical Booklet H to the Building (Northern Ireland) Regulations [8].
For highway drainage systems, the requirements of Highway Authorities for trunk roads can be found
in the Design Manual for Roads and Bridges (DMRB) Volume 4 Section 2 [9]. An overview of highway
drainage design can be found in DMRB Volume 4, Section 2, Part 3 HD 33/16 Design of highway drainage
systems [9]. The requirements of local highway authorities are usually based on, but can vary from the
requirements in DMRB.
Sustainable drainage systems (SuDS) are now frequently being used in place of or in combination with
traditional piped surface water drainage systems. SuDS seek to minimise the impact on the downstream
environment by mimicking the natural runoff characteristics of the undeveloped site. Some SuDS can
also have amenity and biodiversity benefits. Typical SuDS components are described in NA.6.2.
NA.2 Requirements (Clause 5)
NA.2.1 Environmental performance requirements (5.2.2)
NA.2.1.1 Introduction
Where receiving water bodies are affected, the relevant authority should be consulted at an early stage.
The major UK source documents are the Urban Pollution Management (UPM) Manual [10], which is a
planning guide for the management of urban wastewater discharges under wet weather conditions
and the Urban Wastewater Treatment (UWWT) Regulations Guidance [11] [12] [13], which set out the
regulatory policy of the Environment Agency (for England) and Natural Resources Wales in respect
of wastewater discharges and their future consent standards. Reference should be made to these
documents for more detailed information.
NA.2.1.2 Control of pollution
NA.2.1.2.1 General
All legitimate uses recognised for surface waters can be affected to some extent by wet weather
discharges from sewer systems. However, river aquatic life, bathing and general amenity have been
specifically identified in the UWWT Regulations Guidance [11] [12] [13] for England and Wales.
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The UK policy for the protection of the aquatic environment is based on Environmental Quality
Objectives (EQOs) that specify the desired uses of a water body. Environmental Quality Standards
(EQSs) are then defined such that, when achieved, the EQOs are met and the desired uses are protected.
NA.2.1.2.2 Standards for protecting river aquatic life
Over the years, Environmental Quality Standards and procedures of varying complexity have been
developed for protecting river aquatic life. The simpler procedures make a number of conservative
assumptions about the nature of the receiving water, and therefore, include large built-in safety factors.
The more complex procedures require detailed modelling and are likely to produce more cost effective
designs, however this level of detail is not always feasible or justified in many cases. Environmental
Quality Standards have been developed to ensure protection of river aquatic life during short term
pollution events. These fundamental intermittent standards are expressed in terms of maximum
allowable frequencies for specified threshold concentrations and durations of dissolved oxygen (DO)
and un-ionized ammonia and are presented in the UPM Manual [10]. They assume that the wet weather
discharges do not contain unusually high levels of other substances, which can be damaging to aquatic
life. The application of these fundamental standards require the modelling of the environmental
impact of the discharge on the receiving water. This may involve use of a complex dynamic river flow
and quality model or something simpler. Modelling of the sewer system (flow and sewage quality) and,
where relevant, the sewage treatment works is also usually necessary. This modelling may involve
detailed dynamic models or may use simple techniques.
NA.2.1.2.3 Standards for protecting bathing and shellfish waters
Two approaches are used in the UK:
a) Site-specific EQSs
The UWWT Regulations Guidance [11] [12] [13] set out Environmental Quality Standards (EQSs)
for use in England and Wales for coliform bacteria in waters which have been identified under the
provisions of the Bathing Water Directive [14] and the Shellfish Waters Directive [15]. These standards
are defined in terms of bacterial concentration thresholds and exceedance periods and are designed to
ensure compliance with the Bathing Water Directive [14] or the Shellfish Waters Directive [15][14]. The
exceedance period for bathing waters is the average period over a number of bathing seasons (a bathing
season is generally May to September). To use the bacterial EQSs directly for planning purposes it is
necessary to be able to model the transport and fate of bacteria following a discharge.
b) Uniform emission standards
The UWWT Regulations Guidance [11] [12] [13] also set uniform emission standards (see 5.3.3) for
England and Wales, which can be used without the need for environmental modelling studies. The
standards in the guidance limit the average number of discharges from Combined Sewer Overflows
(CSOs) to identified bathing waters or shellfish waters, or in close proximity to such waters, as a result of
independent rainfall events to a specified spill frequency. The spill frequency standards have universal
application and are easily applied and understood, but necessarily have large built-in safety factors.
NA.2.1.2.4 Standards for protecting amenity use
The UWWT Regulations Guidance [11] [12] [13] set out uniform emission standards for England and
Wales in terms of solids separation requirements for CSO discharges to protect amenity use from
aesthetic pollution. There are three levels of standard based on different amenity use categories and
spill frequencies. There is no requirement to modify or upgrade existing satisfactory CSOs to meet these
emission standards. In using the emission standards, it is essential that all areas that could reasonably
be affected by the discharge are considered and the highest amenity category applied.
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NA.2.2 Hydraulic design criteria (See 5.3.2)
NA.2.2.1 Design rainfall frequencies for drainage of paved areas
The Design Manual for Roads and Bridges (DMRB) Volume 4 Section 2 [9] sets out guidance for the
design rainfall frequencies for highways.
For gully spacing on trunk roads, the requirement is to limit the width of the flow in the channel during
a 1 in 5 year rainfall event to no greater than 1.5m in the hard shoulder or 1.0m in the carriageway (see
DMRB Volume 4, Section 2, Part 3, HA 102/00 Spacing of road gullies [9])
For non-trunk roads the requirement is typically to limit the flow in the channel in a 1 in 5 year rainfall
event to no greater than greater than 0.5m within urban locations (see DMRB Volume 4, Section 2, Part
4, HA 83/99 Safety Aspects of Road Edge Drainage Features [9]).
For the design of drainage of areas around buildings the design rainfall frequencies shown in Table
NA.1 are recommended.
Table NA.1 — Recommended design rainfall frequencies for the design of areas
around buildings
Risk category Situation
Design rainfall frequency
Return
p e r i o d Probability of exceedence
(1 in "n" years)
in any one year
Category 1
Normal situations where ponding can be 1
tolerated during heavy rainfall and for a
few minutes afterwards
1
Category 2
Ponding cannot be tolerated
0,2
5
C a t e g o r y 3 Where a building or its contents require 1,5 × design life of building 1/(1,5 × design life of
(see Note a)
additional protection
(see note b)
t he bu i ld i n g ) – (s e e
note b)
Category 4 (see Where a building or its contents require a 4,5 × design life of building 1/(4,5 × design life of
higher degree of security than category 3 (see note b)
t he bu i ld i n g ) – (s e e
Note a)
note b)
Notes:
a)
Categories 3 and 4 should only be used in exceptional circumstances.
b)
Design rainfall intensities for other frequencies and durations can be calculated using the method described
in BS EN 16933-2.
NA.2.2.2 Design rainfall frequencies for full pipe flow (See 5.3.2.2)
Highway drainage systems are designed to accept 1 year return period rainfall events under full pipe
conditions, and 5 year return period rainfall events with no flooding of the carriageway [9].
In England and Wales, systems are designed to accept the following storms under full pipe conditions [1]:
• sites with average ground slopes greater than 1%
1 year;
• sites with average ground slopes less than 1%
2 year; and
• sites where consequences of flooding are severe
5 year.
• sewers
2 year;
• sewers where consequences of flooding are severe
5 year.
In Northern Ireland, systems are designed to accept the following storms under full pipe conditions [3]:
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Design sewer flooding criteria (5.3.2.3)
In the United Kingdom, systems are designed so that flooding should not occur in any part of the site in
a 1 in 30 year rainfall event [1] [2] [3].
Planning policies in the UK [16] [17] [18] require that consideration is given to the effect of rainfall in
excess of 1 in 30 year return period. In England and Wales, planning policy requires that the 1 in 100
year event is considered and in Scotland, the 1 in 200 year event.
Climate Change Allowance (CCA)
To take account of climate change, historically derived rainfall rates specified in this annex should be
multiplied by a Climate Change Allowance (CCA).
For the design of new drain and sewer systems, a CCA of 1.4 should be used unless the system has an
intentionally short design horizon (e.g. for short life developments).
When considering the upgrading of existing systems, it is recommended that designs are tested to
the increased peak rainfall intensity by using CCA values for different design horizons for central
projections and upper end projections. In such cases recommended values of CCA derived from guidance
issued by Environment Agency [19] are given in Table NA.2. The provision of increased capacity should
be explored using an incremental cost benefit approach.
Table NA.2 — Recommended values of Climate Change Allowance (CCA) Source Environment
Agency [19])
End of design life
CCA (Central projection)
CCA (Upper end projection)
Up to 2039
1.05
1.1
2040-2069
1.1
1.2
2070-2115
1.2
1.4
Note: These recommendations are updated periodically in the light of new research. Users
are advised to check for the most up to date guidance.
