Surface water pollution risk assessment for your environmental permit

IfTo youwork doout notthe haveconcentration upstreamafter orsewage backgroundtreatment, datamultiply forthe estuariesrelease orconcentration coastal(RC) watersof andthe freshwaters,substance assumein your discharge released to the concentrationfoul ofsewer eachby pollutantthe issewage 50%treatment ofreduction the EQS. factor:

Calculate

• when theusing concentrationAA ofEQSs pollutant– inuse the dischargeaverage RCs
• when dischargingusing toMAC aEQSs sewer

Sewerage–use treatmentthe worksmaximum willRC

if removeyou ahave proportionany of‘less thethan’ pollutantfigures inwhen calculating the dischargeaverage beforeconcentration, it’sround dischargedthem up to athe freshwaternearest orwhole estuarynumber or(for coastalexample, water.less Youthan must10 takeis thisassumed intoto accountbe when10)

If you calculatecannot thefind concentrationa ofSTRF thefor hazardousa chemicalsubstance, orassume elementnone whichof you will discharge to the riversubstance oris coastalremoved waterwhen throughassessing the sewer.discharge.

If in your discharge released to thefoul sewer inis milligramsvia peroffsite litrewastewater bytreatment, theyou sewagemust treatmentconsider reductionwhether factorthis intreatment milligramsguarantees perprotection litre.

Youof willthe needenvironment toas averagea yourwhole. resultsFor –example, iftransferring yousubstances havefrom aeffluent lessto thansewage figuresludge youwhich mustis roundspread it up to theland nearestis wholenot numberconsidered (foradequate exampletreatment lessor thanabatement 10and isonsite assumedpre-treatment tomay be 10).necessary.

Part For3: AAScreening EQS,tests

Before you shouldstart usescreening

Identify thewhether averageyou releaseneed concentrationsto andcomplete forthe MACscreening EQStests youfor:

• discharges shouldto useinland thefreshwaters maximum– releaserivers, concentration.

  Downloadcanals, thelakes sewageand treatmentreservoirs

• discharges reductionto factors:
  estuarine and coastal waters
  • Sewagedischarges treatmentof reductioncooling factors (ODS,waters 15.7(to KB)inland freshwaters or estuarine and coastal waters)

  Carry

  You outneed to follow the screening tests onrelevant theto your discharge environment.

  Use raw data fromfor the pollutants

  screening tests.

  You mustcan comparecomplete screening manually or by using the measurementsautomated ofH1 pollutantsscreening fromtool. yourContact dischargethe Environment Agency for access to the following:H1 screening tool.

  • environmental

    You qualitymust standardscomplete (EQS)each maximumscreening allowabletest concentrationsfor (MAC)all –the tosubstances evaluatethat theare short-termin environmentalor impactslikely thatto yourbe emissionsin canthe cause

  • environmentaldischarge. qualityIf standardsyou (EQS)have annual2 averageor (AA)more –discharges toof evaluate the long-termsame environmentalsubstance impactsfrom thatdifferent parts of your emissionssite, canthese cause
  need to be tested separately.

  The MACscreening andtests AAare EQSprogressive for– theif pollutantsa aresubstance listedis inscreened theout, followingyou tables:

  • Estuariesdo andnot coastalneed watersto specificcarry pollutantsout andthe operationalremaining environmentaltests quality(unless standards (ODSit is a PHS). PHSs, 8.3need KB)
  • Freshwatersadditional specificscreening pollutantstests andeven operationalif environmentalscreened qualityout standards (ODS,by 7.88earlier KB)
  • Estuariestests.

    Installations and coastalwaste watersoperations prioritymay hazardousalso substances,need priorityto substancesuse BAT-AELs and otherELVs pollutantsin environmentalthe qualityscreening standards (ODS,assessment 7.82(as KB)

  • Freshwatersappropriate).

    Substances prioritythat hazardousdo substances,not priorityscreen substancesout andwill otherneed pollutantsmodelling.

    Screening environmentaltests qualityfor standards (ODS,discharges 6.87to KB)

  inland freshwaters

  NotUse allthe pollutantsEQSs havefor bothinland typesfreshwaters ofto EQS.complete these screening tests as follows:

  When

  • where a pollutantsubstance has both an AA and a MAC EQS, comparefocus the measurementsinitial ofscreening pollutantsprocess fromon your discharge to the AA, apartstandard, frombut testalso 4carry forout freshwaterstest where4 youagainst must use the MAC EQS
  • any asassessment well.

    Youagainst must compare the measurementsMAC ofEQS pollutantsshould fromtake your discharge to the MAC asstandard wellat asface thevalue AA(even if youthe release itstandard inis batchesa rather95 thanpercentile, continuously.

    Yourassume dischargethat mayit containis otheran hazardousabsolute chemicalsvalue)

  • if ora elementssubstance thatis arereleased not listed in thebatches tables,rather forthan example,continuously, pesticides, biocides or disinfectants.if Youthere shouldis includea informationlarge aboutvariation thesein withthe yourconcentration permitof application to the Environmentsubstance Agency.released Youover shouldtime, alsouse includeboth measurementsthe ofMAC theseand pollutantsthe inAA yourEQSs dischargefor orall estimatesscreening oftests
  • if concentrationsa ifsubstance youonly dohas nota haveMAC measurements.

