corrections within design manual for roads and …

CORRECTIONS WITHIN DESIGN MANUAL FOR ROADS AND BRIDGESNOVEMBER 2002

SUMMARY OF CORRECTION - Volume 11, Section 3, Part 10 - Water Quality and DrainageANNEX III - ASSESSMENT METHOD AND WORKED EXAMPLES

It has come to light that the formula for calculating downstream river concentrations of copper and zinc inA3.3 is incorrect. The formula added concentrations, whereas it should add pollution loads and re-calculatethe concentration. The formula has been corrected. The opportunity has also been taken to change thedescription of the design river flow to the 95 percentile flow (Q

95) to accord with common practice, and to

make a small number of updates to the text. It has been necessary to amend all the worked examples, so thewhole of Annex III has been re-issued with the exception of Figures 3.1 and 3.2, which are unchanged.

The formula was sourced from the methods described in CIRIA Report 142 – Control of pollution fromhighway drainage discharges – so care needs to be taken if using the methods from this report directly.

Concentrations calculated in accordance with the original formula will always be greater than if they had beencalculated using the corrected formula. Use of the original formula will therefore have overestimated thepollution potential of discharges, though usually only slightly.

Please remove pages A3/1 - A3/4 and A3/7 - A3/10 dated February 1998 and insert new pages A3/1 - A3/4and A3/7 - A3/12 attached dated November 2002.

We apologise for the inconvenience caused.

Highways AgencyNovember 2002

London: The Stationery Office

August 1998

DESIGN MANUAL FOR ROADS AND BRIDGES

VOLUME 1 1 ENVIRONMENTALASSESSMENT

SECTION 3 ENVIRONMENTALASSESSMENTTECHNIQUES

PART 10

WATER QUALITY AND DRAINAGE

AMENDMENT 1

SUMMARY

This amendment comprises minor corrections to pages3/3 and 3/4 of Chapter 3.

INSTRUCTIONS FOR USE

1. Remove existing pages 3/3 and 3/4 from Chapter3 of Volume 11, Section 3, Part 10 and archive asappropriate.

2. Insert pages 3/3 and 3/4 dated August 1998.

3. Enter the details of Amendment 1 on theRegistration of Amendments sheet, sign and dateto confirm that the Amendments have beenincorporated.

4. Archive this sheet as appropriate.

Note: A quarterly index with a full set of VolumeContents Pages is available separately from TheStationery Office Ltd.

February 1998




PART 10


SUMMARY

This new version of Section 3, Part 10 gives guidance onmethods for the assessment of the impact of runoff fromroads on the environment, and advice on the mitigationmeasures that may be used to reduce the impact ofpollution from runoff, where this is found to be required.

INSTRUCTIONS FOR USE

This is a new document to be incorporated into theManual.

1. Remove the existing Volume 11, Section 3, Part10 and archive as appropriate.

2. Insert the new pages into the Volume.

3. Archive this sheet as appropriate.

Note: A quarterly index with a full set of VolumeContents Pages is available separately from TheStationery Office Ltd.

Water Quality and Drainage

THE HIGHWAYS AGENCY

THE SCOTTISH OFFICE DEVELOPMENT DEPARTMENT

THE WELSH OFFICEY SWYDDFA GYMREIG

THE DEPARTMENT OF THE ENVIRONMENT FORNORTHERN IRELAND


Summary: This document gives guidance on methods for the assessment of theimpact of runoff from roads on the environment, and advice on themitigation measures that may be used to reduce the impact of pollutionfrom runoff, where this is found to be required.

ELECTRONIC COPY NOT FOR USE OUTSIDE THE AGENCY.PAPER COPIES OF THIS ELECTRONIC DOCUMENT ARE UNCONTROLLED

Volume 11 Section 3Part 10

February 1998

REGISTRATION OF AMENDMENTS

Amend Page No Signature & Date of Amend Page No Signature & Date of No incorporation of No incorporation of

amendments amendments

Registration of Amendments



PART 10


Contents

Chapter

1. Introduction

2. Water Quality Control in the UK

3. Pollution Sources and Discharge Quality

4. Pollution Prevention and Mitigation

5. Fisheries Protection

6. Predicting Polluting Potential

7. Stages of Assessment and Drainage Design

8. Regulatory Authorities

9. Glossary of Terms & Abbreviations

10. Bibliography

11. Enquiries

ANNEX I Environment Agency GroundwaterVulnerability Maps

ANNEX II Treatment Systems

ANNEX II I Assessment Methods and WorkedExamples

ANNEX IV Detailed Water Quality Assessment


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1. INTRODUCTION

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Chapter 1Introduction

1. INTRODUCTION

1.1 Water is a vital necessity for all living plants andanimals. For human beings it is not only essential to life,but also of crucial importance in industry andagriculture, for waste disposal, as a means of transportand for informal recreation and organised sports. TheGovernment is committed to maintaining and, wherejustified, improving the quality of Britain’s drinkingwater, watercourses, groundwater and coastal waters. Toachieve these aims, the Government sets standards forwater quality, ensures that performance against them ismonitored, makes regulations to prevent pollution andissues advice on how it can be avoided. The assessmenttechniques described in this PART are directed atmaintaining the quality of controlled waters associatedwith trunk road and motorway projects in the UK butare equally applicable to any project where surface orgroundwater resources are affected by road runoff.

1.2 In England and Wales the term ‘highways’ isequivalent to the Scottish ‘roads’. In this PART ‘roads’will be used as the standard terminology. Traditionally,roads have not been regarded as a major source ofpollution and surface water runoff has been allowed todischarge, often rapidly, with no or minimal treatment.Pollution from road drainage can arise from a variety ofsources: these include accidents, general vehicle androad degradation, incomplete fuel combustion and smalloil or fuel leaks. Pollution impacts on receiving watersappear to be restricted primarily to roads carrying morethan 30,000 vehicles per day (Ellis, 1997), although forroads carrying more than 15,000 vehicles per day thelevel of pollution associated with surface water runoffcould be of concern. The risk of accidental spillageincreases with increased traffic flow.

1.3 Roads are designed to drain freely to preventbuild-up of standing water on the carriageway.Contaminants deposited on the road surface aretherefore quickly washed off during rainfall. Wheretraffic levels are high, the level of contamination andhence the potential for unacceptable harm being causedto the receiving waters, increases. Though there aremany circumstances in which runoff from roads is likelyto have no discernible effect, a precautionary approachand best practice indicate the need for the assessment ofthe possible impact of discharges from proposed trunkroads and motorways.

1.4 Methods are provided for predicting the potentialimpact of the operation of proposed road schemes on theaquatic environment. The impact of the construction ofthe road is not addressed. The methods are intended tobe used during the environmental assessment process toprovide objective and structured evaluation of thepolluting potential of proposed road schemes, and henceallowing:

- the need for the avoidance, and reduction, ofimpacts on the freshwater environment to be takenfully into account in the environmental evaluationof schemes and in route selection;

- selection of appropriate means of preventing anysignificant predicted impacts of the chosen route,through modification of the drainage design,choice of discharge location(s) and/or adoption ofrunoff treatment methods, with the objective ofdesigning potential adverse environmental impactsout of the scheme.


February 1998 2/1

Chapter 2Water Quality Control in the UK

The Regulatory Authorities and their Role

2.1 The Regulatory Authorities (RAs), which are theEnvironment Agency (EA) in England and Wales, theScottish Environment Protection Agency (SEPA) inScotland and the Department of the Environment inNorthern Ireland, have statutory powers and duties forthe protection and monitoring of the quality of controlledwaters. Controlled waters are defined in law and areessentially all waters, either above or below ground,which are neither in the drinking water supply pipe northe sewerage network. The monitoring work undertakenby the RAs includes river flow, water quality andbiology and groundwater quantity and quality. Theyshould always be consulted to obtain relevant existinginformation on waters which could be affected by ascheme.

2.2 In addition to its pollution control role, the EA haspowers and duties for protection of water resources,flood control, fisheries, recreation, conservation andnavigation. In Scotland, the flood defence role of SEPAis limited to flood risk assessment and provision ofadvice thereon, the provision of early warning of floodsand river flow gauging. SEPA has general duties toconserve water resources and to promote conservationand enhancement of natural beauty. It has, however, nonavigation role, nor is it directly responsible for fisheriesprotection, for which responsibility (for salmon and seatrout) falls to the District Salmon Fishery Boards(DSFBs). The British Waterways Board (BWB) isresponsible for the maintenance of a number of inlandwaterways (mostly canals) for both recreational andcommercial navigation. The Department of theEnvironment (Northern Ireland) has similar duties andpowers to those of the EA, although the Department ofAgriculture for Northern Ireland is responsible for flooddefence, fisheries, water recreation and inland waterwaynavigation.

Pollution Control

2.3 Pollution control is exercised by the RAs bymeans of discharge consents, which can stipulateconditions relating to the quality and volume of thedischarge or to the outfall location and process givingrise to the discharge. A road authority will not require aformal discharge consent for road surface waterdrainage, but consents will be required for drainage frommaintenance depots, service areas, picnic areas and thelike. Where consents are required discharges must bemade within the conditions laid down, or an offence will

have been committed. Exceptionally a RA may imposeon any discharge (including a road discharge) either aConditional or an Absolute Prohibition Notice. Therequirements of Conditional Prohibitions can be satisfiedif the RA considers that the design, installation andoperation of the drainage system is appropriate withrespect to pollution control. Absolute Prohibitionsprohibit discharge unless a formal discharge consent isapplied for and granted. It is essential that RAs areconsulted as the scheme develops about all proposeddischarges. Liaison procedures were developed inEngland and Wales in a Liaison Document between theNational Rivers Authority, the Highways Agency andthe Welsh Office and these will be updated in due courseto reflect the wider role of the EA.

Surface Water Management

2.4 Road discharges can affect both watercourse flowand water quality. Potential effects on flooding shouldalways be addressed before pollution control isconsidered, because the former are likely to be moredifficult to resolve and because measures taken to reduceflood risk may have a beneficial effect on runoff quality.Road construction within flood plains in particularrequires detailed consideration. Advice Note HA 71 TheEffects of Highway Construction on Flood Plains,(DMRB 4.2.1) refers. Changes in flow patterns causedby discharges from roads can also cause ecological andother water quality impacts in receiving watercoursesand the potential for such changes must be consideredduring the assessment.

2.5 The RAs manage water quality in the UK usingtwo basic systems: the tracking of quality over time toidentify improvements or deterioration, and the setting oftargets (water quality objectives or standards). Remedialaction can be initiated by failure to meet standards or byevidence of ecological damage. Both of these systemshave relevance to the planning of new or modified roadsand an understanding of the RA approach is necessarybefore undertaking any environmental assessment.

Assessment of Current Water Quality

2.6 Until 1990, the quality of surface waters wastracked using the six class National Water Council(NWC) scheme. The system was adapted to provideboth water quality tracking and target setting data, anduntil recently the similar Scottish Office DevelopmentDepartment Classification Scheme was in use inScotland. SEPA has now revised the Scottish approach

2. WATER QUALITY CONTROL IN THE UK


February 19982/2


and has added a new River Quality Classificationscheme to the existing Coastal Waters, Standing Watersand Estuary Classification schemes.

2.7 The General Quality Assessment (GQA) shown inTable 1 has now replaced the NWC scheme in Englandand Wales. All rivers have been sub-divided intostretches (or reaches), each characterised by a singlewater quality monitoring site. Routine water qualitysamples are collected over a three year period and theresults used to establish the GQA class. In common withthe NWC scheme, a limited number of parameters areincluded in the analysis, though these are moreappropriate to detecting organic pollution (such assewage effluent) than the effects of largely inorganicdischarges such as those contained in road runoff. Abiological GQA will be added in future, based on acomparison of the observed freshwater invertebratefauna at a site with that which would be expected if nopollution were present. GQAs for nutrients and aestheticquality are also planned.

Setting Targets and Water Quality Objectives

2.8 Water Quality Objectives (WQOs) will be used toplan future improvements in water quality and areimportant in considering the acceptability of anyproposed discharge. With knowledge of the present andfuture uses which a stretch of water needs to support,the water quality requirements can be derived.

2.9 Statutory WQOs will be progressively introducedby the Secretary of State. The Surface Water (RiversEcosystem) (Classification) Regulations 1994 are thefirst step towards this. Five river use classes areenvisaged:

i. Rivers Ecosystem (RE)ii. Special Ecosystem (SE)iii. Abstraction for Potable Supplyiv. Agricultural/Industrial Abstractionv. Water Sports

2.10 The RE classification covers the parameters listedin Table 2. Similar specifications will be developed forthe other designated uses and non-statutory WQOs mayapply on a regional basis in the interim period. StatutoryWQOs have not been adopted in Scotland.

2.11 Other uses which have specific water qualityrequirements include abstraction for drinking water: thequality of water at the abstraction point is controlled

under the Surface Waters (Classification) Regulations1989 (in England and Wales, with similar Regulationsapplying in Scotland). These regulations implement ECDirective 75/440/EEC relating to the quality of water forabstraction from a watercourse for human consumption.In addition the EC Freshwater Fisheries Directive(78/659/EEC) specifies water quality standards for theprotection and improvement of water quality needed tosupport fish populations in designated waters.

Table 1. General Quality Assessment chemical grading for rivers and canals

GENERAL QUALITY ASSESSMENT

Water Quality Grade Chemical Parameters

Dissolved Biochemical Ammonia Oxygen Oxygen Demand % Sat mg/l mgN/l 10 %ile 90 %ile 90 %ile

Good A 80 2.5 0.25

B 70 4 0.60

Fair C 60 6 1.3

D 50 8 2.5

Poor E 20 15 9.0

Bad F <20 >15 >9.0

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Chapter 2

Water Q

uality Control in the U

KTable 2. River Ecosystem Classifications

Class Dissolved BOD Total Un-ionised pH Hardness Dissolved Total Zinc Oxygen (ATU) Ammonia Ammonia Copper

Lower limit as% saturation mg/l mg N/l mg N/l 5 percentile; mg/l CaCO

3µg/l µg/l

10 percentile 90 percentile 90 percentile 95 percentile upper limit as 95 percentile 95 percentile95 percentile

RE1 80 2.5 0.25 0.021 6.0-9.0 ≤10 5 30>10 and ≤50 22 200>50 and ≤100 40 300

>100 112 500

RE2 70 4.0 0.6 0.021 6.0-9.0 ≤10 5 30>10 and ≤50 22 200>50 and ≤100 40 300

>100 112 500

RE3 60 6.0 1.3 0.021 6.0-9.0 ≤10 5 300>10 and ≤50 22 700>50 and ≤100 40 1000

>100 112 2000

RE4 50 8.0 2.5 – 6.0-9.0 ≤10 5 300>10 and ≤50 22 700>50 and ≤100 40 1000

>100 112 2000

RE5 20 15.0 9.0 – – – – –



February 19982/4

2.12 There may also be occasions where additionalwater quality specifications apply, for instance where awatercourse is part of a Site of Special ScientificInterest (Area of Special Scientific Interest in NorthernIreland). Similarly waters flowing through high amenityor recreational areas may require specific aestheticcontrol, such as limitation of suspended solids orfloating oils. Physical constraints may also exist, such asthe need to maintain free access for fish passing up anddownstream, protection of angling or other recreationalaccess and protection of river habitat for fish spawningor other ecological uses.

2.13 Canals, lakes, lochs, loughs and ponds should betreated as special cases when considering new dischargesbecause of the lack of flow relative to rivers. The EA areconsidering separate classification systems for canalsand lakes, while the BWB will normally request that theRA imposes a requirement for at least an oil separator tobe fitted to any discharge to a canal.

2.14 Discharges of road runoff to estuaries or tocoastal waters will not normally be a cause of concern,provided that the risk of accidental spillage is acceptableto the RA (and also to the statutory conservationauthority where such sites have designated scientificinterest). WQOs for such waters are available from theRA.

2.15 Where a stretch of water supports more than oneuse, the overall requirements will derive from acombination of the most stringent criteria for any of theuses concerned. No discharge which could cause any ofthe overall requirements to be breached will beacceptable. Hence the assessment of new roads or roadimprovements must include consideration of all of theuses to which the watercourse is put. The receivingwatercourse should be assessed not only downstream ofany discharge or river crossing, but also upstream whereinterests such as migratory fisheries are present. Theappropriate WQO and any physical constraints will beadvised by the RA.

Groundwater

2.16 Groundwater provides a proportion of base flowfor many rivers. In England and Wales approximately35% of all drinking water is drawn from groundwatersources, whilst in Scotland and Northern Ireland thepercentage is significantly less. Aquifers can alsoprovide an important water source for agricultural andindustrial use. Once contaminated, groundwater isextremely difficult to rehabilitate, so discharges toground are strictly controlled.


2.17 Although all waters below ground are classed ascontrolled waters, the focus of the pollution controleffort is mainly on the protection of water in thesaturated zone ,that is the aquifers. This is in conformitywith the Groundwater Directive (80/68/EEC), whichrequires measures to be taken to control the discharge ofcertain dangerous substances, classified as List I or IIsubstances, to groundwater. The effect is to prohibit thedirect discharge to groundwater of List I substances andto prohibit their indirect discharge except where verysmall quantities of the substances are involved and theircomplete removal is impracticable. The introduction intogroundwater of List II substances is to be limited so asto avoid pollution. Their direct discharge is alsoprohibited, but it may be permissible to allow dischargescontaining them to percolate indirectly to the aquiferthrough the unsaturated zone. List I includeshydrocarbons, while List II includes copper and zinc.These substances are present in road runoff. The fulllists are included in Table 3.

2.18 WQOs have yet to be established for groundwaterand, until they are, the RA will advise on the standardswhich must be satisfied for individual aquifers. Whereclean groundwaters are involved, especially those usedfor abstraction of drinking water supply with minimaltreatment, the RA may advise on Drinking Waterstandards to be met for some contaminants. Morerelaxed standards may apply, however, wheregroundwaters are already of poor quality, such as thosesuffering from saline intrusion. The frameworkdocument “Policy and Practice for the Protection ofGroundwater” (NRA, 1992) provides details of thepolicies relevant to proposed discharges to ground. TheScottish equivalent is “Groundwater Protection Strategyfor Scotland” (SEPA, 1997). The Scottish Strategyadopts the same philosophy as that which applies inEngland and Wales, although there are specificdifferences which must be checked.

2.19 The framework is set out as a series of policystatements. Of particular relevance are PolicyStatements F1, F2 and F3 (which all apply in Englandand Wales, with similar Policy Statements applying inScotland):

F1 The RA will seek to prevent any discharge intounderground strata which may result in pollutionof water resources.

F2 The RA expects to be consulted by local and otherauthorities to identify any proposal involvingdischarging of sewage, trade effluent orcontaminated surface water into undergroundstrata. The RA will object if water resources arejudged to be at risk.



February 1998

LIST I OF FAMILIES AND GROUPS OFSUBSTANCES

These substances should be prevented from beingdischarged into groundwater.

List I contains the individual substances which belong tothe families and groups of substances specifiedbelow, with the exception of those which are consideredinappropriate to List I on the basis of a low risktoxicity, persistence and bioaccumulation.

Such substances which with regard to toxicity,persistence and bioaccumulation are appropriate to ListII are to be classed in List II.

1. Organohalogen compounds and substances whichmay form such compounds in the aquaticenvironment

2. Organophosphorous compounds

3. Organotin compounds

4. Substances which possess carcinogenic,mutagenic or teratogenic properties in or via theaquatic environment (Note 1)

5. Mercury and its compounds

6. Cadmium and its compounds

7. Mineral oils and hydrocarbons

8. Cyanides

LIST II OF FAMILIES AND GROUPS OFSUBSTANCES

Discharges of these substances into groundwater shouldbe minimised.

List II contains the individual substances and thecategories of substances belonging to the families andgroups of substances listed below which could have aharmful effect on groundwater.

1. The following metalloids and metals and theircompounds:

1 Zinc 11 Tin2 Copper 12 Barium3 Nickel 13 Beryllium4 Chrome 14 Boron5 Lead 15 Uranium6 Selenium 16 Vanadium7 Arsenic 17 Cobalt8 Antimony 18 Thallium9 Molybdenum 19 Tellurium10 Titanium 20 Silver

2. Biocides and their derivatives not appearing inList I.

3. Substances which have a deleterious effect on thetaste and/or odour of groundwater andcompounds liable to cause the formation of suchsubstances in such water and to render it unfitfor human consumption.

4. Toxic or persistent organic compounds of siliconand substances which may cause theformation of such compounds in water, excludingthose which are biologically harmless or arerapidly converted in water into harmlesssubstances.

