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ThamesTideway.Comparisonofthemodelswithfielddata.

Executivesummary

The EU Urban Waste Water Treatment Directive (UWWTD) requires Combined Sewer Overflow(CSO) spills to occur only in unusual rainfall conditions. This note looks at the reliability of theTidewaysewerandwaterqualitymodelsandwhethertheTidewaymeetstheUWWTDcriteria.

WhereastheEuropeanCourtofJustice(ECJ)reliedontheThamesTidewayStrategicSteeringGroupthattherewereabout60spillsayear,followinglimitedfieldwork,eventhemodeloftheremainingCSOsshowsthat,afterthecompletionoftheLeetunnel,thegreatestnumberwilldroptoabout42.

However Ofwat concludes the sewer modelling considerably overestimates flooding from thesewers. Ofwat states the sewer modelling output for the existing condition is “unreliable andinaccurate”.Thereasonsforthisinclude(a)thelimitedrainfalldataand(b)thatthereisonlyspilldatafor9ofthe57CSOs.EvenThamesWater(TW)state“itisunlikelythatitwilleverbepossibletoacquiresufficientlycomprehensivedata”toproviderobustmodels.

TTSSG selected fish as representing the Tideway ecology. Whereas TTSSG reported an observedbaselineof8fishkillsperyear,since2003onlytwohavebeenreportedduetoAbbeyMillsspillsandtwodueTidewayCSOs(about21fish).Sincefishcanwithstandatleast10%mortalityeachyear,itwouldappearthattheTidewayecologyisalreadysustainable.

TheTWwaterqualitymodelshowsthat,postthe5SewageTreatmentWorks(STW)upgrades,(costabout£1.2bn)thereshouldbeabout3breachesofstandard1andnearly3ofstandard2ayearetc.FielddatashowstheupperTidewaybetweenmid2012andmid2015hadnobreachesand,sincemidSeptember2013,noneinthelowerTideway.Thusthewaterqualitymodellingisnotrobust.

TheWFDgooddissolvedoxygen(DO)conditionwasmet in theupperTideway frommid2012tomid2015and in the lowerTidewaysinceSeptember2014.However theDOconditions in2015 intheupperTidewaydeteriorated.ThamesWaterstatethey“makesureoursewersareasemptyaspossiblewheneverheavyrainisexpected..."Ofwatconsideredthatitis“unlikelythatpropertiescanberemovedfromtheriskoffloodingbyoperational improvementsalone.”ThusTWnewpumpingregimehaslimitedbenefitwhilstcausingenvironmentalharmandtheDOtodropfromWFDgoodtomoderate.TheECJWesercasefindsthatDOdeteriorationfromgoodmustbeprevented.TheWFDrequires that “all practical steps are taken to prevent deterioration”. TW should return to theirpreviouspumpingregimewhichprovidedgoodDOintheupperTideway.

Thus,providedTWreturntotheirpreviouspumpingregimeintheupperTideway,thereshouldbenofailureofanydissolvedoxygenstandard.ThuswouldnottheobjectiveoftheUWWTDtoprotecttheenvironmentagainstdischargesbemet?The UWWTD requires systems which are “in accordance with the best technical knowledge notentailing excessive costs.” The tunnelwas compared in 2003with full sewer separation and fullSuDs.Since thenRealTimeControlhasbeendevelopedand thishas reduced thecostof floodingmeasures in Cardiff from £100m to £5m. No study has been done of a combination of partialmeasuresusingcurrentbesttechnicalknowledge.Suchasystemcouldwellsave£3bnandtime.

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1Introduction

TheobjectiveoftheUrbanWasteWaterTreatmentDirectiveis“toprotecttheenvironmentfromtheadverseeffectsof...waterdischarges.”Atthetimeoftheselectionofthetunnelthesewermodeland the Tideway water quality model were used to assess whether the spill frequency and theTideway water quality breached the particular dissolved oxygen standards set for it. Thus thesolutionselectedtomeettheUWWTDdependedonthereliabilityofthemodels.

TheDirectivesays inthefootnotetoannex1Athatspillsshouldonlybeallowedunderconditionssuch as “unusually heavy rainfall”. Unusual is not defined in theUWWTD but the ECJ judgementOctober2012,para28,statesthattheEuropeanCommission(EC)“doesnotproposeastrict20spillrulebutpointsoutthatthemoreanoverflowspills..themorelikelyitisthattheoverflow’soperationisnotincompliancewithDirective91/271.”

In his letter of 24th February 2014, the thenMinister Lord deMauley stated that ”after the Leetunnelisoperational,spillsofbetween50and60timesayearwillspillfromtheCSOsintothetidalThames.”

Thus it is clear that it is important to know the spill frequency of the CSOs and their impactsufficiently accurately. This note looks at the robustness of the models and whether they aresufficiently reliable to underpin expenditure of about £4bn and whether the Tideway meets theUWWTDrequirements.

2BasisoftheEuropeanCourtJudgement.

Theevidence submitted to theEuropeanCourtof Justice (ECJ)was theThamesTidewayStrategicStudyGroup(TTSSG)reportsof2005.“TheCommission,relyingonaTTSSreportofFebruary2005,observes that therewereapproximately60wastewaterdischarges fromstormwateroverflows inLondonperyear...” ECJ judgementpara 85.TheTTSSG in its costbenefit report, page 20, also statesthattheobservedbaselineis8fishkillsperyear.ThustheECJbaseditsfindingsthattheTidewaywasnon-compliantwiththeUWWTDontheoriginalsituationasfoundbytheTTSSGin2005,beforethebenefitstobeachievedbytheSTWupgradesandLeetunnel.

3OfwatassessmentoftheThamesWaterhydraulicsewermodelforLondon.

ThamesWaterhasuseditssewermodeltoassessCSOspillfrequencyandtoassessthenumberofpropertiesthataresubjecttofloodingwithacertainfrequency.

OfwathasissuedanoticeThamesWater:sewerfloodingdated22July2014.Thissaysthat,basedlargely on its sewer hydraulic model, Thames Water (TW) has misreported sewer flooding data.ThetextandparanumbersbelowaretakenfromtheOfwatreport.

“there should be a goodmatch between the properties themodel predicts as flooding and thosereportedasflooding.”Para47.

“Itisimportanttous”Ofwat“thattheReportersatisfieshimselfthatthehydraulicmodelshavebeendevelopedtoanappropriatestandardandquality.”Para22.“inanumberofcasestherewereverylimitednumbersofactual reported flooding incidents toverify themodelledassessments.We” the

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Reporter “are therefore concerned that a proportion of the Company’s claimed outputs are notadequatelysupported.”Para30.