NA.2.3 Environmental design criteria (Clause 5.3.3)
NA.2.3.1 Surface water discharges
In England and Wales the Building Regulations [4] [5] require that surface water is discharged in
accordance with the following order of precedence:
•
to an infiltration drainage system; or
•
where neither is reasonably practicable, to a sewer.
•
where discharge to an infiltration drainage system is not reasonably practicable to a watercourse; or
In England, non-statutory guidance on sustainable drainage from Defra and CLG [16] recommends
that discharges to a sewer should usually be made to a surface water sewer, and only where this is not
practicable should surface water be discharged to a combined sewer. The discharge of surface water to
a foul sewer is not considered appropriate.
The Welsh Government non-statutory SuDS guidance [20] recommends that water should be collected
for use in preference to disposal, but otherwise follows the same order of precedence as the Building
Regulations in England and Wales [4] [5].
NOTE: Sewerage Undertakers in England and Wales are not presently able to adopt all types of
infiltration drainage system. Further guidance on adoption can be found in the Interim Code of
Practice for Sustainable Drainage Systems [21].
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In Northern Ireland, the same order of precedence as in the non-statutory guidance for England and
Wales applies.
In Scotland, the discharge of surface water to the water environment or to surface water drainage
systems is controlled under general binding rules contained in The Water Environment (Controlled
Activities) (Scotland) Regulations 2011. The regulations require that discharges do not contain drainage
from certain contaminated surfaces and are discharged via SuDS. Further information is available in
Sewers for Scotland [2] and SuDS for Roads [22].
In Scotland, surface water should be discharged in the following order of precedence:
•
to an infiltration drainage system;
•
where discharge to an infiltration drainage system is not reasonably practicable to a watercourse;
where neither is reasonably practicable, to a surface water sewer; or
•
where this is not technically feasible, to a combined sewer.
•
The relevant authority can specify requirements for the depth of rainfall in any event that must be
retained before discharge to any surface receiving water. This is to reduce the number of discharge
events that can impact on receiving water quality.
NA.2.3.2 Discharges from combined sewer overflows
In addition to the requirements arising from NA.2.1.2, there is a requirement for all sewer systems to
be designed to carry flows without spilling until the incoming flow exceeds that calculated by the socalled 'Formula A' (Formula NA.1, [23]).
This calculation is applicable to both foul and combined systems.
DWF + 1360P + 2E litres/day
(NA.1)
where:
DWF = dry weather flow;
P = population served;
E = trade effluent flow.
The constants used in the formula should be adjusted for particular types of trade effluent, for small
receiving water bodies or for sewer systems with large storage capacity.
The water pollution control authority (see NA.7.4) can also impose further discharge requirements.
NA.2.3.3 Infiltration drainage
In order to limit any possible alteration to the quality of groundwater from infiltration drainage,
attention should be paid to the source of the run-off water that is to be collected. In particular, the
water pollution control authority (see NA.7.4) is unlikely to permit infiltration drainage where:
•
the site is close to a groundwater abstraction point (e.g. in groundwater source protection zone 1
(the inner zone) - Information on the location of these zones in England is available from the water
pollution control authority [24] );
•
the risk of contaminated run-off is high (e.g. hard standing and car parking in industrial areas and
lorry parking); or
•
there is a risk of groundwater contamination due to leaching of contaminants from the soil.
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If there is any doubt as to whether any of these conditions arise and for any major infiltration drainage
(e.g. > 1 ha) scheme, advice should be sought from the water pollution control authority (see NA.7.4).
However, in other cases where the risk of contamination is low (e.g. roof drainage and residential or
retail car parking areas), infiltration drainage can usually be used.
NA.3 Integrated sewer system management (Clause 6)
The following guidance documents are available which give additional information on the application
of these principles in the UK:
•
Drainage Strategy Framework [25]
•
UKWIR Common framework [26]
•
The Sewerage Risk Management Manual [27]
NA.4 Health and safety (Clause 7)
Details of UK health and safety authorities are given in clause NA 7.9. Particular attention is drawn to
the Confined Spaces Regulations 1997 and the associated Approved Code of Practice [28], the Explosive
Atmospheres (ATEX) Directives (2014/34/EU and 1999/92/EC), which are transposed into UK law by
The Dangerous Substances and Explosive Atmospheres Regulations 2002.
NA.5 Design principles (Clause 8)
NA.5.1 Materials selection (8.6.4)
NA.5.1.1 General
The materials for pipes, pipe joints, bedding, manholes and their associated fittings, associated building
works and the type of cement and mix to be employed should be selected to ensure a satisfactory design
working life of the drain or sewer system. Pipes and fittings in materials commonly used in the UK (see
Table NA.3) are generally suitable for use in sewers and drains conveying surface water, foul wastewater
and industrial wastewater that can legally be discharged to public sewers. Materials should be specified
in accordance with the relevant European Standard or British Standard. Further information on the
selection of pipes can be found in the relevant product standards, in the Civil Engineering Specification
for the Water Industry [29] or for highways, the Manual of Contract Documents for Highway Works
Volume 2 Specification for Highway Works [30].
NA.5.1.2 Resistance to chemical or biochemical attack
NA.5.1.2.1 General
The ground conditions in which the sewer is to be laid can be corrosive to certain pipe and/or jointing
materials and this can affect the choice of materials. Where a drain or sewer is liable to carry untreated
and corrosive trade effluents, further consideration should be given to possible protective measures.
Liquids at elevated temperatures are likely to be significantly more aggressive than those at ambient
UK temperatures.
Materials can suffer attack from, for example:
•
discharge of effluent from industrial processes (e.g. electroplating works);
•
discharge of sewage, where due to long retention periods septicity occurs;
•
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discharge of effluent from chemical laboratories;
BS EN 752:2017
•
aggressive groundwaters (e.g. in contaminated ground); and
•
less aggressive groundwaters, where there is a convenient drainage path that allows groundwaters
to be continually replenished.
Table NA.3 — Materials and products commonly used in the construction of drains and
sewers in the UK
Material or product
Relevant standards
Concrete
BS EN 206-1;
BS 8500
Notes
Complementary standard to BS EN 206
BS EN 1992
Cement
BS EN 197
Aggregates for concrete
BS EN 12620
Bedding materials for pipes
BS EN 13242
PD 6682-6
BS EN 13055-2
BS 8500-2 specifies requirements for recycled
aggregates
WIS 4-08-02 [31] and the Specification for
Highway Works [30] give guidance on selection
of pipe bedding materials
Clay pipes, fittings and joints, per- BS EN 295; BS 65
forated pipes manholes jacking
pipes gullies and extra chemically
resistant pipes
Precast concrete pipes, inspection BS EN 1916
chambers, manholes and gullies BS EN 1917
BS 5911
Grey iron pipes and gullies
BS 437
BS EN 877
BS 416
Ductile iron sewer pipes and BS EN 598
fittings
PVC-U pipes
BS EN 1401
PP pipes
BS EN 1852-1
PE pipes
BS EN 12666-1
GRP (UP) pipes
BS EN 14364
Mineral modified PP pipes
BS EN 14758
Thermoplastics structured wall BS EN 13476
pipes
Ancillary underground drainage BS 4660
thermoplastics products
Manholes and inspection cham- BS EN 13598
bers (plastic)
Building Regulations still reference BS 7158 and
products to this standard are still permitted and
produced for private drainage systems.
Manhole covers and frames and BS EN 124
gully gratings for roads
BS 9124
BS 7903
BS 7903 is the complementary standard to
BS EN 124
Linear drainage channels
BS EN 1433
Manhole steps
BS EN 13101
Manhole ladders
BS EN 14396
NA.5.1.2.2 Concrete and materials containing cement
Normal domestic sewage is not aggressive to Portland cement concrete or cement composite. However,
sewage which becomes devoid of oxygen will produce hydrogen sulphide that, in turn, can produce
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sulphuric acid that is aggressive to cement products. The majority of ground waters are similarly not
aggressive to such materials (see Concrete in aggressive ground [32] and BS 8500).
The cement content, the water/cement ratio and the compaction will have considerable effect on
the resistance of concrete to chemical attack. These factors should, therefore, be considered when
specifying concrete in cases of potential chemical attack (see Concrete in aggressive ground [32] and
BS 8500). In those cases, where it is shown that concrete can be attacked, specialist advice should
be obtained.
Concrete pipes and fittings complying with BS EN 1916, BS EN 1917 and BS 5911 are normally resistant
to attack by sulphates in solution and acids of pH 5 and above.
NA.5.1.2.3 Protection of ductile iron
BS EN 598 defines the standard protection for ductile iron drain and sewer pipes. Generally, the pipes
are externally coated with zinc (or zinc/aluminium) with an epoxy topcoat. Where external conditions
are particularly aggressive, additional external protection should be considered (e.g. polyethylene
sleeving complying with BS 6076; or in extreme circumstances, tape wrap). Generally, the pipes are
internally lined with calcium aluminate cement mortar. Various alternative internal coatings are
available giving different levels of protection, the manufacturers advice should be sought regarding
these special pipe linings.