5. Inorganic compounds of phosphorus andelemental phosphorus.

6. Fluorides

7. Ammonia and nitrites

Note 1 - when certain substances in List II arecarcinogenic, mutagenic or teratogenic they are includedin category 4 of List I

Table 3. List I and List II substances as defined by EC Groundwater Directive (80/68/EEC)

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F3 The RA will control discharges into undergroundstrata within areas where groundwater is judgedto be at risk.

2.20 Major roads are perceived by the RAs to bepotential sources of pollution, although it is acceptedthat discharge via soakaway (with oil interception ifappropriate) does not necessarily result in contaminationof controlled waters. The degree of risk and theimportance of the receiving water are key factors indetermining acceptability.

2.21 The RAs have established three groundwaterSource Protection Zones, to be defined for eachabstraction source (springs, wells, boreholes), which aimto protect vulnerable aquifer resources. The process ofestablishing the location of source protection zones isongoing. The zones can be summarised as follows:

Zone I (Inner Source Protection)

Immediately adjacent to the source and based upon a 50day travel time from any point below the water table tothe source (50 days being the decay period for biologicalcontaminants).

Zone II (Outer Source Protection)

Defined by a 400 day travel time (to provide delay andattenuation of slowly degrading pollutants).

Zone III (Source Catchment)

Defined by the entire catchment area of a groundwatersource.

2.22 The policy statements are supported byAcceptability Matrices, which indicate, for each type ofdischarge, its acceptability within the protection zonesfor an abstraction source and within the groundwaterresource as a whole. Where applicable, the measuresthat have to be taken for the discharge to be permittedare shown. The matrix for discharges of surface water isAcceptability Matrix 3c, which is reproduced from“Policy and Practice for the Protection of Groundwater”(NRA, 1992) as Table 4. This Matrix indicates that nodischarge of runoff from major roads to ground will beaccepted within Zone I of an abstraction source, and willonly be acceptable in exceptional circumstances withinZone II. Discharges in all other areas will be acceptedsubject to satisfactory site investigation and withappropriate pre-treatment such as a soakaway with anoil separator. Site investigation may include ahydrogeological assessment. Notwithstanding the notesin the Key to Matrix 3c a highway or road authoritydoes not require consent for discharge from a road drain.RAs do, however, have power of prohibition of a

discharge and can, by this means, impose conditions onany discharge to ground waters. It is essential, therefore,to consult RAs on proposed discharge in accordancewith the established liaison procedures.

2.23 As part of the framework policy document, theEA have produced ten Regional Appendices. Theseprovide more detailed information on groundwaterresources within each of the regions, and are beingsupported through the production of GroundwaterVulnerability maps at 1:100,000 scale. The mostvulnerable are categorised as major aquifers with a highsoil leaching potential. The least vulnerable are the non-aquifers. In England, Wales and Northern Ireland, sevenvulnerability categories apply. This is simplified to fivein Scotland. The current EA maps and publication datesfor others are listed in ANNEX I.

2.24 In Scotland, vulnerability maps at a scale of1:100,000 are proposed for the main aquifers only.Isolated valley deposits within the Highlands and Islandswill be presented as collective maps. In NorthernIreland, the equivalent vulnerability maps are scaled at1:250,000. For areas where no maps are published, theRA can advise on vulnerability.

2.25 Also relevant to the disposal of road surfacerunoff are the Groundwater Policy Statementsconcerning diffuse pollution of groundwater in Englandand Wales (Policies G1-G4), particularly with referenceto the leaching of herbicides and other maintenancechemicals from road verges and landscaped areas. TheSEPA Policy Statements G1 and G2 cover the Scottishcontext. In addition, the Highways Agency regularlyreview their maintenance practices which may have linkswith diffuse contamination. Specific guidance for the useof chemical sprays and application of de-icing agents iscovered in the Highways Agency’s Trunk RoadMaintenance Manual Volume 2 “Routine and WinterMaintenance Code” (1996). This code of practiceadvocates the use of herbicides only in exceptionalcircumstances or where there is a particular need such asaround motorway marker posts and along kerb lines.Mechanical clearance of central reservations is normallyundertaken. Only herbicides covered by the Control ofPesticide Regulations 1986 and the Control ofSubstances Hazardous to Health 1988 may be used.Operatives applying the chemicals must hold aproficiency certificate for the method of application.

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Table 4. Discharges of surface water to underground strata (Matrix 3c)Policy and Practice for the Protection of Groundwater (Environment Agency/NRA - 1992)

SOURCE PROTECTION

I II IIIACTIVITY INNER ZONE OUTER ZONE CATCHMENT ZONE

DISCHARGES OF SURFACEWATER TO SOAKAWAY FROM:

No Objection (R5)Roof Drainage (provided for sole use No Objection (R5) No Objection (R5)

of roof drainage)

Impermeable Areas

- public/amenity Not acceptable (R1) Acceptable (R4) Acceptable (R4)

- large car parks Not acceptable (R1) Acceptable (R3/4) Acceptable (R4)(with interceptor) (with interceptor)

- lorry parks Not acceptable (R1) Presumption against (R2) Acceptable (R4) (with interceptor)

- garage forecourts Not acceptable (R1) Presumption against (R2) Acceptable (R4)(with interceptor)

Presumption against (R2) Acceptable only if- major roads Not acceptable (R1) Acceptable only in investigation favourable and

exceptional circumstances with adequate precautions (R4)

Acceptable only ifIndustrial Sites Not acceptable (R1) Presumption against (R2) investigation favourable

and with adequateprecautions (R3/4)

RESOURCE PROTECTION

ACTIVITY MAJOR MINOR NON- AQUIFER AQUIFER AQUIFER

DISCHARGES OF SURFACEWATER TO SOAKAWAY FROM:

Roof Drainage No Objection (R5) No Objection (R5) No Objection (R5)

Impermeable Areas

- public/amenity Acceptable (R4) Acceptable (R4) Acceptable (R4)

- large car parks Acceptable (R4) Acceptable (R4) Acceptable (R4)(with interceptor) (with interceptor) (with interceptor)

- lorry parks Acceptable (R4) Acceptable (R4) Acceptable (R4)(with interceptor) (with interceptor) (with interceptor)

- garage forecourts Presumption against (R2) Acceptable (R4) Acceptable (R4)(with interceptor) (with interceptor)

- major roads Acceptable (R4) Acceptable (R4) Acceptable (R4)(subject to investigation and (subject to investigation and (subject to investigation and

with interceptor) with interceptor) with interceptor)

Acceptable only if Acceptable (R4) Acceptable (R4)Industrial Sites investigation favourable and (subject to investigation and (subject to investigation and

with adequate precautions (R3/4) with interceptor) with interceptor)

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Table 4 (cont). Discharges of surface water to underground strataKey to matrix 3c

Response 1 (R1) - Prohibit/object in principl e -The RA will normally object inprinciple to such activities whichwould involve a high risk ofcontamination of controlledwaters or a source.(Uncontaminated surface waterdoes not require the consent of theRA under COPA 1974).

Response 2 (R2) - Presumption against - The RAwill seek to prohibit this activityby serving an absoluteprohibition notice whereverpossible. An objection will onlybe withdrawn in exceptionalcircumstances or where detailedinvestigation can demonstrate thatthe activity does not represent ahigh risk of contamination tocontrolled waters and can beadequately controlled byconditions that form part of astatutory consent or agreement.

Response 3 (R3) - Consent to discharge - The RAwill normally have no objection inprinciple to this type of discharge,providing it is controlled underthe planning system withappropriate conditions and aconsent to discharge is obtained.

Initial screening of a consentapplication will identify whetherfurther investigation andassessment is required prior to theconsent being determined.Consent conditions may restrictthe quality and quantity ofeffluent discharged and whereassessment identifies a potentialfor significant change ingroundwater quality, long termmonitoring of both the dischargeand remote observation pointsmay be required.

Response 4 (R4) - No objection subject tostandard conditions - The RAwill normally have no objection tothis discharge subject to standardconditions in a consent orplanning permission to protect thequality of controlled waters or asource. An investigation may berequired to determine the risk ofcontamination and theformulation of appropriateconditions. Long term monitoringof controlled waters in thevicinity of such activities may berequired.

Response 5 (R5) - No objection - The RA willnormally have no objection inprinciple to this discharge whichit considers will have nodiscernible impact on waterresources or quality. Noconditions or monitoring arelikely to be required.

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2.26 A balance needs to be struck when consideringwhether road runoff should be discharged to surfacewaters or to ground. In some cases the effect onreceiving surface waters could be such that discharge toground may be appropriate. This could apply where thedischarge would aggravate an existing flooding risk, orwhere it could have a potentially disproportionate effecton pollution within the receiving waters. Additionaladvice can be found in “A Guide to Sustainable UrbanDrainage (SEPA/EA, 1997) and in CIRIA Report 156“Infiltration Drainage - Manual of Good Practice”(1996). The latter describes various means of draining toground and addresses the water quality issues. It must bestressed, however, that important water resources mustnot be put at risk and that the groundwater protectionpolicy requirements must always be satisfied. The RAwill advise on the importance of any aquifer or groundwaters and will give guidance as to the acceptability ofany proposed discharge to ground.

Potential Spillages - Pollution Control

2.27 In addition to consideration of the implications ofa proposed scheme with respect to routine runoffdischarges and any physical constraints, theacceptability of any discharge will be determined by therisk that an accidental spillage which leads to a waterpollution incident will occur. That risk can be calculatedby the Design Organisation, with mitigation in the formof spillage control measures to be adopted if the risk inthe absence of control is unacceptable to the RA.

2.28 Pollution control measures for major spillagesnormally require the drainage system to be ‘shut down’until such time as the pollutants can be removed ortreated. In any event the provision of a schedule ofcontingency plans, emergency procedures, monitoringand maintenance should be discussed with the RA. Thismay include a memorandum of understanding betweenthe RA and the Fire Service or some form of bindingagreement as covered in DoT Circular Roads 7/87 -Spillages of Hazardous Substances on the Highway.

2.29 Methods of dealing with spillages vary in detailfrom one incident to the next, but the principles ofprocedure are generally consistent in practice. In theevent of an accident the emergency services arecontacted. The Fire Brigade has a statutory duty toprotect life and property from fire. If they causepollution while undertaking this duty they will not beguilty of an offence providing that they take allreasonable steps in the circumstances to minimise itseffects (see Section 89 of the Water Resources Act 1991which deals with exemptions from prosecution inEngland and Wales and Section 30J(i) of the Control ofPollution Act 1974 (as amended by Schedule 16 of theEnvironment Act 1995), which covers similar ground inthe Scottish context).

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General

3.1 Runoff from roads produces a highly variabledischarge, both in terms of quality and volume.Discharge quality will be determined predominantly bylocal and site specific factors. Hence, while certain keycontaminants are universally present, theirconcentrations in the discharge can vary between sitesand between and within rainfall events at individualsites.

Reported Discharge Quality

3.2 Table 5 presents a range of recorded qualities ofdischarges from operational roads. The data, which arefrom a wide range of studies, require updating(particularly for the lead content of runoff, where thedeclining use of lead additives in petrol has markedlyreduced potential concentrations in runoff since the early1990s), but are the best currently available. They tend tobe skewed by the over-representation of ‘first flush’runoff in the analyses reported, giving a false impressionthat the maxima occur regularly. Table 6 presentslimited data from newly constructed (early 1996)sections of a motorway. The motorway is drained usingcombined filter drains which are considered to berelatively effective in removing insoluble pollutants inthe early stages of their design life (the efficiency ofvarious runoff treatment methods are discussed inANNEX II).

3.3 Table 7 presents a summary of runoff quality datafrom highway sites in America. In this case the waterquality is expressed as the Event Median Concentration(EMC), that is a flow weighted median qualitymonitored over complete storms. The values areinfluenced by ‘first flush’ effects but provide a morerealistic assessment of the overall quality dischargedduring a storm event. The EMC and associated variationabout the median provide a more reliable statistical basefor predicting likely runoff quality than does the simpleexpression of the range of qualities given in Tables 6 and7 above. It is suggested that EMC values are used forplanning and environmental assessment purposes.

Relationship to Traffic Flow

3.4 The main sources of pollutants in roadsdischarges are vehicular and this suggests that a closecorrelation between traffic volume and runoff qualitycould be expected. American experience indicates thatthis is not always the case, suggesting that traffic flows

are a useful, but not necessarily robust, indicator oflikely runoff quality at specific sites. Table 8 gives asummary of published data on pollutant build-up rateson roads related to traffic flow.

3.5 Several authors have reported that at AverageAnnual Daily Traffic flows (AADTs ) of less than15,000 there are virtually no noticeable effects ofdrainage on receiving water quality (Bascombe et al,1990; Ellis and Revitt, 1991; CIRIA Report 142, 1994).At AADTs in the range 15,000-30,000, only minorimpacts have been reported (Maestri et al, 1988; Ellisand Revitt, 1991) The effects of discharges from roadscarrying AADTs exceeding 30,000 will depend on thespecific local circumstances at the discharge points.

3.6 In addition to discharge from operational roads,construction site runoff can cause serious pollution if theRA guidelines for controlling discharges from temporaryworks are not adequately followed. Mud, fuel oil andconcrete liquors are the main contaminants of concern,although discharges of sewage and of other pollutedwaters from construction sites will also be strictlycontrolled by the RA. These issues are currently beingresearched.

Dilution and Dispersion

3.7 The principal factors determining the impact ofany pollutant are dilution and dispersion. Where theavailable dilution is high and the pollutant dispersesrapidly the resultant concentration will be low. Assuspended solids form the largest part of contaminants inroutine runoff and dissolved contaminant concentrationsare likely to be low, significant pollution is unlikelyprovided that adequate measures are taken to deal withthe solids and that there is sufficient dilution.

3.8 There is no evidence currently available in the UKto suggest that contamination of groundwater fromroutine road runoff is a serious problem. Road runoff isnormally only weakly polluting and this, combined withthe physical processes through which it may pass toreach the groundwater (absorbtion and immobilisation inthe soil, bacterial degradation and storage) means thatthe effects will normally be negligible. Inappropriatelyused pesticides entering the runoff can, however, pose arisk to groundwater.

3. POLLUTION SOURCES AND DISCHARGEQUALITY

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Table 5. Ranges of pollutant levels in runoff from roads(Colwill et al, 1984; Strecker et al, 1990)

Pollutant Rainfall Urban 1 Urban 11 Urban 111 Rural

Electrical Conductivity (µS/cm) 8-80 6-20000 - - -

Total Solids(mg/l) 18-24 145-21640 11-40 - -

Total Dissolved Solids (mg/l) - 66-3050 - - -

Total Volatile Solids (mg/l) - 12-1600 - - -

Volatile Suspended Solids (mg/l) - 12-1500 - 20-78 6-25

Total Suspended Solids (mg/l) 2-13 2-11300 - 68-295 12-135

Oil/hydrocarbons (mg/l) - 0-400 3-31 - -

COD (mg/l) 2.5-32 5-3100 - 57-227 28-85

Chloride (mg/l) 1-11 4-17000 4-27 - -

Bromide (mg/l) - 0.02-6.0 - - -

Total Lead (µg/l) 0.024-10.4 10-14500 10-150 102-1562 24-272

Total Zinc (µg/l) 0.02-4.9 1000-15000 20-1900 192-564 35-185

Total Cadmium (µg/l) 0.013-0.056 2-400 - - -

Total Copper (µg/l) 0.06-0.48 7-2500 10-120 25-119 10-50

Total Chromium (µg/l) 0.023-0.08 18-270 - - -

Total Nickel (µg/l) - 20-1500 - - -

Total Organic Carbon (µg/l) 1-18 5-120 - 8-74 3-17

Nitrate & Nitrite (mg/l) 0.01-5.0 0.3-6.9 - 0.4-1.5 0.2-0.9

Total Nitrogen (mg/l) 0.5-9.9 0.2-14 0.2-1.0 1.0-3.2 0.3-2.2

Total Phosphorus (mg/l) 0.001-0.35 0.3-4.4 - 0.2-1.0 0.1-0.5

BOD (mg/l) 1-15 25-700 8-25 - -

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Table 6. Motorway Runoff Quality - M74, Dumfriesshire, 1995-1996

Receiving Watercourse pH Suspended Solids (mg/l) Zinc (Total) (µg/l) Copper (Dissolved) (µg/l) Drain Catchment

No. Median No. Median No. Median No. Median Length AreaSamples (Range) Samples (Range) Samples (Range) Samples (Range) (km) (sq m)

R. Annan 0 1 3 1 38 1 4 0.2 17400

R. Annan 16 7.4(4.2-7.8) 14 30(9-123) 17 23(3-77) 17 14(5-26) 0.85 22200

Dalmakethar Burn (east) 7 7.3(2.9-8.6) 6 36(16-256) 8 49(2-100) 8 12(3-23) 0.6 19100

Ryecastle Burn 2 (6.6-7.1) 2 (9-22) 2 (26-36) 2 (7-12) 1.25 26400

Nethercleuch Burn 9 7.2(6.4-8.7) 9 21(5-76) 10 24(9-132) 10 11(4-36) 2.9 96600

Dryfe Water 1 7.1 1 26 1 11 0.4 13500

Kirk Burn (North) 5 7.2(6.8-7.8) 5 20(8-87) 6 36.5(5-48) 6 10(5-15) 0.94 30300

Kirk Burn (Becton) 2 (7.3-7.4) 3 16(8-22) 3 36(28-48) 3 3(3-6) 2.12 68400

Kirk Burn (South) 5 7.0(6.9-8.1) 3 19(1-56) 5 7(<1-40) 5 8(1-19) 0.49 15700

Northcroft Burn 5 7.5(7.2-10.7) 5 1(<1-19) 6 6.5(<1-36) 6 3.5(<1-9) 2.05 67100

Northcroft Burn 4 8.3(7.0-10.1) 3 10(7-19) 4 19(4-54) 4 7.5(5-18) 0.4 22300

Basic Road Parameters

Drainage Design - Combined Filter DrainsAADT - 27,000 - 30,000 , % Heavy Goods Vehicles - 40Annual Average Rainfall - 1062mm% Days with >2 mm Rain - 34Three Lane Dual Carriageway Motorway with permeable central reservation and hard shoulders, opened to traffic 1994-95.

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August 1998ELECTRONIC COPY NOT FOR USE OUTSIDE THE AGENCY.PAPER COPIES OF THIS ELECTRONIC DOCUMENT ARE UNCONTROLLED

Table 7. Summary of Runoff Quality from Highway Sites in America

Event Median Concentration (EMC) - Urban HighwaysAverage daily traffic usually more than 30,000 vehicles per day

POLLUTANT Percent of sites having a median EMC less than indicated concentration

10% 20% 50% 80% 90%of sites of sites of sites of sites of sites

Total Suspended Solids (mg/l) 68 88 142 230 295

Volatile Suspended Solids (mg/l) 20 25 39 61 78

Total Organic Carbon (mg/l) 8 12 25 51 74

Chemical Oxygen Demand (mg/l) 57 72 114 179 227

Oxidised Nitrogen (mg/l) 0.39 0.49 0.76 1.18 1.48

Total Kjeldahl Nitrogen (mg/l) 1.06 1.27 1.83 2.62 3.17

Phosphate as P (mg/l) 0.15 0.21 0.40 0.76 1.06

Total Copper (µg/l) 25 32 54 91 119

Total Lead (µg/l) 102 163 400 980 1562

Total Zinc (µg/l) 192 231 329 469 564

Event Median Concentration (EMC) - Rural HighwaysAverage daily traffic usually less than 30,000 vehicles per day

POLLUTANT Percent of sites having a median EMC less than indicated concentration

10% 20% 50% 80% 90%of sites of sites of sites of sites of sites

Total Suspended Solids (mg/l) 12 19 41 90 135

Volatile Suspended Solids (mg/l) 6 7 12 19 25

Total Organic Carbon (mg/l) 4 5 8 13 17

Chemical Oxygen Demand (mg/l) 28 34 49 70 85

Oxidised Nitrogen (mg/l) 0.23 0.29 0.46 0.72 0.91

Total Kjeldahl Nitrogen (mg/l) 0.34 0.47 0.87 1.59 2.19

Phosphate as P (mg/l) 0.06 0.08 0.16 0.33 0.48

Total Copper (µg/l) 10 13 22 38 50

Total Lead (µg/l) 24 36 80 179 272

Total Zinc (µg/l) 35 46 80 139 185

Source: Driscoll et al (1988)

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Pollution sources and discharge quality

Table 8. Annual pollutant build up on road surfaces relative to traffic flow

Vehicles/Day Highway Type Suspended COD Oil NH4-N PO

4-P Pb Zn Cu Study area Study date Source of data

(AADT, thousands) Solids

<5 Residential 2218 0.30 0.40 0.39 Germany 1986-89 Muschack (1990)

Residential 3640 UK 1991-92 Butler (1993)

5-15 Urban Roads 4978 0.68 0.89 0.87 Germany 1986-89 Muschack (1990)

Various Urban 7289 UK 1991-92 Butler (1993)

<30 Various Urban 550 245 - 3.6 1.0 2.2 1.4 0.5 USA 1976-77 US-FHA (1981)

41 Rural Motorway 873 672 43 4.6 1.6 1.3 2.3 0.6 Germany 1978-81 Stotz (1987)

47 Rural Motorway 848 557 27 3.2 1.5 1.1 2.9 0.5 Germany 1978-81 Stotz (1987)

>50 Various Motorways 1930 1391 1682 3.3 - 3.1 4.6 1.2 UK 1980s Ellis (1991b)

Urban Motorways 10410 1.68 2.06 3.19 Germany 1986-89 Muschack (1990)

>60 Urban Motorway 6289 - - - - 12.9 19.0 3.8 UK 1973-74 Hedley and Lockley (1975)

65 Rural Motorway 1000 - 85 - - 3.0 5.8 - UK 1980-81 Colwill et al. (1984)

Motorway 770 - - - - 2.4 1.9 - Switzerland 1970s Dauber et al. (1978)

Motorway 650 - - - - 1.2 1.9 - France 1970s Cathelain et al. (1981)

1 = BOD52 = Total hydrocarbons

Units expressed as kg/ha/yr unless otherwise statedSource CIRIA Report 142 (1994)


February 1998

3.9 Where protection of water quality is concerned,one of the main considerations is to ensure that therelevant water quality standards (which are usuallyexpressed as 95 percentiles, allowing the limits to beexceeded for five percent of the time) are not breached.The upstream water quality of the discharge, availabledilution and the rate at which the discharge is mixed(dispersed) within the receiving water are the key factorsin determining whether standards may be breached.

