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EVALUATION OF NITROGEN TARGETS AND WWTF LOAD REDUCTIONS o FOR THE PRO\TDENCE AND SEEKONK RIVERS o o o

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RHODE ISLAIID DEPARTMENT OF ENVIRONMENTAL MANAGEMENT OFFICE OF WATER RESOURCES DECEMBER 2OO4 a EVALUATION OF NITROGEN TARGETS ANID WWTF LOAD REDUCTIONS FOR THE PROVIDENCE A}ID SEEKONK RI\IERS.

APPROACHESFOR ESTABLISHINGA NITROGEN LOAD REDUCTION PLAN The Providenceand SeekonkRivers are impacted by low dissolvedoxygon levels and high phytoplanktonconcentrations that are related to excessivenitrogen loadings. DEM has collected data and has been working with a contractorto develop a water quality model and a water quality lestoration plan (Total Maximum Daily Load (TMDL)) for the area.It has recently been determinedthat due to problemsencountered when modeling the interaction betweenthe deepcharurel and shallow flanks ofthese water bodies,the masstransporl componentof the modelsystem cannot be successfullycalibrated and validated. This problemhas been encountered in otherestuaries and has not beenresolved with stateofthe art numericalsolution techniques. Because water doesn't mix in the modelas it doesin the rivers,we areunable to simulatethe chemicaland biological behavior ofthe systemin the waterquality phase of the modelingeffort.

Our inability to adequatelyvalidate the masstransport model also preventsus from applying the Massachusettsapproach to settingload allocationsthat usesambient total nitrogen concentrationas the indicator.which is describedbelow. Other elements ofthe Massachusettsapproach were found to be helpfulin the goal-settingphase ofthis discussion, however.

When functioning properly, a water quality model predicts an accuratewater quality conditionthat results from a setofinputs (pollutantloadings) to the system.A computer- basednumerical model is typicallyused, however a physicalmodel can also serve as the analog for the river. In this case,information is available from the MERL (Marine EcosystemsResearch Laboratory) enrichment gradient experiment (Oviatt et al, 1986),DEM had initially usedrelationships observed during the MERL experimentto establishkinetic tems in the numericalmodel, however the experimentalresults themselves can also be used.

THE MERL EXPERIMENTAND BEHA\'IOR OF KEY PROCESSES The enrichmentgftdient experimentwas conducted continuously between May 1981and September1983. A completeset of environmentalvariables and water column parameters weremeasured throughout the periodofthe study.These included weekly samplingof chlorophyll-a,DIN, DO from consecutivedawn-dusk-dawn measurements, daily production, and monthly benthic uptake.

The experimentwas conducted in nine 13,000L tanksat URI. Threecontrol tanks, consistingof lower Bay waterwith no enrichmentcomprised the first group.The next group consistedofthe low treatrnents:1{ 2X, and4X tanks,where the 1x additionrate represented the meanaddition rate fuer unit area)of inorganicnitrogen, phosphorus, and siliconto NarragansettBay. The final groupconsisted ofthe high treatrnents:8X, 16X, and32X additions,where the 8X casewas considered representative of the ProvidenceRiver, and the 32X caserepresented the HudsonRiver regionofNew York Harbor.In general,the 1X- 32X

Page1 of 32 o

loadinggradient was selectedto reproducethe rangeof enrichmentlevels seen in real a estuaries.The loadinggradients and conesponding DIN loadingrates are listed in Table 1.

Table l. MERL Loading Gradients and DIN Loading Rates

Loading DIN LoadingRate o Gradient mmoleim2/day ke/m?ldav I 2.88 4.032E-05 z ). /t) 8.064E-05 4 11.52 1.6i3E-04 c 23.04 3226E-04 o 16 46.08 6.451E-04 )z 92.16 1.2908-03

As an initial phaseof herproject to refinethe WASP kineticsfor DEM, Dr. Aimee Keller evaluatedthe MERL results to extract information that would be usedin the proposed o applicationof the WASP modelfor the ProvidenceRiver. Fromt}re mesocosm data, Dr. Keller documenteda number of characteristicsof the MERL tanks that have sienificance for the Providenceand SeekonkRivers:

Dissolvedoxygen: The DO observationsfor the three groupsoftanks are shownbelow. o The most significant featuresof DO behavior are that as the nutrient addition level increases,DO minimum levelsdrop precipitously and the variabilityincreases. Figures 1, 2, and 3 summarizeDO for the control tanks (mouth of bay water with no nutrient addition),low treatments(1X, 2X, and4X) andhigh treafrnents(8X, l6X, and 32X), respectively.The three figures show a distinct increasein deviation from the saturation o concentrationshown by the solid red line in eachfigure with increasingaddition rate. Another significant featureis an exponentialdrop in minimum summervalues with increasingnutrient loadings (Figure 4). Summerminimum values for the threehighest enrichmentsare less than 2 mg/I. The meanof obsewedDO concentrationsalso increases somewhat with increasins loading.(Figure 5). Seasonalmaximum values also increase. o r Ternperatureappears to be the principal factor that affectsDO at lower loading rates (Figure6). At higherloadings, DO conelatessignificantly with ambientsilica andnikate concentrations.