NA.5.1.2.4 Protection for grey iron pipes
BS 437, BS 416 and BS EN 877 define the standard coatings for grey iron drain pipes. Generally, above
ground pipes are coated externally with a synthetic paint, whilst below ground pipes have an additional
layer of zinc under the synthetic paint. Internally, pipes are coated with a two-pack epoxy paint. Where
conditions are particularly aggressive, additional protection should be considered (e.g. polyethylene
sleeving complying with BS 6076 or in extreme circumstances, tape wrap, for below-ground pipes;
additional coats of epoxy paint for above ground pipes).
NA.6 Physical layout of the system (Annex D)
NA.6.1 Layout and profile (D.2)
NA.6.1.1 Layout of paved areas
NA.6.1.1.1 Introduction
The drainage of paved areas can be achieved in a number of different ways:
•
provision of gullies set at low points within the paved area or individual sections of paved area that
drain directly to the below-ground drainage system. This is particularly suitable for parking areas
or other areas of hard standing on level ground;
•
provision of a channel or series of channels, usually formed in the paved surface or the paved surface
together with a kerb, that collect the run-off from the paved area discharging to the below-ground
drainage system through gullies situated at intermediate points along the channels and at their
downstream ends;
•
provision of linear drainage inlets that collect the run-off from the paved areas and discharge
directly to the below-ground drainage system;
•
drainage of run-off from the edge of the paved area to a permeable pavement, filter drain, filter
strip, or in some cases just directly onto adjacent land. This is particularly suitable for linear paved
areas such as footpaths or roads;
•
a permeable pavement; or
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•
a combination of the above.
The drainage system should be arranged so as to prevent surface water from flowing across the
entrance, "to or from" a public road.
The levels of a paved area should be determined in relation to the levels of:
1) existing ground;
2) available outfall;
3) floors and damp-proof courses in adjoining buildings;
4) access points to the paved area;
5) the top water level of receiving water bodies;
6) drainage pathways.
Water draining from a paved area should not be allowed to concentrate along the side of a building.
Where the general ground levels might cause this to happen, a reverse fall should be applied to a narrow
strip around the building so that the water is kept away from the walls.
If a paved area provides access to workshops, underground garages or storage accommodation that are
at, or below, the level of the paved area, linear drainage inlets should be used and these should be placed
a minimum of 500 mm away from the building, in order to intercept any water that would otherwise
drain into the building. In addition, to limit the inflow of water, the threshold of the entrance should be
set at a higher level than the general surrounding ground
The edge of a paved area may be finished against, and level with, the surrounding natural ground,
provided that the subsoil is suitable and the edge is not subject to heavy loading by traffic or materials.
This method of drainage should not be used where heavy traffic reaches or overruns the edge of a paved
area, or where an adjacent unpaved area could drain a significant amount of flow on to the paved area.
To avoid damage, gully gratings and frames should be adequately supported against movement.
Surfacing materials should be selected to take account of the differential movement between the gully
and the surrounding paved area. Gratings for linear drainage channels should be fixed in accordance
with the manufacturer"s instructions.
NA.6.1.1.2 Layout of gullies
The spacing of gullies is determined by hydraulic requirements (see BS EN 16933-2).
Gullies without channels
Small paved areas can be drained to central terminal gullies. Larger areas can be split into panels each
with a central terminal gully. This is particularly useful in areas that are relatively flat. A typical layout
is shown in the inset to Figure NA.1.
Gullies with channels
Larger paved areas can be more conveniently drained by means of collecting channels with intermediate
and terminal gullies. The channels can be part of the paved surface itself, formed by the use of a kerb at
the edge of the paved surface or be purpose-built channels.
Gully gratings should be installed in collecting channels as close to the kerb as possible.
A combined inlet consists of a gully grating and an adjacent kerb inlet that has the same length as the
grating (see Figure NA.1 and Figure NA.2). The benefit of this type of inlet is that it is less susceptible to
blockage than either the gully grating or kerb inlet used separately, as its capacity will normally be only
slightly greater than that of the gully grating.
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For concrete paved areas, construction or expansion joints should not coincide with the lines of
collecting channels, or cross areas in which ponding occurs at terminal gullies.
NA.6.1.1.3 Layout of linear drainage inlets
Instead of channels and gullies, it is sometimes more convenient to use linear drainage inlets. These can
take a variety of forms some of which incorporate kerbs. The inlet can take the form of a continuous
slot, a series of holes or a continuous grating. Linear drainage inlets can be particularly useful where the
longitudinal gradient of the paved area is low. However, if self-cleansing conditions cannot be achieved,
more frequent maintenance should be carried out to ensure that they operate successfully. The layout
of the linear drainage inlets and the profile of the paved area should be designed to limit the depth of
flow across the paved areas to acceptable limits.
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Key
Road with camber section A - A
Road with cross fall section B - B
Arrows indicate direction of fall of final paved surfaces, except where
otherwise captioned
Terminal gully
Intermediate gully
Linear drainage inlet
Figure NA.1 — Drainage of typical roads and paved areas by gullies and channels
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Key
Channel drain section A - A
Kerb drain section B - B
Arrows indicate direction of fall of final paved surfaces, except where
otherwise captioned
Linear drainage inlet
Figure NA.2 — Drainage of typical roads and paved areas by linear drainage
NA.6.1.2 Drainage from the edge of paved areas
It is not always necessary to have gullies or linear drainage channels. Surface water can often be
effectively drained by direct run-off to the sides of the paved area or by the use of well-maintained
permeable pavements (see NA.6.2.3).
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NA.6.1.3 Exceedance flow
Drainage systems comprise minor and major sub-systems. The minor drainage system is the network of
sewers and associated infrastructure. The major drainage system is the system of formal and informal
above ground flood pathways, including open and culverted watercourses and dry rivers.
Exceedance flow occurs when the capacity of the minor system is no longer sufficient and the flow
enters the major system. Flood pathways convey exceedance flow from the point of origin. These
pathways can be either natural or designed. Where practicable, flood pathways should have another
compatible primary function. Highways, footpaths, car parks, ditches, swales and other vegetated areas
can be used as flood pathways.
Flood pathways should be designed to convey the expected flow to a surface receiving water with
adequate flow capacity. The pathways should follow the natural topography a far as practicable and
should avoid buildings and other vulnerable infrastructure. The public should be made aware that the
area can flood, using appropriate signage and depth markers.
The design of flood pathways will considerably affect property flood risk. Flood pathways can transfer
the flow over significant distances, so that flooding can occur at locations remote from the original
point of discharge. This is particularly important in areas with a high consequence of flooding.
In areas of significant redevelopment, the design of flood pathways should be considered in the same
way as those for new developments, including the use of natural drainage pathways and sympathetic
design of building layout to accommodate them.
The design of flood pathways is difficult in existing developments due to the restrictions of existing
building layouts in urban areas. Where it is not possible to limit the risk to property by use of flood
pathways, consideration should be given to increasing the design capacity of the minor drainage system.
NA.6.1.4 Dual-purpose surface storage
Surface storage can be included in the design of flood pathways to reduce peak flows by utilizing areas
that are used for other purposes for most of the time, e.g. playing fields can often be used as flood
storage ponds in extreme events.
The following issues should be considered during the design of surface storage areas:
a)
the depth of storage required to accommodate the flooding volume;
c)
how the temporary storage of flood volume will affect the primary use of the area;
e)
the risks to public health or safety caused by standing water.
b) the length of time taken for the area to drain after the event;
d) any damage or important loss of use that can occur as a result of using the area for surface storage;
Further information can be found in the National Annex to BS EN 16933-2.
NA.6.2 Sustainable Drainage Systems
NA.6.2.1 Introduction
NA.6.2.1.1 Flow attenuation
Flow attenuation is the temporary storage and gradual release of water using a flow throttle device and
accompanying storage.
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Flow attenuation can be achieved either:
•
•
online, in which case the attenuation storage is integrated with the sewer and flow always passes
through the attenuation device; or
offline, in which case the attenuation storage is separate from the sewer and flow is spilled into the
storage only when the flow exceeds a specified outflow rate.
Attenuation devices can be used to manage flows in existing combined or surface water sewer systems.
NA.6.2.1.2 Infiltration systems
General
Under certain circumstances infiltration drainage systems can be used to dispose of surface water.They can be designed with or without an overflow.
If surface water drainage is to be discharged to an infiltration drainage system, the subsoil and the
general level of the ground water should be investigated.
Infiltration drainage systems can be used to dispose of surface water by allowing the surface water to
infiltrate into the soil over a period of time. The water pollution control authority (see NA.7.4) usually
requires that any discharge is made to the unsaturated zone above the groundwater table and not
directly to the groundwater table itself. Detention storage is provided to store the peak flows during
heavy rainfall allowing it to infiltrate into the ground when the flow has reduced. The volume of
storage required therefore depends on the hydraulic properties of the soil, the area which the system is
draining, the topography and the chosen design rainfall events.