    ScreeningEQS, tests:use freshwaters

    Carrythis outstandard for the followingscreening tests

  • bioavailable toEQSs checkshould whetherbe yourused dischargefor ofscreening hazardousmetals chemicalswhere andavailable elements(for tozinc, freshwaterscopper, ismanganese, anickel riskand to lead)
  • the environment.measured Forconcentration eachfor testsubstances youshould willhave needthe tosame provideunit moreof datameasurement thanas for the previousEQS one.(you Ifmay yourneed pollutantto isconvert units)

  A substance can be screened out byand ano test,further youassessment dois notneeded, needif toat completeleast theone rest of the tests.following criteria are met:

  Contact

  • test 1 theis Environmentpassed
  • test 2 Agencyis topassed
  • both gettest access3 toand thetest screening4 toolare topassed

  PHSs helpmust youalso carrypass outthe thesesignificant tests.load test.

  TestDischarges 1

  Checkto whetherdesignated theprotected concentrationareas of– theinland chemicalfreshwaters

  Modelling andmay elementbe inrequired thefor dischargeany issubstances morewhich thanexceed 10% of the environmental quality standard (EQS).

  If it’sif lessyour thandischarge 10%is youdirect doto nota needdesignated toprotected collectarea the(for dataexample fora theSite nextof 3Special testsScientific Interest – youSSSI).

  Test do1: notInitial needconcentration tocheck

  This dotest anythingchecks morehow asthe yourconcentration hazardousof chemicalsthe andsubstance elementsin arethe notdischarge acompares riskwith to the environment.

  IfEQS it’s(whether it is more than 10%,10% carryof outthe test 2.EQS).

  IfTo youcomplete havethe 2test, oryou moreneed dischargesto ofcompare the samesubstance chemicalconcentration andin element from different parts of your plantdischarge you will need to test10% themof separately.

  Environmentalthe quality standards (EQS) for freshwaters

  .

  DownloadIf the EQSconcentration for freshwaters:is:

  • Freshwatersless specificthan pollutants10% andof operationalEQS environmental– qualitystop standards (ODS,here, 7.88no KB)
  • Freshwatersfurther prioritytests hazardousneeded substances,(unless prioritythe substancessubstance andis othera pollutantsPHS)
  • greater environmentalthan quality10% standards (ODSof EQS, 6.87– KB)go to test 2

  Test 2

  This2: testCompare introduces the dilutionprocess availablecontribution in(PC) with the receivingEQS

  This water.test Youchecks willwhether needyour thedischarge riverexceeds flowacceptable datalevels andafter dailyaccounting dischargefor volumedilution forin thisthe test.receiving watercourse.

  CheckTo whethercomplete thethis processtest, you contributionwill (PC)need ofto yourcollect:

  • river chemicalflow anddata
  • the elementdaily isdischarge morevolume

  The than 4% of the EQS. PC is the concentration of a discharged chemicalsubstance and element in the receiving water after it’sdilution. beenTo diluted.

  Docalculate the following steps to work out the PC., complete these formulas:

  1. Multiply[Effluent the effluent flow rate (EFR), bym³/s)] thex release concentration ([RC) (µg/l) of the pollutantsubstance in the effluent.effluent]

  2. Add your value for the [EFR, tom³/s] the+ [the river flow rate (RFR)., m³/s)]

  3. Divide[Result the result of step 11] by÷ the[result result of step 2.2] = PC (µg/l).

  IfFor yourAA valueEQS foruse PCthe average EFR isand 4%RC. orFor lessMAC ofEQS use the EQSmaximum EFR, youand doRC.

  RFR notrepresents needthe toQ95 carryRFR out(equalled testsor 3exceeding 95% of the time and 4.represents low flow conditions).

  If the PC isvalue moreis:

  • equal to or less than 4% of the EQS you– willstop needhere, tono carryfurther outtests needed (unless the substance is a PHS)
  • greater than 4% of the EQS – go to tests 3 and 4.
    4

  Test 3

  You3: needCheck how the difference between background water quality and the predicted environmental concentration (BCPEC) datacompares forwith thisthe test.EQS

  This Contacttest thechecks Environmentwhether Agencyyour todischarge getincreases the BCconcentration forof the watersubstance youdownstream areby dischargingmore tothan or10% useof estimatedthe data.EQS.

  CheckBefore whethercompleting yourthis dischargetest, increasesyou theneed concentrationto ofknow the pollutantBC indata for the riverwater downstreamyou ofare thedischarging dischargeto.

  If byBC moredata thanis 10%not ofavailable, theuse chemicalestimated anddata.

  Calculate element’sthe EQSPEC value.

  TheTo predictedcomplete environmentalthis concentrationtest, (you need to work out the PEC) of the substance in the water downstream of your discharge.

  If the dischargeRFR is amore combinationthan often times the PCEFR, andthe backgroundPEC concentration.