“Ofwatcarriedoutdetailedanalysisof832outof867propertiesreportedasremovedbycompanyaction.Thesepropertieswerechosenbecausetheywerecoveredby4 largescheme inLondonandrepresented96%oftherelevantproperties”identifiedasfloodingbythehydraulicmodel.Para33.

“TheresultsofOfwat’sinvestigationindicatesthatabout73%ofthepropertiesreviewedshouldnothavebeenremovedbycompanyactionastheyshouldnothavebeenonthehighriskregisterinthefirstplace.”Para80

“Adiscrepancyofsuchmagnitude leadsOfwattoconcludethatThamesWater’shydraulicmodelsarenotverified in theway that the reporting requirementsdescribeandare thereforenotverifiedhydraulicmodelsforthispurpose.”para47

“Putsimply,inlightofthereportingrequirementsahydraulicmodelcannotbeusedonastand-alonebasistoverifyitsownresults.”Para43.

“OfwatissatisfiedthatThamesWatersubmittedunreliableandinaccurateinformation”,whereasva,

Conclusion.

ThusOfwatconsidertheThamesWatersewermodelisnottoanappropriatestandard,considerablyover-predicts sewer flooding, and provides unreliable and inaccurate information. Further such amodelcannotbeusedtoverifyitsownresults.

4Reasonsofoverestimateofmodelledspillfrequency

Thedata inputtothemodels isdescribedbyThamesWater intheTTTT2006Vol2ModellingandCompliancepage10whichstates“Obviously,comprehensiveflowandqualitydataisessentialforallthesedischarges if individualrainfalleventsaretobemodelledprecisely.“Many individualrainfalleventsweremodelled. “Of the57CSOswhichdischarge to theTideway, indicative flowdataonlyexistsforaround9ofthepumpeddischargesandthereissomehistoricaldata.Thereisnoflowdataandvirtuallynoqualitydatafortheremainder.”

As an illustration, the rainfall radar plots show substantial local rainfall variation across London,rainfallchangingappreciablyoverjustafewhundredmetres.

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Whilsttheradarplotswouldhaveprovidedagoodrepresentationoftheactualrainfall,theywerefoundtobeinsufficientlyreliable,sowerenotused.

Insteadrainfallonabout80%oftheareacontributingtothecombinedsewerstobeconnectedto

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the Thames tunnel is based on just 4 single point raingauges spaced many kms apart, Thepreparationandapplicationofthemodellingframeworkforthecompliancetestingofoptions,Auditreport24thSeptember2003.

These4pointraingaugescannotprovideanaccuratebasisformodellingstormsoveralargeurbanarea.

Further there is no record shown, ormention in the report, of runoff variation between virtuallyimpermeablepavedareasandparklandareaswithterracegravelsubsoil,suchasHydePark,wherestormrunoffwouldhavebeenmuchlower.

The Audit report continued “Under these conditions it is unlikely that it will ever be possible toacquiresufficientlycomprehensivedata.”tomodelspillfrequencysufficientlyaccurately.

Thus the rainfall and runoffmodel does appear tobebasedon insufficiently comprehensivedataandtosignificantlyoverestimatespillfrequency.

5Reliabilityofmodelledspillfrequencyforfutureyears.

PopulationgrowthinLondon.

IthasbeensaidfrequentlybyThamesWaterthat,becauseLondon’soverallpopulationisgrowing,then spill frequency will also grow. “The population figure used in the model represents 2023conditions”DevelopmentConsentOrderApplication(DCO)7.23page14.

It is true that the population of Greater London is now growing. However, it is interesting tocomparethepopulationdensitiesin1939withthatin2015,seeplansonpage25oftheEconomistof 7th February 2015. The total population of London is much the same, having gone downappreciably in themeantimeand then risen in recent years.However thepopulation in the innerboroughshasgonedownandintheouterboroughshas,andiscontinuing,togoup.

For reasons of historical growth, London is split into the old central part that is predominantlycombined sewers collected by the interceptors and with combined sewer over flows into theTideway. The more modern suburbs are where the sewers are largely separated foul and stormwater.MuchofthemoremodernsuburbsaretakentonewerSTWsuchasMogdenandDeephamsrather than connected by the interceptors to Beckton and Crossness STW. Thus it is not thepopulation of all of London that matters but the population contributing to the combinedinterceptorsystemintheoldcentralpartofLondon.

TWassumptionofincreaseinsewerdryweatherflow

ThehistogrambelowshowshowThamesWaterhaveprojectedthesewerflowsintheBecktonandCrossnessSTWcatchment.Thisassumesasewerinfiltrationflowinblueandaflowinredbasedonflowfromagrowingpopulationwithaconstantpercapitawateruse.Thus,theyassumethatthereareappreciableincreasesinsewerdryweatherflowoverfutureyears,andhenceinspillfrequencyfromthe2006baseyeartothedesignyear,assumedatthattimetobe2021.

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Projectionofwatersupplied

TheareasservedbytheTidewaysewersarenotexactlythesameastheareasservedbytheThamesWater water supply system but they are not much different and one could assume a similarrelationship.

In their water supply zones Thames Water are promoting water demand management andincreasingsmartmeteringofwatersuppliedso, in reality, thewater supplied,andhencereachingthesewers,willbeaffectedbythosemeasuresandwillbegoingdown.ThenumbersintheThamesWaterfinalWaterResourcesManagementPlansWRMP09and14forwaterintosupplyare

2006 2180Ml/d

2012/13 2028Ml/d

2020/21 1948Ml/d.

2039/40 1993Ml/d

TheeffectofthisontheflowinthesewersisshownbytheblackmarksonthehistogramabovefortheBecktoncatchment.Crossnesswouldbesimilar.

Sinceitistheexcessflowabovesewercapacitythatleadstospills,thespillfrequencyandvolumeassumptions in the TW sewer model would be significantly greater than those based on flowsprojectedbyTWitself.

Comparisonofassessments

Thus,fromthequotedpopulationprojections,by2020thedryweatherflowhasbeenassumedbyThamesWater to increase from2006byabout24%, see imageabove. TheDevelopmentConsent

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Order Application (DCO) document states that “at peak times some sewers are running at 80%capacity”,page13.Thustheflowinthosesewerswould,by2023,reachabout99%capacity,hencespillveryfrequently.