In some cases, an overflow is provided from the infiltration drainage system either to a surface water
sewer or direct to a surface receiving water.
Access
Below-ground infiltration drainage systems should be designed with facilities for inspection and
maintenance. The working life of an infiltration drainage system will be reduced if its flow paths
become clogged by silt or debris.
Proximity to buildings
Soils can be affected in various ways by the action of water. It is not desirable to site an infiltration
drainage system in any position where the ground below foundations is likely to be adversely affected
by water. In particular, a below-ground infiltration system that concentrates significant volumes of
water in a small area (e.g. soakaways) could damage vulnerable foundations by:
•
localized differential movement of shrinkable clay soils under the foundations;
•
dissolution of certain rocks under foundations;
•
collapse of certain open-textured, wind-blown soils in the presence of water leading to voids under
foundations;
•
reduced strength of certain types of soil in the presence of water.
If there is a risk of any of these conditions then specialist geotechnical advice should be obtained.
The infiltration of surface water into the ground over a large area at rates similar to those that existed
when the land was in its undeveloped state does not normally cause problems unless there are specific
geological hazards.
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NA.6.2.2 SuDS components
NA.6.2.2.1 Detention tanks
A detention tank is an underground space having a throttled outlet to reduce the downstream flow
rate. Detention tanks are typically constructed using modular concrete systems, over-sized pipes, box
culverts or modular geocellular systems.
NA.6.2.2.2 Detention basins
A detention basin is a depression that collects water during wet weather but is dry at other times.
Detention basins are often used as part of a multi-purpose installation and can be incorporated into
playing fields or other open spaces.
NA.6.2.2.3 Green roofs
A green roof is a planted roof that retains and evaporates water.
NA.6.2.2.4 Infiltration trenches
An infiltration trench is a drain consisting of permeable pipe at the bottom of a trench filled with gravel.
It is used for conveyance and infiltration of surface water.
An infiltration trench is usually filled with permeable granular material, designed to promote
infiltration of surface water to the ground following convenient contours.
This type of soakaway provides better infiltration characteristics for a given excavation volume than
traditional soakaways.
An Infiltration trench should have at least two inspection access points, one at each end of a straight
trench. These should be linked, near the top of the granular fill, by a horizontal perforated or porous
distributor pipe. Where more than one drain feeds an infiltration trench, each connection should be via
a suitable access chamber.
The use of catch pits at drain outlets and the use of T-piece inlets (see Figure NA.3) to the perforated or
porous distributor pipes will improve performance by limiting the sediment that could otherwise block
the distributor pipe.
Detailed design guidance is given in CIRIA report 156 [33].
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Figure NA.3 — A T-piece inlet to an infiltration trench
NA.6.2.3 Permeable surfaces
A permeable surface is a surface designed to allow water to infiltrate.
These systems are predominantly flat and their shape is commonly such that there is little storage per
unit of infiltration area. A layer of fill material underlying the surfacing, is therefore generally used to
provide storage during a rainfall event. Depending upon the nature of the fill and the overlying surface
material, a filter or geotextile is sometimes used to separate the materials. Although they are mainly
used to dispose of just the rainfall falling into the surface itself, they can also be used to dispose of
water from the roofs of adjacent buildings and paved areas.
The systems can be porous (i.e. where the water drains through voids that are integral to the pavement
material) or permeable (i.e. where the solid parts of pavement are impermeable but the water drains
through voids between the solid parts of the pavement).
Permeable pavements will usually require maintenance of their surface. Porous pavements will usually
require periodic cleaning to maintain infiltration rates.
NA.6.2.4 Ponds
A pond is a permanent surface water body used for storage.
NA.6.2.5 Soakaways
A soakaway is a void or tank with no outlet except its permeable walls.
A pit soakaway consists of a pit from which water can infiltrate into the surrounding ground. Small
pits can be unlined and filled with hardcore, larger pits can be unfilled but lined, e.g. with brickwork
laid dry, jointed honeycomb brickwork, perforated precast concrete rings or segments laid dry, and the
lining surrounded with suitable granular material. An unfilled pit should be safely roofed and provided
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with access for maintenance purposes. Although square or circular pits are compact, it is often easier,
and cheaper, to excavate trench soakaways if excavating equipment is available.
Provision should be made to remove sediments from the incoming flow to prevent the flow paths in the
surrounding soil from becoming clogged.
A soakaway can be used most effectively in pervious subsoils, such as graveI, sand, chalk or fissured
rock, and where it is completely above the water table. Seasonal variations in the water table can
necessitate an increase in the storage capacity.
Access points enable the point of discharge of the drain to be viewed. For small filled soakaways, a 225
mm perforated pipe can be used as an inspection well.
Guidance on design of soakaways can be found in BRE Digest 365 [34].
NA.6.2.6 Swales
A swale is an open, planted channel for the conveyance only, or conveyance and infiltration of water.
NA.6.3 Sewers with steep gradients
Research has demonstrated that high velocities of flow in drains and sewers laid at steep gradients do
not cause increased erosion of pipes [35] or deposition of solids [36] for commonly used sewer materials.
Experience has shown that drains may therefore be laid at gradients to optimize excavation and cost.
Care should be taken with the design and construction of manholes so that excessive turbulence is not
caused, which can lead to fouling. Where necessary, this can be mitigated by replacing the channel with
an access pipe.
Where sewers with steep gradients are required, consideration should be given to consequences of
high velocities such as:
•
air entrainment and its effects;
•
release of hydrogen sulphide;
•
•
the need for energy dissipation measures on super-critical flow to sub-critical flow;
•
the need for special safety measures for operatives.
the need for thrust restraint;
Backdrop manholes, ramp manholes or vortex manholes may be installed in a sewer system to dissipate
excessive static head in a controlled manner, thereby avoiding the installation of sewers with steep
gradients and meeting any imposed velocity limitation.
Where large grit volumes are included in high energy flows and there are either sharp changes in
direction or significant steps in the pipe invert, erosion of pipe material or coating can occur unless
resistant materials are used. In particular, the bottom bend of a backdrop manhole can be vulnerable.
NA.6.4 Access to drains and sewers (D2.3, D.3)
NA.6.4.1 General
Access points are required to drain and sewer systems for testing, inspection, maintenance and removal
of debris. Every drain and sewer length should be accessible for maintenance and cleaning without the
need to enter buildings. There are four means of achieving this:
a)
Rodding points - small diameter connections at the upstream end of a drain or sewer that permits
entry into the system for cleaning or inspection downstream of the connection. This can include a
gully incorporating a rodding point.
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b) Access fittings - fittings that are normally located near the upstream end of a drain or sewer and
permit entry into the system for cleaning or inspection. The restricted access offered by these
fittings means that operations such as removal of debris using suction hoses is not possible.
c)
Inspection chambers - chambers with working space at ground level only, used to introduce
equipment for testing, inspection and maintenance. The working space in a chamber normally
permits additional operations to those carried out through an access fitting, such as removal of
debris using suction hoses and over-pumping from one chamber to another.
d) Manholes - chambers with working space at drain / sewer level used for entry of personnel
and equipment.
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Figure NA.4 — Types of access point
Cleaning in both directions can be carried out from manholes, inspection chambers and access fittings;
rodding points allow for cleaning in a downstream direction only.
To meet the requirements of the Confined Spaces Regulations 1997, operations should be carried out,
where it is reasonably practicable, without entering the space.
The preference is therefore for working at ground level i.e. to carry out work without man entry
wherever possible. Therefore a drain or sewer system may contain points for access without provision
for entry by personnel and with entry by personnel.
The use of manholes less than 1.5 m deep should be avoided and only considered if there is a
demonstrable need.
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The recommended dimensions given in this National Annex for construction of new access points
reflect the dual consideration of safety of public and personnel and operational space for inspection
maintenance activities.
NA.6.4.2 Provision and spacing of access
Access should be built on drains and sewers at every:
•
Head of branch;
•
Change of alignment (direction) or gradient;
•
Junction of two or more drains or sewers;
•
Change in pipe size.
Where the regular maintenance of individual drainage fittings, such as intercepting traps, anti-flooding
devices, CSO screens, weirs, siphons, penstocks or backdrops could not be carried out from the surface,
manholes should be provided.
Manholes at each change of alignment (direction) are not always necessary; however, in these cases,
special measures need to be taken to allow the position of the drain or sewer to be located accurately.
Manholes should be placed at every significant change in gradient or size, and at major junctions.
Access points need to be located at a spacing that allows inspection, maintenance and removal of debris
from the whole drain / sewer.
An access point may be positioned at the head of a lateral drain (i.e. at the property boundary or point
of demarcation between public sewer and private drain) to mark change of ownership in the drainage
system. This "demarcation chamber" has no specific operational requirements which define the type
of access point to be installed, and it is recommended that consideration be given to designing the
system such that this "demarcation chamber" may also be used for testing, inspection, maintenance
and removal of debris.