3.10 Potential sources of road runoff contamination arediverse and may be generated from construction, traffic,maintenance (including the application of de-icing salts),accidental spillage and from other sources such asatmospheric deposition. Road associated contaminantsconsidered to have the greatest potential impact onreceiving waters include suspended solids,hydrocarbons, metals, pesticides and herbicides, de-icingagents, nutrients and those arising from accidentalspillages. Where the road drain enters the general urbandrainage network or where service areas are involvedthere may also be microbiological contamination. Whilediverse in form and origin, the pollutants present inroutine runoff can be conveniently grouped into threecategories: those that are insoluble (likely to settle on thebed of a watercourse), those that are soluble (affectingwater quality and/or aesthetic values) and those arisingfrom accidental spillages (which are concentrated).

Routine Runoff Components - Insoluble Pollutants

Vehicle Oil and Other Hydrocarbons

3.11 Up to 70% of the oil deposited onto a road bymoving vehicles becomes associated with the sedimentfraction and may ultimately settle on the bed of thereceiving water. The proportion increases afterprolonged dry weather periods (Colwill et al, 1984). It isonly when relatively large quantities of fuel or oil arespilled that a significant oily sheen will form on thesurface of water and remain visible for a long distancedownstream, although even small spillages will bevisible where the water surface remains relatively calm.Such spillages, in the absence of accidents, are morenormally associated with lorry parking areas and garageforecourts than with roads carrying moving traffic.

3.12 Polynuclear Aromatic Hydrocarbons (PAHs),derived from unburnt fuel, have a higher affinity for thesediment fraction than most other hydrocarbons (Ellisand Revitt, 1991). Some PAHs are toxic to certainbottom dwelling freshwater invertebrates, which may

be affected in streams downstream of significant roadsdischarges.

3.13 Hydrocarbons are List I substances under theterms of the Groundwater Directive (see Table 3) andhence direct discharge of runoff into groundwater is notpermitted. The Groundwater Protection Policies (GPPs)also limit the locations where indirect (via soakaway)discharges are acceptable, with the provision of an oilseparator being the minimum requirement for theprotection of either an abstraction Source or an aquiferResource for discharges from a major highway.

Suspended Solids

3.14 A significant proportion of the total polluting loadarising from a road is associated with the solid fractionof a discharge, which may contain over 90% of theinorganic lead, 70% of the copper and 56% of thecadmium arising from a rural road. Several workershave determined that it is the fine sediment fraction(<63µm) which is the most important source of pollution(Hamilton and Harrison, 1991).

3.15 Insoluble and settleable materials may not cause afailure of water quality standards but could, under somecircumstances, cause an unacceptable accumulation ofsolids on the bed of the receiving watercourse. Even ifthese solids are inert, fish, invertebrates and plants canbe adversely affected by smothering. Currently there areno sediment quality or quantity standards to use asreference points (although standards are now availablefor use in America and research is currently in progressin the UK). Some hydrocarbons and byproducts ofincomplete fuel combustion are toxic, and the types andquantities of fauna present can be changed if thesebyproducts are allowed to accumulate on the bed of thereceiving water in large quantities. In this situation theavailable dilution is of little importance in determiningimpact: solids will settle rapidly in still or slow-flowingwaters, so will not disperse far from the outfall and willnot come into contact with the majority of the wateravailable for dilution.

3.16 Provided good engineering design practice isfollowed (as outlined in CIRIA Report 156) alldischarges to ground will pass through an area designedto remove the majority of sediment before the waterpercolates towards the saturated zone. Hence insolublepollutants will be largely removed and are effectively ofless concern for groundwater resources than they are forsurface waters.

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Routine Runoff Constituents - Soluble Pollutants

Metals

3.17 Concentrations of metals in runoff are normallylow and may be related to factors such as traffic volume,surrounding land use and atmospheric deposition. Theyare therefore site specific. Metals present in runoff(which include lead, zinc, copper, iron and cadmium)may be derived from accidental spillage or from thedegradation of vehicles, road surface wear andatmospheric sources. A significant proportion of theheavy metals component is associated with the solidparticles in road runoff. Metals may also be transportedas soluble salts or as insoluble compounds.

3.18 The use of lead in petrol is declining, andalthough present at relatively high concentrations in roadrunoff in the 1970s and 1980s, the low solubility (andlow toxicity of the insoluble form) of this metal is suchthat biological impacts would not now be anticipated.Cadmium use is also in decline, leaving copper, zinc andiron as the key metals in roads discharges. Usually, it isonly copper and zinc which are potentially ecologicallysignificant at the range of concentrations present inrunoff. They are toxic in certain forms, more so inwaters of low hardness (soft water), although recordedconcentrations in road runoff are predominantlyrelatively low.

3.19 Most of the analysis carried out on road runoffcovers only the total metal content (including bothdissolved and insoluble forms) although theconcentration of the dissolved form of copper presentprovides the best estimator of likely ecological effects ofthis metal (WRc, 1992). Estimates of copper present inthe dissolved fraction vary from 10-40% of the total.Factors which are important in determining thebioavailability, and therefore toxicity, of metals includethe presence of humic and fulvic acids. These arecompounds present at relatively high levels in watersdraining areas of peat, which tend to complex withcopper, forming an insoluble, non available compound.Acidity can also increase dissolved metal concentrationsand toxic effects.

3.20 Heavy metals which are predominantly present inthe insoluble form will be trapped at the soakawaywhere runoff discharges to ground. Only the dissolvedform is likely to pass to groundwater. There are norecorded instances in the literature where the totalcopper levels in road runoff exceed the drinking waterstandard (3 mg/l). Only in exceptional circumstances hasthe drinking water standard for zinc (5 mg/l) beenexceeded. Hence there should be no circumstanceswhere copper concentrations, and virtually no cases

where zinc levels, are of concern in discharges of roadrunoff to ground.

Organic Toxic Matter and Pesticides

3.21 The use of herbicides and pesticides in themaintenance of road verges is a potential source ofcontamination of discharges. The risk of suchcontamination can be reduced through judicialapplication of sprays according to best environmentalpractice and the selection of degradable compounds.

3.22 For discharges to ground, oil separators andsoakaways will have negligible effect on theconcentration of any contaminant present in thedissolved form and having negligible affinity forabsorption onto solids. While certain contaminants candegrade in the ground, unless there is specific localknowledge to indicate that attenuation is always assuredit should be assumed that none will occur. In practice,risks to groundwater arising from herbicide and pesticideusage can only be effectively reduced through judiciousapplication and selection of the least persistentchemicals.

Rock Salt and Alternative De-icing Agents

3.23 Road salting is undertaken during winter to ensurethe safety of road users, and the application of salt toroads between November and March is one of thesources of potential contamination of road runoff. As aconsequence, winter runoff can intermittently containhigh chloride levels; Table 9 provides estimated pollutantloads for each salting. In addition to sodium chloride,de-icing salt may contain clay, cyanide and a number ofmetals at low concentrations. De-icing practices duringthe winter months may therefore also cause the solidscomponent of road runoff to be significantly increasedfor short periods of time. While sudden increases inchloride concentration can adversely affect fish andfreshwater invertebrates, any winter runoff wouldnormally be very rapidly diluted and dispersed. Anyecological effects would then be temporary and highlylocalised. There are no incidences in the literature of UKgroundwater resources being significantly affected bysalt in road runoff (CIRIA Report 142, 1994).

3.24 Urea, a compound of nitrogen, is highly solubleand is easily flushed into waters receiving road runoff.Its use is restricted to certain bridges, where prolongeduse of road salts would cause structural damage. Itshould not, however, be used in proximity toenvironmentally sensitive sites due to its potentially toxiceffects. Urea hydrolyses to ammonia, which can besubsequently converted to nitrate by the process of

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nitrification. Nitrogen is an essential nutrient for algaeand elevated concentrations may stimulate algal growthleading to subsequent disruption of the ecosystem. Also,ammonia (in the un-ionised form) is toxic to fish even atlow concentrations.

Nutrients

3.25 Routine road runoff (in the absence of de-icingagents) can also contain small quantities of ammonia,oxidised nitrogen and phosphates. Concentrationsreported in the literature are very low, however, andecological effects would rarely, if ever, be expected.Only small enclosed ponds or lakes would be at risk.Where trapped gully pots are part of the drainagesystem, the trapped water can become anaerobic duringprotracted dry weather periods. Under those conditions,ammonia concentrations can increase and metals whichhad previously been bound to organic compounds can bere-mobilised, producing a poor quality ‘first flush’following summer storms.

3.26 As stated above, hydrolysis of urea may leadindirectly to the release of biologically availablenutrients. If discharged to aquifers in intensively farmedareas where groundwater nitrate concentrations arealready high, the nitrate generated could exacerbate anyexisting potable water quality problems, but is highlyunlikely to be their sole cause.

Atmospheric Deposition and Dispersion

3.27 In reviewing reported differences in runoff qualitybetween urban and rural roads, Driscoll et al, (1988)concluded that urban discharges were of poorer quality.Although traffic levels were higher in the urban areas,only poor correlation existed between traffic flow anddischarge quality. Hence it was concluded that areduction in air quality, leading to increased depositionof pollutants on the road surface unrelated to the volumeof traffic, was more influential in determining runoffquality than was the volume of traffic itself.

3.28 Dispersion of pollutants deposited on the roadsurface during dry periods through vehicle inducedturbulence has also been cited as influencing dischargequality (Colwill et al, 1984). Contaminants which wouldotherwise have washed into the drainage system duringrainfall can be blown onto adjacent land.

Exhaust Emissions

3.29 Pollutants released from vehicle exhausts tend tobe limited to the area near the road, with rapiddispersion and dilution reducing exhaust concentrationlevels (DMRB 11.3.1 refers).

3.30 Typical compounds released from exhausts whichmay create problems in road discharge include lead andhydrocarbons. Traditionally concerns have beenassociated with lead from exhausts. Since April 1991,however, all petrol engine vehicles have had to bedesigned to run on unleaded fuel and the quantity ofleaded fuel sold is declining rapidly. Pollutantsassociated with unleaded fuel may require furtherresearch, including the release of PAHs in unburnt fueland the highly soluble fuel additive MTBE (Methyl -Tertiary - Butyl - ether) (CIRIA Report 142, 1994).

Accidental Spillages

3.31 All road schemes can be expected to maintain orimprove road safety. Hence new or improved roads aredesigned to reduce the accident rate, which usually leadsto a reduction in the potential for accidental spillages.Few accidents cause the spillage of polluting materialsand fewer still result in those materials passing throughthe drainage system to a receiving water, largely becauseof the efficiency of the emergency services and RApollution control staff in containing such spillages.Where spillages do reach a watercourse the pollutionimpact can be severe but is usually of short duration.

3.32 Dangerous goods transported as road freight andwhich pose a threat to human safety are covered by theHAZCHEM classification system, which allows rapididentification of the materials present and providesguidance on how to handle those materials safely. Othermaterials which could cause significant water pollutionmay not be classified as hazardous; these include manyliquid foodstuffs such as milk and fruit juices.

3.33 On average one or two significant or majorpollution incidents occur on roads within the whole ofScotland and within each of the EA regions each year.70% of these pollution incidents involve the spillage ofhydrocarbons.

Table 9. Road Salt Pollutants per Salting (kg/ha)

Activity Sodium Na+ Chloride Cl- Iron Fe

Precautionary salting 35 55 0.15

Snow or Ice 140 220 0.60

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3.34 The emergency services’ response time isimportant in determining the effects of a spillage. Inmany cases spillages can be contained on the roadsurface or at least prevented from spreading far from thedischarge point if services reach the site in time.Thorburn Colquhoun Transportation (1996) estimatethat the probability that a spillage on a road will cause aserious pollution incident in an adjacent high qualitywatercourse will be 45% if the emergency services reachthe site of the accident within 20 minutes, but that therisk of pollution is 75% if the response time is longerthan 20 minutes (Table 3.3 of ANNEX III refers).Where spillages do reach the aquatic environment, theconsequences are dependent upon the material, thesensitivity of the receiving water (both biologically andaesthetically) and the uses which the water supports (forexample water abstraction, recreation).

3.35 Where the assessed risk of an accident leading toa discharge to the environment is high, that risk can besuccessfully mitigated through installation of suitableisolation or treatment units and/or designing the drainagesystem to increase runoff retention times. Unpollutedwaters may be more severely damaged by, and takelonger to recover from, isolated pollution incidents thanthose exposed to constant background pollution(Thorburn Colquhoun Transportation 1996). The timetaken for recovery depends on the nature of the spill andsize of the area affected. A combination of dilution,dispersion, settlement and attenuation of contaminantsdetermines the area affected by either routine dischargeor accidental spillage.

3.36 The consequences of spillage of highly mobilepollutants such as fuel oil on groundwater resources arepotentially the most severe. Halting the spread of suchpollutants and remediation are difficult.

Overview

3.37 The highly variable nature of road runoff, and thediverse nature of studies reporting on the subject in theliterature, make prediction of likely routine dischargequality from completed roads difficult. Where local, andstatistically representative, data exist these will providethe most reliable guide for assessment purposes. Wherethey do not, data presented as Event MedianConcentration (EMC) from other studies may providethe best estimator of expected quality. The use of EMCin preparing a detailed water quality assessment isdiscussed in ANNEX IV. For preliminary assessment oflikely effects of discharges, the use of pollutant build-updata drawn from the literature also has value.

3.38 In circumstances where there is insufficientdilution available for the pollution load, or where therisk of accidental spillages is unacceptably high, theeffects of runoff on the receiving water can besignificant. Where the potential for unacceptable effectson receiving waters exists, pollution prevention can beachieved through selection of appropriate drainagedesign and/or treatment methods (ANNEX II outlinesavailable options). Mitigation to prevent pollution willnot be required in every case, although the need formitigation should be assessed for every outfallindividually.

3.39 During road construction, pollution control shouldbe exercised through measures agreed with the RA totreat unacceptable discharges from site.

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General

4.1 The assessment of measures to prevent pollutionand to reduce impacts should start at an early stage inthe planning of a scheme. The risk of causing anunacceptable deterioration of water quality or fisheriescan be greatly reduced by ‘designing out’ that risk. Theobjective is to convey surface water runoff from the roadsurface to ground or to a receiving watercourse safely,without detrimental effect on water quality or on anyassociated ecosystem.

4.2 The aquatic environment can be affected in anumber of different ways by a road scheme. Physicalchange, to stream hydrology or to habitat structure, mayarise as a consequence of the construction process.Pollution may arise during construction and may alsooccur due to the discharge of routine surface runoff or toaccidental spillages from completed roads. Pollutionarising from construction works or from accidentalspillages can have very serious environmentalconsequences, although the effects are normally shortterm. Routine runoff discharges can pose a long termthreat. Table 10 outlines the range of factors whichcould cause changes to the aquatic environment andwhich should be considered during the EnvironmentalAssessment, and summarises the potential effects ofsuch changes on the aesthetic and ecological value ofaffected surface waters.

4.3 The assessment of aquatic impacts should not beundertaken in isolation. Within the context of this DesignManual, the relationships between the assessments forDisruption Due to Construction, Air Quality, Ecologyand Nature Conservation, Geology and Soils, LandscapeEffects and Land Use to that for water quality should beexamined. This is particularly important whenconsidering possible mitigation measures. There willalso be occasions where it is appropriate to considerhydrological change in a wider context than theassessment of the risk of flooding of properties and landdownstream.

4.4 The requirements of the assessment will dependupon the size of the potential change and thevulnerability of the affected water to that change. Forthe majority of schemes only a small proportion of therange of possible change will be relevant, and in manycases the effects of the changes which do occur will beof little or no significance. Consultation with the RA(and if appropriate the statutory conservation agency)will identify those aspects which warrant detailedconsideration.

Mitigation

4.5 When assessing what containment or treatmentfacilities are appropriate to mitigate pollution effects andeffects on fisheries, basic decisions have to be made.Facilities which are cheap to install may have expensivemaintenance requirements. Whole life costing shouldtherefore be considered.

4.6 The conventional methods used to remove theprincipal contaminants from road runoff involvesettlement, filtering and removal. The methods may beused individually or in combination. Any measure thatwill increase the length of time from source ofcontamination to receiving watercourse will providesettlement, containment and possibly degradation ofpotentially harmful materials. Much will depend ontopography, land availability, the closeness of thereceiving watercourse to the outfall and receiving watersensitivity. When discharge to ground is an option,topography is less important, but careful considerationwill need to be given to the effects on groundwaterquality, especially within the catchment of aquifers usedfor water supply.

4.7 There has been recent interest in the use ofvegetative systems for the treatment of runoff. Althoughthere is little evidence to date to show whether suchsystems are appropriate for road drainage, it is knownthat settlement lagoons having shallow margins withaquatic vegetation can provide both effective settlementof solids and filtering of contaminants (Ellis and Revitt,1991). They can also contribute positively to schemelandscaping while providing ecological variety.

4.8 ANNEX II provides details on the general rangeof management and treatment systems available andtheir relative merits. Guidance is also given on the rangeof capital and maintenance costs that can be expectedfor the various treatment systems, although these datamust be treated with caution. Treatment measures thatmay be used vary from an entirely hard engineeringsolution, such as a sedimentation tank or lined lagoon, toa purely vegetative system, such as swales. Liaison withthe local RA during the assessment will ascertain theirviews as to the most appropriate treatment system forthe circumstances.

4.9 Reducing the impact of a road on receiving waterquality is just one of the factors which must beconsidered in route choice and design. In addition tofulfilling the intended purpose, any mitigation measuremust perform to an acceptable level in traffic, roadsafety and economic terms.

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Comments

Accumulation of solids close to discharge points can affect recreational use of the receiving water. If the oil content ishigh, malodours can be produced during microbial degradation and surface oil sheens are possible. Adverse impacts aremost likely in slow flowing watercourses and lakes.

Accumulation of solids on the bed of the watercourse can adversely affect fish spawning and nursery areas. Where salmonor trout spawning gravels are present, solids can clog the intra-gravel spaces and cause suffocation of eggs. If freshwaterinvertebrates are killed by polluted sediments or water there will be less food available for fish. Provided there is time,fish will usually actively avoid areas of poor water quality and if there is space for them to move to areas of cleaner water,they are unlikely to be directly affected. Accidental spillages of toxic or organic materials (which are rapidly decomposedin water by microbial action, hence reducing the oxygen concentration) or sudden changes in pollution level are mostlikely to affect fish directly. Any significant pollution impact in waters used for spawning or as nursery areas may havelong-term consequences if an entire year class is lost.