  Toshould workbe outcalculated theas PECfollows addwith the PC totaken thefrom averagetest BC.

  If2, thestep result3: of[PC step(µg/l)] 2+ in[BC test(µg/l)] 2= showsPEC that(µg/l).

  If the riverRFR flowis rateequal isto or less than 10ten times the effluentEFR, dischargethe flowPEC rate you should alsobe docalculated theas following calculation.follows:

  1. Multiply [EFR by(m³/s)] x [RC. (µg/l)]

  2. Multiply [RFR by(m³/s)] x [BC. (µg/l)]

  3. Add[Result the results of step 11] and+ 2[Result together.of step 2]

  4. Add [EFR to(m³/s)] + [RFR. (m³/s)]

  5. Divide[Result the result from step 33] by÷ the[Result result from step 4.4] = PEC (µg/l)

  For AA EQS use the average EFR and RC. For MAC EQS use the maximum EFR and RC.

  If the difference between BCbackground water quality and the PEC :

  • is moregreater than 10% of the EQS the– Environmentmodelling Agencyis willneeded need(if tothe carrysubstance outis modellinga (ifPHS, you arealso dischargingneed to acomplete canalthe orPHS lakescreening youtests)
  • does willnot needexceed to10% doof the modelling).EQS If– itgo isto not, carry out test 4.
    4

  Test 44: Check if the PEC exceeds the EQS in the receiving water downstream of the discharge

  CheckThis whethertest checks if the EQS is complied with in the receiving water by checking whether the PEC (calculated in test 3) is higher than the EQS.

  You need to complete this check against the AA EQS and the MAC EQSs:

  1. Compare the average PEC with the AA EQS.

  2. Compare the maximum PEC with the MAC EQS.

  If itthe is,PEC exceeds either EQS, modelling is needed. If the Environmentsubstance Agencyis willa PHS, you also need to carrycomplete outthe modellingPHS (youscreening willtests.

  If needneither toEQS dois exceeded and the modellingsubstance ifpassed youtest are3, dischargingstop tohere a– canalno orfurther lake).tests needed (unless the substance is a PHS).

  Screening tests:tests estuariesfor anddischarges to coastal and estuarine waters

  CarryUse out the followingEQSs testsfor coastal and estuarine waters to checkcomplete ifthese yourscreening planttests.

  The Environment Agency will dischargecheck potentiallythat hazardousthe chemicalscorrect andtests elementshave been carried out depending on whether the discharge is to estuariesa andlow-water channel, a riverine estuary or to other coastal waters. ForYour eachapplication testmay yoube willdelayed needif youthe toscreening provideassessment moreis datanot thanrepresentative forof the previousdischarge one.environment.

  If

  Discharges yourto processcoastal involvesand usingestuarine coolingprotected waterareas

  You youwill mustneed carrymodelling outfor theseany alternativesubstances tests.

  Contactwhich exceed the EnvironmentEQS Agencyif toyour getdischarge accessis direct to a designated protected area (for example a SSSI), even if the substance would screen out in subsequent screening tooltests. This is because the discharge conditions will need to helpbe youconsidered carryin outthe thesecontext tests.of site-specific conservation objectives.

  Test 11: Compare the discharge concentration with the EQS

  CheckThis test checks whether the levelconcentration of pollutanta substance in the discharge is more than the the EQS.

  To limits.complete Youthis test, you need to testcompare forthe bothconcentration annualof averageeach limitssubstance andin maximumyour allowabledischarge concentrationagainst ifthe relevant EQS. Test both the chemicalAA and elementMAC EQSs if the substance has both types of of EQS.

  If the chemicalconcentration andof elementthe substance:

  • is more thanthan the EQS limits,(or carryEQSs) out– testgo 2.to Iftest it’s2
  • is below the EQS limits(or youEQSs) do– notstop needhere, tono anythingfurther moretests asneeded your(unless pollutantthe substance is not a riskPHS)

  Test to2: Check if the environment.

  Environmentaldischarge qualityis standardsto (EQS)a forriverine estuariesestuary andor coastallow waterswater channel

  DownloadThis thetest EQSchecks forwhether estuariesyour anddischarge coastallocation waters:

  • Estuariesrequires andfreshwater coastalscreening watersmethods.

    You specificwill pollutantsneed andto operationalcheck environmentalif qualityyou standards (ODS,are 8.3discharging KB)

  • Estuariesto andparts coastalof watersthe priorityestuary hazardouswhere substances,the prioritywater substancesis andmainly otherfresh pollutants(riverine environmentalestuaries qualityor standards (ODS,low 7.82water KB)
  channels).

  Test 2

  CheckRiverine whetherestuaries you are dischargingthe toupper thereaches lowof wateran channelestuary (ifwhere the water doesis notpredominantly fresh and flow acrossforms thea estuarystraight bedline at(rectilinear) anywhich stagemay ofreverse with the tide)tide.

  Low inwater channels are the upperroute partstaken ofby ana estuaryriver at low water where the waterestuary bed is mainlyexposed fresh.