BasedontheThamesWaterWRMPsnumbers,by2023,therewouldbeareductionofabout10%inwatersuppliedandhenceinsewerdryweatherflow.Thus,forthosesewerswhichwererunningat80%capacityasquotedbyTWintheDCOdocument,thecapacityusedatpeaktimesin2023wouldactuallybeonlyabout72%ofcapacity.Thisreductionindryweatherflowfrom99%ofcapacityto72%ofcapacity,wouldmakeasignificantdifferenceinthefrequencyandvolumeofspill.

Conclusions

Thus the TW sewer model for the future further underestimates the spare sewer dry weathercapacity,andthusfurtheroverestimatestheCSOspillfrequency.

6Modelledspills.

Dataavailability

AsfarasIamawaretherearefew,ifany,reliableflowmeasurementsinthesewernetwork,so,ifthatisstillso,itwouldbedifficulttoeitherassesstheparticulareventconditionsortocalibratethesewermodelwithreliability.

“Ofthe57CSOwhichdischargetotheTideway,indicativeflowdataonlyexistsforaround9ofthepumpeddischargesandthereissomehistoricaldata.Thereisnoflowdataandvirtuallynoqualitydata for the remainder. Obviously, comprehensive flow and quality data is essential for all thesedischarges if individual rainfalleventsaretobemodelledprecisely.“ ThamesTidewayTunnelandTreatment-OptionDevelopment(TTTT)2006Vol2page10

AtthetimeoftheTTSSGtheonlydataaboutthevolumeofspillsthatwasavailablewasthepumprunhoursofthe8pumpingstations.Thevolumedischargedbythemwasbasedonassumedpumpdischargecharacteristics.Consideringthatthesepumpsareforsewageandareofvariableageandthedifficultyofcalibratingthem,thentheaccuracyoftheassumeddischargecharacteristicmaynotbethatreliable.Further,asflowsfromdifferentcontributingsewersarrive,itispossiblethatpumpsstartandstopseveraltimesduringasingleevent.Thusthepumpsmaystopandstartseveraltimesduringasinglestorm,makingitlooklikeseveraldifferentspills.

LetuslookatthemostfrequentspillingCSOs.ThebasecaseshouldbeoncetheSTWupgradeshavebeencompletedandoncetheLeetunnelisoperational,dueabouttheendof2015.

Greenwich

The quoted modelled existing spill frequency at Greenwich in the Needs Report of 2010 is 51spills/year. This is shownDCOEngineeringDesign Statement7.18,Table 3.2 asbeing28 in thebasecondition, 2020s. This drop is believed to be because the uprating of the Crossness STW hasremovedabottleneckinthesystem,thushalvingthespillvolumeatGreenwichandabouthalvingthespillfrequency.Thisimprovementisbelievedtohavealreadytakenplace.

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AbbeyMills

OncetheLeetunnel isoperational,abouttheendof2015,thentheabout50modelledspills/yearwilldroptozero.

WestPutneyCSO

TheoriginalmodellingoftheWestPutneyCSOshowedamodelledspillfrequencyof59spills/year.ThisCSOwasmonitoredforaboutayearanditwasfoundthattheactualspillfrequencywasabout26spills/year,TWNeedsreport2010AppendixE.SimilarcorrectionsreducedthemodelledspillsatFrogmoreBuckholdRoadfrom29spills/yearto19spills/year.

ActonCSO

TheprovisionoffurtherdetentiontanksatActonhasreducedthemodelledspillfrequencyforActonCSOfrom40modelledspills/yearto17spills/year.

SavoyStreetCSO

Modelling intheDCOhasshownthatSavoyStCSOmodelledspill frequencyhasdroppedfrom47spills/yearto20spills/year.

MogdenSTW

The thenMinister, LorddeMauley, stated in Parliament that in its first formal year of operation,2013/14,Mogdenspilledon54days.TheMogdenstormspill is fromthestormtankssodoesnotreceive secondary treatment so,under theUWWTD, ithasalso tobecounted asan intermittentspillsimilartoCSOspills.TheEnvironmentAgency(EA)emailtoChrisBinnieof24thJuly2014,states“...theoverflow fromMogdenSTWstorm tanks is regardedas satisfactoryunder the termsof theUrbanWasteWaterTreatmentDirective.”OntheassumptionthatsignificantspillsonadjacentdaysarethesameeventthenIassessedthattherewere17spillevents.Thisisclosetothefrequencyof20suggestedbytheECand ispresumablywhytheEAconsiderthattheMogdenspill frequency isacceptable.Hammersmith

ThemodelledspillfrequencyforHammersmithwas50spills/year.ThamesWaterprovidedischargenotificationstorowersandothersonawebsitewhenevertheHammersmithPumpingStationspills.Oneassumptionisthat, liketheMogdenassessmentabove,dischargenotificationsonconsecutivedays are the same stormevent. This is reasonable as the contributing sewer network is long andstormflowsfromthesamestormcanarrivefromdifferentsewercatchmentsatdifferenttimes.ThedischargenotificationsshowHammersmithPShasdischarged61timesfromJuly2012toFebruary2015. This is an average of 24 spills a year. This includes 2014which the Centre for Ecology andHydrology(CEH)describeas“the4thwettestyearonrecordbackto1910”.Thusit isreasonabletoassumethatthemodelled50spills/yearisactuallyabout24spills/year.

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Overall.

Thusonecanassumethat,becausethereduction inwater intosupply inTWWRMP14meansthesewer dry weather flowwill be less in the 2020s than in the base case of 2006, then the worstcondition is not the 2020s but the existing condition. The DCO 7.18 Table 3.2 shows the highestmodelledspillfrequencyas42spills/yearatFalconbridgePSandnoothersabove40spills/year.

Thusitisclearthat,withoutevenconsideringwhetherthemodelover-estimatesspillfrequency,themodelled spill frequency post the Lee tunnel, due at the end of 2015, is not the stated 50 to 60spills/yearbutnomorethanabout42spills/year.

Clearly,asthenotehasdemonstratedthatthemodelsoverestimatespillfrequency,theactualspillfrequencyismuchclosertothe20spillsayeartalkedaboutbytheECthanpreviouslyassumed.

7Importanceofspills

The European Commission Additional Reasoned Opinion dated 27/11/2008 states in para 21 “anacceptable spill frequency ...taking place at times of heavy rainfall with a varied spill frequencydependingonlocalsituationsandinparticularthestatusofthereceivingwatersineachcase.”ThustheECconsiderparticularlythestatusofthereceivingwaters.