Figure4 is probablythe mosttelling graphicof this $oup. Daily minimumDO valuesdrop a precipitously,to lessthan 2 mg/I, at the 8X, 16X, and32X tanks.The regressionequation derivedfrom the tank datapredicts DO minima of 3.7 mgll,3.0 mg/I, and 1.98mg/l for the 2X, 4X, and8X cases,respectively,

I

Page2 of 32 a DissolvedOxygen - Controls

MJJASSONDJ FMAMJJAASONDJ FMAMJJJAS 19E1-1983

Figure 1: DO for the control tanks, May 1981- September1983.

DissolvedOxygen - LowTreatments 25

20

15

10

0 M J J A S S O N D J F M A M J J A A S O N D J F I,IAM J J J A S 1981-1983

Figure 2: DO for the low level treatment tanks, May 1981- September1983,

Page 3 of 32 a

o Dissolved Oxygen - High Treatments a mg'-

10 o

0 MJJASSON FMAMJJAASONOJ FMAMJ J o 1981-1983

Figure 3: DO for the high leyel treatment tanks, May 1981- September1983, a OxygenMinimum 1981-1983

o 4

E'3

o I 1

0 40 60 a Nitrogen Load (mmol/m?/d)

Figure 4: The relationshipbetween the inorganic nitrogen loading rate and minimum observedoxygen concentration, which showsthat the oxygenminimum drops rapidly with increasingloadings. a

Page4 of 32 Avg. Oxygenvs N-Load

11 y=0.27Ln(x)+8.5 10 O_f = 0.+S El O I 8 20 40 60 80

N-Load lmmol m'2d-1)

Figure 5: Graph of mean MERL tank DO as a function of loading, showingthat the averageDO goesup slighfly as nutrient loadingsare increased.

OxygenConcentration vs Temperatute t0 Tank 0 ' Control

t4

t0

a at 1t l.l-'

2 Y34,3ox+11.90 R: = 0.79 0

Figure 6: The relationshipbetween D0 and temperaturein a control tank.

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Phvtoolankton: o . Figures 7 - 9 show observedchlorophyll levels in the three setsof tanks during the experiment.As with DO, the variabilityas well asthe meanlevels of chlorophyllincrease asnutriurt additionlevels are increased. o The 4X and abovetreatments experience peak chlorophyll levels of 100 ug/l or greater. . The variability ofchlorophyll in the 8X andhigher tanks could best be describedas o chaotic(Figure 9). Adjacentweekly measulernents in thesetanks appear to haveswung fiom one extremeto anotheron a weekly basis. The 8X is somewhatdisparate because the tank was inadvertently colonizedby a disparatelyhigh number of filter feedersthat uffealisticallydepressed both the variationsand the meanlevels ofphytoplankton. This result indicatesthat filter feederscan rnitigate the effects of increasednutrient loadings by reducingphytoplankton blooms, however filter feedersexert an oxygendemand o through their respfuationthat may exacerbateh;poxia under someconditions. r The meanlevel ofphytoplanktonincreases linearly with increasingnitrogen loading rate (Figure 10). o Chlorophyll a - Controls

o 20

aDt5

10 o

0 o

Figure 7: Phytoplankton biomassin the control tanks, May 1981- September1983. a a

Page6 of 32 o Chlorophylla - Low Treatments 120

100

80

rD 60

40

20

0 M J J A S S O N D J F M A M J J A A S O N D J F M AM J J J A S 1981.1983

Figure 8: Phytoplanktonbiomass iu the low treatment tanks, May 1981- September 1983.

Chlorophylla - HighTreatments 180

r60 --+- i6 x l-,.'r, x 140

t20

_ 100 l'r 580

40

0 M J J A S S O N D J F M AM J J A A S O N D J F M A M J 1981-1983

Figure 9: Phytoplankton biomassin the high treatment tanks, May 1981- September 1983.

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Avergage Chlorophyll vs N Load o 70

60

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oru o ozo o 10

0

Nitrogen Load (mmol,/m'/d) a Figure l0: Mean phytoplankton biomassas a function of loading from the experiment.

. At higherloading rates (> 8x), light penetrationdepth decreases in the upperwater columnas a resultofshading by phytoplanktonto thepoint wherephytoplankton growth becomeslimited by light, not nitrogen.In essence,nutrients are over-abundant at these o enrichments. Ambient nitroeen concentrations o The MERL tanksshow a linearincrease in the meanconcentration ofinorganic nitrogen in the tanksas a functionof the loadingrate (Figure 11). I MeanMERL tank DINvs, enrichmentlevel

5

4 o Er 5J = o Et E 1 I 0

o Figure 11r Relationshipbetween tank DIN concentrationand NJoading rate.

Page8 of J2 o HOW DOES THE PROVIDENCEAND SEEKONKRIVER SYSTEMCOMPARE WITH THE MERL EXPERIMENT?

The presentcondition of the Providenceand SeekonkRivers and sourcesis basedon the 1995- 1996study by DEM WaterResources. The studyconsisted of measurementsof loading from the principal sourcesto the area,which included the three WWTFs and the five major tributaries. The frequencyof samplingof the sourceswas proportional to the magnitudeof the source.The four principalsources: Bucklin andFields WWTFs, and the Blackstoneand SeekonkRivers, were sampledmore than 50 times during the two years. Loadsincluded flows takeneither ftom plantrecords or USGSgages.