The distance between access points depends on the types of access used. Table NA.4 indicates the
recommended maximum distances between rodding points, access fittings, inspection chambers and
manholes. These are based on manual cleaning techniques and the need for removing debris. This is
shown schematically in Figure NA.5.
Table NA.4 — Recommended maximum spacing of access provision (in metres)
To junction /
branch
To access fitting To inspection
chamber
To manhole
From start of external drain
-
12
22
45
From rodding point
12
12
22
45
From access fitting
12
12
22
45
From inspection chamber
12
22
45
45
45
90(a)
From manhole
(a)This may be increased to 200 m in places where only remotely operated equipment will be used for maintenance.
Where only remotely operated and automatic equipment is to be used for maintenance (e.g. jetting),
the spacing between access points may be increased. In these cases it is recommended that the spacing
between access points does not exceed 200 m for drains and sewers up to DN 1800. When proposing
such increased spacing, due consideration should always be given to the capability of remote inspection
equipment, adequacy of ventilation in the drain / sewer, the safety of personnel working in the drain or
sewer and the distance which accumulated material, repair materials and casualties can be conveyed at
sewer level.
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Where a branch joins a main pipe without an inspection chamber or manhole at the junction, access
should be provided on the branch within 12 m of the junction.
Figure NA.5 — Recommended spacing between access points
NA.6.4.3 Clear opening size at surface
To maximize the safety of the public and personnel working on the drain / sewer, the dimensions of
openings to access points should be chosen to reflect the intended purpose.
a)
Rodding points – opening is determined by operational needs only, see.NA.6.4.4.1.
b) Access fittings - opening is determined by operational needs only, see NA.6.4.4.2.
c)
Inspection chambers - chambers are designed for working at ground level, the clear opening
(cover size) is a minimum dimension sufficient to provide the introduction of equipment.
i)
The minimum clear opening size should be the same as the nominal internal dimensions of
the chamber.
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ii) For inspection chambers > 1m depth (from cover to invert of pipe), safe egress cannot be
achieved. To prevent unauthorized access, a recommended maximum clear opening size is 300
mm x 300 mm rectangular (350mm circular).
d) Manholes – the clear opening size is a minimum dimension determined by the need for both safe
access and egress.
i)
The minimum clear opening size is 600 mm x 600 mm rectangular (600 mm circular).
ii) For manholes, < 1.5 m depth (from cover to the working platform e.g. benching), the
recommended minimum clear opening size is larger to permit standing / crouching during
working and is dependent on the size of the pipe served by the manhole. The minimum clear
opening size is 1200 mm x 675 mm (circular covers not applicable due to working space needed).
NA.6.4.4 Dimensions for operational needs
NA.6.4.4.1 Dimensions of rodding points
Rodding points are intended for the introduction of cleaning and inspection equipment to the drain /
sewer. They should be not less than DN 100 and preferably the same diameter as the drain or sewer.
They should be no steeper than 45° from the horizontal. The clear opening size should be the same as
the pipework.
NA.6.4.4.2 Dimensions of access fittings
Access fittings are intended for inspection and maintenance in more than one direction and for testing.
They should permit the introduction of equipment for the following activities into the incoming or
outgoing pipes:
a)
Inspection of drain or sewer by CCTV;
b) Clearance of the blockages by rodding or jetting.
The minimum dimensions of an access fitting are determined by the entry radius needed by the
equipment as it passes into the pipe. The clear opening should, therefore, have a minimum diameter
greater than 50% of the internal diameter of the fitting subject to a minimum of 90 mm. Rectangular
access fittings shall have minimum opening dimensions of 150 mm and 90 mm measured on their
longitudinal and transverse centre lines.
NA.6.4.4.3 Dimensions and internal layout of inspection chambers
Inspection chambers are intended for inspection and maintenance activities. They should permit the
introduction of equipment for the following activities into any of the incoming or outgoing pipes:
a)
Inspection of the drain or sewer by CCTV;
b) Clearance of blockages by rodding or jetting;
c)
Sealing the end of the incoming or outgoing pipe and undertaking a leak-tightness test using either
the water or air pressure test method.
Dimensions
Inspections chambers conforming to BS EN 13598-1, BS 13598-2, BS 7158, BS 5911-4 and BS EN 295-6
are designed in size and profile to accommodate the most commonly used equipment as it passes from
the chamber into the pipe. In general, the circular diameter of the chamber should be no less than the
nominal internal diameter of the pipe, subject to minimum of 180mm.
In some cases, the size of the equipment required depends on the diameter of the pipe. For example,
a CCTV camera unit needs to be mounted so that the centre of the camera moves along the axis of the
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pipe. The complete camera unit for use in a large pipe could therefore be larger than one designed for
use in a small pipe. Dimensions of the chamber would therefore be dependent on the size of the main
pipe and the number, size and position of branches.
Inspections chambers are designed for working from ground level. Whilst inspection chamber products
are available for depths up to 6 m, the accurate introduction of flexible equipment becomes more
difficult at greater depths (see NA.6).
Figure NA.6 — Use of inspection chambers
It has to be presumed that the personnel undertaking operations would select equipment appropriate
to the task and the access available on site.
Internal layout
The main channel should extend the whole length of the chamber. Channels should comprise a halfround section plus vertical benching from the top edge of the half-round section to a height of not less
than that of the soffit of the outlet where it should be rounded off to a radius of approximately 25 mm
and sloped upwards to meet the wall of the chamber. Where the connecting angle between the main
pipe and the connection is greater than 45°, three-quarter section bends should be used. Vertical and
side benching should be shaped so as to contain the flow without permitting fouling and to facilitate the
cleaning of branches.
In inspection chambers, the benching slope should be approximately 1:12.
Where pipes connect at an inspection chamber the flows should combine in preformed swept channels.
The horizontal angle between any incoming pipe and the outgoing pipe should not be less than 90°.
Bends with an angle of not more than 45° may be used immediately outside inspection chambers on the
inlet, the outlet or both pipes. Bends may also be accommodated using a curved open channel within
the inspection chamber.
Branches should enter the main channel discharging in the direction of flow at an angle of no more than
45° to the main flow subject to the provisions above. Where sharper angles are to be accommodated
bends of up to a maximum 45° may be sited immediately outside the chamber. Bends may also be sited
inside the chamber; however, in these cases they should be in the form of open channels to facilitate
access by equipment.
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Where pipes serving a total of three properties or less connect to a pipe up to, and including, DN 150
the branch connections should be set so that the soffits of all the pipes are at the same level. In all other
cases, branch connections should be set with the soffit levels no lower than that of the main pipe and
with the invert level of the branch connection at least 50mm above the invert of the main pipe.
A lead-in should be provided where rods or jetting hoses or cables are likely to be damaged due to the
tight radius at the pipe entry.
Where available, bends should be made with curved bend fittings. The radius of the centreline of the
bend should not be less than the nominal internal diameter of the pipe. Where curved bend fittings are
not available mitre bends may be used. The angle of each mitre should not be more than 22.5° where
the nominal internal diameter of the pipe is less than 600 mm and not more than 45° where the nominal
internal diameter is of the pipe is greater than or equal to 600 mm.
NA.6.4.4.4 Dimensions and internal layout of manholes
Dimensions
Manholes are intended for entry by trained maintenance operatives for inspection and maintenance
activities. They should therefore provide safe entry and egress and safe working conditions inside the
chamber. The preference is for working at ground level, so manholes should also facilitate for activities
to be undertaken from the surface as far as possible. The minimum dimensions of a manhole are
determined by the need for safe access and egress and the provision of adequate working space along
with its depth, size of pipe, number of branches and change of direction. See NA.6.4.3 and Table NA.5 for
minimum recommended dimensions.
Additionally, adequate safe working space should be provided within the system. Further information
can be found in Safe Working in Confined Spaces [28].
Means of access and egress
A permanent means of access and egress can be provided by ladders, stairways or steps. Where ladders
or steps are in use, a means of fall prevention should also be provided. Due allowance should be made
for facilitating the use of fall prevention equipment when designing and constructing manholes.
In order to deter unauthorized access, some manholes are not fitted with permanent ladders or steps.
In such cases, personnel are normally winched into and out of the manhole, however, an alternative
means of rapidly removing personnel including casualties from the manhole, should be provided for use
in an emergency.
Facilities should be included to provide handholds during the transition of a person from being partly
above ground to wholly in the manhole. Alternatively, when access is by means of steps, handholds
fulfilling the same function, may be provided. Stairs should be fitted with proper guardrails.
Where frequent access is required, a staircase should be provided to at least the lowest dry landing.