The Advocate General’s Opinion of the infraction proceedings, January 2012 para 48 states “Onseveraloccasions,however,bothinthepre-litigationstageandbeforetheCourt,theCommissiondidindicate that, as a rule,exceeding the limit of 20 overflows a yearwould be a cause for concern,suggestingapossible failure to fulfil obligations”Clearly theECdo considermore than20 spills ayearaspotentiallyacceptableprovidingtheobjectiveoftheUWWTDofprotectingtheenvironmentwasnotbreached.

The EnvironmentAgency have stated in the notes of themeeting on 25th September 2014 “Spillsalone is not regarded by the Environment Agency as an indicator of failure to comply with theUWWTD.” “provided spills have not caused a significant adverse impact on the quality of theriver...overflowisregardedassatisfactory.”ThisisaftertheissueoftheECJJudgementsomusthavetaken that, and the Directive footnote about unusual rainfall, into account, in affirming that it ismeetingtheobjectiveof theUUTWDofprotectingtheenvironmentthatmatters. Inwhichcase itwouldbetheimpactofCSOspillsonthewaterqualityoftheTidewaythatwouldmatter.

8Alternativemeasurestoreducespillfrequencyfurther.

The UWWTD directive states Annex 1 A “The design, construction andmaintenance of collectingsystems shall be undertaken in accordance with the best technical knowledge not entailingexcessivecosts.”Myemboldening. TheDefraRiverBasinPlanningGuidance20089.5states”TheWFDrequirement istomakejudgementsaboutthemostcosteffectivecombinationofmeasures...”Myemboldening.

The current selection of a tunnel would reduce spill frequency to about 3 spills/year but theselection process has not taken account of current best technical knowledge, and at about £4bnmight be described as excessive cost. How can this Directive requirement be met withoutconsideringacombinationofthelatesttechnicalknowledge?

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WereitconsiderednecessarytoreducetheCSOspillsfurther,thentherearemanywaysthiscouldbe done. The alternatives considered at the time the tunnel was selected, 2003, included sewerseparationoftheentireCSOareaandSuDscoveringthewholearea.Noconsiderationwasgiventoacombinationofpartialmeasuresusedwheretheycouldprovidemostbenefit.

Since2003 technologyhasadvancedmuch.RealTimeControlhasbeendeveloped.Whenused inCardiffthecostofreducingfloodingwasreducedfrom£100mforaconventionalschemetoabout£5m.

Partial SuDsat Llanellihas reduced thecostofa conventional schemeof£600mtoabout£145m.Whereas TW instructed its consultants to ignore infiltration as a means to reduce sewer flows, Bloomberg reportTunnelVisionp19 states“ infiltrationSuDscouldbedeveloped, subject tosometechnicaladjustments,across67%ofLondon’ssurfacearea.Thisconclusionis incontradictionwithThamesWater’sargumentthatSuDscannotbeimplementedinLondonbecauseitwasbuiltonclay.”

The storm water from new developments along the Tideway could be connected direct to theTidewayratherthanthecombinedsewersystem.ThiswasdonesuccessfullyineastLondonbytheLondonDocklandsDevelopmentCorporation.DetentiontanksatActonreducedtheActonCSOspillfrequencyfrom40spillsayearto17spillsayear.

ThusastudyofhowacombinationofpartialmeasurescouldreduceCSOspillfrequencytowhateverfrequency was chosen might well reduce expenditure by about £3bn and shorten the time toachievebenefit.

AnyactiontoreduceCSOspillfrequencyfurther,would,ofcourse,furtherimproveTidewaywaterquality.

9FishkillsintheTideway

TheTTSSGinitscostbenefitreport,page20,statesthatthe“observedbaselineis8fishkillsperyear”.Thus the selection of the tunnel and its benefit assessment was based on this information. Thiswouldbetheequivalentof80fishkillsovertenyears.

TheEnvironmentAgencyRecordoffishkillsintheTideway,senttoChrisBinnieon13thJanuary2014givestherecordedfishkillsintheTidewayoverthe10yearsfrom2003to2013.DuringalmostallofthistimetherehadbeennoupgradingoftheSTWs.Thisrecordshows3fishkillsduetotheMogdenSTWspillsofuntreatedsewage,2duetoAbbeyMillsspills,andone,ofonefish,duetospillsfromtheCSOstobeconnectedtotheThamestunnel. Whilst it ispossiblethatotherfishkillsoccurredduringthisperiod,becausefishkillsoccurduringthesummerwhenthedaylighthoursarelongandtheriveristidalsoanydeadfishcouldbeseenovera15kmtidalexcursion,itisdoubtfulifmany,orany,morewouldhaveoccurred.ThustheTTSSGassessmentanditscostbenefitassessmentwouldhavebeendoneonafalsepremiseaboutfishkills.

Duringthesummerof2015therewasonefurtherfishkillofsome20fishrelatedtoCSOdischargeinthe Hammersmith/Cadogan area. However this period is considered as anomalous, as discussedlater. Whatever, fishermen could fish this number every week and the numbers of fish in theTidewaystillbeclassifiedassustainable,seebelow.

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Further,theobjectiveoftheUrbanWasteWaterTreatmentDirectiveis“toprotecttheenvironmentfrom the adverse effects of... water discharges.” The TTSSG selected fish as the representativespeciesfortheenvironment.TWNeedsreportAppendixFpage23setsoutthepercentagemortality

which is sustainable. For instanceaproportionof fish caughtby fishermencan stillmean the fishpopulationissustainable.Forallspeciesthesustainablemortality is10%ormore.TherearemanytensofthousandsoffishintheTideway.Thus,accordingtotheEArecordoffishkills,thenumberoffish,andhencetheenvironmentoftheTideway,wouldappeartohavebeensustainableforthelastdecade.

10Dissolvedoxygenmodeloutputs

AtthetimeoftheTTSSGstudiestherewerenospecificecologicalrequirementsfortheTideway.TheTTSSGconcludedthatfishwerethebest indicatorspecies.Trialsoftheimpactofdissolvedoxygenconditions on a representative suite of fish species were carried out and four dissolved oxygenstandardswereset.

The water quality model was run to demonstrate dissolved oxygen conditions under varioussituationsEftecUpdateoftheeconomicvaluationofThamesTidewayEnvironmentalBenefits2015.TableA2.3

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Thiscoversa41yearperiod.Thusthecurrentsituation isofSTWimprovements,Mogden inearly2012,andBeckton/Crossnessinearly2013,butnoLeetunnel.Thusthemodelshowsthereshouldbeabout3failuresofthe4mg/lstandard1eachyear,nearly3failures/yearof3mg/lstandard2andonefailure/yearof1.5mg/lstandard1.

11Comparisonofmodelledandactualdissolvedoxygenconditions.