Eleven snapshotsof water propertieswere also collected during the May- October time frame duringthe two years,six during 1995and five during 1996.The estuarysurveys included high and low lide measurementsofhydrographic properties (temperature,salinity, DO) and chemical(ch1orophyll-a, nitrogen, phosphorus, and silicon)at sixteenstations. Production and light penehationmeasurements were madeacross the photic Qight penetration)zone at three stations.The suweys measurednearly all the parametersmeasured during the MERL experiments.

The first basisfor comparisonis in termsofloadings per unit area.Loadings used for the MERL experimentwere represented in units of massper unit areaper day,with the lX case representingthe estimatedtotal inorganic nutrient (e.g. dissolvedinorganic nitrogen (Dn\O) loadto the enthetyofNarragansett Bay from all sources(2.88 mmole/m2lday or 4.03E-05 kglm2/day).For the 1995-1996study period, loadings to the Providenceand SeekonkRivers wereestimated by combiningthe observedammonia Q.{H) andtotal nitrate (NO2 + NO3) concentrationswith concurrentflows (valuesscaled to themouths oftributaries). The Providenceand SeekonkRivers were next dividedinto four reachesfollowing Chinmanand Nixon (1985),with the areaofeach reachincluding those ofupstream reaches. For example, Element2 in this analysis(nodh ofFields Point)woutd include loads and areas to the upstreamElement I (SeekonkRiver). The surfacearea of eachelement is listedin Table2. For futurereference, the load to eachelement corresponding to the 2x loadingcondition is alsoincluded in the table.

Table 2: Surfacearea bv reach and dailv load to the reacbfor the 2x load condition. Element Area Loadat 2X (m2) (mmoleidav) (ke/day) Seekonk 2.81E+06 1.628+07 LLO.J Fields 5.818+06 3.34E,+07 468.2 Bullocks 1.43E+07 8.26E+01 I I Jb.) ProvidenceR. 2.418+07 i.39E+08 1945.7

A comparisonofloads per unit areafrom the 1995-1996DEM studyto the MERL enrichmentgradient experiment is presentedin Figure 12.The figue showsthat on a unit areabasis, using measurements ftom the 1995-1996DEM Study,the Providence- Seekonk River systemreceives loads at a ratebetween the 4X and 8X case(6X). The SeekonkRiver receivesloads at a ratebetween the 16X and32X cases(24X). It is worth notins that the

Page9 of 32 a

majority of the DEM measuredloads for the tributaryrivers were collected during fpical o summerseason flows ind assuch do not accountfor

Comparisonof obseruedsummer loadsto the Providence and SeekonkRivers with MERLtank levels o o

^70 o o o'"

q,

i: .u a o z

O

a 0

Tankcase ("x") Figure 12: Comparisonbetween observed loads per unit area to reachesofthe o Providenceand SeekonkRivers with the MERI- enrichment experimenttanks.

wet weatherloadings. Neither the DEM datanor the MERL experimentsdirectly accounted for atmosphericdeposition to the Bay surface.The DEM dataalso do not accountfot CSO loads,or for stormrunoff enterinsdownstream of the mouthsof the tributaries. a

Page10 of 32 a The dissolved oxygen and chlorophyll data derived ftom Sea-Birddata supportedby surface andbottom water grabs ftom the 1995-1996DEM surveys,averaged by depthfrom the daily high and 1owtide surveys,are shownas a function of distancealong the river and depth in Figures13 through16. DO andchlorophyll-a data averaged for the top 2 m of the water columnfor station5 locatedat the north endofFields Pointare shown in Figures17 and 18. The 1995 data show a systemthat is alternatingbetween extremes of oxygen and chlorophyll duringthe four mid-summersurveys. Beginning on June29, DO is well abovesaturation in the upper water column throughcut the length of the system.June 29 chlorophyll levels are very high, exceeding200 ug/I- in the SeekonkRiver and 100ug/l in ProvidenceHarbor. Threeweeks later (July 20),with no significantrainfall, andBlackstone River discharge downnear its 7Q10value (the lowest 7-day mean discharge over a 1O-yeatperiod), the bottomwaters of the SeekonkRiver areessentially anoxic and the areaupsfeam ofsabin Pointis hlpoxic (3.80mg/l at the surface,Fields Point). Chlorophyll levels are near zero throughout the area,except near the mouth ofthe ProvidenceRiver. Three weeks later on August 10,the conditionsof June29 haveretumed: supersaturated DO levelsnear the surface,and relatively high (20-30ug/l) chlorophylllevels in the upperriver. Two weeks later on August24, DO hasagain dropped to low values.The entirearea is h)?oxic, andis anoxicnear the boftomin the upperreaches. Surface DO at FieldsPoint (Figure 17) is 3.4 mg/l on August24. Levelsonly occasionallyexceed 4 mg/l downto ConimicutPoint. Chlorophylllevels remain high at somelocations in the river, with peakvalues above 30ug/l betweenthe southend ofFields Pointand SabinPoint. On September21, DO levelshave increasedsomewhat, but are still low near the bottom in the SeekonkRiver.

In summary,the behavior ofdissolved oxygen during 1995may be characterizedas s$/inging betweenextremes, in a mamer qualitatively similar to that of the higher enrichmenttanks (e.g.16X and 32X). In general,dissolved oxygen levels were not sufficientto supportfish populationsnear the surfaceduring many periods in 1995.

