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River Almond valley water quality modelling strategic study for Scottish Water


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River Almond valley water quality modelling strategic study for Scottish Water - Dr Vera Jones (Atkins)

MIKE by DHI 15th UK User Group Meeting - Tuesday 19 March 2013

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River Almond valley water quality modelling strategic study for Scottish Water

  1. 1. River Almond Valley Water QualityModelling Strategic StudyClient: Scottish WaterContextAtkins was commissioned by ScottishWater to produce a dynamic waterquality model of the River Almond,using DHI MIKE-11 Ecolab.The study, which is subject toregulatory sign-off from the ScottishEnvironmental Protection Agency(SEPA), consisted of two keyelements: Assessing the impact of ScottishWater wastewater treatment works(WwTWs) and combined seweroverflows (CSO) on the waterquality of the River Almond and itstributaries. Identifying strategic options tomeet the requirements of theWater Framework Directive (WFD)and Urban Wastewater TreatmentDirective (UWWTD).MWH was appointed as the leadconsultant for this study and alsoundertook maintenance of thedrainage system hydraulic models forthe catchment during the first phaseof the work.Understanding ofcatchment issuesReview of background informationindicted that wastewater pollution is asignificant pressure on the waterquality of entire main stem of theRiver Almond.Additionally, there is limited storagecapacity at wastewater treatmentworks (WwTWs) and untreateddischarges from combined seweroverflows (CSOs). Pollution fromseptic tanks and other privatedischarges is also affecting certaintributaries.Finally, the area suffers from pollutionassociated with historic mining andsurface water outfalls from industrialestates; these two last issues arebeing considered by separate studiesundertaken by SEPA and ScottishWater (respectively), which Atkins isalso involved in.Water qualitymonitoringIt was recognised during the scopingphase that a high frequency andspatially extensive water quality dataset was needed to inform this work.As a result, a 4-month-long waterquality survey of the River Almondcatchment was commissioned, withsite work being undertaken by AspectSurvey and co-ordinated by Atkins.26 monitoring locations were selected,aiming to capture potential impacts ofScottish Water assets. Monitoringincluded automatic monitoring, spotsampling and wet weather surveys.Model developmentThe results of the monitoringprogramme formed the basis for thedevelopment of a Mike 11 Ecolab(DHI) hydrodynamic water qualitymodel by Atkins, which alsoincorporated inputs from the updatedRiver Almond sewer model, producedby MWH.A standard Ecolab template was used,with some modifications to meet therequirements of this project. Thewater quality determinands modelledwere: temperature, dissolved oxygensaturation, ammonia, nitrate, ortho-phosphate, particulate phosphorus,biochemical oxygen demand (BOD).The model was calibrated againstobserved data from severalmonitoring locations. Simulatedresults showed an overall very goodmatch with the observed data.Review of the calibration andverification was carried out anddeemed the model ‘fit for purpose’.Study OutcomesOnce model development wascomplete, 10-year stochastic modelruns were carried out, aiming toidentify the key sources of impacts onwater quality. The results of thesestochastic runs indicated that keyparameters of concern with regardsto WFD compliance are ortho-phosphate, BOD and ammonia. Themost significant cause of WFDfailures appears to be continuousdischarges from WwTWs. HoweverWwTWs also have a beneficial effecton water quality, by diluting the CSOinputs. Operation of key WwTWs at‘Best Available Technology’ treatmentlevels, even when this was simulatedwithout any CSO spills, was notsufficient to bring the whole system tothe required WFD Good/High status.ConclusionThese results suggest that, assumingthe current amount of wastewaterload to the system, achieving therequirements of the WFD throughinvestment in Scottish Water assetsalone will be challenging.During the next phase of the work,the model developed will be appliedto test different strategic options toachieve the requirements of the WFDand UWWTD in the River AlmondsystemContact: Dr Vera JonesSenior Environmental