Healthy watercourses have a diverse fauna which colonises the bed (the benthic invertebrates). Many species areintolerant of both water and sediment pollution, and can thus be affected by road schemes. Pollution intolerant speciesmay move elsewhere, allowing the development of a less diverse, pollution tolerant community. In extreme cases, usuallyonly associated with accidental spillages of toxic materials, the fauna can be destroyed, although recovery is usually rapidonce the bed of the watercourse has returned to normal and the polluted water has dispersed. Invertebrates are monitoredby the RAs to track pollution levels. Simplified biological indicators, such as the BMWP score, are frequently used. Mostof these indicators were developed to assess the effects of organic effluents such as sewage. Care is needed in interpretingthese scores where discharges such as roads runoff, which does not generally have a high organic content, are concerned.However, invertebrate species and their relative abundance are valuable in assessing changes in watercourse health.

Changes in sediment transport can lead to physical removal of plants by smothering the stream bed with sediment. Plantgrowth can also be encouraged (through increases in nutrient levels) or discouraged (through increased water turbidity)dependent on local and site specific characteristics. The effects of such changes could include both conservation impactsand changes in stream bed roughness characteristics with consequential effects on flooding potential etc.

Sites of Special Scientific Interest (SSSIs) and other areas of conservation designation may be protected for a range ofreasons. For some sites highway drainage is unlikely to affect the characteristics for which they were selected. However,many sites are designated directly or indirectly because of the sensitivity of their plants, animals or habitats to pollution.Some designated sites such as rivers, still waters, estuaries and peat bogs may be sensitive to pollution from roaddrainage and discharge to these, either directly or indirectly, should be avoided where possible (although the extensivedilution in estuaries may make them suitable receiving waters).

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4/2 Table 10. Causes and Potential Effects of Environmental Change

Comments

Land-use changes caused byroad construction can affectsurface and groundwaterboth locally and furtherafield through removal andre-disposal of depositedwaste material along theroute during construction,interception and diversion oftip leachates, minewatersetc. Chemical spills duringconstruction, particularlyoils and concrete liquors,can be particularlydamaging, as can dischargeof mud from constructionareas. Runoff fromoperational roads, bothroutine and accidentalspillages, can directly affectwater quality and indirectlyaffect both human andecological uses of the water.

Recipient/Issue

AestheticIssues

Fish

Invertebrates

Plants

ConservationInterest

Cause

A. Pollution

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Cause

B. Physical

1. Hydrology

2. Structures

Comments

Changes in surface andgroundwater flow can becaused by interception ofnatural drainage pathways(cuttings through peatdeposits, interception of fielddrainage or groundwaterflow, tree clearance etc).

New structures inwatercourses, such asculverts and bridge aprons orstream diversions can havewide ranging impacts.

As the UK canal network isrestored for recreational use,those waterways which donot currently allownavigation (even abandonedand dry canal routes) may besubject to restorationproposals and it is essentialthat the Restoration Societyis consulted wherever canalsare, or could be made,navigable as new bridges etccould sterilise thoseproposals.

Recipient/Issue

Stream flow

Invertebrates

Plants

ConservationInterest

Fish/fishing

Invertebrates

Other species

Comments

Potential consequences include modification of stream flow characteristics (increases or decreases in flow range, velocityetc) with associated effects on stream biota, changes in the dispersion of industrial or sewage effluent discharges madefurther downstream and reduction in the yield of groundwater abstractions.

Many species have specific habitat requirements (stream flow, substrate type etc). Road schemes can change watercourseflow characteristics, substrate types etc and these changes can affect the invertebrate community.

Changes in stream flow characteristics can lead to either an increase in plant growth (where water velocity is reduced) orto physical removal of plants (by significantly increasing water velocity). The effects of such changes are similar to thosedescribed above for pollution.

Some designated sites may be reliant on an existing hydrological regime, alterations to which may have a severe effect onthe site and should be avoided.

New structures could affect fish and fishing through temporary or permanent loss of pools and riffles and otherhydrological changes, which could reduce adult and juvenile fish holding capacity or remove fish spawning areas. Loss ofbankside cover/habitat; physical barriers and/or increased water velocity restricting fish movement/migration; increasedwater turbidity during road construction reducing the potential for angler success; smothering of fish breeding areas withsediment during construction works or downstream of surface water discharges; in-river works such as piling, temporaryriver crossings etc could all affect fish and fishing.

New structures could cause changes to flow or sedimentation patterns, which could have an impact on shellfish growingareas and commercial fisheries.

Other species which are dependent on water quality or volume for survival could also be indirectly affected. Fish andamphibian predators such as some birds and otters may be affected directly by removal of habitat or restriction ofmovement along the river bank or indirectly through changes in the population of their prey. Gully pots may act as lethaltraps to such species as crested newts, frogs and toads if the road passes too close to important breeding sites.

Table 10. Causes and Potential Effects of Environmental Change (cont)


February 1998

5.1 The RAs will seek to ensure, through the earlyconsultation process, that each scheme is located,designed and constructed to minimise impact on thewater environment. Where possible the route should alsoavoid the need for permanent river diversions. Suchdiversions can exert a particularly damaging anddestabilising effect on the biological and physicalfeatures of a river. The effects may extend beyond thelimits of the diversion. Where such work is unavoidablethe river diversion must be sympathetically designed.The diversion should take full account of availableinformation on geomorphological processes to recreate ariver habitat which is as natural as possible andconforms to the RA flood defence requirements. Also,where new structures such as culverts or bridge apronsare required in-river, the designs should be such that fishcan pass both up and downstream. The Scottish OfficeDevelopment Department, National Roads Directorateand the Scottish Office Agriculture, Environment andFisheries Department (SOAEFD) are jointly in theprocess of producing design guidelines to assist in thisrespect.

5.2 In addition to diversions, other physical impactson the water environment may occur. Where suchimpacts are unavoidable, mitigation will be required.Mitigation options for fishery protection include:

- The use of ‘soft’ river engineering methods whereacceptable, to minimise habitat damage.

- The construction of channels specifically topermit continued fish movement and migration.This may include mathematical or physicalmodelling of water velocities.

- The planning and implementation of mitigationworks elsewhere within the catchment whereunavoidable fishery resource damage is expected.This could, for example, include the opening up ofnew migratory fish spawning areas, habitatimprovements or fish restocking. The calculationof temporary or permanent resource loss is to becarried out using a methodology acceptable to theRA (and SOAEFD/DSFB in Scotland).

5.3 In England and Wales the role of the EA is toprotect and manage the fishery resource which willnormally include the determination of measures topromote fishery mitigation in liaison with the fisheryowner. The EA will also seek to ensure that the activity

of fishing is protected within any scheme. The matter ofpossible civil claims for loss of fishing (as opposed todamage to the fishery resource) is, however, theresponsibility of the fishery owner.

5.4 In instances where a fishery is unavoidablyaffected by a road scheme, the scheme promoter mayalso be involved in discussion with the fishery owner.The interests of the RA and the fishery owner mayoverlap.

5.5 In Scotland the role of the DSFB is to protect andto manage the migratory fish resource. Matters ofdetermination of migratory fish compensation willnormally include liaison with the fishery owner and theDistrict Valuer, but may also involve SOAEFD and theDSFB where spawning and nursery areas are affected.

5. FISHERIES PROTECTION

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General

6.1 This CHAPTER describes the approach to betaken in assessing the potential impact of all surfacewater discharges. Guidance on the scope of work and theappropriate level of detail at each key stage of theassessment is provided in the next CHAPTER.

6.2 The primary aim of environmental assessment isto determine objectively the risk of damage associatedwith a road and its likely magnitude. Where the risk ofsignificant adverse impact is unacceptably high, theprocess should also include the identification of the mostcost-effective solution to bring this within acceptablelimits, together with an assessment of the significance ofany residual impacts. For surface water runoff, thatcould involve simple forms of mitigation such asrelocating a point of discharge or modifications to thebasic drainage design. It should not be assumed that theonly solution is end of pipe treatment units, nor should itbe assumed that all discharges will need extensivetreatment.

6.3 When selecting a risk assessment technique it isimportant to balance the effort expended in determiningthe risk against the Stage (1, 2 or 3) that the assessmenthas reached. The likely size of the threat and the possiblecost of providing mitigation should also be considered.Detailed quantification of the possible effects ofindividual discharges will only be required at Stage 3.While all proposed outfalls must then be individuallyconsidered, the fact that discharges from lightlytrafficked roads pose a less serious environmental threatwill also influence the extent of work required.

6.4 Key risks to be considered are the contaminationof surface water or groundwater by accidental spillageor routine runoff. Risks to surface water can beconveniently considered under the separate topics ofinsoluble and soluble pollutants. Methods forquantifying the risk of pollution arising from accidentalspillages and from soluble pollutants in runoff areavailable, but further research is required to developmethods to predict the likely effects of insolublepollutants in surface waters.

Spillage Risk Assessment

6.5 A general aim of new roads and improvementschemes is to improve road safety and to reduce thenumber of accidents. Where accidents occur, however,

the environmental consequences of any spilledmaterials will be reduced only through the efficiency ofthe emergency services and/or the inclusion of spillagecontrol measures within the drainage design.

6.6 ANNEX III contains a step by step guide to thecalculation of the risks that:

- An accident involving spillage of pollutants ontothe carriageway will occur, assuming trafficvolumes predicted for the design year at hightraffic growth rates (both hazardous and non-hazardous materials such as acids and certainfoodstuffs are included).

- Pollutants spilled on the carriageway willsubsequently pass through the road drains andcause a pollution incident on discharge to thereceiving water.

6.7 These risks can be conveniently expressed asreturn periods, allowing objective decisions to be madeas to their acceptability or whether measures are neededto reduce the risk. Pollution risks are calculated foreach receiving water or reach within the receivingwater. Reaches are usually delineated by majortributaries or physical structures such as weirs; the RAwill advise on selection of appropriate boundaries.Hence, where several individual discharges are to bemade to one reach of a watercourse, it is the combinedrisk to that reach arising from all of the dischargesfrom the relevant length of road which is to be considered.

6.8 It is important that the number of outfallsassociated with any road section be minimised. Thisapproach complies with both environmental andeconomic best practice. In environmental terms, areduced number of outfalls minimises the potential forconfusion between the emergency services should anaccident occur, and allows for an increased degree ofcontrol to be built into each outfall structure. Ineconomic terms the balance needs to be struck betweena reduced number of outfall locations with containmentstructures and potential increases in drainage pipe sizesand depth to achieve the reduced number of outfalls.

6.9 The Overseeing Organisation will advisegenerally on acceptable pollution risks, although forindividual cases the risk criteria should be discussedwith the RA. The criteria adopted will depend on thesensitivity of the receiving waters. All sensitive surfaceand groundwaters (including those used for water

6. PREDICTING POLLUTING POTENTIAL

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serious pollution (EA category 1 (major) and 2(significant)) are a subset of the HGV (greater than 1.5tonne) personal injury accidents and are distributedover the road network in the same way. Seriouspollution accident rates presented in Table 3.2 ofANNEX III, were estimated from the average billiongoods vehicle km/yr for each RA region, together withan estimate of the total road length and the proportionof that length which comprises the various types ofjunctions. Finally, an assumption of the proportion ofthe average billion goods vehicles km/yr travelled inurban and rural areas was made.

6.15 Allowing for a threefold under-reporting ofserious spillages, the analysis indicates that, onmotorways and trunk roads, about three seriousspillages occur for every 1000 HGV personal injuryaccidents, compared with two for every 1000 HGVpersonal injury accidents on non-trunk roads. Thisanalysis indicates that the previous method advocatedby DMRB over-estimated spillage risk (that methodassumed ten spillages per 1000 HGV accidents for allroads).

Surface Waters

Soluble Pollutant Assessments

6.16 This assessment focuses on dissolved copperand, although not strictly a dissolved pollutant, totalzinc. These are known constituents of road runoff forwhich there are published Environmental QualityStandards (EQS). These determinands are two of themost important pollutants present in soluble form.They have been selected as a proxy for other dissolvedpollutants and to serve as an indicator of whether thereis sufficient dispersion and dilution within the receivingwater. They also provide a convenient base forpredictive modelling of potential soluble pollutantloadings.

6.17 For flowing receiving waters the preliminaryassessment method described in this CHAPTER willidentify all discharges which warrant further, moredetailed, evaluation to determine whether mitigation isrequired. The preliminary assessment method, firstdeveloped and fully described by CIRIA (Report 142,1994), is presented in ANNEX III. Where this methodsuggests that mitigation measures may be necessary, adetailed water quality assessment should be undertaken.The precise nature and scope of any detailed waterquality assessment will vary between schemes, butguidance on key issues to be considered is given inANNEX IV. As a detailed assessment is likely toinvolve mathematical modelling, it is important that the

abstraction, used intensively for recreation, or having ahigh ecological value) should normally be protectedsuch that the calculated risk of a pollution incident isless than once every 100 years. All other watercoursesshould normally be protected against one event every50 years. These criteria compare with the indicativestandards of flood protection recommended for highdensity urban areas subject to non-tidal flooding (1:100years), published by the Ministry of AgricultureFisheries and Food (MAFF).

6.10 The pollution risk is initially calculatedassuming that the drainage system incorporates nomeasures for protection against spillage. Where thecalculations indicate that the risk to a river reach is toohigh a form of spillage containment is required.

6.11 Subject to consultation with the RA, the risk of aspillage causing pollution at any outfall can bereduced, to 35% of that calculated without spillageprotection measures, for every containment or controlunit incorporated into the design. The designer shouldfocus initially on the largest outfalls, adding treatmentunits to each outfall in turn, until the residual risk tothe reach as a whole is acceptable.

6.12 It is considered extremely unlikely that twoindependent facilities would fail simultaneously andthus there would rarely, if ever, be a need for anyoutfall to be protected by more than two containmentand control facilities. If the design engineer hasincluded two containment facilities at every outfall to agiven reach there would be little point in adding moreat any of the outfalls even though the residualcalculated risk to the reach might still theoretically beunacceptable. This approach can be applied only ifevery outfall to the reach has dual containment and ifthe RA are satisfied as to the detailed design of everyproposed containment.

6.13 The detailed method advocated for assessing anddetermining spillage risk, and when facilities to controlthat risk are needed, is given in ANNEX III. Alloutfalls, irrespective of calculated spillage risk, mustbe designed such that pollution incident controlcontingency plans can be expected to be effective incontaining the spread of hydrocarbons, since these arethe most frequently spilled materials. Their spread canbe controlled by use of booms and/or absorbentmaterials if the drainage design, or the profile of thereceiving watercourse, allows them to be effectivelydeployed in an emergency.

6.14 Regional records are maintained by the RA ofpollution incidents categorised by seriousness andcause. It has been assumed that accidents which cause

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- The assumed runoff coefficient is low (a morerealistic coefficient would be in excess of 0.7),hence the pollutants are assumed to be washed offin a low volume of rain, producing a higherdischarge concentration.

- It is assumed that 40% of the total copperdeposited on the road will reach the discharge indissolved form and that there will be no change inchemical state within the receiving water.Similarly, it is assumed that all of theaccumulated zinc which washes off the road willremain in the water column following discharge tothe environment. These are worst caseassumptions.

6.20 The only site specific data required by the modelare an estimate of the road surface area to be drained toeach point, an indication of receiving water hardness andan estimation of the 95% exceedence flow in thereceiving water. The latter can be made based on rainfalland catchment characteristics or taken directly fromrelevant river gauging data, where they are available.

6.21 Because of the conservative assumptions made,the method provides a safe means of identifying thoseproposed discharges which will not adversely affectreceiving water quality with respect to solublepollutants. However, decisions on the need forinvestment in runoff treatment require more preciseestimation of the likely downstream impact on qualitythan is provided by the preliminary assessment.

6.22 In common with the advice on spillage riskcontrol, it is considered best environmental practice tominimise the number of proposed discharges. Inprinciple, small but otherwise environmentally importantwatercourses (e.g. tributaries used by spawningsalmonids) should be avoided in favour of makingdischarges to larger watercourses where the availabledilution is greater.

6.23 The specific local value of each potentialreceiving water should always be evaluated and the finaldecision on discharge location will take account of theviews of the RA.

Insoluble Pollutant Assessment

6.24 Removal of coarse and a significant proportion ofthe fine (settleable) solids from road discharges willremove much of the potentially polluting load. Sincemost of that polluting load is associated with the solidand settleable phase of the discharge, insolublepollutants are considered to be of greater importance indetermining the environmental effects of runoff.

preliminary assessment is undertaken sufficiently earlyto allow time for this work to proceed. Wheredischarges to still or very slow moving waters (such ascanals) are proposed, a detailed water qualityassessment will be appropriate for all but very minorproposed discharges. Since metal toxicity to freshwateranimals increases as water hardness reduces, allproposed discharges to receiving waters with hardness<50 mg/l CaCO

3 warrant detailed consideration fromthe outset. Similarly, those subject to episodic acidpollution (where receiving water pH is reduced) shouldalso be investigated in detail because the toxicity ofcopper is higher at low water pH.

6.18 The CIRIA Report 142 method assumes thatpollutants are allowed to accumulate on the roadsurface for five days, with the build up rate beingdependent on traffic flow. A proportion of thepollutants are then assumed to be washed off the roadand into the receiving water during a 24 hour summerstorm. The build up period and storm intensity havebeen selected to represent the 95% concentration ofpollutants, that is the concentration that would beexceeded for only 5% of the time. On discharge it isassumed that the receiving water flow is low (at the95% exceedence level) and hence that the availabledilution is minimal. Fifty percent of the incident rain isassumed to reach the discharge point (i.e. a runoffcoefficient of 0.5), while the design storm forcalculation purposes is taken as 30% of the one year 24hour storm. The model is used to calculate downstreamriver concentration during this storm. Thatconcentration is then compared with the EQS for thereceiving water.

6.19 The calculation method produces a conservativeestimate of the potential impact on water qualitydownstream of a discharge. Specific conservativeassumptions include:

- The pollutant build up rates recommended areselected from old studies and are biased towardsthe higher values quoted in those studies.

- Pollutant build up rates do not always provide anaccurate indication of likely discharge quality,with several studies indicating that only a poorcorrelation between traffic flow and dischargequality exists.

- The model assumes that the 95% storm willoccur while the river is at 95% exceedence flow,producing the long term 95% downstreamquality. This could be expected to occur onlyvery rarely.

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6.25 Solids arising in runoff generally have lowparticle size diameter (predominantly less than 100µm)and have relatively high density. The larger particles willtend to settle initially onto the bed of the receiving waterclose to the point of discharge. Their eventualdistribution depends on the turbulence of the receivingwater.

6.26 Many techniques are available to reduce the solidfraction prior to discharge to the environment. At eachoutfall the need for solids removal facilities should beidentified using expert judgement, following discussionwith the RA. Mitigation to prevent solids build-up in thereceiving water (either through drainage designmodification or relocation of outfall positions) should beconsidered in any of the following situations:

i) The flow pattern in the receiving water is suchthat fine sediments may accumulate to significantlevels within a short distance downstream of theproposed outfall and that area of the watercoursehas significant ecological or high amenity value.

ii) The available dilution for the discharge is low.

iii) The receiving water has existing discharges whichare causing solids pollution in the immediatevicinity of the discharge.

iv) There is a water abstraction downstream of theoutfall which could be affected.

v) There are particular local circumstances whichsuggest that the solids content of the dischargewill be higher than is normally expected.

6.27 Specific oil removal facilities should also beconsidered where the receiving water has high ecologicalor amenity value or supports water abstraction.

6.28 As the majority of the total solids loading wouldbe expected to be released during the ‘ first flush’,consideration should be given to treating only aproportion of the total flow from each discharge. Thiswould capture the ‘first flush’ liquor, allowingsubsequent and cleaner runoff to bypass to the receivingwater.

Groundwater Assessment

6.29 Discharges from major roads within the InnerSource Protection Zone of an abstraction source from anaquifer are not acceptable. Otherwise the level ofinvestigation required to assess the acceptability ofdischarges to ground decreases significantly as follows:

Inner Source Protection Zone II for an abstractionsource (most extensive) to Non-Aquifer resourceprotection (least extensive).

6.30 Discharges to Source Protection Zones II and IIIare not prohibited by the Groundwater ProtectionPolicies (GPP). The level of investigation needed todemonstrate to the RA that such discharges areacceptable is, however, such that the presence of anySource Protection Zone along a route corridor should beconsidered a severe constraint at Stage 1 of theassessment.