Mid-summer1996 dissolved oxygen levels in the ProvidenceRiver appearto be morestable, This stability appearsto result from vertical stratification causedby higher river flow that occunedduring that summer.Bottom water oxygen levels remained below 4 mg/l to the mouth ofthe ProvidenceRiver, probably betweenmid-June through late September.Values nearthe bottomof the channel(below lOm depth)were tlpically nearzero down to Sabin Point duringthis period.Chlorophyll-a levels were lower in 1996;peak values were an order of magnitudelower, probably because flushing times were low.

The field chemistrydata are summarized in Table3 below asaverages by stationfor the center of channelstations for both years.Wlen comparedto the MERL results and the MA guidelinesdiscussed below, the ProvidenceRiver concentrationdata indicate that the areais enriched.TN levelsare above 0.4 mg/l throughoutthe area,up to nearly1.5 mg/l at station1. DIN concentrationsare significantly greater than a 10 uM (0.14mg/l) guidelineused by Massachusetts.Mean chlorophyll levels obtained from watersamples exceed 10 ug/l at all stationswith the exceptionof4 at Fox Point,and increase to abovenearly 30 ug/l in the SeekonkRiver, which approachedthe 16xMERL tank condition.

Pageli of 32 o

Mean DIN concentrationsobserved in the Providenceand SeekonkRivers were significantly o lower than those seenin the MERL experimentfor an equivalentloading rate per unit area. For example,DIN at station1 in the upperSeekonk River wasless than I mgll. An expected concentrationfrom the MERL data in Figure 1I for that location would be approximately 3.9 mgA.This differencemay possiblyresult from the shortercharacteristic flushing time ofthe ProvidenceRiver. Empirically derived relationshipsbetween freshwater inflow and flushing o time developedby Asselin(1991) indicate that themean residence time of freshwater in the Providenceand SeekonkRiver duringthe May- Octoberperiods of 1995and 1996would be about3.5 days.This is significantlyshorter than the 27-day time usedby MERL. The higher removal rate by flushing would accountfor the difference.DIN uptakeby macroalgaeand denitrification in tlre bottom waters are additional reasons.Significant areasflanking the dredgedchannel in both rivers are shallow, and sigdficant $owth ofmacroalgae occurs in a the areaeach year. Enrichmentexperiments in shallow mesocosmshave observeda similady diminishedDIN buildupin the watercolumn that is possiblyconnected to uptakeby macroalgaeand benthic flora (Nixon et al,2001). Nixon et al alsosuggests that in shallow systems,the residencetime of nitrogenmay be muchlonger than a conservativesubstance, such as ftesh water. The disparity betweenthe observedand predicted DIN showsthat the MERL systemis not a perfect analog.We feel, however,that the other relationshipsmake the o coffrectionadeouate.

Table3: : MMeansofthe fthe 1995-f996DEM data.

,I to.2 9.2 8 6.2 5 4 3 2 I Upper Lower Fields Point o Bullocks Pt. Reach SeekonkRiver Reacb Bav River Reach 0.06 0.08 0.12 0.I6 0.18 o.25 0.28 0.37 0.3'7 0.31

0.06 0.08 0.12 0,11 0.19 0,13 0.16 0.41 0.54 0.65 o 0.12 0.16 0.24 0.27 0.37 0.37 0.44 0,78 0.92 0.96 0.10 0.11 0.09 0.08 0.10 0.05 0.05 0.09 0.11 0.10 TN fms/) 0.'13 a 0,06 0.08 0,09 0.10 0.13 0.14 0.15 0.25 0.22 0.10 0.1I 0.tz 0.13 0.1'7 0.17 0.18 0.26 0,31 0.29

2.18 2.86 2.60 3.61 2.82 3.46 2.17 5.09

15.33 a 14.93 23.s6 I 1.16 r4.14 17.52

a

Page12 of 37 a SeekonkRiver ProvidenceHarbor ProvidenceRiver Narragansett Bay Figure13: Tidally averaged dissolvedoxygen vs. depth and location during the 1995surveys. Whiteareas:<2 mg/|. Green areas: B^11e,areas >3 mg/l at 1mg/lincrements. $fmgt. o

e a = o

E .q o

o -=:

o

O

o a

Upper SeekonkRiver providenceHarbor ProvidenceRiver Narragansett a Bay Figure14: Tidally averaged dissolved oxygen vs. depthand location during the 1996surveys Whiteareas:<2 mg/|. Green areas: 2-3 mg/|.Blue areas >3 mg/lat '1mg/lincrements. Pas.e14 of 32 SeekonkRiver ProvidenceHarbor PrwidenceRiver Narragansett Bay Figure15:Tidally averaged chlorophyll-a vs. depthand locationduring the 1995surveys lsoplethsare at 10 ug/lincrements Pase15 of 32 o o o o o a

t

a

a

ProvidenceHarbor ProvidenceRiver Upper SeekonkRiver Nanagansett a Bav Figure16: Tidally averaged chlorophyll-a vs.depth and location during the 1996 surveys. lsoplethsare at 10ug/l increments. Pase16 of 32 E

6/10/95 6/30/95 7t20195 8/9/95 8/29/95 9/18/95

Figuro17: Tldallyav€ragod dlssolvod oryg€n and chlorophyll-a h the too 2m otthe watercolumn In ProvidsncaHa6o. durins tho summsrot 1995

!