  Ifon theeither dischargeside isand directflow tocontinues theeven at low waterwater.

  If channel,discharging doto thea screeningriverine testsestuary foror freshwaterlow startingwater at test 2.channel:

  In

  • use the calculationsscreening test for freshwaterinland testswaters 2(freshwaters), tostarting 4at test 2
  • use the freshwater flow rate and upstreambackground quality butin your calculations
  • continue to use the EQSs for estuaries and coastal waters.
    waters (not the freshwater EQSs)

  If theseyou doare not applydischarging to youra dischargeriverine site,estuary carryor outlow water channel, go to test 3.

  Test 3

  3: Check whetherif yourthe discharge is to a location withhas restricted dilution or dispersion.

  dispersion

  AroundThis thetest coastchecks therewhether areyour adischarge numberlocation ofhas locationslimited wherewater dilution,exchange dispersionthat orwould flushingaffect isdilution.

  You tooneed limitedto check if your discharge is to carrya outlocation testwith 5.restricted Examplesdilution areor dispersion. For example, enclosed bays (such as Lulworth Cove in Dorset), docks andor ports.

  If Inyour thesedischarge:

  • has locationsrestricted theredilution isor limiteddispersion exchange– ofmodelling wateris betweenneeded (if the pointsubstance ofis dischargea andPHS, offshore waters.

    If you also need to checkcomplete whetherthe yourPHS dischargescreening istests)

  • does tonot ahave location with restricted dilution or dispersion,dispersion email– thego Environmentto Agencytest at marine_modelling_requests@environment-agency.gov.uk.
    4

  If you need help checking whether your discharge is to a location with restricted dilution or dispersion, checkcontact the sectionEnvironment onAgency modellingat marine_modelling_requests@environment-agency.gov.uk.

  Test If4: not,Compare carrythe outdischarge testlocation 4.

  Testwith 4chart datum

  IfThis thetest waterchecks youwhether your discharge tois doestoo notclose haveto restrictedshore dilution or dispersionin andwater thethat discharge is submergedtoo atshallow.

  To allcomplete statesthis oftest, the tide, you need toto:

  1. Use online measurenavigation charts to check the discharge location.

  2. Measure the minimum distance between theyour point you discharge wastepoint water from and where the pointseabed (oris line)at wherechart thedatum water(shown depthsas are0 shown on nautical chartscharts).

  3. Check asthe zeroseabed (whichdepth isat knownyour asdischarge chart datum).location.

  UseIf onlineeither navigationof charts to check the locationfollowing apply, you are discharging to.

  You will need to carrystop outscreening and modelling ifis theneeded discharge(if containsthe pollutantssubstance atis concentrationsa abovePHS, EQSyou andalso eitherneed ofto complete the followingPHS apply:screening tests):

  • the discharge location is less than 50m50 metres offshore from where the sea bed is at chart datum
  • the seaseabed bed at the discharge location is less than 1m1 metre below chart datum

  If these do not applyapply, go to your discharge site, carry out test 5.

  Test 55: Assess the effective volume flux of the discharge

  YouThis cantest onlychecks carrywhether outthe thisdischarge testvolume ifand substance concentration are within allowable limits for the water depth.

  Step 1: Check if discharge is buoyant.

  buoyant

  Most discharges to estuaries and coastal waters are buoyant, as they are mainly freshwater discharges to a saltysaltwater environment.

  If the discharge discharge:

  • is not buoyant,buoyant for(for example ifan theeffluent receivingfrom waterevaporative iscooling fresh,or thendesalination) you– willstop needscreening, tomodelling carryis outneeded modelling.

    Check(if if the effectivesubstance volumeis fluxa ofPHS, you also need to complete the dischargePHS screening tests)

  • is withinbuoyant the– allowablecontinue limits.
    to step 2

  The

  Step maximum2: Determine allowable effective volume flux

  The youallowable canlimit workdepends withon iswater proportionaldepth tobelow thechart water depth, datum:

  • for depths from 1m, up to 3.5m below thechart depthdatum of– waterallowable ateffective thevolume pointflux whereis charteredproportional waterto depthsthe arewater showndepth on(for nautical charts (chart datum). For example, if the water depth below chart datum is 2m2m, the allowable effective volume flux is 22m³/s)
  • for cubic metres per second. For water depths more than 3.5m below chart datum,datum the– allowable effective volume flux is fixed3.5m³/s

  Step at3: 3.5Calculate cubicyour metresdischarge’s pereffective second.

  volume flux

  WorkComplete out the effectivefollowing volumecalculation fluxusing ofthe AA EQS and the discharge.MAC EQS (if available):

  1. Multiply[Effluent the effluent discharge rate (in(m³/s)] cubicx metres[RC per(µg/l)]

  2. [EQS] second)− by[Average BC at the releasedischarge] concentration(make ofsure units are the chemicalsame)

  3. [Result andfrom elementstep (in1] micrograms÷ per[result litre).from step 2]

  Step 4: Compare and decide

  If the effective volume flux is:

  • Subtractmore than the averageallowable backgroundeffective concentrationvolume offlux – modelling is needed (if the dischargesubstance locationis froma PHS, you also need to complete the EQS.