General

TheEnvironmentAgencyhasestablished9AutomaticQualityMonitoringStations(AQMS)alongtheTideway. Thesemonitor a number of parameters including dissolved oxygen (DO) conditions andrecordtheseevery15minutes.AresearchstudentatExeterhasplottedthedissolvedoxygenforthevarious AQMS up to the end of 2014, see Annex A. Formal assessment ofwhether the Tidewaybreachesthestandardsisbyhalftideplots.Ihavethoseforthecriticalsummerperiodof2014and2015butnotfortheearlieryears.However,theannualplotsoftheworstAQMSstationsdogiveaverygoodindication.ThisisbecausetheyshowwhethertheDOdropsbelowaparticularthresholdandifitdoesnotthentheTidewaycannotfailthatparticularstandard.ThecriticalperiodwhenDObreachesoccur isbetweenearly July and theendof September,becausewater temperaturesarehigher and river flows lower during this period. Since some of the standards have return periodslongerthanoneyear,theEnvironmentAgencyconsidersthatoneneedsthespecificlengthoftimebeforeonecanbesurethattheDOstandardsaremet.Thataspectisconsideredinalatersection,thissectionjustconsideringifthestandardswerebreachedinaparticularyear.

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UpperTideway

TheupperTideway(BrentfordtoChelsea) is impactedbytheHammersmithtoHeathwallpumpingstations.After analysing thehalf tideplots Putneyappears as the representativeof theworstDOconditions.Unfortunately the annual plot for 2012 is not correct so, for 2011 and 2012, the nextdownstreamAQMSCadogan(Chelsea)hasbeenshown,seeAnnexA.

Lookingat2011,beforeMogdenSTWwasupgraded,onecanseethatdissolvedoxygenconditionsdropped below 3mg/l on a number of occasions, and clearly the Tideway failed to meet thestandards.Looking at 2012 therewas only one occasionwhenDOdropped below4mg/l and dipped below3mg/lforonly5hourscomparedwiththe19hoursallowedinthestandard.Theseappeartobefortooshortaperiodtobreachthestandardsthatyear.Looking at 2013 itwould appear that theDOonly droppedbelow4mg/l for a fewhours andnotbelow3mg/latall.In 2014, the Environment Agency state, Douglas/Binnie 27th March 2015 “I have attached plotscovering theperiod14th July Flood to 15th Sept Ebb inclusive. Youwill see that this is a significanteventinthattherewasnobreachoftheDOstandards...“LookingattheAnnexAplot,onecanseethatbreachescouldnothaveoccurredduringtherestoftheyear.

LowerTideway

ForthestretchoftheTidewayaffectedbyAbbeyMillsandBecktonSTWspills,definedhereasthelowerTideway,themostrepresentativeAQMSisBarrierGardens.BeforetheBecktonandCrossnessSTW were upgraded, about the end of 2013, this stretch failed standard 1, 4mg/l, regularly.However,sinceSeptember2013,therehasbeennobreachofthestandards.NotethisisbeforetheLeetunnel,whichwillabouthalvethevolumeofCSOdischarges,becomesoperational,dueabouttheendof2015

Comparisonwiththemodelling

The 41 years of modelling for the STW upgrade condition shows that there should be about 3failures of standard 1 and nearly 3 failures of standard 2 each year. Thus themodelling clearlyconsiderablyoverestimatesbreachesofthestandards.

Conclusion

In conclusion the water quality modelling cannot be considered robust and does not sufficientlyreflectactualconditionstobeusedasabasisforexpenditureof£4bnonthetunnel.

12WaterFrameworkDirective(WFD)Toachievegoodecological statusunder theWFDthedissolvedoxygenhas tobeabove5mg/l for95%ofthetime.ThetablebelowfromtheExeterUniversityanalysisbyLaurenceClaxtonshowsthe

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dissolvedoxygencontent inmg/lat the95%condition.Thusallnumbersabove5mg/lwouldpasstheWFDDOstandard.Notethenumbersfor2015wereforthefirstpartoftheyearonlysoarenotrelevant.Pleaseignoreallthecolourcodingasitismisleading.

For 2013, and 2014 this shows that for the upper Tideway, Brentford to Cadogan Gardens, thedissolved oxygen was above 5mg/l for more than 95% of the time at each AQMS. Thus Gooddissolvedoxygenwasachieved.LookingattheannualplotforBrentfordin2012showsthatallthereadingsbelow5mg/loccurredbeforeJunebaroneshortdipinJuly.Thus,postmid2012,Brentfordalsopassed.Thus, frommid2012tomid2015,theWFDconditionsforgoodwereachieved intheupperTideway.ThelowerTideway,BarrierGardens,etc,the95%wasgenerallyjustbelow5mg/l,(albeitPurfleetin2014at5.02wasverymarginallyabove.)Thusduring2014DOinthelowerTidewaywasmoderate.

13Anomalyof2015waterquality

ChangeinwaterqualityintheupperTidewayThusthankstotheMogdenSTWupgrade,theperiodfrommid2012tomid2015doesseemtohaveestablishedanewandbetternormintheupperTidewaywithnobreachesofthestandards.In contrast for 2015, bymy analysis, the upper Tideway drops back tomoderateWFD dissolvedoxygenandbreachesstandards2and3.Based on the plots I have received from the EA for the critical 2015 summer period, the lowerTidewayhasalmostnoAQMSreadingswhicharebelow5mg/l,thusitsDObecomesgood.Thusforalmostadjacentstretchesinthesameriver,andhencesubjecttothesameriverconditions,theupstreamwhichwasgoodhasbecomemoderateandthedownstreamthatwasmoderatehas

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becomegood!ThustheupperTidewayDOreadingsfor2015appeartobeanunexplainedanomaly.It would appear that this could only be caused by a change of operational regime of the upperTidewaypumpingstations.Asanillustrationbelowisthehalf-tideplotofwhatisprobablytheworstconditionin2014and2015.

In2014 thedissolvedoxygen in theupper Tidewayand the lowerTidewayare similar. TheupperTidewayconditionwassimilarin2013.Howeverin2015,forasimilarevent,thedissolvedoxygenisconsiderablydifferentbetweentheupperTidewayandthelowerTideway,asshownbythehalftideplotbelow.ThisshowsconsiderabledeteriorationintheupperTideway.

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ReasonforthedeteriorationintheupperTideway

Couldthedifferencebebecauseofachangeintherainfall?Ihavebeenunabletoobtainrelevantdailyrainfallfigures.HoweverIhaveobtainedmonthlyrainfalltotalsforHeathrow.Fortherelevanttwomonthsintheplotsabove,theAugust2014amountwas97.6mmandtheJuly2015amountwas71.8mm.ThiswouldindicatethatthesubstantialdeteriorationinwaterqualityintheupperTidewayisunlikelytobebecauseofchangeinrainfall.