=

5/96 6/4/96 6t21196 7114t96 aB/96 8/23/96 9t12196 1AtZ96 10122t96 .1.1t.11t96 Fisuro lE: Tldallylveraged dissolved oxygen.nd chlorophyll.a h thslop 2rn ofth€ wat6. columr duri.g the summerof 1996

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USING THE MERL R-ELATIONSHIPSTO PROJECTTHE IMPLICATIONS OF FUTURE o NITROGEN LOAD REDUCTIONS TO THE PROVIDENCE AND SEEKONK RiVERS

As noted in the Initial Report From the Nutrient and BacteriaPollution Panel of the Govemor'sBay andWatershed Planning Commission, several analyses have been conducted which agreethat waster/ater treatmentplants are the major sourceofnitrogen to Nax(agansett I Bay (Nutrientand BacteriaPollution Panel, 2004). This sectionpresents a summaryofan analysisthat DEM hasconducted to gvaluateoutcomes for reducingnitrogen levels.

ConsiderationsRegardine WWTF loading reductions The Long IslandSound TMDL for DO setthe degreeof nutrientreduction at a WWTF based on the relativeenvironmental impact ofeach discharge.This issuewas addressedin the Long a Island SoundDissolved Oxygen TMDL (llrYDEC and CTDEP, 2000) by establishingtwo "equivalencyfactors" to accountfor the lossof nitrogenbetween the point ofdischargeand the point of impact. Thesewere: 1) attenuationduring tributary river transpod, called river deliveryfactors, and 2) transferefficiency from the "edge-of-Sound"to the areaofmost significant degradation. o River deliveryfactors are predicated on the ideathat somedegree ofnitrogen removal due to permanentuptake or denitrification occurs in the river betweenthe WWTF dischargeand the mouth.It is expressedas the percentageofthe point sourceload discharged to the river that reachesthe Sound.In the Long Island Sound Study, dver delivery factors rangedbetween 52%- 90%. River delivery factors may increaseas nutrient inputs are restricted to control o low dissolvedoxygen and excessivealgae growth in the rivers. Reductionsin WWTF phosphorusinputs have been required and are in variousstages of completionalong the Blackstoneand Pawtuxet Rivers.

BlackstoneRiver Detailedsource and river loads(i.e. concunentWWTF andriver data)were computed as part a ofthe 1991interstate Blackstone River Initiative study. Basedon samplingconducted during three sampling surveys(July, August and October),the load dischargedfrom the mouth of the BlackstcneRiver into the Seekonkfuver is estimatedto rangefrom 27o/o to 84%(average 60%) of the summednitoogen loads ftom the WoonsocketWWTF andthe UpperBlackstone WaterPollution Abatement District WWTFs. Basedon DEM's 1995and 1996sampling at a the mouth of the Blackstoneand monthly averageWWTF dischargemonitoring report data, 87o/oof the loadingliom the two sourcesis dischargedfrom the BlackstoneRiver. Stated anotherway, reducing the total nitrogen from the WWTFs to 8 mg/l is equivalentto 7.0 mgll dischargednear the mouth of the BlackstoneRiver. The differenceis attributableto uptake and denitrification along the length of the river. Given the large range observedduring the BlackstoneRiver Initiative,and sinceconcurrent WWTF andriver datais not availablefor a the othertributaries rivers the 1995- 1996data was used to calculatedelivery factors for all tributariesto the Providenceand SeekonkRivers.

PawtuxetRiver Attenuationof the WestWarwick, Warwick and CranstonWWTFs loadingis anticipated when discharsedfiom the mouth of the PawtuxetRiver into PawtuxetCove which in tum

Pagel8 of 32 dischargesto the ProvidenceRiver at PawtuxetNeck. Using the method describedabove, it was estimatedthat 82% of the WWTF load is dischareedfrom the mouth of the river.

TenMile River In the Ten Mile River,the DIN dischargeto tlre SeekonkRiver was foundto be 61% of the concurrentload estimateftom the Attleborough and North Attleborough WWTFs using 1995-1996flows. The Attleboroughfacilities did not monitornitrogen during that period, so concentrationsreported in 2000-2002discharge monitoring reports (DMRs) wereused to representthe facility loads.

Considerationofthe hansfer efficiency from the edgeofthe Providenceand SeekonkRivers acknowledgesthat areasof the Providenceand SeekonkRivers with the most severehlpoxia arelocated ftom the mouthofthe BlackstoneRiver to GaspeePoint. Although sufficient information is not available to quantitatively evaluatethis "equivalency factor", a qualitative approachis alsoinstructive.

Edge ofthe SeekankRiver Sourcesto the edgeof the SeekonkRiver include the BlackstoneRiver, the Ten Mile fuver and the Bucklin PointWWTF. Giventhe closeproximif of thesesources it is reasonableto concludethat on a unit loading basis,these sources equally impact the SeekonkRiver. As suchit is not appropriateto establishtransfer efficiency factors for thesesources.