    PHS screening tests)

  • Divideless than the resultallowable ofeffective stepvolume 1flux by– stop here, no further tests needed (unless the resultsubstance ofis stepa 2.

    PHS)

  Screening tests for discharges of cooling water

  CheckThis section covers how to assess substances diluted by cooling water at your chemicalsite andbefore elementthey againstreach the maximumreceiving annualwater. concentrationThis (MAC)includes EQSdischarges asof wellcooling aswaters againstto theinland AA.freshwaters and estuarine and coastal waters.

  IfFor cooling waters discharging to:

  • a freshwater river, riverine estuary or direct to a low water channel in the effectiveupper volumereaches fluxof isan moreestuary than– use the allowablescreening effectiveor volumemodelling fluxapproach for discharges to freshwater
  • coastal or estuarine areas with restricted dilution or dispersion characteristics, or to the dischargemiddle locationreaches youof estuaries – dilution will need to carrybe outconsidered modelling.on Ifa it’ssite-specific lessbasis
  • lower youestuaries doand notcoastal needwaters to– dofollow anythingthe further.

    Screeningmethod tests:for dischargespredicting intoconcentrations in cooling water

  Predicting whichconcentrations arein thencooling dischargedwater

  Calculate topredicted estuariesconcentrations orin coastalcooling waters

  water

  YouFor these tests you need to checkknow howthe:

  • average muchand maximum substance load in the chemicalswaste andstream
  • average elementsprocess arewaste dilutedstream byflow rate
  • process waste stream flow relevant to the coolingmaximum watersubstance load in yourthe plantwaste beforestream
  • average theand dischargeminimum reachesoperational thecooling receivingwater water,flow torate
  • average checkand whethermaximum modellingBC isin needed.
    abstracted cooling water

  WorkUse the following calculations to work out the predicted average concentration in the cooling water.water:

  1. Multiply[Average theBC] averagex background[average concentration by the average cooling water flow.flow]

  2. Add[Average thesubstance average load of the chemical and element in your waste streamstream] to+ the[result result from step 1.1]

  3. Add[Average the average process waste stream flowflow] to+ the[average average cooling water flow.flow]

  4. Divide[Result thefrom resultstep of2] step÷ 2[result byfrom thestep result3] of= steppredicted 4.average concentration

  Work

  Calculate out the predicted maximum concentrationconcentrations in the cooling water.

  water

  1. MultiplyWhere the EQS is marked as a ‘95th percentile’ in the EQS tables, the maximum backgroundBC concentrationcan byalso be a 95th percentile value.

     Complete the minimumfollowing calculations:

     1. [Maximum BC] x [minimum cooling water flow.flow]

     2. Add[Maximum thesubstance maximum load of the pollutant in your waste streamstream] to+ the[result result from step 1.1]

     3. Add[Process the average process waste stream flow relevant to themaximum minimumsubstance load in waste stream] + [minimum cooling water flow.flow]

     4. Divide[Result the result of step 22] by÷ the[result result of step 4.3] = predicted maximum concentration

     Compare concentrations with EQSs

     You will need to carrycompare:

     1. The outpredicted modellingaverage ifconcentration in the concentrationcooling ofwater with the chemicalAA andEQS.

     2. The elementpredicted maximum concentration in the cooling water iswith the MAC EQS (if available).

     If the concentration of the substance in the cooling water is:

     • more than the relevantrelevant AA or MAC EQS – modelling is needed (if the substance is a PHS, you also need to complete the PHS screening tests)
     • less than the relevant AA or MAC. IfEQS it’s– lessstop youhere, dono notfurther needtests toneeded do(unless anythingthe further.
       substance is a PHS)

     ScreeningAdditional test:screening ‘prioritytests hazardousfor pollutants’PHSs

     You mustwill need to carry out this additional screening step for allPHSs priorityin hazardousdischarges pollutantsto forinland freshwaters and priorityto hazardous pollutants for coastal waters and estuaries (including via the foul sewer or for discharges of cooling waters).

     Complete this test even if the pollutantssubstance didhas notbeen needscreened modellingout asby athe resultprevious of screening teststests.

     You can identify which PHSs can be used in this test using Table 1 to‘Significant 4load limits for freshwatersPHSs’.

     Significant orload teststest

     This 1test tochecks 5whether the annual load discharged for estuariesthe andPHS coastalis waters.greater than the significant load limit set for the PHS.

     Calculate the annual load

     TheUse prioritythe hazardousfollowing pollutantscalculation areto listedwork inout the followingannual tables:load: 

     1. [Average discharge concentration (µg/l)] x [average flow (litres per day)]

        Estuaries

     2. [Result andof coastalstep waters1] priority÷ hazardousby substances,1,000 priority= substancesresult andin othermg pollutantsper environmentalday

     3. [Result qualityof standards (ODS,step 7.822] KB)÷ by 1,000 = result in g per day

     4. [Result of step 3] ÷ by 1,000 = result in kg per day

        Freshwaters

     5. [Result priorityin hazardouskg substances,per priorityday] substancesx and[number otherof pollutantsdischarge environmentaldays qualityper standards year] = annual load (ODSkg, 6.87per KB)year)

  YouIf needthe todischarge findis outcontinuous whetherthroughout the annualyear, limitthe number of pollutantsdays youwill be 365 days.