Inarecentpressrelease,Builder&Engineer3rdNovember2015,RichardAylardofTWstates.“Wework really hard to make sure our sewers are as empty as possible whenever heavy rain isexpected..."

ThiscanonlybedonebyThamesWaterpumpingsewage fromthecombinedsewers. If thiswerealong the sewer system, then there would be less storm discharge to the upper Tideway, henceconditions in theupperTidewaywould improve.Howevertheydeteriorate.Thus, toprovideextrasewer capacity and hence potentially reduce on- land storm flooding, the sewer contents wouldhavetobepumpedtotheTideway.Howeverthesewagebeingpumpedfromthecombinedsewerswouldberawsewageorthefirstflush.Thisismuchmoreconcentratedthanthemixtureofstormwater and sewage pumped previously to the Tideway and hence the revised pumping system ismore polluting of the Tideway. That would explain why the 2015 dissolved oxygen in theHammersmith/ChelseasectionoftheTidewayisappreciablylowerduringstormeventsthanthatin2014.HencetheworseDOconditionsintheupperTidewayinthesummerof2015.DidThamesWaterneedtopumptoalleviatehousehold flooding? Thenumbersofpropertiesaresetoutfor2008-9and2009-10,OfwatThamesWater:sewerfloodingpage13.Therewereatotalof5.77 million domestic properties connected to the sewer system in the whole Thames Waterseweredareain2009-10ofwhichtheCSOareatobeconnectedtotheThamestunnelmightbeoftheorderofaboutathird.Floodingcanoccurforanumberofreasonsincluding,equipmentfailure,blockagessuchasfatballs,sewercollapses,andsevereweather.Asanillustration,thetable,Ofwatsewerfloodingnoticepage13,showsthatin2008-9therewere19propertiesinthewholeTWsewerareafloodedduetosevereweather.Thisnumberwouldvaryfromyeartoyeardependingonactualweatherconditions.ThereisnobreakdownofthisnumbertoshowthenumberintheTidewayCSOarea,but,consideringthattheuppersewersandhighandmediumlevelinterceptorshavefixedlevelinterconnecting weirs, then the area of the London CSO that could benefit from pumping actionmust be small, maybe a tenth of the whole Thames Water sewer area, hence the number ofpropertiesaffectedbyflooding intheLondonCSOareathatcouldbenefit, ienot floodbecauseofoperationoftheCSOpumpingstations,mustbeverysmall.Ofwat ThamesWater: Sewer flooding states para 15 “It is unlikely that properties can be removedfromtheriskoffloodingbyoperationalimprovementsalone.”

Thus, there does not seem to be sufficient reason for Thames Water to have changed its CSOpumpingregimeandthuscausedeteriorationofthedissolvedoxygenandharmtotheecologyandtheenvironment.

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ECJrulingondeteriorationintherecentWesercase.

On1stJuly2015theEuropeanCourtruledintheWesercaseC-461/13.

“MemberStatesshallimplementthenecessarymeasurestopreventdeteriorationofthestatusofallbodiesofsurfacewater(obligationtopreventdeterioration).”

“The concept of “deterioration of the status” of a body of surface water in Article 4(1)(a)(i) ofDirective2000/60mustbeinterpretedasmeaningthatthereisdeteriorationassoonasthestatusofat least one of the quality elements, within the meaning of Annex V to the directive” Annex Vincludes“oxygenationconditions”“fallsbyoneclass,evenifthatfalldoesnotresultinadropoftheclassificationofthebodyofsurfacewaterasawhole.”

Indeed, as shown above, the dissolved oxygen in the upper Tideway water body, Brentford toChelsea,hasdeterioratedfromgoodinmid2012tomid2015tomoderatein2015.

“It follows that, unless a derogation is granted” which I understand has not happened “anydeteriorationof the statusof abodyofwatermustbeprevented, irrespective of the longer termplanningprovidedby managementplansandprogrammesofmeasures.Theobligationtopreventdeterioration of the status of bodies of surface water remains binding at each stage ofimplementation ofDirective 2000/60.” Thus the future benefit of the tunnel, or othermeasures,cannotremovetheobligationtomaintaingooddissolvedoxygenconditionsnow.

Thereisanallowancefortemporarydeteriorationundercertaincircumstances.“Article4section6Temporarydeteriorationinthestatusofbodiesofwatershallnotbeinbreachoftherequirementsofthis Directive if this is the result of circumstances of natural cause or force majeur which areexceptionalorcouldnotreasonablyhavebeenforeseen,inparticularextremefloodsandprolongeddroughts, or the result of circumstances due to accidents which could not reasonably have beenforeseen,whenallthefollowingconditionshavebeenmet.

However the unusually low dissolved oxygen happened on 24/25th July 2015 and again on 27thAugust2015,sotherainfalleventswerenotexceptional.

Sincethedeteriorationappears tobetheresultofpredetermineddirectactionbyThamesWater,thenthecircumstanceswerenotduetoaccidentswhichcouldnothavebeenforeseen.AccordingtoRichardAylard theyweredue todeliberateactsbyThames Water“Wework reallyhard tomakesureoursewersareasemptyaspossiblewheneverheavyrainisexpected..."

WFDArticle4 section6continues“Allpractical stepsare taken toprevent furtherdeterioration instatus...” Thus ThamesWatermust be instructed to return to the operational regimewhich tookplacebetweenmid2012andmid2015andresultedingooddissolvedoxygenintheupperTideway.

Itmightbearguedthateitherthelengthoftime,3years,ortheextentofthewaterbody,Brentfordto Chelsea, was not sufficient. However it is clear that, as the section from Barrier Gardens toPurfleetalsomeetsthegooddissolvedoxygen,then,withouttheactionwhichresultedinthe2015anomaly , thewhole Tideway, with the Lee tunnel but without the need for the Thames tunnel,would in futurebe classifiedas gooddissolvedoxygenat some time in the future, thuswouldbedeterioratedbythecontinuingactionwhichcausedthe2015anomaly.

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Conclusion

Thus, in conclusion, should not 2015 dissolved oxygen conditions in the upper Tideway beconsideredananomaly,andThamesWaterberequiredtoreturntotheCSOpumpingregimewhichithasoperatedintheprevious3yearswhichresultedinWFDgooddissolvedoxygenconditionsintheupperTideway?