Edge of the ProvidenceRiver Significantnitrogen sources to the edgeof the Providencefuver includethe SeekonkRiver, FieldsPoint WWTF, EastProvidence WWTF andPawtuxet Cove. Based on the close proximity of the SeekonkRiver, Fields Point WWTF andEast Providence WWTF to one anotler andto the areasof mostsevere hypoxia, it is reasonableto concludethat on a unit loadingbasis, all sourcescause equal environmental impacts. The PawtuxetRiver discharges to PawtuxetCove, which thenempties into the ProvidenceRiver at the southemextent ofthe areaof severehypoxia. As a result, the impact of nutrient loadings ftom Pawtuxet Cove would qualitatively expectedto be less than that thoseftom sourcesto the edgeof the ProvidenceRiver or to the edgeofthe SeekonkRiver.

Loads from unstreamWWTFs in the Pawtuxet.Blackstone and Ten Mile Rivers WWTF loads to the tributary rivers were calculatedusing DischargeMonitoring Report (DMR) datacollected May - October1995-1996.Inorganic nitrogen data were not collected by the UpperBlackstone or Ten Mile facilitiesduring that period. As a consequence,data collectedfor May throughOctober 2000 - 2002were used to representthe facilif loadsftom the UpperBlackstone facility (LIBWPAD)in Worcester,Attleborough and North AttleboroughWWTFs.

Loads reachingthe mouths of the rivers ftom the WWTFs were calculatedin two ways for this analysis.The first approachassumed that the DIN loadreleased from the facilities reachedthe mouthofeach river with no lossor uptakein the river. This term wasassumed to be representativeofthe casewhere either no denitrificationwas occurring, or wherenitrogen was not accumulatingannually in the bottomsediments ofthe river. The secondapproach assumedthat somenet uptakelosses were occurring in therivers. This lossterm was

Page19 of 32 o

calculatedas a percentageofthe combinedplant load (otherwatershed sources, including o smallerWWTFs in the upperBlackstone are assumed to be negligible),based on observedor estimatedplant loads during the summermonths of 1995- 1996,and the loadsobserved leaving tlte mouths of the rivers. The ratios (load leaving river/load introducedby WWTFs) werc 87o/o,82Vo,and 60%o for the Blackstone,Pawtuxet, and Ten Mile rivers,respectively. a A componentofeach plant's TN load was assumedto be reftactorynitrogen. A refiactory nitrogenconcentration of 2.0 mg/I, the upperlimit of the 0.5 to 2.0 mgll rangesuggested in the literatute(WEF andASCE. 1992),was used as the meandifference between TN and DIN. The meandifference measured by DEM at Bucklin, Fields,and East Providence WWTFs during its 1995- 1996 study was 1.4 mg/l. The DIN loadings from facilities in the tributary watershedsfor eachreduction scenariothen equalodthe product of the (TN- a refractory N) concentrationand plant flow. As an example,for the TN=5 case,the DIN load from a facility would be (3.0mg/l) x (meanflow). For facilitiesnot dischargingdirectly to tlte Providenceor SeekonkRivers, and where river attenuationwas assumedto occur, this load would be further reducedas describedin the paraglaphabove. DIN loads from facilities directly on the Providenceand SeekonkRive(s were calculatedas the product ofthe (TN- a refractory I,f concentrationand the meanflow. Calculationswere also made for the casein which projectedloads were based on plant flows at 90% of theirapproved design flows. A comparisonof WWTF datarevealed that the averageMay-October 1995-1996 flows were90% ofthe January-December 1995-1996 flows. WWTF designflows arelisted in Table4. o Table 4: WWTF flows and flows usedfor the load evaluations. o EAST PROVIDENCEWWTF ARRAGANSETT BAY COMM-BUCKLIN ARRAGANSETTBAY COMM-FIELDS o WESTWARWICKWWTF

TTLEBOROUGHWWTF ORTHATTLEBOROUGH WWTF o Baseloads Basenutrient loads from the Blackstone,Ten Mile, andPawtuxet tributary rivers were calculatedto establisha DIN concentrationthat would exist in the absenceof wastewater treatmentfacilities. This minimumDIN concentrationof 0.30mg/l wasderived from data collectedin the northbranch of the PawtuxetRiver upstreamof the WWTFS(Liberti, 1987). a The baseloads for eachriver werethen calculated as the productof this concentration(0.30

Page20 of 32 o mg/l) andthe meandaily flow on the dayssamples were collected for the 95-96TMDL study.. For the BlackstoneRiver, the baseload of370 kg/dayresulted from a mean dischargeof 14.3m3/s (dischargeat Woonsocketscaled up to the valueat the mouth), Estimatedbase loads calculatedin a similar mannerfor tlre Ten Mile and PawtuxetRivers were 50 and 161kgiday, respectively. These values were also used whenever the contributions ftom WWTFs reachinethe mouthsof the tributarv rivers were lessthan the baseloads.

Combining loadsand areas The impact of theseloads on water quality in the areais a function ofboth the size ofthe loading and the size of the area,and would be expectedto increaseupriver from Conimicut Point to the head ofthe SeekonkRiver. Consistentwith this idea, the study areawas divided into the four sub-areaspresented in Figure3 of Chinmanand Nixon (i985). Surfaceareas and sourcesare presented in Table5. Eachelement receives loads from WWTFs and tributaries discharging.tothat reach,in addition to the loads to upstreamreaches. For example,element 4 in the tablereceives loads from all sourcesin elementsI through3. The areareported below for element4 includes the summedareas of elementsI through 3. Loads entedng eacharea ftom the Blackstoneand PawtuxetRivels are quantified as outlined above.