Landings provide a safe working platform within a manhole access system and should conform to
the current statutory requirements for safe working platforms at height. A landing covering the full
area of the chamber or one covering only part of the area of the chamber (e.g. a half-landing) should
be provided at vertical intervals not exceeding 6 m in the manhole. There should be a minimum height
of 2 m between each landing. Access openings in successive landings should be staggered to limit the
height of an accidental fall from the access ladder. Guardrails should be provided on each landing at the
base of the ladder to ensure that it is not possible to step inadvertently from the bottom of one ladder
into the access opening for the next ladder or through any opening in an adjacent landing slab edge
guardrail. Separate openings should be provided for the movement of materials, tools, safety devices,
casualties and for the use in pumping/jetting and other maintenance operations. These should be
suitably protected by trap doors that can be secured in the open position, directly below each other.
Openings in guardrails should be barriered off at top- and mid-rail level with a self-closing gate or
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equivalent, which does not depend on human intervention. In this context, hooks and chains have been
proved to form an ineffective barrier.
Internal layout
Where pipes connect at a manhole the branch flows should merge with the main channel using swept
channels. Where available, preformed channels should be used. The horizontal angle between any
incoming pipe and the outgoing pipe should not be less than 90°.
Bends in the main channel may also be accommodated using a curved open channel within the manhole.
Bends with an angle of not more than 45° may be used immediately outside manholes on the inlet, the
outlet or both pipes. On pipes with a nominal internal diameter greater than DN225, a bend outside a
manhole is only permitted at one end of a pipe. Where bends occur outside manholes, this can restrict
access for CCTV surveys in small diameter pipes.
Branches should enter the main channel discharging in the direction of flow at an angle of no more than
45° to the main flow subject to the provisions above. Where sharper angles are to be accommodated
bends of up to a maximum 45° may be sited immediately outside the chamber. Bends may also be sited
inside the chamber; however in these cases they should be in the form of open channels to facilitate
access by equipment.
Side branches of diameters up to, and including, DN 150 should discharge to the main channel in the
direction of flow, preferably with the invert at a minimum of 50 mm above.
A branch with a diameter greater than DN 150 should be set with the soffit level of the branch at
the same level as the soffit of the main drain. At a change in diameter of drains or sewers and where
conditions permit, the soffits of the pipes should be at the same level.
The main channel should extend the whole length of the chamber, comprising a half-round section plus
vertical benching from the top edge of the half-round section to a height of not less than that of the soffit
of the outlet where it should be rounded off to a radius of approximately 25 mm and sloped upwards
to meet the wall of the chamber. Where the connecting angle is greater than 45°, three-quarter height
bends should be used. Vertical and side benching should be shaped so as to contain the flow without
permitting fouling and to facilitate the cleaning of branches .Steeper gradients are preferred to the use
of vertical drop pipes. Where a drain or sewer connects with another at a significantly lower level, a
drop manhole may be built on the lower pipe incorporating a vertical or nearly vertical drop pipe. The
drop pipe may be outside the chamber or supported inside the chamber, in which case, the chamber
should be suitably enlarged. External drop pipes (backdrops) should be encased in concrete. Access
should be provided to the incoming pipe at the top of the drop pipe and to the vertical drop pipe for
inspection and maintenance.
Where the difference in level between the invert of the incoming drain or sewer and the invert of the
manhole is less than 1,8 m, a 45° ramp is often preferable to a vertical drop pipe.
Drop pipes should terminate at their lower end with a bend to discharge into the main channel at 45° or
less. The bend at the base should be adequately supported.
Consideration should be given to incorporating some form of energy dissipation for backdrops on
drains and sewers larger than DN 450 and for drops greater than 1.8 m.
In manholes, the benching slope should not be between 1:10 to 1:30, in order to provide a working surface.
Benching
Where ladders or step rungs are used, a minimum width of benching of 450 mm should be provided
between the face of the ladder rungs and the channel to provide a working area. Pipes and access covers
may be positioned off centre to facilitate access and to maximize the working space.
For manholes with depth from cover level to pipe soffit of less than 1,5 m giving access to pipes not
exceeding DN 450, the width of the chamber should allow at least 225 mm wide benching on each side.
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BS EN 752:2017
In all other cases, the width of the chamber should allow at least 325 mm on one side of the chamber and
at least 450 mm on the other. In shallow manholes, consideration should also be given to decreasing the
level of the benching to not less than half pipe height in order to achieve this recommended headroom.
Not less than 900 mm clear space should be provided on the benching at the face of the base of a ladder
or run of steps. For channel widths less than, or equal to, 450 mm, at least 450 mm of this should be
provided between the face of the base of the ladder and the channel (see Figure NA.7). For channel
widths greater than 450 mm, this should be provided on the same side of the channel as the steps.
This is usually most economically accommodated by placing the ladder normal to the channel (see
Figure NA.8).
Figure NA.7 — Working space around a ladder or steps (pipe size ≤ DN 450)
Figure NA.8 — Working space around a ladder or steps (pipe size > DN 450)
Sizes of shafts and entries
Manholes deeper than 3 m from cover level to soffit may be constructed with an access shaft rather
than extending the chamber to ground level. Access shafts should have a clear space of approximately
900 mm between the steps or ladder and the back of the shaft, see Table NA.5. Consideration should be
given to the size of equipment likely to be required to use the shaft; but shafts should not be oversized
as this would prevent the back of the shaft being used to break a fall.
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Landings
The landings and platforms should be of adequate size to accommodate at least two operatives with
safety harnesses; and to minimize the risk of falling, open edges should be provided with double
guardrails (i.e. top- and mid-rail) and toe boards.
Not less than 900 mm of clear space should be provided on any landing between the face of the steps
and any wall or handrail.
Manhole steps should be Type D Class I double steps conforming to BS EN 13101 with a minimum width
of tread of 320 mm.
Manhole steps should be built into the wall at regular height intervals of between 230 mm and 300 mm.
The top step or toe hole should be not more than 675 mm below the surface; the lowest not more than
300 mm above the benching.
Manhole steps should not be used for access/egress in manholes deeper than 3,0 m.
Where covers larger than the minimum size given in NA.6.4.3 are used, one or more handholds should
be built into the sides of the shaft beneath the cover frame.
Not less than 150 mm foot room should be provided between the steps and the chamber wall behind
them, when measured at the centre of the step.
When steps are provided in the side of the channel they should not protrude into the flow. In these
circumstances recessed steps or toe holes should be used in association with hand holds.
Fixed, corrosion resistant ladders conforming to BS EN 14396:2004 (or stairs) may be used in place of
steps and should be used for depths over 3,0 m. Where there are landings these should preferably break
the line of the ladder.
Not less than 200 mm foot room should be provided between the rungs of ladders and the chamber wall
behind them, when measured at the centre of the step. Stringers should be adequately supported from
the manhole wall at intervals of not more than 3 m. Stringer supports should not be built into the wall
but bolted to built-in cleats to facilitate renewal.
Fixed ladders should not protrude into the flow. Where steps are to be provided in the side of the
channel recessed toe holes in association with hand holds, or movable sections of ladder should be used.
The top rung should be within 675 mm of the ground level and ladders should be positioned relative to
the access, so that the minimum clear opening is not obstructed.
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Table NA.5 — Recommended internal dimensions for the construction of new manholes and
manhole shafts
Type of access
Manhole b)
Depth to pipe DN largest pipe in
sof f it f r om manhole/means
cover level
of descent into
shaft
(m)
<1,5
<1,5
Manhole shaft i)
>3,0
Min. internal dimensions a)
R e c t a n g u l a r – Circular – diamlength and width eter
(mm)
(mm)
≤ 150
750 × 675c)
1000 d)
225
1200 × 675
1200
300
1200 × 750
1200
375 – 450
1350 × 900
1350
500 – 700
1500 × 1150
1500
750 – 900
1800 × 1350
1800
> 900
1800 × (DN + 775) DN + 900
≤ 225
1200 × 1000
1200
300
1200 × 1075
1200
375 – 450
1350 × 1225
1350
500 – 700
1500 × 1475
1500
750 – 900
1800 × 1675
1800
>900
1800 × (DN + 775) DN + 900
Steps
1050 × 800
1050
Ladder
1200 × 800
1200
Winch j)
900 × 800
900
a)
These sizes apply to straight-through pipes, for turning chambers or chambers with several
side branches or where specific maintenance requirements are necessary, e.g. disconnecting
traps the minimum sizes should be increased.
b) Chamber with a removable cover constructed on a drain or sewer to permit entry by
personnel.
c) The minimum size of any manhole serving a more than one property should be 1200 mm
diameter or 1200 mm × 675 mm rectangular.
d)
See footnote c.
i)
Minimum internal height of chamber in shafted manhole 2m from benching to underside of
reducing slab.
j)
Winch only – no steps or ladders (permanent or removable)
NA.6.4.4.5 Construction
General
Inspection chambers and manholes should be watertight, durable and designed to minimize the risk
of blockage.
Inspection chambers and manholes should be designed to carry the worst combination of superimposed
and ground loading. Foundations should be designed to carry all the imposed loads. The chamber walls
and base should also be designed to take into account any lateral loading and/or hydrostatic upthrust
and to prevent flotation.