  If the discharge is not constant, multiply the result of step 4 by the number of days per year the discharge is active.

  If there are 2 or more thandischarges of the significantsame loadsubstance limiton (anthe same permit from the same site, combine the loads for the annual load limitcalculations.

  Compare thatwith hassignificant beenload setlimits

  Check foryour priorityresult hazardousagainst pollutants).the relevant significant load in Table 1.

  Table 1: Significant load limits

  for PHSs 

  PollutantHazardous chemical or element	Annual significant load limit in (kg)
  	Anthracene	1
  	Brominated diphenyl ether	1
  	Cadmium	5
  	Chloroalkanes C10-13	1
  	Dioxins	0.0001
  	Endosulphan	1
  	Hexachlorobenzene	1
  	Heptachlor	1
  	Hexachlorobutadiene	1
  	Hexachloro-cyclohexane	1
  	Mercury and its compounds	1
  	Nonylphenol (4-Nonylphenol)	1
  	Pentachlorobenzene	1
  	Polycyclic aromatic Hydrocarbonshydrocarbons (PAHs)(PAHs)	5
  	Tributyltin compounds (Tributylin-cation)	1

  Calculate

  If the annual load is less than the significant load

  limit, the outcome will depend on the previous screening results:
  • if the initial screening suggested no modelling is needed – no modelling is needed
  • if the initial screening suggested modelling was needed – modelling is needed

  MultiplyIf the averageannual dischargeload concentrationis bymore than the averagesignificant flowload (litreslimit, go to ‘check you have enough samples above the MRV’.

  Check you have enough samples above the MRV

  This test identifies whether a day).PHS is likely to be in the discharge by comparing your sample results with the MRV. This check can only be completed if your MRV is 10% of the EQS or less. Complete this test separately for each PHS in your discharge.

  1. Count how many samples you have in the assessment period.

  2. DivideCount thehow resultmany byof 1,000your sample results are equal to giveor youabove mgthe aMRV day.(do not count ‘less than’ results).

  3. DivideCompare the resultnumber byof 1,000sample toresults givefrom youstep g2 awith day.the minimum number of samples given in the table below.

  Divide

  Number of samples in assessment period	Minimum number of samples that need to be equal to or greater than the resultMRV
  12 byto 1,00014	4
  15 to give20	5
  21 to 27	6
  28 to 34	7
  35 to 41	8
  42 to 48	9
  49 to 56	10
  57 to 63	11
  64 to 71	12
  72 to 79	13
  80 to 86	14
  87 to 94	15
  95 to 102	16

  If your count from step 2 is equal to or less than the minimum number in the table, stop here – you kgdo anot day.need to continue PHS screening or data clean up.

  If your count from step 2 is greater than the minimum number in the table:

  1. Follow the data clean-up steps in ‘Data clean up steps for PHS screening’.

  2. MultiplyRepeat the resultsignificant byload 365screening totest giveusing youcleaned-up kgdata.

  3. Compare athe year.new results with the significant load limit.

  CheckIf yourthe resultcleaned-up againstannual theload relevantis still more than the significant load limit:

  • the Environment Agency will assess the discharge
  • an emission limit may be included in significantyour loadpermit limitsto table.
    control the substance

  If the loadcleaned-up youannual calculateload is less than the significant load forlimit, you will need to check if the pollutantsubstance andpassed the pollutantother didscreening nottests:

  • if needsubstance modellingfailed asone aor resultmore ofother screening tests 1– tomodelling 4is forneeded
  • if freshwaterssubstance orpassed all other screening tests 1– tono 5modelling is needed

  Data clean up steps for estuariesPHS andscreening

  Check coastaldata waters,is thecurrent

  Check pollutantwhether your data is insignificantcurrent and youreflects doany recent treatment processes that might have altered the discharge.

  If your data does not represent current discharge conditions, collect more data. You may need to dorepeat anythingthe further.screening tests.

  If theyour loaddata youdoes calculaterepresent iscurrent lessdischarge thanconditions, continue with the significantdata loadclean up steps.

  Check for thestep pollutantchanges and(significant thechanges)

  There pollutantmay didbe needstep modellingchanges asin ayour resultdata ofover screeningtime. testsYou 1may tobe 4aware forof freshwatersthese, or teststhey 1may toonly 5show forup estuarieswhen andlooking coastalat waters:the data. For example:

  • thechanges Environmentin Agencyeffluent willtreatment
  • changes needin trade inputs to carrysewerage outworks

  If modellingthere are step changes:

  • select a time period reflecting current discharge quality (even if this means using less than 3 years’ worth of data) – you will need a minimum of 12 samples
  • continue with the data clean up steps

  If there are dischargingno tostep freshwaterchanges, (exceptcontinue lakeswith andthe canals)data clean up steps.