14Tidewaywaterquality

Thiswouldmean that the Tidewaywould revert to the previous condition. Since there appear tohavebeennoDObreaches in theupperTidewaybetweenmid2012andmid2015 it seemsmostunlikely that therewouldsufficientbreachesof thedissolvedoxygenstandards tocause failureoftheTTSSGstandards.

ForthelowerTideway,sincetheupgradingoftheBecktonandCrossnessSTWtherewasnobreachofthestandardsin2014orinthesummerof2015,thusonewouldexpectthatsituationtocontinue.InanycasetheLeetunnelisduetobecomeoperationalattheendof2015thusreducingthetotalspillintotheTidewaybyabouthalf,sotherewouldbenegligibleriskofthelowerTidewayfailingthestandardsinfuture.

Lookedatanotherway,standard1allows1breacheveryyearbuttherewerenobreachesin2014or 2015. The provision of the Lee tunnel, due at the end of 2015, will much reduce the risk ofbreachesoccurring.

For standard 3 the model, see table A 2.3 in section 10, shows that, without the Lee tunnel,modelledbreachfrequencywouldbe66breachesin41years.HowevertherewerenobreachesintheupperTidewayfrommid2012tomid2015andnoneinthelowerTidewayin2014and2015.TheLee tunnel would reduce modelled breaches from 66 to 12 breaches. Thus it is clear that theaddition of the Lee tunnel will much decrease breach frequency. In any case the modelled 12breacheswiththeLeetunnelisnotmuchinexcessofthe8breachesallowed.ThusitappearsalmostcertainthattheadditionoftheLeetunnel,duebytheendof2015,willensurethatStandard3willbemetthen.

Similarly,forstandard4wherethemodelledspillfrequencywithouttheLeetunnelwas41breachesin41years. Inactual fact therewerenone in theupperTideway frommid2012 tomid2015andnone inthe lowerTidewaysince late2013andtheupgradingoftheBecktonandCrossnessSTWs.The addition of the lee tunnel is modelled to reduce breach from 41 breaches in 41 years to 7breaches, a dramatic drop. Even the model shows this almost reaching the requirement of 4allowablebreaches.ThusthereseemslittledoubtthatwiththeLeetunnelthestandard4wouldbemet.

Thus,providingTWreverts to theprevious seweroperating regime, there seemsnegligible riskoftheTidewaynotmeetingallthestandards.

In addition, should any action be taken to reduce CSO spill frequency, then the Tideway waterqualitywouldimprovefurther.

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15PeriodrequiredtodemonstratecompliancewithUWWTDstandards.TheTTSSGDOstandardsrefertoonceinayearforstandard1uptooncein10yearsforstandard4.TheEnvironmentAgencyhassuggestedthataperiodof10yearswouldberequiredtodemonstratecompliance.The implicationofthis is thatonewouldhavespentthe£4bnconstructingthetunnelbeforeonewouldbeabletodemonstratethatonedidnotneedit!Isthissense?Asacomparison,flooddefenceschemesmaybeconstructedwithadesignfloodof1in100year.Noonewaits100yearstofindoutiftheyconform.SimilarlytheThamesBarrierisdesignedagainsta1in1,000yeareventbut isconsideredcompliantbytheEnvironmentAgencywithoutwaiting1,000years.Thus, one method of assessment would be to adapt the models so they replicated the currentsituationandthencheckwhetherallthestandardsweremet.IncontrasttheEnvironmentAgency,emailSimonHughes/ChrisBinnie24thJuly2014regardingspillsfromMogdenSTWafteraboutoneyearsoperation,stated“TheEnvironmentAgencyisnotawareofanyinstanceswhenstormdischargesfromMogdenSTWhavecausedasignificantadverseimpactonthequalityoftheriversincetheupgradeoftheworks.Onthisbasis,theoverflowfromtheMogdenSTWstormtanksisregardedassatisfactoryunderthetermsoftheUrbanWasteWaterTreatmentDirective.” Mogden spills from the storm tanks arenot fully treated soneed tobe considered inaccordancewiththeTTSSGdissolvedoxygencriteria.

ThusitwouldseemappropriatetofollowthisEnvironmentAgencyapproachofusingoneyearsdataintheassessment.

16ConclusionofthewaterqualityassessmentoftheTideway.

Theconclusionisthat,asabouttwoyearsdataforthelowerTidewayandaboutthreeyearsfortheupperTidewayshowitnotbreachingthestandards,thensubjecttoThamesWaterreturningtoitspreviousoperational regimeand continuingmonitoring, the Tidewaywould continue tomeet theTTSSGandWFDdissolvedoxygencriteria.

Ifthereisanydoubtaboutlongertermevents,thenthesewerandwaterqualitymodelsshouldbecorrectedtoreflecttheresponsetoactualrainstorms,andthenrunforthefullsuite.

17Costofthetunnel

Thecontractfortheconstructionofthetunnelincludespaymentforthetunnel,theconstructionofwhichisestimatedatabout£4bn.Inadditionthecosttobepaidincludesthefinancingcostsduringtheperiodfromtheconstructionuntilthetotalcosthasbeenwrittenoffmanyyearshence.Thiswillsignificantly increase the cost of the tunnel.Whilst this is funded by the Infrastructure Provider,Bazalgette, most of the cost has to be repaid by the Thames Water sewerage bill payers. Thecontractisatargetcostcontract.Thus,iftheconstructionhitsproblems,thenthecosttoberepaidcould escalate appreciably. Whilst all reasonable precautions have been taken, tunnels are riskyventuresandtunnelsunderwaterevenmoreso.TheLondonWaterRingMaintunnelwasstopped

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ontwooccasions.Oneofthesewaswhenithitawaterbearingfault.Thisrequiredthefaulttobefrozenwhichtookmanymonths.Inthatcaseitwasunderanopencommonsohadeasyaccess.InthiscasethetunnelisundertheTideway,potentiallyamuchmoreonerousandexpensivesituation.ThustheTidewaytunnel,despitealltheeffortstoreducetherisk, isasignificantlyriskyproject.Aproportionofthecostoverrunisbornbythegeneraltaxpayer.

Does not the government owe a duty to the ThamesWater sewage customers and the generaltaxpayers,todiscusswiththeEuropeanCommissionwhetherthecurrentwaterquality,andhencetheenvironment,meetstheUWWTDoratleastidentifytheminimumalternativemeasurescenarioneeded to do so? TonyBerkeley has reported that his discussionswith the EC a fewmonths agoindicatedthat,atthattime,suchadiscussionhadnothappened.