Where a pipeline is built into any manhole or inspection chamber, or other structure such as a
groundbeam or concrete surround, some differential settlement between the pipeline and structure is
to be expected.
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BS EN 752:2017
To avoid the consequent high shear loads on the pipe built-in to the structure, the first flexible joint
on the pipeline should be provided as close to the face of the structure as practicable. This should be
within 150 mm for pipe diameters less than 300 mm.
A short-length rocker pipe should be laid between the structure and the first full-length pipe to isolate
the pipeline from small relative movements caused by differential settlement. The maximum length of
the rocker pipe should be as shown in Table NA.6. Short length pipes with pre-formed joints are available
from manufacturers or plain-ended pipes may be cut to size. Some materials such as polyethylene and
polypropylene can be sufficiently flexible to accommodate the high shear loads on the pipe without
using rocker pipes and with no detrimental effect on the structural performance of the pipe. Where this
can be shown to be the case, a rocker pipe would not be required.
Table NA.6 — Recommended maximum length of rocker pipes
Nominal pipe diameter
Maximum length
[m]
< 300
0,6
301–450
0,75
451–750
1,00
> 750
1,25
Where large differential settlements are anticipated, e.g. in waterlogged soils, peat silt or made ground,
and the ground cannot be stabilized either by excavation of the unsuitable soil and replacement with
suitable material, other ground stabilization techniques or the use of piled foundations, the number of
short-length pipes should be increased. Shallow gradients should be avoided in this situation, in order
to minimize the possibility of deposition of solids.
For pipe diameters greater than DN 1500, consideration should be given to the angular performance of
the joints of short rocker pipes subject to significant settlement.
Inspection chambers and manholes that are constructed in situ without using prefabricated units
should be covered either by a concrete slab or by engineering brickwork arches and corbelling, with
lintels as necessary, designed to resist dead and superimposed loads (see BS EN 1991). In situ slabs
should not be less than 150 mm thick.
Cover frames should be bedded on one, two or three courses of engineering brickwork or precast
concrete adjusting units.
Where practicable, the channel should be of the same material as the drain or sewer. Where this is not
practicable, pre-formed channels of other materials or concrete with a granolithic finish may be used.
Pipes should be built into manholes as construction proceeds.
All manholes on drains and sewers of DN 600 diameter and over should be provided with a safety
chain or bar for placing across the mouth of the outgoing sewer when operatives are at work. Double
guardrails (i.e. a top rail and mid-rail) should be provided on the edges of benching and at platforms,
etc. from which a person might fall into the sewer and toe-holes should be provided in the benching to
allow access into the drain or sewer.
Inspection chambers and manholes in agricultural land should be sited, if possible, near to hedges or
other boundaries of fields.
In low-lying agricultural land the possibility of flooding should be taken into account. Consideration
should be given to building the chamber up to approximately 600 mm above natural ground surface and
mounded on all sides with earth. Alternatively, the chamber may be covered with a concrete slab, the
top of which should be at least 600 mm below ground level to avoid conflict with agricultural activities.
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BS EN 752:2017
The burying of covers should be avoided, especially at changes of direction. However, wherever a
chamber is slabbed over (where a cover cannot be allowed on, or near, the surface), carefully referenced
measurements should be made to some fixed points to enable them to be located quickly and accurately.
Materials for construction of access fittings, inspection chambers and manholes include:
a)
engineering brickwork;
b) concrete, in situ and precast;
c)
plastics;
d) vitrified clay;
e)
cast iron.
The choice of material and the chamber design may necessitate a concrete surround after considering
such factors as:
•
The depth of excavation
•
Ground conditions
•
The highest likely ground water level
•
Risk of flotation
•
Any exceptional or eccentric loads (including any exceptional construction loads),
Where a concrete surround is provided it should be, a minimum 150 mm GEN3 concrete in
accordance with BS 8500 should be provided; any joints should be staggered with the joints of the
component material.
Segmental manhole units, especially those sunk as caissons, should be provided with grout holes so
that voids can be filled.
Chambers and shafts made from engineering brickwork should normally be built with solid engineering
bricks in English bond but resistance to water penetration can be increased if the brickwork is built in
"water" ("manhole") bond. The wall thickness should be adequate to resist external pressures due, e.g.
to soil and ground water but in any case not less than 200 mm. Where ground water pressures are
continuously high, double leaf (collar jointed) construction (see BS 5628-1) or tanking should be used to
maintain water pressure resistance. In granular soils above the water table, inspection chambers 900
mm or less in depth (unless in roads or other areas subject to vehicular traffic) may be built in brickwork
not less than 100 mm thick. Joints should be filled with well-compacted mortar 4 mm to 6 mm thick,
completely filled and flushed pointed as the work proceeds. Pipes through chamber walls should be
bedded on mortar. DN 300 or larger pipes should have either a one-brick relieving arch over the pipe
to the full thickness of the brickwork, or a concrete lintel or other effective means of relieving the load.
For chambers constructed of in situ concrete the thickness of the walls should be not less than that
stated for brick manholes and the concrete should be in accordance with BS 8500. The design should be
in accordance with BS EN 1992-2 or BS EN 1992-3.
The shafts of some inspection chambers and manholes are designed to take a vertical imposed load,
others are not designed to take these loads. Where a shaft does not have the strength to take these
vertical loads it shall be constructed in such a way that the traffic loads are not transmitted onto the
shaft. This can be achieved by bedding the cover and frame on a concrete slab that is appropriately
supported to avoid settlement and is separated from the shaft by sleeving.
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NA.7 Relevant authorities
NA.7.1 Introduction
The different legislative arrangements in various European countries make it impossible for an EN to
refer to statutory authorities by name. EN 752 therefore refers to such organizations using the term
"relevant authority".
This national annex lists the names of those relevant authorities, which have powers relevant to this
standard. It gives their name and function together with the principal legislation relating to EN 752 and
any published guidance. The lists of legislation and published guidance are not exhaustive and other
publications could be relevant.
Where the term "Local Authority" is used, unless otherwise stated, this should be taken to mean:
a)
in England: the District, Metropolitan District, London Borough or (in some areas) Unitary Council;
b) in Wales: the County or County Borough Council;
c)
in Scotland: the Unitary, or Island Council;
d) in Northern Ireland: the District Council.
In some parts of England, functions are split between County Councils and District Councils. In these
areas, where a function is carried out by the County Council this is indicated.
The reference documents include dates, however, users should ensure that they are using the most up
to date edition.
NA.7.2 Sewerage Undertaker
NA.7.2.1 Relevant functions
Provision of sewerage services including the design, construction, maintenance and operation of public
sewer systems.
NA.7.2.2 England and Wales
The Sewerage Undertaker is a company appointed by the Secretary of State for the Environment food
and Rural Affairs to carry out sewerage functions in an area.
NA.7.2.3 Scotland
Scottish Water.
NA.7.2.4 Northern Ireland
The Sewerage Undertaker is a company appointed by the Department for Regional Development
(Northern Ireland).
NA.7.3 Building control
NA.7.3.1 Relevant functions
To ensure a satisfactory drainage system from a building to a point of discharge.
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BS EN 752:2017
NA.7.3.2 England and Wales
The Local Authority (Building Control Department). Certain functions can be delegated to
approved inspectors.
NA.7.3.3 Scotland
The Local Authority (Building Control Department).
NA.7.3.4 Northern Ireland
The Local Authority (Building Control Department).
NA.7.4 Water pollution control
NA.7.4.1 Relevant functions
Protection from pollution of all receiving water including groundwaters. Control of effluent discharge
into rivers and into other receiving water bodies.
NA.7.4.2 England
The Environment Agency.
NA.7.4.3 Wales
Natural Resources Wales.
NA.7.4.4 Scotland
The Scottish Environmental Protection Agency.
NA.7.4.5 Northern Ireland
The Northern Ireland Environment Agency.
NA.7.5 Rivers and land drainage
NA.7.5.1 Relevant functions
Overall supervision of the management of rivers and flood defences.
NA.7.5.2 England
The principal land drainage authority in England is the Environment Agency. Internal Drainage Boards
and local authorities also have some land drainage functions.
NA.7.5.3 Wales
The principal land drainage authority in Wales is Natural Resources Wales. Internal Drainage Boards
and local authorities also have some land drainage functions.
NA.7.5.4 Scotland
The principal land drainage authority in Scotland is the Scottish Environmental Protection Agency
(SEPA). Local authorities also have some land drainage functions.
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BS EN 752:2017
NA.7.5.5 Northern Ireland
The principal land drainage authority in Northern Ireland is the Rivers Agency.
NA.7.6 Waste regulation
NA.7.6.1 Relevant functions
The control of disposal of waste.
NA.7.6.2 England and Wales
The Environment Agency.
NA.7.6.3 Scotland
The Scottish Environmental Protection Agency.
NA.7.6.4 Northern Ireland
The Department of the Environment (Northern Ireland) – Environment and Heritage Service.