Table 5: of sourcesand r areas Element Element Sourcesincluded: Number area (sourcesalso contribute to downstreamelements) (m2) I 2.8r8l{6 BlackstoneRiver. Bucklin PointWWTF, andTen Mile River 2 5.81E+06FieldsPoint WWTF, WoonasquatucketRiver, MoshassuckRiver 3 1.43E+07PawtuxetRivel East ProvidenceWWTF 4 2.418+07 Providenceand SeekonkRivers

Results Figure 19 showsobserved or projectedloads per unit areafor eachof the four elementsof the ProvidenceRiver asa functionofconcentration and flow case(described on thex-axis) for threescenarios. For this example,loads fiom WWTFs in the tributariesare attenuated prior to reachingthe Providenceand SeekonkRivers. The leftrnost group ofbars representsthe projectedloading condition of eacharea with no treatmentplants. The remaininggroups representt}te conditions for the periodof 1995-1996,all plantsat TN of 5 mg/l anddesign flows, andall plantsat TN of3 mg/l anddesigt flows.

The figure showsthat in the absenceof the WWTFs listedin Table4, loadingconditions in the areawill rangefrom less that the lX condition for the areaas a whole to slightly lessthan 4X for the Seekonkriver. The secondgroup ofbars showsthe present loading condition. The following two groupsofbars showconditions seen under the TN:5 andTN:3 scenariosand assumeddesign flow conditions.For the TN=3 case,the loadsper unit areadrop to under5x in the Seekonkfuver andto slightlymore than lX for the areaas a whole.Areas north of the Gaspee-Bullockline would receiveloads equivalent to the 2X caseunder this condition.This scenarioassumes that someftaction of WWTF loadsto tributariesdo not reachthe

Page21 of 32 o

Providenceand SeekonkRivers. For the assumptionofno river attenuation,the projected o condition of the areais shownin Figure 20. Note that the TN:3 results are identical in Figures19 and20 becauseWWTF loadsdelivered to the moutls of the rivers droppedbelow the baseload values,hence the baseloads were used. As expected,the TN:3 casefeld the lowestenrichment scenarios throughout the area.These enrichment levels would be consideredto be essentiallyequivalent to the no-WWTFcase. The load per unit areafor the TN:5 mgll caseeffectively doublesthe loading index for eacharea. a Enrlchm.rt lewls .s.umlng tlbut!ry aronu6rbn a

= z a a Figure 19: Summary ofprojected DIN loading rates to selectedreaches ofthe Providenceand SeekonkRivers under four scenarios.

Enrlchrn nt l.vel5 ssumlng no lrlbuiary .tronuatlon

I

o = o

Figure 20: Summary ofprojected DIN loading rates to selectedreaches ofthe Providenceand SeekonkRivers under four scenariosassuming no uptake ofnitrogen o along river.

Page22 of 32 o WHAT GOALS SHOULD BE SETFOR THE AREA?

Table2 in Rule 8.D of the WaterQuality regulations (DEM, 1997)lists the dissolvedoxygen standardfor RhodeIsland's Class SB marinewaters:

SB waters: Not lessthan 5 mg/l at anyplace or time,except as nafiirally occurs.Normal seasonal and diurnal varictionswhich result in in situ concentrationsabove 5.0 mg/l not associatedwith cultural eutrophication will be maintainedin accordancewith the Antidegradation ImplementationPolicy.

Culturaleutrophication is definedas the human-inducedacceleration of primary productivity in a surface waterbodyresulting in nuisanceconditions of algal blooms and/or dense . macrophytes.

The regulationsalso contain a definitionoflow qualitywaters that states:

"Low quality waters eansany water whosequality falls below any ofthe criteria of rule 8.D. in accordancewith ApplicableConditions of rule 8,E.and cotresponding to its classification as designatedin rule 8.C., as determinedby the Director, shall be considereddegraded for that particular criterion and in violation of its water quality standardsand, therefore,unsatisfactory for any designateduses which the Director tleterminesare affectedby theparticular criteion which is violated. Wdtersin their natural hydraulic condition mayfail to meettheir assignedwater quality criteriafrom time to time due Io naturalcauses, without necessitdting the modificationof assignedwater quality standard. Suchwaters will not be consideredto be violating their water quality standardsif violations of criteria are due solely to naturally occurring conditions unrelated to human aclivities.

Rule 8-Ementioned above defines critical adverseconditions under which the standards apply;Rule 8.C categorizeswater quality classifications.

Examination ofFigure 4 showsthat the water quality standardfor DO cannot be met under any loading scenario,because DO minima for the three control ta.nks(containing un-enriched water from the mouth of NarragansettBay) are all below 5 mg/L during the experiment.DO minima for the enrichedtanks also drop further below the standardas the enrichmentlevel increases.Although the numericwater quality standard of 5 mg/l is not met in the un- enrichedtanks, they arenot consideredto violatethe standardbecause ofthe "exceptas naturallyoccurs" clause in the standard- humanactivities do not contributeto an exceedence ofthe standard.The final sentencein the definitionof low qualitywaters clarifies that levels below 5 mg/l arenot considereda violationof standardsif the violationsare due "solely" to 'tnrelated conditions to humanactivities". The presentregulations coupled with the analysis presentedabove indicate that, amongother reduction actions,WWTF nitrogen contributions mustbe reducedto the limit oftechnologyin the Providenceand SeekonkRivers.