  Check data distribution

  If your data are not evenly distributed (for example if there is seasonal variation):

  • data can still be used – continue with the data clean up steps
  • consider the uneven spread when you willinterpret needthe toresults carry– outyou modellingcan ifanalyse seasonal variation using a statistics package
  • you aremay dischargingneed to contact the Environment Agency to anhelp estuaryyou orinterpret coastalthe watersdata

  If theyour loaddata youis calculateevenly isdistributed, morecontinue thanwith the significantdata loadclean up steps.

  Check for outliers

  Check your data for very high or low values ‘outliers’ as these may not be accurate and could distort your data.

  You can identify high values resulting from exceptional circumstances or normal performance by looking at other substances sampled on the pollutant,same youdate mustor repeatresults from the testsame withtime cleaned-upperiod datain (thisdifferent meansyears.

  A makingvalue somemay changesbe considerably higher or lower than the rest of the dataset because it is:

  • incorrect due to makesampling, surerecording or coding errors – exclude these values from your dataassessment
  • correct but relates to exceptional circumstances (such as treatment failure) – exclude these values from your assessment
  • correct and is accurate).a high value but part of the normal performance of the permitted activity – include this value in your assessment

  If you have fewer than 12 samples, do not remove outliers.

  Calculate

  You can use statistical analysis to help identify if the significantoutlier loadis usinga cleaned-up‘true data

  outlier’.

  RepeatIf it is not a true outlier, leave it in your data and repeat the significant load screening test using cleaned-up data.

  If yourit calculationsis witha cleaned-uptrue dataoutlier, areremove moreit thanfrom your data and repeat the significant load forscreening thetest pollutant,using thecleaned-up Environmentdata.

  Adjust Agency‘less willthan’ includeand anlow emissionvalues

  You limitneed into youradjust permitall which‘less willthan’ tellvalues youto howhalf totheir controlface thevalue pollutant.(by dividing by 2). For example:

  • < 10 (less than 10) becomes 5
  • < 50 (less than 50) becomes 25

  If thepositive pollutantvalues did(not notless passthan onevalues) orare morereported ofbelow the screeningMRV, tests:take them at face value.

  • the

    Part Environment4: AgencyModelling

    Modelling will need to carrybe completed for:

    • any substances that were not screened out modellingby ifthe youscreening tests
    • discharges that are dischargingdirect to freshwatera designated protected area of estuarine or coastal waters where a substance exceeds the EQS
    • youdischarges directly to a designated protected area of inland freshwaters where a substance exceeds the EQS

    The Environment Agency will needcomplete modelling for most discharges to carryinland outfreshwaters.

    You must complete modelling iffor youdischarges areof discharginghazardous tochemicals anand estuaryelements orto:

    • freshwater lakes, canals and reservoirs
    • estuarine and coastal waters

    You domay not need to doemploy anythinga furtherconsultant ifto complete the loadmodelling. The best modelling approach to take depends on the specific characteristics of the discharge, the substances in the discharge and the receiving water environment. Before starting any modelling work, you calculatecan discuss which approach to modelling is lessmost thanappropriate with the significantEnvironment loadAgency. 

    Modelling uses ‘cleaned-up’ data and assesses each substance in more detail. Follow the steps in ‘Preparing data for modelling’ before to prepare your data for modelling.

    We are updating our guidance on carrying out modelling. For further details, contact the pollutantEnvironment andAgency. 

    If itthe passedmodelling tests 1show that your discharge could cause harm, the Environment Agency will include conditions to 4control forthe freshwatershazardous chemical or 1element toin 5your forpermit.

    If estuariesthe andimpact coastalon waters.the surface water environment is unacceptable, the Environment Agency may refuse your permit application.

    CleaningPreparing data for modelling

    You need to clean up your data in preparation for modelling. These steps apply to all discharge environments. You should complete these steps before generating summary statistics to use in modelling.

    1. Check you have enough samples above the MRV

    CheckThis thattest identifies whether a minimumsubstance numberis likely to be in the discharge by comparing your sample results with the MRV. This check can only be completed if your MRV is 10% of the EQS or less. Complete this test separately for all substances in your discharge which did not screen out:

    1. Count how many samples exceedyou have in the assessment period.

    2. Count how many of your sample results are equal to or above the MRV. (do not count ‘less than’ results).

    3. Compare the number of sample results from step 2 with the minimum number of samples given in Table 2.

    Table 2: Minimum number of samples equal to or above the MRV according to sample size

    Number of samples in assessment period	Minimum number of samples which need to be equal to or above the required required MRV
    12 to 14	4
    15 to 20	5
    21 to 27	6
    28 to 34	7
    35 to 41	8
    42 to 48	9
    49 to 56	10
    57 to 63	11
    64 to 71	12
    72 to 79	13
    80 to 86	14
    87 to 94	15
    95 to 102	16

    If ayour minimumcount numberfrom ofstep your2 samplesis:

    • equal doto notor exceedless than the MRV,minimum number in the pollutanttable is– notstop ahere, riskmodelling tois theunlikely environmentto andbe youneeded do(unless notany needof tothe carrypositive outsamples modellingexceeded (thisthe onlyMAC appliesEQS if– yourthen MRVmodelling wasmay 10%be ofneeded)
    • greater than the EQSminimum ornumber less).