NA.7.7 Environmental health
NA.7.7.1 Relevant functions
Responsible for protecting the health of the public including nuisance caused by noise and by public and
defective private sewers and drains.
NA.7.7.2 England, Wales, Scotland and Northern Ireland
The Local Authority (Environmental Health Department).
NA.7.8 Highway authority (roads authority in Scotland and Northern Ireland)
NA.7.8.1 Relevant functions
The construction and maintenance of highways including highway drainage, regulation of traffic and
regulation of work carried out in highways.
NA.7.8.2 England
Trunk roads: Highways England.
Other roads: Local Authority. (In those parts of England with separate County and District Councils this
is a County function).
NA.7.8.3 Wales
Trunk roads: Welsh Government.
Other roads: Local Authority.
NA.7.8.4 Scotland
Trunk roads: The Scottish Executive.
Other roads: The Local Authority.
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BS EN 752:2017
NA.7.8.5 Northern Ireland
The Department for Regional Development (Northern Ireland) – Roads Service.
NA.7.9 Occupational health and safety
NA.7.9.1 Fundamental statutory principles
Legal obligations are placed on employers to ensure, so far as reasonably practicable, the health, safety
and welfare of all employees. These legal obligations include the provision and maintenance of safe plant
and safe systems of work and the provision of the information, instruction training and supervision,
which is necessary to ensure the health and safety of employees and of others who could be affected by
the work activity.
NA.7.9.2 England, Wales and Scotland
NA.7.9.3 The Health and Safety Executive. Northern Ireland
The Health and Safety Executive for Northern Ireland is sponsored by the Department of Enterprise,
Trade and Investment The legislation is identical in its requirements to that for Great Britain. Some
legislation listed in NA.8.2 applies throughout the UK. Where that is not the case, the regulations are
similar to those for Great Britain but incorporate the text "(Northern Ireland)" in their titles.
Northern Ireland uses the same guidance as for Great Britain.
NA.7.10
Planning authority
NA.7.10.1
Relevant functions
Responsible for controlling development in an area.
NA.7.10.2
England and Wales
The Local Authority (Planning Department).
NA.7.10.3
Scotland
The Local Authority (Planning Department).
NA.7.10.4
Northern Ireland
The Department of the Environment (Northern Ireland) Planning Service.
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BS EN 752:2017
Bibliography
[1]
Sewers for Adoption, Water UK, 7th Edition 2012, WRc.
[2]
Sewers for Scotland, Scottish Water, 3rd Edition 2015, WRc. Available at http://www.scottishwater.
co.uk/business/connections/connecting-your-property/sewers-for-scotland-and-suds
[3]
Sewers for Adoption for Northern Ireland, 1st Edition 2010, WRc.
[4]
Building Regulations 2010, Approved Document H: Drainage and waste disposal. 2015 Edition,
HMSO. Available at https://www.gov.uk/government/publications/drainage-and-wastedisposal-approved-document-h
[5]
Building Regulations 2010, Approved Document H: Drainage and waste disposal (Wales). 2002
edition incorporating 2010 amendments (updated 2016). Available at http://gov.wales/topics/
planning/buildingregs/approved-documents/part-h-drainage/?lang=en
[6]
Technical Handbook to Building (Scotland) Regulations 2004. Technical Handbook
–
Domestic.
Available
at
http://www.gov.scot/Topics/Built-Environment/Building/
Building-standards/publications/pubtec
[7]
Technical Handbook to Building (Scotland) Regulations 2004. Technical Handbook –
http://www.gov.scot/Topics/Built-Environment/Building/
Non-domestic.
Available
at
Building-standards/publications/pubtec
[8]
DOE Technical Booklet N – Drainage. Department of Finance and Personnel (Northern Ireland),
2012. Available at http://www.buildingcontrol-ni.com/assets/pdf/TechnicalBookletN2012.pdf
[9]
Standards for Roads and Bridges Volume 4, Section 2. Highways England, Transport Scotland,
Welsh Government, The Department for Infrastructure Northern Ireland. HMSO. Available at
http://www.standardsforhighways.co.uk.
[10]
UPM Manual, 3rd Edition – A Planning Guide for the Management of Urban Wastewater Discharges
During Wet Weather. Foundation for Water Research, 2012. Available at http://www.
fwr.org/UPM3/.
[11]
The Urban Waste Water Treatment (England and Wales) Regulations, 1994: Working document for
dischargers and regulators: a Guidance note. DETR and the Welsh Office, 1997.
[12]
[13]
The Urban Waste Water Treatment (Scotland) Regulations 1994: A working document for dischargers
and regulators. A guidance note issued by the Scottish Office Agriculture, Environment and
Fisheries Department, 1998.
The Urban Waste Water Treatment Regulations (Northern Ireland) 1995: A working document for
dischargers and regulators. The Department Of The Environment (Northern Ireland), 1999.
[14]
Council Directive 2006/7/EC of the European Parliament and of the Council of 15 February 2006
concerning the management of bathing water quality.
[15]
Council Directive 2006/113/EC of the European Parliament and of the Council of 12 December
2006 on the quality required of shellfish waters.
[16]
[17]
Non-statutory technical standards for sustainable drainage systems. Department for
Environment, Food and Rural Affairs, 2015. Available at: https://www.gov.uk/government/
publications/sustainable-drainage-systems-non-statutory-technical-standards
Technical Advice Note 15 Development and Flood Risk. Planning Policy Wales, 2004 (Updated
2013). Available at http://gov.wales/topics/planning/policy/tans/tan15/?lang=en
125
BS EN 752:2017
[18]
Scottish Planning Policy 2014. Scottish Government, 2014. Available at: http://www.gov.
scot/Publications/2014/06/5823
[19]
Flood risk assessments: climate change allowances. Environment Agency, 2016. Available at:
https://www.gov.uk/guidance/flood-risk-assessments-climate-change-allowances. (Updated
February 2017).
[20]
Recommended non-statutory standards for sustainable drainage (SuDS) in Wales – designing,
constructing, operating and maintaining surface water drainage systems. Welsh Government,
2016. Available at: http://gov.wales/docs/desh/publications/151230-suds-standards-en.pdf
[21]
Interim Code of Practice for Sustainable Drainage Systems, National SUDS
http://www.susdrain.org/files/
Working
Group,
2004.
Available
at:
resources/other-guidance/nswg_icop_for_suds_0704.pdf
[22]
SUDS for Roads (Scotland). SUDS Working Party, SCOTS, 2010. Available at: http://www.
scottishwater.co.uk/business/connections/connecting-your-property/sewers-for-scotlandand-suds/suds-for-roads-final
[23]
Technical Committee on Storm Overflows and the Disposal of Storm Sewage, Final Report. Ministry
of Housing and Local Government, 1970.
[24]
Environment Agency. Groundwater Source Protections Zone Maps. http://www.environmentagency.gov.uk/maps/info/groundwater
[25]
Drainage Strategy Framework - For water and sewerage companies to prepare Drainage
Strategies. Halcrow Group Limited, 2013. Available at http://www.ofwat.gov.
uk/wp-content/uploads/2015/12/rpt_com201305drainagestrategy1.pdf
[26]
UKWIR Capital Maintenance Planning: A Common Framework. UKWIR, 2002.
[27]
WRc Sewerage Rehabilitation Manual. Available at http://srm.wrcplc.co.uk/
[28]
Safe work in confined spaces, Approved Code of Practice, Regulations and Guidance. Health & Safety
Commission, Third Edition, HSE Books, 2014.
[29]
Civil Engineering Specification for the Water Industry, UKWIR, 7th Edition, 2011, WRc.
[30]
Manual of Contract Documents for Highway Works Volume 1 Specification for Highway Works.
HMSO. Highways England, Transport Scotland, Welsh Government, The Department for
Infrastructure Northern Ireland. Available at: http://www.standardsforhighways.co.uk
[31]
Specification for bedding and sidefill materials for buried pipelines. UK Water Industry. Available
at: https://www.water.org.uk/publications/WIS-IGN/general
[32]
Concrete in aggressive ground (Special Digest 1). BRE, 2005. Available at http://www.brebookshop.
com/details.jsp?id=149036
[33]
Infiltration Drainage – Manual of Good Practice (R156). CIRIA, 1996.
[34]
Soakaway Design (DG 365). BRE, 2016.
[35]
JRD Francis, JA Vickers, AW Grant et al. Erosion of Sewers and Drains. CIRIA Report R014M, 1968.
[36]
Design of sewers to control sediment problems. CIRIA Report 141, 1996.
[37]
Materials selection manual for sewers, pumping mains and manholes. Foundation for Water
Research, 1993.
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The knowledge embodied in our standards has been carefully assembled in
a dependable format and reined through our open consultation process.
Organizations of all sizes and across all sectors choose standards to help
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Our British Standards and other publications are updated by amendment or revision.
Save for the provisions below, you may not transfer, share or disseminate any
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We continually improve the quality of our products and services to beneit your
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Storing and using standards
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• Standards purchased in hard copy format:
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Useful Contacts
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