6.31 In Resource Protection Zones where aquifers andground waters are not at risk from pollution it may bebeneficial, subject to satisfactory control of spillage riskand water quality, to adopt discharge to ground. Inprinciple such an approach should always be consideredpotentially viable (subject to the agreement of theOverseeing Organisation and the RA), although thepracticality in terms of likely infiltration rates willclearly be an important issue.

6.32 Detailed investigation of all potential outfalls isinappropriate, so a tiered approach is recommended. Atthe first stage, the methods published by CIRIA (Report142, 1994) should be applied to all discharges; these aredescribed in ANNEX III. In this method, an annualbuild-up rate for pollutants accumulating on the roadsurface is assumed according to the appropriate (highgrowth for the design year) AADT flow. All of thismaterial is then assumed to be washed off the roadsurface, diluted by the total annual rainfall for the site toa calculated concentration in the runoff for the pollutantsunder investigation (dissolved copper, zinc, iron andchloride). It is further assumed that there is noattenuation or removal at the soakaway of the pollutantsunder investigation. Where the calculated concentrationin runoff is greater than the relevant EQS, more detailedevaluation will be required to determine whetheradditional pollution control measures are needed. Whereit is lower than the EQS, a discharge via infiltrationdrainage should be acceptable in water quality terms andno further investigation is needed in this respect. Thedischarge remains subject to the requirements of theGPPs regarding oil separation and the need for anyadditional accidental spillage control or containmentfacilities.

6.33 As for the assessment of discharges to surfacewaters the assumptions made in this model areconservative:

- The pollutant build up rates recommended areselected from old studies and are biased towardsthe higher values quoted in those studies.

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- Pollutant build up rates do not always provide anaccurate indication of likely discharge quality,with several studies indicating that only a poorcorrelation between traffic flow and dischargequality exists.

- The assumed runoff coefficient is low (a morerealistic coefficient would be in excess of 0.7),hence the pollutants are assumed to be washedoff in a low volume of rain, producing a higherdischarge concentration.

- No allowance is made for dilution or dispersionof pollutants within the aquifer.

- No allowance is made for attenuation on passagethrough the drainage system, the soakaway orthe unsaturated zone.

- 40% of the total copper and all of the zinc andiron deposited on the road surface is assumed toremain in the water and enter the aquifer.

6.34 The preliminary groundwater assessment ispotentially even more conservative than that for surfacewaters. This is considered appropriate given the longtime before the effects of any pollution may beapparent and the severe difficulty of taking measures toclean up the ground water resource. As an alternativeto the above method, where the average or EMC runoffquality for a particular pollutant can be estimated withreasonable accuracy, this figure can be directlycompared against the relevant groundwater (or surfacewater) EQS. If the figure is less than the relevant EQSit can be assumed that no further investigation isneeded for that pollutant. Where detailed investigationis required ANNEX IV outlines important issues forconsideration during that investigation. The RA shouldbe consulted in advance about the details and methodfor any site specific investigation.

Overview

6.35 In assessing the need for mitigation under eachof the separate topics (spillage risk, groundwater,soluble and insoluble pollution of surface water), theassessment may lead to the conclusion that treatment toprevent two or more separate problems is required at asingle outfall. In such cases it will normally be possibleto provide a single solution. For example an isolatablefilter drain system or suitably designed oil separatormay be acceptable where there is a need both to containor control spillages and to remove solids. Similarly,where flood attenuation measures are needed togetherwith measures to prevent pollution, a single design tosatisfy both requirements may be feasible. By

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undertaking each assessment separately, the designobjectives for the mitigation measures can be clearlyspecified, fully justified and satisfied in the most cost-effective way. Liaison with the RA during theassessment will also ensure that the best informationabout the receiving waters is obtained and their inputinto the design is obtained at an early stage.


February 1998

7.1 Assessments should become increasingly detailedas a scheme develops, and be commensurate with thesignificance of predicted water-related effects in thearea affected. It is also important that, as theassessment becomes more detailed, it both informs andtakes account of the development of mitigationmeasures. Assessment and design are part of aniterative process.

7.2 The following levels of detail will generally beappropriate at the key stages, although moreinformation might be needed if effects are potentiallysignificant.

Stage 1

7.3 The objective at this stage is to undertakesufficient assessment to provide an appreciation of thelikely key constraints and consequences for waterquality of a new or improved road within the broadlydefined route corridors, as defined by the DesignOrganisation and agreed with the OverseeingOrganisation.

7.4 The steps to take at this stage are:

(i) Consult the RA to determine:

- the location of flood plains and areasparticularly at risk to flooding;

- the location within the overall route corridor ofthe principal watercourses (and their waterquality classification) and groundwaterprotection zones;

- the location of any other areas which may besensitive to water pollution, changes in thehydrological regime (for example, source ofpotable water, fisheries, amenity, wetland, andwildlife areas) or the effects of new structuressuch as bridges (for example canals, bothoperational and derelict).

This can be done by a desk top study of the corridoralong which possible routes are being considered, takinginto account the fact that effects can potentially bewidespread and even outside the study area itself. Ifcanals could be affected BWB should also beapproached to obtain details of any restorationproposals. Restoration proposals are also shown on twomaps: The Inland Waterways of Great Britain - A

Complete Route Planning and Restoration Map(published by Waterways World, British Waterways andThe Inland Waterways Association) and InlandWaterways of Britain (published by GEO Projects (UK)Ltd). These should also be consulted if the presence ofabandoned navigable waterways is suspected.

(ii) In respect of fisheries identify:

- any river, still water or coastal fisheries whichmight be affected by a scheme option (effects mayextend upstream or downstream beyond thelocation of the physical impact);

- the nature of the fishery and in particular whethermigratory fish may be affected (these areprimarily salmon, sea trout and eels).

(iii) identify other bodies, public and private, thatmight have an interest in water quality issues.

(iv) using predicted two way AADT flows (highgrowth to the design year), assess the overall riskof a serious accidental spillage for the entirescheme length in the absence of mitigation. Byestimation sub-divide the route into lengths whichare likely to discharge into each water body(surface and/or groundwaters) and estimate thelikely risk of an accidental spillage causing aserious pollution incident.

7.5 The results of the Stage 1 assessment to beincluded in the Stage 1 Report should consist of:

(i) a map showing surface watercourses, theirclassification and the extent of their flood plains,together with the area designated as groundwaterprotection zones, designated fisheries, areas ofhigh amenity value and any other areas ofenvironmental sensitivity related to watercourses;

(ii) a provisional estimate of the likely risk ofaccidental spillage and the risk of pollution to anysignificant waters;

(iii) a statement on the potential significance of theinformation in (i) and (ii) on the possible routecorridors.

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Chapter 7Stages of assessment and drainage design

7. STAGES OF ASSESSMENT AND DRAINAGEDESIGN


February 1998

Stage 2

7.6 The objective at this stage is to undertakesufficient assessment to identify the likely impacts onwater quality and on fisheries. These can then be takeninto account by the Design Organisation in developingand refining route options in agreement with theOverseeing Organisation.

7.7 The steps to take at this stage are:

(i) For the areas affected by the route optionsconfirm the Stage 1 assessment with the RA (andBWB if appropriate).

(ii) Mark those locations considered to be mostsensitive to changes in water quality, hydrologicalor physical change on a map showing thealternative routes.

(iii) Use the procedure in CIRIA Report 142 (asoutlined in ANNEX III) to calculate the potentialfor localised pollution effects for the area inquestion. If the results indicate a significantproblem in terms of water quality, to the extentthat mitigation could prove difficult or impossible,the approval of the Overseeing Organisationshould be sought to undertake specialist computermodelling using local and site specific data.

(iv) Refine the spillage risk calculations.

(v) Review available data on affected fisheries andidentify additional data requirements needed toassess the direct and indirect impacts of eachoption on the physical and biological habitat ofthe river corridor. This may require biologicalresource mapping using methods which should beagreed with the RAs.

7.8 The results of the Stage 2 assessment to beincluded in the Stage 2 Report should consist of:

(i) an updated map from the Stage 1 assessmentshowing the centre line of each alternative routeand those areas considered to be most sensitive tothe consequences and risk of accidental spillagesand change in water quality, hydrological orphysical change;

(ii) a statement describing the possible affects of eachof the alternative routes on water quality ingeneral and on those areas considered to be mostvulnerable in particular.

The results of the preliminary assessment as calculatedfrom the procedures given in ANNEX III and thespillage risk assessment should also be included. Whereassessment has taken account of proposed mitigationthese measures should be explained and quantified.

Stage 3

7.9 The Department's road design standards forrunoff drainage and treatment aim to ensure that thereare no significant pollution impacts associated withroutine surface water runoff, or spillages of hazardousmaterial. All individual discharges identified as posingpotential threats to water quality or fisheries duringStage 2 should be evaluated in detail, using specialistmathematical modelling or ground investigation topredict water quality impacts where appropriate.Suitable mitigation measures should be identified andspecified in terms of their design objectives.

7.10 The Design Organisation should seek the adviceof the Overseeing Organisation before undertaking anysuch assessment. Where a detailed assessment ofpollution from runoff is to be undertaken bothconstruction and operational phases should beconsidered. It should begin by assessing the sensitivity ofwatercourses in the area and identifying groundwaterconsiderations and then continue to assess the effect ofsoluble pollutants, insoluble pollutants and the risk ofspillages on water quality. Details of the methods aregiven in CHAPTER 6 and ANNEXES III and IV.

7.11 If a route traverses a groundwater protectionzone, or if discharges to ground are proposed, theproposed drainage and treatment arrangements should beagreed with the RA prior to completion of the Stage 3assessment.

7.12 If the scheme might have a significant effect onfloodplain capacity, an assessment should be made of thesize of the reduction, the efficacy of the proposedmitigation works, and the residual effect of the schemein increasing the risk of flooding. Where other potentialsignificant hydrological effects which could impinge onany of the current or proposed uses of the receivingwater are identified, appropriate additional studiesshould also be undertaken.

7.13 Water-related ecological effects should be takenfully into account and cross-referenced to the ecologicalassessment (see DMRB 11.3.4), with references alsomade to the assessment of Disruption Due toConstruction, Geology and Soils, Landscape Effects andLand Use where appropriate.

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7.14 The result of the Stage 3 assessment should beincluded in the Environmental Statement. It shouldrecord the existing, as well as the predicted, waterquality of all receiving waters, and details of existinguses of potentially affected waters including any relevantgroundwater protection zones or drinking waterabstractions. Areas vulnerable to a change ofhydrological regime or water quality should beidentified. Measures to be taken to mitigate potentialadverse effects on water quality, aquatic ecology,groundwater and hydrological regime should bedescribed, as should outline design requirements toensure the free passage of fish. A summary outlining thepredicted impact on the receiving water (both with andwithout mitigation) and the risk of pollution fromaccidental spillage should be presented.

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8.1 The RA regional boundaries for England, Walesand Scotland are shown in Figures 1 and 2 respectively.The regional contacts and the address of the RA for thewhole of Northern Ireland are given below.

ENVIRONMENT AGENCY REGIONALOFFICES

Anglian

Kingfisher HouseGoldhay WayOrton GoldhayPeterboroughPE2 5ZRTel: 01733 371 811Fax: 01733 231 840

North East

Rivers House21 Park Square SouthLeedsLS1 2QGTel: 0113 244 0191Fax: 0113 246 1889

North West

Richard Fairclough HouseKnutsford RoadWarringtonWA4 1HGTel: 01925 653 999Fax: 01925 415 961

Midlands

Sapphire East550 Streetsbrook RoadSolihullB91 1QTTel: 0121 711 2324Fax: 0121 711 5824

Southern

Guildbourne HouseChatsworth RoadWorthingWest SussexBN11 1LDTel: 01903 832 000Fax: 01903 821 832

South West

Manley HouseKestrel WayExeterEX2 7LQTel: 01392 444 000Fax: 01392 444 238

Thames

Kings Meadow HouseKings Meadow RoadReadingRG1 8DQTel: 0118 953 5000Fax: 0118 950 0388

Welsh

Rivers House/Plas-yr-AfonSt Mellons Business ParkSt MellonsCardiffCF3 0LTTel: 01222 770 088Fax: 01222 798 555

DEPARTMENT OF THE ENVIRONMENTNORTHERN IRELAND

Environment and Heritage ServiceCalvert House23 Castle PlaceBelfastBT1 1FYTel: 01232 254 754Fax: 01232 254 777

SEPA’s REGIONAL OFFICES

North Region

DingwallTel: 01349 862 021Fax: 01349 863 987

ThursoTel: 01847 894 422Fax: 01847 893 365

Fort WilliamTel: 01397 704 426Fax: 01397 705 404

8. REGULATORY AUTHORITIES (RAs)

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Chapter 8Regulatory Authorities (RAs)


February 1998

KirkwallTel: 01856 871 080Fax: 01856 871 090

LerwickTel: 01595 696 926Fax: 01595 696 946

ElginTel: 01343 547 663Fax: 01343 540 884

FraserburghTel: 01346 510 502Fax: 01346 515 444

AberdeenTel: 01224 248 338Fax: 01224 248 591

StornowayTel: 01851 706 477Fax: 01851 703 510

East Region

Riccarton, EdinburghTel: 0131 449 7296Fax: 0131 449 7277

ArbroathTel: 01241 874 370Fax: 01241 430 695

PerthTel: 01738 627 989Fax: 01738 630 997

StirlingTel: 01786 461 407Fax: 01786 461 425

GlenrothesTel: 01592 759 361Fax: 01592 759 446

GalashielsTel: 01896 754 797Fax: 01896 754 412

West Region

East KilbrideTel: 01355 238 181Fax: 01355 264 323

LochgilpheadTel: 01546 602 876

AyrTel: 01292 264 047Fax: 01292 611 130

Newton StewartTel: 01671 402 618Fax: 01671 404 121

DumfriesTel: 01387 720 502Fax: 01387 721 154

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Chapter 8Regulatory Authorities (RAs)


February 1998 8/3

Chapter 8Regulating Authorities (RAs)


February 19988/4

Chapter 8Regularatory Authorities (RAs)

Figure 2


February 1998

Glossary of Terms

Absorption: the process by which a molecule or ion is attached to a substance.

Adsorption: the taking up of one substance at the surface of another.

Anaerobic: a condition in which no oxygen is available in any form.

Aquatic: growing, living or found in water.

Aquifer: water bearing underground strata.

Biofiltration: a process whereby contaminated waters are treated through interaction withvegetation and soil.

Biochemical Oxygen Demand: BOD is a representation of the oxygen demand created by biodegradation oforganic matter in water. It attempts to emulate in controlled conditions theoxidation of organic matter which occurs in a river. The BOD test is normallycarried out over a five day period.

BMWP Score: a simplified scoring system based on the intolerance of certain groups ofstream invertebrates to water pollution. Clean waters contain mainly pollutionintolerant groups and have a high BMWP score.

Compound: a substance that contains atoms of two or more chemical elements heldtogether by chemical bonds.

Eutrophication: the enrichment of waters by nutrients primarily nitrogen (N) and phosphorus(P) and the consequent deterioration of quality due to the luxurious growth ofplants and its effect on the ecological balance within the water body.

Groundwater: water which saturates subterranean strata and which can be abstracted bysinking wells or boreholes. The saturated zone is called an aquifer.

Heavy Metals: Lead(Pb), Zinc(Zn), Copper(Cu), Chromium(Cr), Cadmium(Cd),Manganese(Mn), Iron(Fe), Nickel(Ni) & Cobalt(Co) - A group of ferrous andnon-ferrous metals commonly known as heavy metals found in motorway orroad surface runoff. Pb is a specific product of vehicle exhaust emissionsfrom petrol driven engines, Zn is present in car tyres and motor vehiclecomponents and Cu, Cr & Cd are released principally as corrosion products.

Leaching: the washing out of a soluble constituent.

Oil: viscose liquid of vegetable or mineral origin. Inflammable and usuallyinsoluble in water. Chiefly composed of carbon and hydrogen.

Organic: the description of a material composed of carbon combined with hydrogenand also often containing oxygen, nitrogen and other elements.

9. GLOSSARY OF TERMS & ABBREVI ATIONS

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Chapter 9Glossary of terms & Abbreviations


February 1998

Abbreviations

AADT Annual Average Daily Traffic

BMWP Biological Monitoring Working Party Score

CIRIA Construction Industry Research and Information Association

COD Chemical Oxygen Demand

CSO Combined Sewer Overflow

DSFB District Salmon Fisheries Board

EA Environment Agency

EMC Event Median Concentration

EQS Environmental Quality Standards

GPP Policy and Practice for the Protection of Groundwater document covering England andWales

GPSS Groundwater Protection Strategy for Scotland

GQA General Quality Assessment

HA Highways Agency

HGV Heavy Goods Vehicle

HSE Health and Safety Executive

NRA National Rivers Authority: previously water regulation authority for England and Wales

PAH Polynuclear Aromatic Hydrocarbons

PCB PolyChlorinated Biphenyl

RA Regulatory Authority: the Environment Agency in England and Wales, the ScottishEnvironment Protection Agency and the DoE for Northern Ireland

RF Risk Reduction Factor

SEPA Scottish Environment Protection Agency

SOAEFD Scottish Office Agriculture, Environment and Fisheries Department

SPZ Source Protection Zone

SS Suspended Solids

SSSI (ASSI) Site (Area in Northern Ireland) of Special Scientific Interest

TSS Total Suspended Solids

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February 1998

TN Total Nitrogen

TP Total Phosphorus

TPb Total Lead

TPH Total Petroleum Hydrocarbons

TS Total Solids

TZn Total Zinc

WQO Water Quality Objectives

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February 1998

10.1 Bascombe A D, Ellis J B, Revitt D M and Shutes R B E (1990). The Development of EcotoxicologicalCriteria in Urban Catchments. In Urban Stormwater Quality and Ecological Effects upon Receiving Waters. EdsAalderink R H, Lijklema L & Ellis J B. Pergamon Press, Oxford.

10.2 CIRIA Report 142 (1994). Control of Pollution from Highway Drainage Discharges.

10.3 CIRIA Report 156 (1996). Infiltration Drainage, Manual of Good Practice.

10.4 Colwill D M, Peters C J and Perry R (1984). Water Quality of Motorway Runoff. TRRL SupplementaryReport 823.

10.5 Colwill D M, Peters C J and Perry R (1985). Motorway Run-Off - The Effect of Drainage Systems on WaterQuality. TRRL Research Report 37.

10.6 DOT (1992). Trunk Road Maintenance Manual Vol 2, Part 3 Routine and Winter Maintenance Code.Department of Transport (London).

10.7 Driscoll E D, Shelley P E and Strecker E W (1988). Evaluation of Pollutant Impacts from HighwayStormwater Runoff, Design Procedure. FHWA/RD-88/006 prepared for U.S. Department of Transportation FederalHighway Administration, Washington DC.

10.8 Ellis J B, Harrop D O and Revitt D M (1986). Hydrological Controls of Pollutant Removal from HighwaySurfaces. Water Research, Volume 20, No 5.

10.9 Ellis J B (1990). Bioengineering Design for Water Quality Improvement of Urban Runoff. Developments inDrainage. Polylink Paper 1.4, Institute of Water and Environmental Management (CIRIA).

10.10 Ellis J B (1996). Sediment Yield and BMP Control Strategies in Urban Catchments Erosion and SedimentYield: Global and Regional Perspectives (Proceedings of the Exeter Symposium, July 1996). IAHS PublicationNo 236.

10.11 Ellis J B and Revitt D M (1991). Drainage from Roads: Control and Treatment of Highway Runoff. ReportNRA 43804/MID.012.

10.12 Ellis J B, Revitt D M and Llewellyn N (1997). Transport and the Environment: Effects of Organic Pollutantson Water Quality. Journal of Chartered Institute of Water and Environmental Management.

10.13 Extence C A (1978). The Effects of Motorway Construction on an Urban Stream. Environmental PollutionNo 17.

10.14 Hamilton R S and Harrison R M (1991). Highway Pollution. Elsevier Science Publications (London).

10.15 Hammer D A (1989). Constructed Wetlands for Waste Water Treatment: Municipal, Industrial andAgricultural (LEWIS).

10.16 Harrison R M and Wilson S J (1985). The Chemical Composition of Highway Drainage Water. The Scienceof the Total Environment, 43.

10.17 Head K H (ELE International Ltd) (1984). Manual of Soil Laboratory Testing, Vol 1.

10.18 Maestri B, Dorman M E and Hartigan J (1988). Managing Pollution from Highway Stormwater Runoff.Transportation Research Record (No 1166).