      Followin thesethe stepstable – continue to checkstep that2

    2. yourCheck the data represent the current situationconditions

    Check atdata youris plant.

    current

    1. Check whether thereyour aredata significantis changescurrent (changesand thatreflects areany obviouslyrecent differenttreatment whenprocesses youthat lookmight athave altered the datadischarge.

       Check particularlyfor ifstep youchanges know(significant thechanges)

       There reasonsmay forbe thestep change)changes in your data over atime. periodYou may be aware of time,these, foror examplethey may only show up when looking at the data. For example:

       • changes in effluent treatment or
       • changes in trade inputs to a sewerage works.
         works

       If there are significantstep changes, changes:

       • select a time period whichreflecting reflects current discharge quality even(even if this means using less than 3 years’ data.worth Yourof datadata) must– includeyou will need a minimum of 12 samples.
         samples
       • continue with the data clean up steps

       If there are no step changes, continue with the data clean up steps.

       Check data distribution

       If your data isare not evenly distributed,distributed for(for example if there is seasonal variation,variation):

       • data it can still be used,used but– youcontinue shouldwith the data clean up steps
       • consider the uneven spread when you interpret the results.results You– you can analyse seasonal variation using a statistics package.
       • you You may need to contact the Environment Agency to help you interpret the data.
         data

       CheckIf your data is current,evenly fordistributed, example,continue youwith shouldthe includedata anyclean recentup treatmentsteps.

       Check processesfor that might have altered the discharge.

    2. outliers

       Check your data for very high or low values (‘outliers’)‘outliers’ as these may not be accurate and could distort your data.

       You Forcan example,identify ahigh values resulting from exceptional circumstances or normal performance by looking at other substances sampled on the same date or results from the same time period in different years.

       A value may be considerably higher or lower than the rest of the dataset because it is:

       • incorrect due to sampling, recording or coding errors – exclude these values from your assessment
       • correct but relaterelates to exceptional circumstances such(such as treatment failure,failure) so– youexclude shouldthese notvalues includefrom it in your assessment.assessment
       • correct Orand is a high value mightbut bepart correctof andthe a normal partperformance of yourthe activity,permitted soactivity you– should include itthis value in your assessment.
         assessment

  Modelling

  YouIf needyou tohave findfewer athan consultant12 tosamples, carrydo outnot detailedremove testsoutliers.

  You calledcan modellinguse ifstatistical youranalysis screeningto testshelp foridentify estuariesif andthe coastaloutlier watersis dida ‘true outlier’.

  If it is not screena outtrue theoutlier, pollutants.leave it in your data.

  WeIf areit updatingis oura guidancetrue onoutlier, carryingrun outthe modelling.modelling Iftests youwith wouldthe likeoutlier advice,included pleasein contact the Environmentdataset Agency.and then again without.

  The

  3. EnvironmentAdjust Agency‘less willthan’ carryand outlow thevalues

  You modellingneed teststo foradjust youall if‘less yourthan’ screeningvalues teststo forhalf freshwaterstheir showedface thatvalue your(by dischargedividing isby a2) riskbefore tocalculating thesummary environment,statistics unlessfor youmodelling. areFor dischargingexample:

  • < into10 a(less lakethan or10) canal,becomes then5
  • < you50 must(less carrythan out50) modelling.
    becomes 25

  ModellingIf testspositive willvalues show(not whetherless yourthan dischargevalues) willare causereported pollution.below If the modellingMRV, teststake showthem thatat yourface dischargevalue willfor causemodelling. pollution,For example, if the EnvironmentMRV Agencyfor willa includesubstance conditionsis to10, controlbut the hazardousreported chemicalvalue orwas element8.8, inthe yourvalue permitof or8.8 theyshould maybe refuseassumed yourto permitbe applicationaccurate ifand theused impactfor onmodelling.

  Once you have assessed and adjusted the environmentdata, iscalculate unacceptable.mean and standard deviation values to use in modelling.

  Submit your results

  Submit the results of your screening testsor modelling results to the Environment Agency alongwhen withyou youreither:

  • apply application for a new permit 
  • apply or to change an existing permit.

  You will need to include:

  • results of screening or modelling tests
  • raw data used for screening (in spreadsheet format where available)
  • cleaned up data used for modelling (where applicable)

  You can submit your results in the screening tool if you have used this to carry out the screening tests.

  You

  If must also include the raw data you usedneed for screening.

  Contacthelp

  Contact the Environment Agency if you have queries.questions or need more advice.

  General enquiries

  National Customer Contact Centre
  PO Box 544
  Rotherham
  S60 1BY

  Email enquiries@environment-agency.gov.uk

  Telephone 03708 506 506

  Telephone from outside the UK (Monday to Friday, 8am to 6pm GMT) +44 (0) 114 282 5312

  Monday to Friday, 8am to 6pm.