18EuropeanCommissionfines

OnthebasisofthesituationreportedbytheTTSSGin2005of60spills/yearand8fishkills/year,theEuropeanCourtofJusticein2012foundtheUKinbreachoftheUWWTDfortheThamesTideway.

The UK government could be fined for the breach. The basis of the fine is a country factor, anenvironmentalimpactfactor,andalengthofoccurrencefactor.Basedonthereportedconditionin2005,andtheperiodfromwhenUKwassupposedtoconformwiththeUWWTDof2000towhentheThamestunnelisexpectedtobeoperational,currentlyprogrammedfor2023,thefinecouldbelarge,maybeuptoabillioneuros.

WereitpossibletoagreeaprogrammeofalternativemeasuressuchasRealTimeControltoreducespill frequency, then thesecouldbe implementedmuchsooner than the tunnel thus reducing thetimefactor.

Were itpossibletoconvincetheECthat,afterspending£1.2bnontheSTWupgradesandtheLeetunnel, the objective of protecting the environment, ie achieving the dissolved oxygen standards,hadbeenmet,thenthefineswouldbereducedconsiderably.

ThisfinewouldhavetobepaidbytheBritishtaxpayer.ShouldnotsuchdiscussionwiththeECbeundertaken?

19Conclusions

UWWTD requires CSO spill only to occur “in conditions such as unusual rainfall “. The TW sewermodelling showed that, even with the Lee tunnel, the spill frequency was too high and thusreductionofspillfrequencywasrequired,hencethetunnelrecommendation.

WhereastheECJreliedontheTTSSGthattherewereabout60spillsayear,followinglimitedfieldwork,eventhemodeloftheremainingCSOsshowsthat,posttheLeetunnel,thegreatestnumberwilldroptoabout42spills/year.

HoweverOfwat shows the sewermodelling considerablyoverestimates flooding from the sewers.73%ofpropertiesinvestigatedbyOfwataspredictedbythemodeltoflood,werefoundtohavenoevidence of flooding. Ofwat concludes the sewer modelling output for the existing condition is“unreliableandinaccurate”.Reasonsforthisincludethelimitedrainfalldataandthatthereisonly

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spilldatafor9ofthe57CSOs.EvenTWstate“ it isunlikelythatitwilleverbepossibletoacquiresufficientlycomprehensivedata”toproviderobustmodels.

Themodelfurtherover-predictsfuturespillfrequencybecauseitassumesnochangeinpercapitawater use, and hence increasing sewer dry weather flow. However TWWRMPs showwater intosupplylowerin2020and2040thaninthebaseyearof2006.

The UWWTD requires systems which are “in accordance with the best technical knowledge notentailing excessive costs.” The tunnelwas compared in 2003with full sewer separation and fullSuDs. Since then Real Time Control has been developed and this has reduced the capital cost offlooding measures in Cardiff from £100m to £5m. Other partial measures such as some sewerseparationtodischargedirecttotheTideway,wouldalsobecosteffective.Nostudyhasbeendoneof a combination of partial measures using current best technical knowledge and how such asystemcouldmeettherequiredspillfrequency.Suchasystemcouldwellsave£3bnandtime.

TTSSGselectedfishasrepresentingtheTidewayecology.TTSSGreportedanobservedbaselineof8fishkillsperyear,andthiswaspartof theevidenceonwhichtheECJ foundthesystemfailedtheUWWTD.Since2003onlytwofishkillshavebeenreportedduetoAbbeyMillsspillsandtwoduetoTidewayCSOs(about21fish).FurtherAbbeyMills relatedfishkillswillbedealtwithoncetheLeetunnel is operational about theendof2015. Since fish canwithstandat least 10%mortality eachyear,itwouldappearthattheTidewayecologyisalreadysustainable.

Thewaterqualitymodel shows that,post theSTWupgrades, thereshouldonaveragebeabout3breachsofstandard1andnearly3ofstandard2ayear.ActuallyintheupperTidewaybetweenmid2012 andmid 2015 therewere none and sincemid September 2013 none in the lower Tideway.ThustheTWwaterqualitymodellingisnotrobustandisnotsufficienttosupporttheexpenditureof£4bnonthetunnel.

TheAQMSdataandanalysisshowsthattheWFDgooddissolvedoxygenconditionwasmetintheupperTideway,BrentfordtoChelsea,frommid2012tomid2015andinthelowerTideway,BarrierGardenstoPurfleet,sinceSeptember2014.

Thedissolvedoxygenconditions insummer2015 intheupperTidewaydeterioratedfromthose inmid2012tomid2015,seehalf-tideplotsabove.ThamesWaterstatetheyadoptedanoperationalregimeto“makesureoursewersareasemptyaspossiblewheneverheavyrainisexpected..."Thisappears to be by pumping from the sewers to the Tideway. In 2008-9 only 19 properties wereflooded in their entire sewer area due to severe weather. Because of the fixed level of thesewer/highandmediumlevelcollectorsinterconnections,itwouldappearthatveryfewpropertieswouldbenefitfromthealteredregime.Ofwatconsideredthatitis“unlikelythatpropertiescanberemovedfromtheriskoffloodingbyoperationalimprovementsalone.”ThusitisconcludedthatTWrevised operational regimehas very limited benefit in reducing household floodingwhilst causingdeteriorationfromgooddissolvedoxygenconditionandecologicalandenvironmentalharm.

The result of the recent ECJWeser case judgement is thatdissolvedoxygen conditionsmustnotdeterioratefromgoodtomoderateandthatallpracticalstepsaretobetakentopreventthis.Thiswould require TW to revert to the previous sewer operational regimewhich gave good dissolvedoxygenconditionsintheupperTideway.

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Thus,providedTWreturntotheirpreviousoperationalregimeintheupperTideway,thereshouldbenofailureofthedissolvedoxygenstandards,thusitwouldappearthat,withtheadditionoftheLee tunnel due by the end of 2015, the objective of the UWWTD to protect the environmentagainstwastewaterdischargeswillbemet.Shouldreductionsinspillfrequencyalsoberequired,thenthereareseveralmeasureswhichcouldbe used in a combination of partial measures to achieve the required spill frequency at asubstantiallylowercostthantheTidewaytunnel.Suchasystemhasnotyetbeenstudied.

ProfChrisBinnieMA,DIC,HonDEng,FREng,FICE,FCIWEM

TTTmodellingspillfrequency22.11.2015

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AnnexAPlotsoftheannualdissolvedoxygenfromAnInvestigationintotheneedfortheThamesTidewaytunnelbyLaurenceClaxtonUniversityofExeter,September2015.

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