10.BIBLIOGRAPHY

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Chapter 10Bibliography


February 1998

10.19 Mallett M J, Vine S, Murgatroyd C, Whitehouse P, Jerman E, Ashby-Crane R E, Fleming R, Wilson K andSims I (1992). Toxicity of Common Pollutants to Freshwater Aquatic Life: A review of the Effects of Ammonia,Arsenic, Cadmium, Copper, Cyanide, Nickel, Nitrate, Phenol and Zinc on Indigenous Species. WRc Report No NR3084/023, NRA.

10.20 Maltby L, Forrow D M, Boxall A B A, Calow P and Betton C I (1984a). The Effects of Motorway Runoff onFreshwater Ecosystems: 1 Field Study. Environmental Toxicology and Chemistry, Volume 14, No 6.

10.21 Maltby L, Boxall A B A, Forrow D M, Calow P and Betton C I (1984b). The Effects of Motorway Runoff onFreshwater Ecosystems: 2 Identifying Major Toxicants. Environmental Toxicology and Chemistry, Volume 14, No 6.

10.22 National Coal Board Mining Department (1982). Technical Management of Water in the Coal MiningIndustry.

10.23 Thorburn Colquhoun Transportation (1996). Accidental Spillages of Substances on Highways andCountermeasures to Reduce the Risk of Pollution. Produced for The Highways Agency.

10.24 Policy and Practice for the Protection of Groundwater (1992). National Rivers Authority(ISBN 1 873160 37 2).

10.25 An Assessment of the Condition of Shrubs alongside Motorways (1982). TRRL Report 1061.

10.26 A59 Burscough and Rufford Bypass Water Quality Report (1986). Environmental Resources Ltd.

10.27 Bickmore C and Dutton S (1984). Water Pollution in Motorway Run-off. The Surveyor, 3 May 1984.

10.28 Bickmore C and Dutton S (1984). Environmental Effects of Motorway Run-off. The Surveyor, 10 May 1984.

10.29 Bickmore C and Dutton S (1984). Oil and Toxic Spillages in Motorway Run-off. The Surveyor, 24 May1984.

10.30 River Quality: The Government’s Proposals (December 1992). Department of the Environment.

10.31 Rivers and Wildlife Handbook (1995). Publishers RSPB/RSNC.

10.32 Eds Cooper P F and Findlater B C (1990). Constructed Wetlands in Water Pollution Control. Pergamon.

10.33 Donald A Hammer (1989). Constructed Wetlands for Waste Water Treatment: Municipal, Industrial andAgricultural. Lewis.

10.34 Road Accidents, Great Britain, 1991. The Casualty Report. DOT 1992.

10.35 Department of the Environment (Annual Publication). Digest of environmental protection and water statistics.HMSO.

10.36 Price M (1994). Drainage from Roads and Airfields to Soakaways: Groundwater Pollutant or ValuableRecharge? JIWEM, 8 October 1994.

10.37 Startin J and Landsdown R V (1994). Drainage from Highways and other paved areas; Methods of Collection,Disposal and Treatment. JIWEM, 8 October 1994.

10.38 Groundwater Protection Strategy for Scotland. SEPA, 1997.

10.39 Urban Pollution Management (UPM). A Planning Guide for the Management of Urban WastewaterDischarges during Wet Weather (1994). The Foundation for Water Research Manual, November 1994, ref noFR/CL002.

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ELECTRONIC COPY NOT FOR USE OUTSIDE THE AGENCY.


February 1998 10/3


10.40 Hall M J, Hockin D L and Ellis J B (1993). Design of Flood Storage Reservoirs. CIRIA & Butterworth -Heinemann Ltd.

10.41 Water Resources Act 1991. HMSO.

10.42 Environment Act 1995. HMSO.

10.43 DoT Circular Roads 7/87. Spillages of Hazardous Substances on the Highway.

10.44 The Inland Waterways of Great Britain. A Complete Route Planning and Restoration Map. Published byWaterways World, British Waterways and The Inland Waterways Association.

10.45 Inland Waterways of Britain. Published by GEO Projects (UK) Ltd.


February 1998

Title of Publication

West Northumberland Sheet 01Coastal Northumberland Sheet 02North west Cumbria Sheet 03North Pennines Sheet 04Tyne and Tees Sheet 05South west Cumbria Sheet 06Yorkshire Dales Sheet 07Central North Yorkshire Sheet 08North East Yorkshire Sheet 09Central Lancashire Sheet 10South Pennines Sheet 11Vale of York Sheet 12Humber Estuary Sheet 13Anglesey Sheet 14North Wales Coast Sheet 15West Cheshire Sheet 16Derbyshire and N. Staffordshire Sheet 17Nottinghamshire Sheet 18Lincolnshire Sheet 19Meirionnydd/Dyfed Sheet 20/27West Shropshire Sheet 21S Staffordshire and E Shropshire Sheet 22Leicestershire Sheet 23North Northants Sheet 24West Norfolk Sheet 25East Norfolk Sheet 26Powys Sheet 28Worcestershire Sheet 29Northern Cotswolds Sheet 30Bedfordhsire Sheet 31North Essex Sheet 32East Suffolk Sheet 33Pembroke Sheet 34West Glamorgan Sheet 35Gwent, Sth and Mid Glamorgan Sheet 36Southern Cotswolds Sheet 37U Thames & Bedfordshire Downs Sheet 38West London Sheet 39Thames Estuary Sheet 40North West Devon Sheet 41Somerset Coast Sheet 42E Somerset and S West Wiltshire Sheet 43North West Hants Sheet 44West Sussex and Surrey Sheet 45East Sussex Sheet 46East Kent Sheet 47East Cornwall Sheet 48South Devon Sheet 49East Devon and South somerset Sheet 50Dorset Sheet 51Southern Hampshire Sheet 52West Cornwall Sheet 53

ANNEX IENVIRONMENT AGENCY GROUND WATERVULNERABILITY MAPS

ISBN Number

011 885865 3011 885877 7011 885879 3011 885870 X011 885876 9011 885882 3011 885871 8011 885846 7011 885836 X011 885862 9011 885872 6011 885850 5011 885830 0011 885880 7011 885881 5011 885832 7011 885863 7011 885839 4011 885852 1011 885875 0011 885849 1011 885869 6011 885868 8011 885838 6011 885837 8011 885886 6011 885867 X011 885847 5011 885857 2011 885856 4011 885834 3011 885848 3011 885873 4011 885861 0011 885864 5011 885853 X011 885854 8011 885831 9011 885855 6011 885866 1011 885858 0011 885883 1011 885835 1011 885851 3011 885860 2011 885829 7011 885878 5011 885884 X011 885885 8011 885845 9011 885859 9011 885874 2

Date Available(where not yet published)

Oct 1997

May 1998May 1988

May 1998

May 1998

May 1998

May 1998

May 1998May 1998

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Annex IEnvironment Agency groundwater vulnerability maps


February 1998A1/2

Annex IEnvironment Agency groundwater vulnerability maps

England and Wales Scale = 1:100,000

Northern Ireland Scale = 1:250,000i) Groundwater Vulnerability of Northern Ireland. Published by the British Geological Society for the DoE for

N.I.ii) Hydrogeological Map for Northern Ireland. Published by the British Geological Society for the DoE for N.I.To accompany these is a book: Robins, N.S. (1996) The Hydrogeology of Northern Ireland. London.


February 1998

A2.1 Where the assessment has indicated the need fortreatment of road runoff there are a number of drainagesystems that can provide, either individually or incombination, a measure of treatment. These aredescribed in outline below. Selection of the appropriatetype of treatment will have to take account of thecircumstances at the site, such as topography and landavailability, as well as the nature and type of receivingwaters.

A2.2 Table 2.1 gives approximate capital andmaintenance costs for the various treatment methodsdescribed. Table 2.2 gives data on the removal efficiencyof the systems for various pollutants, based on the bestavailable information from the literature.

Gully Pots

A2.3 Trapped gully pots are more efficient atseparating oil for later removal by gully emptier thanuntrapped gully pots, but can require more maintenance.During summer storms, contaminants such as oil areoften flushed out of gully pots causing relatively highconcentrations of contaminants to enter the roaddrainage system. Untrapped gully pots retain more siltby virtue of their greater sump depth but theirperformance is again very dependent on adequatemaintenance.

A2.4 Any treatment that may occur in gully pots isusually ignored for the purposes of determining thesubsequent treatment of runoff once it has entered theroad drainage pipe network. Indeed, trapped gully potsmay represent a potential threat of contamination, asaccumulated anaerobic pollutants can be flushed out atthe onset of summer storms. Gully pots do, however,provide a good first line of defence in the event of anaccidental spillage if well maintained.

Oil Separators and Other Containment Facilities

A2.5 Oil separators are installed in drainage systems toprovide a means of separating oil from runoff. Theyprovide a moderately effective removal facility forhydrocarbons. Solids removal from runoff willinevitably occur as flows pass through the body of waterretained in oil separators. Storage volume for siltaccumulation should be allowed for in the design. Thereare several types of separator in use of which the twomain ones are the full retention and the bypass separator.Where all runoff must be intercepted, retained, andtreated full retention separators are used. Their

application is normally reserved for garage forecourtsand similar areas known to be susceptible to pollutionfrom oil.

A2.6 Bypass oil separators have been generallyaccepted as an economical and reasonably effectivemeans of controlling discharges of oil, particularly assuch discharges primarily occur in first flush runoff. Intreating road runoff, these separators are normallydesigned to provide treatment volume sufficient to detain10% of the runoff from a storm intensity of 50 mm/hrfor six minutes, that is rainfall in excess of 5 mm/hr. Theother 90% of the storm bypasses the separator.Separation of 99% of influent oil is claimed by themanufacturers. Where the contributing area is large it ispossible for the working volume of the separator to fillup and spill to the bypass before the first flush from thefurthest part of the catchment can enter the separator.Under such circumstances a single separator may not beideal and catchment areas should be consideredaccordingly. The use of by-pass separators should besubject to consultation with the RA both as to thesufficiency of the treatment and as to the appropriateextent of catchment for each separator.

A2.7 Where necessary, on major new road schemes andon those involving the widening or improvement of theexisting roads, an oil separator can be used forcontainment of accidental spillages.

A2.8 There are other facilities, less expensive than theinstallation of a separator, that can achieve a reasonabledegree of containment for spillages, given suitabletopography and land availability. Such pollution trapsystems might rely on a lined ditch being placed betweenthe road drain and the receiving watercourse, with aminimum of 20 m3 capacity and with a control gate thatcan be shut in the event of accidental spillage ofpollutants on the road. The control gate could bereplaced, if appropriate, by a hanging baffle wallcontained within a box structure so that floating oil canbe contained and surface runoff can pass beneath thebaffle wall and so continue to the watercourse.Structures of this type need to be carefully designed sothat they function correctly and the RA should beconsulted about their use.

Combined Filter Drains

A2.9 Combined filter drains consist of perforateddrainage pipes normally laid along the edge of roads intrenches backfilled with graded granular filter material.

ANNEX IITREATMENT SYSTEMS

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Annex IITreatment systems


February 1998

They are used to collect surface runoff from the road aswell as groundwater. They provide a dual function ofconveyance and of treatment system.

A2.10 Combined filter drains can contributesignificantly to the treatment process of contaminantsflushed off road surfaces (Table 2.2). There are,however, problems that may arise from their installationand these are described in HD 33 (DMRB 4.2.3). Fullaccount of this advice should be taken when consideringthe use of filter drains for pollution control and it shouldbe ensured that their use is compatible with andappropriate to other aspects of the road design.

A2.11 The use of combined filter drains should alwaysbe assessed in conjunction with the risk of groundwaterpollution. Impermeable trench liners may be appropriatewhere groundwater pollution risks are high. Regularmaintenance of combined filter drains is required toprevent the build up of grass kerbs. The frequency ofthis maintenance will vary but must be carried out toensure the continued proper performance of thecombined filter drain.

A2.12 The total life span of a combined filter drain hasbeen predicted to be 10 years (Colwill et al, 1985). Afterthis time the voids below the perforated pipe may beexpected to be full of fine oily material resulting in asubstantial reduction in the treatment efficiency of thesystem. Replacement of the filter media orreconstruction of the combined filter drain is thenrequired. Increasing the depth of the trench below thepipe invert would increase the life span of the combinedfilter drain in terms of treatment efficiency. Combinedfilter drains can provide some protection against releaseto the receiving water of accidental spillages in that theydelay the release of pollutants.

Filtration Basins

A2.13 Filtration basins comprise sand and gravel filterbeds that are inundated by runoff. The water percolatesthrough the beds and is collected by an underdrainagesystem. Basins are designed on the volume of inflow andfiltration rate. A filtration rate of 5 m3/h/m2 has beenused to provide total solids removal efficiencies of 60-90%.

A2.14 Their usefulness should be considered against thelikely harm that may be done to an aquifer underlyingthe filtration basin if no impermeable membrane wereused. They provide an effective level of treatment but areprone to failure due to blocking of the sand filtermedium with silt and debris. Regular replacement of thesand filter medium is required to maintain effectiveperformance.

A2.15 Filtration basins are, in effect, a type of filterdrain or soakaway with an expanded surface area. Theywould be unsuitable for the containment of spillages.Their use could also be constrained by topographicaldifficulties and limited land availability.

Sedimentation Lagoons and Tanks (SettlementPonds)

A2.16 Sedimentation lagoons and tanks consist ofdetention storage structures containing permanent bodiesof standing water that reduce the velocity of runoffflowing through them sufficiently to promote thedeposition of suspended solids. These structures shouldbe constructed remote from flood plains.

A2.17 Sedimentation lagoons normally take the form ofearth basins or roadside excavations, whereassedimentation tanks are constructed using hard buildingmaterials, such as bricks, blocks or concrete, with aconsequent practical limitation on size. Emergent aquaticgrowth is usually not encouraged in settlement tanks andwater depth is limited to 1.0 - 1.5 metres. Aquaticgrowth in lagoons acts as a filtering mechanism forsuspended particles and pollutants. Details of removalefficiencies for pollutants are given in Table 2.2.

A2.18 In order to achieve a high quality effluent a lowdesign settling velocity of the order of 0.50 mm/seccorresponding to a particle size of 20 µm (medium -coarse silts) should be adopted. The level of treatmentachieved using this settling velocity should be sufficientfor most sensitive locations where even low levelcontamination would be unacceptable on environmentalgrounds. Where the required land area for such lagoonsis very high, incorporation of by-pass facilities may bepossible such that only first flush runoff is given fullsettlement, subject to consultation with the RA.

A2.19 In less sensitive locations a lower level oftreatment may be adopted. A design settling velocity inthe order of 2.00 mm/sec corresponding to particle sizeof 50 µm should be appropriate. Settling velocitiescorresponding to specified particle size diameters cannotbe specified exactly as there are many physical factorsthat can influence this, such as turbulence, material typeand shape. Table 2.3 gives a rough guide to the range ofsettling velocities that might be expected.

Balancing and Storage Ponds

A2.20 Balancing Ponds are constructed impoundingbasins. Their main function is to limit the rate of runoffpassing to the receiving waters such that the capacity ofthe downstream channel or other controlling criteria arenot exceeded. They are constructed in two different

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February 1998

forms, either dry or wet ponds. In terms of pollutioncontrol balancing ponds act in the same way assedimentation lagoons but, because retention times maybe less, the removal efficiency of pollutants is not likelyto be as high. There is also a higher risk that previouslysettled materials are re-suspended and washed out duringpeak rainfall events.

A2.21 Dry ponds are normally used where the solefunction is flow balancing. Excess flows are stored inthe impounding area and discharged gradually.Relatively modest solids removal rates up to 35% maybe expected from dry ponds due to re-suspension ofsolids during high flows. Nevertheless, this can providea useful first stage treatment.

A2.22 Wet ponds contain a permanent body of waterwhich may be colonised by local flora and fauna. Theymay therefore be used in situations where similarexisting features have been affected by construction ofthe road. Usually, a solids removal efficiency of about55% may be expected.

A2.23 The criteria to be used in balancing pond designare, principally, the receiving watercourse capacity andthe design storm return period. These need to beestablished in consultation with the RA. Balancingponds may, however, be constructed so as to providetemporary storage in the event of an accidental spillageby installing isolation devices at the outlet, such asorifices, hydrobrakes, weirs, syphons, or penstocks.

Swales

A2.24 Swales are shallow grassed channels normallylocated adjacent to carriageways. They are similar toroadside ditches and, like a ditch, provide a means ofconveyance for surface water runoff. Ditches, however,are designed to dispose of water quickly whereas runoffwill be retained for extended periods in swales to allowwater treatment by sedimentation, and, where possible,infiltration and biofiltration. Rainfall exceeding theretention capacity of the swale will be collected forretention and treatment elsewhere, or discharge directlyinto receiving waters.

A2.25 Contaminants contained in the runoff, such asheavy metals and nutrients, may be reduced and retainedby vegetation in the swale. Swales need to beconstructed on fairly shallow gradients to allowparticulate contaminants to be filtered out by the grasscover and settle as sediments at the vegetation base.These contaminants are exposed to various dry and wetperiods and are slowly degraded, followed by releaseand relocation. Dissolved contaminants within the runoffinteract with the surrounding water, soil and biota and

can be degraded. As most swales are designed to operateby infiltration to subsoil they cannot be easily lined inpractice and should therefore not be used close tosensitive groundwaters.

A2.26 A design method for grass swales is given inEllis and Revitt, 1991. The design approach assumesinfiltration to subsoil but may readily be used for swalesdischarging to a sewer or watercourse. Design flowvelocity must be reduced to a minimum if sedimentationand filtration are to be successful. Flow rates in excessof 0.5 - 0.8 m/s can dislodge grass from the uprightposition and inhibit sedimentation.

A2.27 The adoption of swales as road side channels forthe conveyance and treatment of surface runoff wouldresult in a significant increase in the width of roadcorridors, though this would apply more to sections ofroad constructed in cut than on fill. There is no reasonwhy embankment slopes could not be used as part of theswale, so long as the slopes were not susceptible toerosion. They would also require regular maintenanceand inspection and their use should therefore not beconsidered as a viable option where land acquisition iscritical, or where receiving waters are particularlysensitive to pollution. Swales may be adapted forcontainment of spillages by incorporating suitable stop-logs, sandbags or penstocks.

Biofiltration Techniques

A2.28 Biofiltration refers to the process wherebycontaminated waters are treated, through interactionwith vegetation, soil and bacteria, either naturallyoccurring or introduced, so that the effluent can bedischarged to a watercourse. Use of biofiltrationtechniques as a means to treat urban and road runoff andindustrial wastewaters has been limited until the lastdecade. The most commonly used biofiltration system isa wetland system, either natural or constructed, used forthe treatment of domestic sewage.

A2.29 There are few design criteria available at presentwhich can be used to design and reliably predict theperformance of artificial wetlands, such as reed-beds ormore varied vegetative systems, for road runofftreatment. Long-term operational and management dataare also lacking with respect to precise requirements andpracticalities of the system for specific locations andapplications, though some trials are being undertaken.With regard to the use of bacteria the state of currentknowledge means that there is a strong presumptionagainst the introduction of bacteria into road drainagesystems. Any proposed contribution from bacteria inreducing pollutant levels must be from those naturallyoccurring, albeit that designs may be such to

A2/3



February 1998

TREATMENT Capital Cost* Maintenance COMMENTSSYSTEM £’000s Cost £/pa

Gully/CarrierPipe System 180 - 220 1000 Regular de-silting of gullies

Containment Facilities(Oil separators) 10 - 30 300 Regular de-silting of separator

Combined Filter/FrenchDrains 160 - 200 5000 - 15000 Low annual maintenance

(annualised cost- Requires stone replacement or cleaningstone replacement) after 10 -20 years

Filtration Basin 20 - 50 2500 Low annual maintenanceAssume sand replaced every 5 years

Sedimentation Lagoon(Settlement Pond) 30 - 60 2000 Low annual maintenance

De-silting after 5 years

Sedimentation Tank 60 - 100 300 Annual de-silting

Balancing/Storage PondsDry 15 - 45 350 Assume no maintenance in first 5 yearsWet 25 - 55

Swales 15 - 40 350 Assume no off-site disposal of cuttings

Biofiltration Techniques (a) 2500 Annual maintenance in first 3 years15 - 60 (b) 1000 Annual maintenance after 3 years

* Based on 1 km of 6 lane motorway

Note: Few data are available on the costs of treatment systems installed to remove contaminants from road runoff.The figures presented above have been gleaned from various sources, and combined with professional assessment arepresented as first order cost estimates (based on 1995 costs).

encourage their activity. At present there is no formaldesign process for road runoff treatment and there islittle evidence that wetlands, as described above, are anappropriate form of treatment for road runoff (see alsoLagoons). Texts such as Cooper and Findlater, 1990,give a basic outline of wetland design.

Table 2.1. Capital and Maintenance Costs

A2/4



February 1998

Table 2.2 Treatment Systems Efficiency

REMOVAL EFFICIENCY (%)TREATMENTSYSTEM ZINC COPPER IRON LEAD SUSPENDED HYDRO-

(Total) (Dissolved) SOLIDS CARBONS

Gully/CarrierPipe System 10 - 30

Combined Filter/French Drains 70 - 80 10 - 30 80 - 90 80 - 90 80 - 90 70 - 90

Filtration Basin 70 - 80 10 - 30 80 - 90 80 - 90 60 - 90 70 - 90

Sedimentation LagoonSettling Pond 60 - 80 20 - 30 90 + 80 - 90 60 - 90 70 - 90

Sedimentation Tanks& Oil Separators 30 - 50 < 10 30 - 40 40 - 60 30 - 80 40 - 99

Balancing Ponds - Dry 35 - 45 < 10 20 - 30 30 - 50 30 - 60 30 - 60- Wet 30 - 40 < 10 30 - 50 40 - 60 40 - 70 30 - 60

Swales/Grassed Ditches 70 - 90 50 - 70 90 + 80 - 90 60 - 90 70 - 90

Biofiltration Techniques 50 - 80

Note: Few data are available on the efficiency of treatment systems installed to remove contaminants fromroad runoff. The figures shown above have been gleaned from various sources and combined with professionalassessment to give first order estimates. Further research is required to substantiate these figures.

Table 2.3 Settling Velocities for Solids of Varying Particle Size

Particle Size Diameter Typical Material Type Range of Settling Velocities (microns) mm/sec

100 Very fine sands 5 - 10

50 Coarse silts - very fine sands 1 - 5

20 Medium - Coarse silts 0.1 - 1.0

5 Fine - medium silts 0.01 - 0.1

1 Fine clays 0.001 - 0.01

A2/5



November 2002 - Correction

A3.1 This ANNEX outlines procedures for predictingdissolved copper and total zinc concentrations and therisk of accidental spillage to both surface waters andgroundwaters. Both assessments should be carried outto determine whether mitigation is needed. In all casesthe assessments should be based on design year, twoway traffic flow data assuming high growth.

Water Quality Assessment - Discharges to SurfaceWaters

A3.2 Data to be Obtained from the RegulatoryAuthority

1 The division of all proposed or potentialreceiving waters into separate reaches. Eachreach will usually be delineated by majorconfluences or in-river structures such as weirs,and on significant watercourses would beexpected to be represented by a single waterquality monitoring station.

2 For each reach, the uses to which the water is put(fisheries, recreation, water abstraction etc) andthe consequent EQS which the RA wish to apply.

3 Any existing water quality data (Cb - expressed as

mg/l) for locations upstream of proposed orpotential discharge locations. Where no dataexist, and no inference on quality can be madefrom nearby watercourses, assume that eachsubstance referenced in the EQS is currentlypresent at a concentration of half that given in theEQS. If this assumption has to be made, theaccuracy of the assessment will suffer.

4 The 95 percentile flow (Q95

- the flow exceededin the reach for 95% of the time). Where nogauging data are available this can be calculatedusing the catchment area and characteristicsupstream of the proposed discharge point.

A3.3 Data to be generated by the Design Organisation

1 Identify all roads with AADT flows of more than5000 which are to drain to each reach (whetherthey are to drain to a single or to multipledischarge points within that reach).

2 For each road, determine the surface area to bedrained to each reach and obtain pollutant build-up rates for each section of road separately (fromTable 3.1).

3 Calculate the 5 day pollutant build-up (M -expressed as kg/5 days) for each section of roadto be drained.

4 Read the appropriate rainfall data for the schemelocation from Figure 3.1.

5 Obtain the runoff coefficient applicable to thescheme. If no data exist, assume that thecoefficient is 0.5.

6 Calculate the downstream copper and zincconcentration using the approach outlined below.

A3.4 Calculations

For each reach, calculate the total runoff volume (V) asfollows:

V = road area (sq m) x Runoff coefficient xrainfall (m/day)

Calculate the dilution available for discharges fromthese roads:

Dilution = Q95

÷ V

Calculate resulting downstream river concentrations, Cr,

for both copper and zinc:

Cr = {(C

b x Q

95) + (1000 x M)} ÷ (Q

95 + V)

A3.5 If the downstream river concentration, Cr, is

greater, for either dissolved copper or total zinc, thanthe relevant EQS then a detailed

water quality

assessment is required. This may involve mathematicalmodelling. No particular mathematical model isprescribed. The assessment method should be selectedby the specialist consultant in consultation with theOverseeing Organisation and the RA (see ANNEX IV),but, before proposing such a method the specialistshould be satisfied that it is warranted by the accuracyand quality of the input data.

Water Quality Assessment - Discharges toGroundwaters

A3.6 Except in the case of accidental spillages, theannual loading arising from runoff is likely to be ofgreater importance than the concentration discharged atany one time. A preliminary assessment of the effects ofrunoff on groundwater concentrations can be obtained

ANNEX IIIASSESSMENT METHODS AND WORKED EXAMPLES

A3/1

Annex IIIAssessment methods and worked examples



using annual pollutant build-up rates and assuming thatall of those pollutants are washed into the aquifer. Oncethe runoff has reached the aquifer, the preliminaryassessment described here assumes that there is nodilution available and that the groundwater is static (iethere is no flow through the aquifer). Such situations donot arise in practice, as there will always be some flowwithin the aquifer. The assessment therefore providesonly an indication of whether special care may beneeded in designing discharges to ground at particularlocations.

A3.7 Data to be obtained from the RegulatoryAuthority

1 The EQS for the aquifer concerned.

A3.8 Data to be Generated by the Design Organisation

1 Calculate the annual pollutant build-up ofdissolved copper and total zinc for the road areasto be drained to ground using Table 3.1 and theAADT flow for each section of road.

2 Estimate the annual average rainfall from Figure3.2 for the scheme location.

3 Obtain the runoff coefficient applicable to thescheme. If no data exist, assume that thecoefficient is 0.5.

4 Calculate the total volume of runoff per yearusing the runoff coefficient and the annualaverage rainfall.

5 Divide the total annual pollutant loading by thecalculated runoff volume to give the worst caseprediction of groundwater quality.

6 Where the worst case predicted quality exceedsthe EQS for the aquifer, undertake a detailedwater quality assessment as discussed in ANNEXIV.

A3.9 It must be stressed that this approach gives a veryconservative estimate of the effects of discharges toground, as discussed in CHAPTER 6. The results of thepreliminary assessment should not be used to justifyinclusion of mitigation measures.

Table 3.1. Typical Pollutant Build-up Rates (kg/ha/a)

Traffic Total COD NH4-N Copper Copper Zinc Zinc

Flow Solids (Kg O2) Total Soluble Total SolubleTwo WayAADT

<5000 2500 250 4.0 0.4 0.2 0.4 0.2

5000-15000 5000 400 4.0 0.7 0.3 1.0 0.5

15000-30000 7000 550 4.0 1.0 0.4 2.0 1.0

>30000 10000 700 4.0 3.0 1.2 5.0 2.5

A3/2


Method for Predicting Serious Accidental Spillage

A3.10 The spillage risk, that an accident will occur onthe new road network involving a serious spillage ontoany part of the road surface which drains into eachseparate reach (either through a single or throughmultiple discharge points), is initially calculated. Thepollution risk is then obtained by factoring the spillagerisk, according to the time the emergency services areexpected to take to arrive at the accident site, to give theprobability that the spillage will pass through the drainscausing a pollution incident in the receiving waters.

A3.11 If the pollution risk, expressed as a returnperiod, is unacceptable, the process is repeated for eachindividual discharge point within each reach to identifythose discharges which would provide the greatestbenefit in terms of reducing the risk if measures tocontain the spillage were to be installed. Through thisprocess of iteration (which could involve relocation ofproposed discharge points to discharge to differentreaches as part of the overall mitigation measures) therisk to each receiving reach can be reduced toacceptable levels.



8 Recalculate the overall risk to each reach bysumming all of the revised individual risks,repeating the process of including mitigation atthe highest risk outfalls on an iterative basis untilthe risk to the reach is acceptable.

9 In some instances, more than one containment orcontrol measure will be needed at individualdischarge points to control the risk. If theiteration process leads to the conclusion that alldischarges to any reach will need two suchmitigation measures, yet the calculated risk isstill apparently unacceptable, then subject to theagreement of the RA that the proposedcontainment measure designs are acceptable,there will be no requirement to add any furthermeasures.

A3.14 Calculations

The probability of a serious accidental spillage iscalculated as follows :

Pacc

= RL x SS x (AADT x 365 x 10-6) x(% HGV ÷ 100)

where:

Pacc

= probability of a serious accidentalspillage in one year over a given roadlength

RL = road length in kilometresSS = serious spillage rates from Table 3.2

(or local data if available)AADT = annual average daily traffic% HGV = percentage of Heavy Goods Vehicles

The probability that a spillage will cause a pollutionincident is calculated thus:

P pol/year

= Pacc

x Ppol

where:

Ppol

= The risk reduction factor, dependent uponemergency services response times, whichdetermines whether a serious spillage willcause a serious pollution incident. The valueis to be selected from Table 3.3, using thequality of the reach proposed to receive thedischarge.

A3.12 Data to be obtained from or discussed with theRegulatory Authority

1 Discuss the Overseeing Organisation’s proposedpollution risk criteria for each separate reach andseek agreement to these with the RA. Theacceptable risk of a pollution incident shouldnormally be 1 in 100 years for discharges toaquifers and to reaches of sensitive watercourses.For all other receiving waters the acceptable riskshould normally be 1 in 50 years. In exceptionalcases the RA may identify specific local reasonsto depart from these criteria.

A3.13 Data to be generated by the Design Organisation

1 Determine the total length of road in each of thecategories given in Table 3.2 to be drained intoeach separate reach.

2 For each section of road identified above,determine the AADT flow and the percentage ofthat flow which will comprise HGVs.

3 For each section of road, calculate the probabilitythat a serious accidental spillage will occur usingthe method outlined below.

4 Calculate the total risk to each reach bysummation of all individual risks from eachcontributing section of road.

5 Factor that total risk according to the time theemergency services will take to arrive at the siteof the accident and express that risk as a returnperiod.

6 If the return period for any reach is unacceptable,repeat the above steps for each individualdischarge point to determine the risk arising fromeach discharge.

7 Select the discharge with the highest individualrisk. If it is not possible to relocate that outfall toa different receiving water reach, identify asuitable form of spillage containment asmitigation at that discharge point; additional landmay have to be acquired and the feasibility ofthat acquisition should be considered.Recalculate the individual risk assuming that,properly designed to the approval of the RA, thecontainment measure will reduce the individualrisk by 65%.

A3/3



November 2002 - CorrectionA3/4


Table 3.2 Serious Accidental Spillages Per Million HGV km/year

Junction Type Motorway All purpose

Urban Rural Urban Rural

No Junction 0.0022 0.0014 0.0039 0.0017

Slip Road* 0.0032 0.0023 0.0058 0.0035

Side Road* 0.0106 0.0042

Roundabout* 0.0296 0.0119

Cross Road* 0.0159 0.0044

Overall 0.0024 0.0019 0.0075 0.0025

Note: * Risk factor applies to all road lengths within 100 m of these junction types, that is for a side road joiningan All Purpose Road the risk is 0.0106 for 100 m of the side road and for a 200 m length of the All Purpose Roadcentred on the junction itself.

Table 3.3 Probability of a Serious Accidental Spillage Leading to a Serious Pollution Incident

Receiving Watercourse Emergency services Emergency serviceresponse time to site is response time to site within 20 minutes exceeds 20 minutes

River Classification RE1 orRE2 (High Quality) 0.45 0.75

River Classification RE3 orRE4 (Moderate Quality) 0.3 0.5

Aquifer 0.3 0.3

If the road traverses a particularly sensitive region or if there are any other special circumstance, these factors mayneed to be adjusted. Where the watercourse has a significant amenity value, the effect of pollution on this amenityshould be considered. Source Thorburn Colquhoun Transportation, 1996.


February 1998


A3/5

Figure 3.1 Depth of rain for assessing pollutant runoffReproduced from "The Wallingford Procedure - Volume 1" by kind permission of HR Wallingford.


February 1998A3/6


Figure 3.2 Average annual rainfall 1941-1970Reproduced from "The Wallingford Procedure - Volume 1" by kind permission of HR Wallingford.



Worked Examples

Example 1

A3.15 A new 3 km long, two lane motorway with atwo-way AADT flow of 18,000 and 8% HGV traffic isto be constructed in urban Yorkshire. Two slip-roads,one entering and another exiting the motorway, arelocated within the catchment of the new scheme andmeasure 100 metres in length. The surface water willdischarge into a river of RE2 classification, supportinga good quality coarse fishery. No specific flood controlmeasures are required.

Different serious spillage rates (SS) are applied tosections of road within 100 metres of a junction. Theserious spillage rate varies, depending on junction androad type. In this example, the slip road junction SS rateapplies to 100 metres of the motorway carriagewayeither side of the junction plus the total length of theslip-roads.

(i) Data from the Regulatory Authority

95%ile river flow (Q95

) - 0.016 m3/secRiver Class - RE2Average hardness - 610 mg/lUpstream dissolved copper (C

b) - 0.04 mg/l

Upstream total zinc (Cb) - 0.12 mg/l

Permitted EQS copper (from Table 2) - 112 µg/lPermitted EQS zinc (from Table 2) - 500 µg/l

(ii) Other Data

Road lengths (RL) comprise 3000 m motorway plus200 m slip roads of which:motorway > 100 m from slip roadjunctions - 2800 mmotorway < 100 m from slip roadjunctions - 200 mexit slip road - 100 mentry slip road - 100 m

Width of new road - 21.5 mWidth of slip road - 8 mAADT of motorway - 18,000AADT of exit slip road - 2,000AADT of entry slip road - 2,500Percentage HGVs - 8%Emergency response time - < 20 minutesRunoff coefficient - 0.5Rainfall depth from Figure 3.1 - 11 mm/day

Serious Spillage rates (SS) from Table 3.2:for urban motorway >100 m fromslip roads - 0.0022 (per

106 HGVkm/year)

for urban motorway < 100 m fromslip roads - 0.0032 (per

106 HGVkm/year)

for slip-roads - 0.0032 (per106 HGVkm/year)

Risk reduction factors (from Table 3.3) - 0.45

A3.16 Calculation of Spillage Risk

a) Probability of serious accidental spillage (Pacc

) isgiven by:

Pacc

= RL x SS x (AADT x 365 ÷ 106) x(HGV% ÷ 100)

For the new motorway > 100 m away fromslip-road junctions

Pacc

= 2.8 x 0.0022 x (18,000 x 365 ÷ 106 )x (8 ÷ 100)

= 3.2377 x 10-3

For the new motorway < 100 m away fromslip-road junctions

Pacc

= 0.2 x 0.0032 x (18,000 x 365 ÷ 106 )x (8 ÷ 100)

= 0.3364 x 10-3

For the exit slip-road

Pacc

= 0.1 x 0.0032 x (2000 x 365 ÷ 106 )x (8 ÷ 100)

= 0.01869 x 10-3

For the entry slip-road

Pacc

= 0.1 x 0.0032 x (2500 x 365 ÷ 106 )x (8 ÷ 100)

= 0.02336 x 10-3

Total risk of spillage for all new motorway andslip-roads combined

Pacc

= (3.238 + 0.3364 x + 0.01869 +0.02336) x 10-3

= 3.616 x 10-3

A3/7




b) Risk of serious pollution incident per year isgiven by:

Ppol

= Pacc

x risk reduction factor= 3.616 x 10-3 x 0.45= 1.627 x 10-3

Return period is 1 : 615 years

c) Assuming an allowable risk of pollution of 0.01,the probability of a serious pollution incidentoccurring should not exceed once every 100years (the level of allowable risk will be advisedby the Overseeing Organisation). This analysisindicates that no further pollution controlmeasures are required to reduce the spillage risk.

A3.17 Water Quality Prediction

Impermeable area of new road with AADT < 5000Slip-roads = 200 m x 8 m

= 1600 m2 (0.16 hectare)

Impermeable area of new road with AADT in range15000-30000

New motorway = 3000 m x 21.5 m= 64500 m2 (6.45 hectares)

Total impermeable area of newroad = 1600 m2 + 64500 m2

= 66100 m2 (6.61 hectares)

Runoff volume (V) = Total impermeable areax runoff coefficient x(rainfall depth ÷ 1000)

= 66100 x 0.5 x (11 ÷ 1000)= 363.6 m3/day

Q95

(converted fromm3/s to m3/day) = 0.016 x 3600 x 24

= 1382.4 m3 /day

Build up rates for copper from Table 3.1

For slip-roads where AADT <5000

Dissolved copper 5 day build up(M

cu) = Daily build up x 5 days x

drainage area= (0.2 ÷ 365) x 5 x 0.16= 0.438 x 10-3 kg

For motorway with AADT in range 15000-30000

Dissolved copper 5-day build up(M

cu) = (0.4 ÷ 365) x 5 x 6.45

= 35.342 x 10-3 kg

Total dissolved copper build up on new motorway andslip-roadsM

cu= 35.780 x 10-3 kg= 0.0358 kg

Resulting dissolved copper concentration in the river isgiven by:

Cr

= {(Cb x Q

95) + (1000 x M

cu)} ÷ (Q

95 + V)

= {(0.04 x 1382.4) + (1000 x 0.0358)} ÷(1382.4 + 363.6)

= 0.0522 mg/l (52.2 µg/l)

Build up rates for zinc from Table 3.1

For slip-roads where AADT <5000

Total zinc 5-day build up(M

zn) = (0.4 ÷ 365) x 5 x 0.16

= 0.877 x 10-3 kg

For motorway with AADT in range 15000-30000

Total zinc 5-day build up(M

zn) = (2.0 ÷ 365) x 5 x 6.45

= 176.712 x 10-3 kg

Total zinc build up on new motorway and slip-roadsM

zn= 177.589 x 10-3 kg= 0.178 kg

Resulting total zinc concentration in the river is givenby:

Cr

= {(Cb x Q

95) + (1000 x M

zn)} ÷ (Q

95 + V)

= {(0.12 x 1382.4) + (1000 x 0.178 )} ÷(1382.4 + 363.6)}

= 0.197 mg/l (197 µg/l)

These concentrations are below the permitted EQSconcentrations set by the Regulatory Authority andtherefore the surface runoff requires no pollutioncontrol treatment facilities to treat soluble pollutants.

A3/8




Example 2

A3.18 A rural motorway is to be widened from three tofour lanes. A 3 km length without junctions will bedrained to one outfall leading to a moderate qualitywatercourse. There is a local aquifer used forabstraction. The two way AADT flow for the designyear is 120,000. The HGV content is 10%. Rescueservices are within 20 minutes. No drinking water isabstracted downstream of the outfall and no flowbalancing is required.


95%ile low river flow (Q95

) - 0.011 m3/secRiver Class - RE2Hardness - 97 mg/lUpstream dissolved copper (C

b) - 0.04 mg/l



(ii) Other Data

Road length (RL) - 3000 mWidth of new road - 37.5 mAADT - 120,000Percentage HGVs - 10%Emergency response time - < 20 minutesRunoff coefficient - 0.5Rainfall depth (from Figure 3.1) - 13 mm/daySerious Spillage rate (SS) for ruralmotorway (from Table 3.2) - 0.0014 (per

106 HGVkm/year)

Risk reduction factors(from Table 3.3) - 0.45


a) Probability of serious Accidental Spillage (Pacc

):

Pacc

= 3 x 0.0014 x (120,000 x 365 x 10-6) x(10 ÷ 100)

= 18.396 x 10-3

b) Risk of serious pollution incident per year:

Ppol

= 18.396 x 10-3 x 0.45P

pol= 8.278 x 10-3


c) Assuming an allowable risk of pollution of 0.01,the probability of a serious pollution incidentoccurring should not exceed once every 100

years (the level of allowable risk will be advisedby the Overseeing Organisation). The risk ofserious pollution has a greater return period than1 in 100 years and therefore no containmentfacilities are required.


Total impermeable area for newroad with AADT > 5000 = 3000 m x 37.5 m

= 112,500 m2

(11.25 hectares)

Runoff volume (V) = 112,500 x 0.5 x(13 ÷ 1000)

= 731.25 m3/day

Q95

= 0.011 x 3600 x 24= 950.4 m3/day

Build up rates for copper from Table 3.1


cu) = (1.2 ÷ 365) x 5 x 11.25

= 0.185 kg

Resulting copper concentration in the watercourse isgiven by:

Cr

= {(Cb x Q

95) + (1000 x M

cu)} ÷ (Q

95 + V)

= {(0.04 x 950.4) + (1000 x 0.185)} ÷(950.4 + 731.25)

= 0.133 mg/l (133 µg/l)

Build up rate for zinc from Table 3.1

Total zinc 5 day build up(M

zn) = (5 ÷ 365) x 5 x 11.25

= 0.771 kg

Resulting zinc concentration in the watercourse is givenby:

Cr

= {(Cb x Q

95) + (1000 x M

zn)} ÷ (Q

95 + V)

= {(0.09 x 950.4) + (1000 x 0.771)} ÷(950.4 + 731.25)

= 0.509 mg/l (509 µg/l)

These concentrations breach the relevant EQS (40 µg/land 300 µg/l for dissolved copper and total zincrespectively). More detailed modelling using sitespecific and local data may be undertaken if moreaccurate data is available and reliable. Otherwisetreatment for soluble pollutants will be necessary byintroduction of appropriate systems and/or increasingdilution by runoff retention measures. The approximate

A3/9




impact of the latter can be estimated by relating therelease of the 5 day pollutant build up to the restrictedoutflow from the treatment device for the design storm.

Example 3

A3.21 A new three lane motorway with a 2-way AADTflow of 40,000 and 35% HGV traffic is to beconstructed. A 10 km length passes through a narrowvalley very close to a tributary of a major salmon river.Although there are a range of possible dischargelocations the topography of the surrounding land meansthat all discharges have to drain to this water course.There is no aquifer and no drinking water abstraction.Rescue services are more than 20 minutes away.


95%ile low river flow (Q95

) - 0.063 m3/secRiver Class - RE1Hardness - 65 mg/lUpstream dissolved copper (C

b) - 0.001 mg/l



(ii) Other Data

Road length (RL) - 10,000 mWidth of new road - 30 mAADT new road - 40,000Percentage HGVs - 35%Emergency response time - > 20 minutesRunoff coefficient - 0.8Rainfall depth (from Figure 3.1) - 11 mmSerious Spillage rate (SS) for ruralmotorway (from Table 3.2) - 0.0014 (per

106 HGVkm/year)

Risk reduction factors(from Table 3.3) - 0.75


a) Probability of serious Accidental Spillage (Pacc

):

Pacc

= 10 x 0.0014 x (40,000 x 365 x 10-6) x(35 ÷ 100)

Pacc

= 0.072

b) Risk of serious pollution incident per year:

Ppol

= 0.072 x 0.75= 0.054


A3/10


c) Assuming an allowable risk of pollution of 0.01,the probability of a serious pollution incidentoccurring should not exceed once every 100years (the level of allowable risk will be advisedby the Overseeing Organisation). Then onesuitable control facility would lower the risk, by65%, to 0.019 (once every 53 years) and anadditional facility would further reduce the risk,by 65%, to 0.0066 (once every 151 years). Onthis scheme, dual containment measures areneeded at every outfall. Swales are feasible formost of scheme length, and, if fitted with checkdams, could comprise one of the containmentmeasures. Land acquisition is feasible at only alimited number of locations, with topographiclimitations existing at some potential dischargelocations. Through careful design of the drainagesystem, it is possible to limit the number ofoutfalls and install a sedimentation pond at eachone. By suitable choice of outlet and outletcontrol these can provide the second containmentfacility required. Where swales cannot beinstalled consideration may have to be given toinstalling a by-pass oil separator upstream of thesedimentation ponds.


Total impermeable area for new roadwith AADT >5000 = 10,000 m x 30 m

= 300,000 m2 (30.0 hectares)

Runoff volume (V) = 300,000 x 0.8 x(11 ÷ 1000)

= 2,640 m3/day

Q95

= 0.063 x 3,600 x 24= 5,443 m3/day

Build up rate for copper from Table 3.11


cu) = (1.2 ÷ 365) x 5 x 30.0

= 0.493 kg

Resulting copper concentration in the watercourse isgiven by:

Cr

= {(Cb x Q

95) + (1000 x M

cu)} ÷ (Q

95 + V)

= {(0.001 x 5443) + (1000 x 0.493)} ÷(5443 + 2640)

= 0.062 mg/l (62 µg/l)


November 2002 - Correction A3/11

Build up rate for zinc from Table 3.11

Total zinc 5 day build up(M

zn) = (5.0 ÷ 365) x 5 x 30.0

= 2.055 kg

Resulting zinc concentration in the watercourse is givenby:

Cr

= {(Cb x Q

95) + (1000 x M

cu)} ÷ (Q

95 + V)

= {(0.03 x 5443) + (1000 x 2.055)} ÷(5443 + 2640)

= 0.274 mg/l (274 µg/l)

The dissolved copper concentration breaches the copperEQS (40 µg/l), although the total zinc concentrationcomplies with the relevant EQS (300 µg/l). Moredetailed modelling of dissolved copper, using sitespecific and local data, can be undertaken if moreaccurate data is available and reliable. This modellingshould take into account the estimated treatmentprovided by the vegetative treatment systems proposedabove for spillage containment. It can also take intoaccount the estimated additional dilution provided byretaining the runoff within these systems. This shouldprovide the degree of treatment required to bring copperconcentrations within the EQS.



February 1998

Introduction

A4.1 ANNEX III outlines methods for the preliminaryassessment of the need for pollution control facilitieshaving regard both to the impact of routine discharges ofsoluble and insoluble pollutants and to accidentalspillages. The analysis methods for soluble pollutantassessment provide a very conservative estimate of likelywater quality impacts downstream of each proposeddrainage outfall. Where this first order analysis indicatesthat no water quality problems are expected, and wherethere is no reason for concern regarding insolublepollutant loadings, it can be assumed with someconfidence that the discharge can be made withoutprovision of treatment facilities to control routinedischarge quality. Alternatively, if the analysis identifiespotential problem locations, the conclusion reached isthat a more detailed study is required. This ANNEXoutlines some of the essential considerations in planningsuch a detailed assessment. The detailed study should beplanned and implemented by a water quality specialist.The objective of the study should be to secure the properuse of resources by ensuring that treatment is providedonly where necessary.

A4.2 If the spillage risk assessment indicates thatcontainment or control facilities are needed to preventpollution arising from accidents on the road, furtherinvestigation of that risk will not usually be necessary.The beneficial effects of any such facilities on routinedischarge quality must, however, always be taken intoaccount when undertaking detailed studies of the need tocontrol non-accidental discharges.

A4.3 A major requirement of any detailed study is thatthe specific features of the scheme should be considered.The initial screening procedure takes account of some ofthese details, such as the receiving water quality andflow, but other important features are handled in a moregeneric and very conservative way. Three fundamentalelements requiring more accurate assessment during thedetailed study are:

a) the likely discharge quality, quantity andfrequency;

b) the dispersion of the pollutants in the receivingwater;

ANNEX IV

DETAIL ED WATER QUALITY ASSESSMENT(SOLUBLE AND INSOLUBLE POLLUTANTS)

c) the sensitivity of that water to the pollutants. Thedetailed study should draw upon the knowledgegained of the overall environmental value (interms of conservation, resource, recreation,fisheries etc) in determining the acceptability ofany proposed discharge.

Discharge Characterisation

A4.4 An understanding of the potential impact can onlybe formed with knowledge of the likely quality, volumeand frequency of the proposed discharge. Many factorsaffect these characteristics, and the literature ondischarge quality indicates the degree of variation whichmight exist between locations and even between stormsat specific locations.

A4.5 Estimates of discharge quality can be derived in anumber of ways. The most effective is to use specificlocal data collected from roads carrying identical trafficvolumes, but only in rare cases will the RA hold suchdata. The assessment will therefore normally involveprofessional judgement based on records from otherroads. Care is needed in selecting data sets for referencepurposes. Many more data exist which describe complexurban runoff or storm sewer outfall quality than areavailable for discharges arising from road drains only.Urban discharges are frequently affected by factorswhich do not arise from road drainage, such as illegalcross connections to foul water sewers, runoff fromindustrial areas and deposition of foul waste into roadgullies. These can have significant effects on urbanrunoff quality and use of data from urban areas in thedetailed water quality assessment may over-estimate thelikely impact of the road. Care is also needed inconsidering the use of pollutant build-up rate data forany detailed assessment, because no universallyapplicable relationship between traffic flow andpollutant build-up rates exists.

A4.6 Although there are few available data for UKdischarges, the Event Median Concentration (EMC) andthe variation around that median appear to provide themost reliable statistical estimate of likely runoff quality.As the EMC is a flow-weighted statistic generated bysampling throughout each of many discharge events, theeffects of the ‘first flush’ are taken fully into account,provided that the standard deviation of the EMC is alsoconsidered. Table 7, containing data recorded during

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Annex IVDetailed water quality asessment (Soluble and insoluble pollutants


February 1998

American studies, provides an indication of the range ofEMCs which can be expected. Where the specialist hasreason to believe that a specific scheme could produceworse than average discharge quality, the appropriateEMC can be read from the Table, with the selected limitjustified on the basis of specific local factors. Suchfactors could include the presence of an unusually highproportion of HGVs carrying dusty materials such asquarry stone, or the presence of steep cuttings whichlimit the dispersion of dust and dirt away from the roadsurface during dry weather. Conversely, where the roadis to be at grade and exposed to strong cross winds, thespecialist may decide that a better than averagedischarge quality can be assumed. If no EMC data forlocal discharges are available, those presented in Table 7could be used. The standard deviation was reported byDriscoll et al, (1988) to be approximately 75% of eachspecific EMC recorded. Hence an ‘average’ urbanhighway carrying more than 30,000 vehicles per daywould be expected to produce runoff having a ‘total’suspended solids EMC of 142 mg/l with a standarddeviation of 107 mg/l (no data are available for the UKstandard measurement of suspended solids). Only 10%of all discharges from similar roads would be expectedto have a total suspended solids EMC of greater than295 mg/l. Ellis (1996) also presents a simple, sitespecific and empirical method for estimating the EMC.

A4.7 In some situations it may also be appropriate toconsider separately the impact of the ‘first flush’. It isenvisaged, however, that this would be needed onlywhere there are specific, local and recent data whichshow that ‘first flush’ discharges derived entirely fromroads have a marked and unacceptable impact. The RAwill advise if they believe this to be the case.

A4.8 Discharge volume, frequency and duration arealso important parameters to be estimated before theimpact of a discharge can be more accurately assessed.While road drains only carry water as a result ofrainfall, not all rainfall events will cause a discharge. Atleast a proportion of any rain falling onto a dry road willsimply wet the surface. Some of the water will then bedispersed as spray falling outside the drain catchment,while some will simply evaporate. The literaturecontains a wide range of estimates for the rain necessaryto initiate runoff. For example Ellis et al (1986) quotesbetween 0.1 and 1.5 mm, while Harrison and Wilson(1985), in a study on the M6, found that 2.2 mm wasinsufficient to instigate discharge. Road gradient, surfaceroughness, porosity and time since the last rainfall eventare key factors determining the rainfall needed to initiatea discharge.

A4.9 In addition only a proportion of the rain above thedischarge threshold is discharged by the drainagesystem. The runoff coefficient (the proportion of incidentrain reaching the point of discharge) will be equal to 1for a totally impermeable catchment with no evaporationor spray losses. In the UK a runoff coefficient ofbetween 0.5 and 0.8 would normally be expected.

A4.10Where available, long time-series (greater than 10years) local rainfall data will provide the basis forestimating discharge volume and frequency. Forplanning and assessment purposes, daily average rainfalldata will usually suffice. The more detailed approachadopted for assessing combined sewer overflow impacts,in which hourly rainfall may be synthesised usingcommercially available software, will not usually beappropriate for simple road discharges. It will usually besufficient to determine the drain surface area, to analysethe daily average rainfall record (ignoring those dayswhen less than, say, 2 mm of rain fell) and to apply theselected runoff coefficient to provide the estimate ofrunoff frequency and volume for any individual site.Design storm volumes, used to calculate pipe andcatchment sizes, should not be used as the basis of thewater quality assessment.

Discharge Modelling - Flowing Receiving Waters

A4.11When assessing the likely impact of pollutants onthe receiving water, the assessment should consider bothconcentrations in the water column (soluble pollutants)and deposition on the stream bed (insoluble pollutants).

Soluble Pollutants

A4.12A wide range of models are available for waterquality assessment. These range from simple massbalance calculations to dynamic river impact models.Many of these models are utilised in Urban PollutionManagement (UPM) and are described in the UPMManual (The Foundation for Water Research, 1994).Most of these models have, however, been developed tocater for highly complex discharges, such as particularlypolluting storm sewer overflows. The modelling effortcannot normally be justified where more simple roadsdischarges are concerned; the cost of complex modelcalibration alone could exceed the cost of installing atreatment unit such as a small lagoon. In manyinstances, simple mass balance calculations (once thespecialist has completed the estimation of dischargequality, volume and frequency) may be sufficient toindicate whether treatment to control soluble pollutantsis necessary. In others, it may be appropriate to utilisethe statistical models used by the RAs in dischargeconsent modelling. These include INCARLO (forintermittent discharges), MCARLO (for continuous

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discharges), SIMCAT and QUALSIM. Such modelsrequire input of receiving water flows (usually the 95percent exceedence flow and the average) and knowledgeof upstream water quality. Flow data can either be takenfrom existing RA gauging stations, or can be estimatedusing catchment characteristics and geographic location.Water quality data can either be taken from the nearestRA sampling station or can be estimated based on RAmonitoring of similar waters. Only very rarely would itbe appropriate to instigate a field sampling programmeto determine existing water quality. If such a programmewere to be contemplated, sampling over a period of atleast one year (and preferably three years) would benecessary.

A4.13In all cases, the modelling effort expended shouldbe commensurate with the risk to the receiving water. Nospecific modelling approach is prescribed, although thedetailed proposals must be agreed by the OverseeingOrganisation and the RA before the work is undertaken.Modelling should focus on selected parameters only;soluble copper and total zinc may be appropriate,although for certain schemes, where a wider perspectiveis needed, other pollutants could also be modelled.

Insoluble Pollutants

A4.14While simplified modelling techniques can be ofvalue in assessing the need to control soluble pollutantconcentrations in the discharge, modelling of insolublepollutants is less straightforward. No simple method fordetermining the need for control of settleable materials inroad discharges is currently available. Although morecomplex dynamic river models may be utilised inparticularly complex river catchments, their use in themajority of cases would be inappropriate.

A4.15Relatively few studies have assessed the effect ofroad runoff on freshwater ecology, but a study carriedout by Maltby et al (1994a and 1994b) concluded thatcontaminants from road runoff may accumulate in thesediment, reaching concentrations which are greaterthan those present in the overlying water column.Maltby et al also suggested that most of the resultingmild sediment toxicity could be attributed tohydrocarbons rather than to heavy metals, and thatpolyaromatic hydrocarbons (PAHs) were likely to bethe most important. In laboratory tests, 6% fewerfreshwater shrimps (Gammarus pulex) survived after 14days incubation in sediments taken from downstream ofa discharge than after incubation in sediments takenfrom upstream of the same discharge. On the otherhand 43% of all streams investigated exhibited noecological impacts of the discharges, which arose fromthe M1 in Hertfordshire, notwithstanding that thestream systems studied were in general very small and

have low diluting capacity relative to the runoff volumesdischarged. Previous studies (Extence, 1978 forexample) have demonstrated that particulate materialfrom roads can also alter substrate characteristicsaffecting the distribution of burrowing animals,including chironomid larvae and tubificid worms.

A4.16In the absence of simple models to determine thelikely behaviour of solids in road discharges, thespecialist should consider the general characteristics ofthe receiving water, and the specific sensitivity to solidspollution, in determining the need for solids removal.Receiving waters having a very flat gradient, moderatedepth, flow restricting structures such as weirsdownstream of the proposed discharge, low flowrelative to that of the proposed discharge and anexisting tendency to accumulate sediments (often fromexisting urban discharges) are most prone to thepolluting effects of road runoff. That impact is,however, likely to be local to the point of dischargeitself as the water velocity will be so low thatdischarged solids will not be re-mobilised beyond theinitial point of settlement.

A4.17Discharges from small road drainage catchmentareas may be acceptable to the RA without pre-treatment in such waters, provided they are of lowenvironmental and recreational importance. Those withmoderate or steep gradients, shallow water and highturbulence levels are much less likely to accumulatesolids to a degree which could become environmentallylimiting. Possible exceptions to this are wheredischarges are made directly onto fish spawning areas(particularly those of salmon and trout), whereexcessive sediment accumulation may affect breedingsuccess. While such areas should be avoided wherepossible, they are only utilised by salmonids if thewater velocity is such that sediments are unlikely toaccumulate.

Lakes and Canals

A4.18It is recommended that the water qualityspecialist consider the residence or turn over times ofthe water body, sensitivity to pollution, use, ecologicalvalue, the ratio of road catchment area (and hencedischarge volume) to lake or canal volume and consultthe RA’s local pollution control officer in undertakingthe detailed assessment.

A4.19Canals, particularly those which are notregularly used by boats, can accumulate sedimentsfrom individual discharges at high concentrations. Therelatively low flow through canals is also such thatsmall oil spillages can produce an extensive slick. As aconsequence, the British Waterways Board normally

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request that the RA insist that an oil separator isinstalled prior to all road discharges to canals. Properlydesigned, oil separators can also contain accidentalspillages and remove insoluble pollutants throughsedimentation. Sufficient dilution is also usuallyavailable to ensure that soluble pollutants in routinerunoff do not cause measurable pollution. In normalcircumstances, therefore, further detailed modelling andassessment work will be unnecessary.

A4.20Where discharges are proposed to very small stillwater bodies, the specialist should consider theadditional potential for eutrophication as a consequenceof the discharge. Where larger lakes and ponds areinvolved, the lack of flow will limit the dispersion of anypollutants discharged, and hence consideration of thetotal diluting capacity of the lake, while potentiallyviable when considering the fate of soluble pollutants,will not be appropriate for pollutants which settle outrapidly on discharge. Again, in many instances the RAwill request that an oil separator or similar arrangementbe installed to protect the water from spillages and therisk of oil slicks. If this is the case, more detailedinvestigation is unlikely to be required.

Estuaries and the Coast

A4.21The substantial available dilution, coupled withtidal flows, are such that routine discharges from roadswould be of concern only if the receiving water has veryhigh ecological or recreational value. If the calculatedspillage risk return period is sufficiently high there may,however, be a need for spillage control facilities. It isvery unlikely that further investigation, beyond spillagerisk assessment, will be needed for such discharges.

Groundwaters

A4.22No discharge to ground will be accepted by theRA into those areas which are most susceptible togroundwater pollution (Inner Source Protection Zones),and will only be acceptable in exceptional circumstancesin Outer Source Protection Zones. Hence, discharges toground will only usually be accepted where theperceived risk is very low. In the Catchment Zone of thesource road discharges will be permitted only if theresults of an investigation are favourable and if adequateprecautions are taken. Again the RA will have to besatisfied that the risk of transfer of pollutants to theabstraction source is low.

A4.23Outside the source catchments but in ResourceProtection Zones, detailed investigation will still benecessary, and the RA are likely to request that at leastan oil separator is fitted to each discharge. If an oilseparator is used the risk of accidental spillage causing

groundwater pollution should be adequately controlled;all discharges to ground should also be via a systemsuch as a soakaway which should, if properly designed,remove the majority of the solid phase, and any residualoil associated with it, from the discharge. These factorsserve to limit the extent of any investigation required inthe less sensitive areas where discharge to ground maybe permissible, and in most cases, a deskhydrogeological study is likely to suffice. In all cases,however, the scope of the investigation should be agreedwith the RA at the outset.

Determination of Discharge Treatment Need andDesign

A4.24The primary objective of the assessment of waterquality impacts should be to design out potentialproblems at an early stage. The most effective form ofmitigation will always be to avoid the use of dischargelocations which could result in unacceptable pollution.Where this is not possible, because of engineering oreconomic constraints, the sub-division of the assessmentinto consideration of the need for flood control, spillagerisk, and insoluble and soluble pollutants wil l identifythe specific design objectives for control facilities ateach individual outfall. It will usually be possible toachieve all of the prescribed objectives using a singleengineered design, hence minimising costs and, veryimportantly, minimising land take requirements. Textscontaining design guidance include those listed in theBibliography of this CHAPTER.

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corrections within design manual for roads and …

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