Page23 of 32 a

EPA hasissued revised guidance for DO standardsin marinewaters, and DEM is in the a processof implementing the guiilanceinto a revised standardfor its marine waters.The revisionshave not beenfinalized, but do allow excursionsbelow a basevalue of4.8 mgll, down to approximately3 mgfl for short periods of time. Although the new standardshave not beenestablished, a reviewof Figure4 indicatesthat it is possiblefor the standardto be met undet someofthe lower enrichmentcases. The regressionequation in Figure4 indicatesthat o the DO minima for the 2X and4X casesare 3.7 and3.0 mg/l respectively.Under these conditions,it is possiblefor EPA's recommendednew DO standardto be met.On the other hand, minima for the 8X and higher casesare lessthan 2 mg/I. The watet quality standard couldnot be met underany oftheseconditions. DEM thencould not proposeloading allocationsthat were shown to meetthe 8X or hiehercondition if lower levelscould be achieved. o Referringback to Figures19 and20, onecan see even for the projected"no WWTF" loading case,the enrichmentstatus of the Seekonkand upper ProvidenceRivers varies fiom a high of 'ho 3.7X in the SeekonkRiver, down to 0.8 for the areaas a whole.This WWTF" condition defir-testhe best potential condition for the Providence-SeekonkRiver area. With WWTFs in o the watershedreducing their loadsto a level consistentwith the limit of technology,where eflluent TN is 3 mg,4,enrichment levels in the areawould langeftom 1.1X- 4.7X. This scenariois arguablyquite similarto the no-WWTFcase. For the next higher(TN:5) case, levelsin the upperProvidence River and SeekonkRiver increasesignificantly to 8.0X above FieldsPoint andto 9.3X in the SeekonkRiver. These levels would not be acceptableas water quality goalsfor the area,based on the behaviorobserved in the MERL experiment. o The allowableplant loadsare based on the estimatedMay - Octoberdesign flows, andan effluentTN of 3 mglI, of which 2.0 mg/l is assumedto be reftactory(not DIIrI).These loads arelisted by facilityjn Table6. o Table 6: Plant TN allocations(at TN=3 mg/l and 907odesign flow), DIN loadsused in this o o o

Page24 of 32 o The allowableDIN loadsdue to WWTFs andriver baseflow for eachreach of the Providenceand Seekonkfuvers based on the limit of technology,and not accountingfor sourcessuch as stormwaterdirectly discharging to the riversbecome:

Element1, SeekonkRiver: 526k/day Element2, Areasnorth ofFields Point 877klday Element3, Areasnorth ofBullocks Point 1013kglday Element4, Entire area lO73 k{day

Experimentaldata indicate that the 2X and4X conditions(8.06E-05 kglmZlday ard 1.618-04 kg/mZlday, respectivelg are the likely goal from the perspectiveofconsistency with the State'swater quality standards.Specifically, the enrichmentstatus ofthe SeekonkRiver would be expectedto be consistentwith the 4X condition, and the remaining areaofthe ProvidenceRiver would be at the 2X or a lower condition. Information ftom other agencies and researchersindicates that maximizing the areaofthe Providenceand SeekonkRivers at the 2X level is beneficialfrom the standpointof supportingthe designateduses ofthe area for fisherieshabitat. The following pointsunderscore this decision: r Historicaldata indicate that eelgrassbeds were once present in the ProvidenceRiver, extendingnorthward to GreenJacket Shoal opposite Fox Point (www,edc.uri.edu/ Eelgrass).Eelgrass restoration efforts to date have determinedthat future restoration effortsnorth ofPrudenceIsland are water quality limited. The goal of supportingfish and shellfishpopulations in the ProvidenceRiver is oompatiblewith the retum ofeelgrass,at least in the southernreaches of the ProvidenceRiver and upper NarragansettBay. Dennisonet al. (1993)repoded the following habitatcriteria for SAV: DIN of 0.15mg/l (10.7pM), DIP of 0.33 pM; N:P (atomic)of 32; and chlorophylla of 15 pgll.. The MERL experimentmeans at the 2X caseare 0.26 mg/l for DIN and 12 :ug/l for chlorophyll,which comparewell with theseguidelines. o Locally, Massachusettshas established environmental general guidelines for total nitrogenconcentrations in estuaries.Guidelines began with thosedeveloped by the BuzzardsBay Programthat ratedthe conditionof a waterbody based on ambientwater qualityparameters (Table 7). Eachestuary was scoredon thebasis ofa suiteof parametersthat includedmean DIN, Chlorophyll,and DO concentrations.Impaired estuariesreceived a scoreofzero ifmean DIN levelswere greater than 10 uM (0.14mgll) or chlorophylllevels exceeded 10 ug/I. The40% saturationDO levelswould correspond to a concentrationslightly greaterthan 3 mg/l in estuarinewaters during the summer. Underthe BuzzardsBay approach,SB waterswould haveto meeta scoreof 40%; SA waterswould needto meet50%. r Massachusettshas recently refined its approachto incorporatea land-useloading model, and a receivingwater quality model that simulatesthe TN responseto loading.The TN targetlevels (Table 8) areloosely based on theprevious Buzzards Bay Programresults, but alsoinclude site-specific consideration ofnitrogen concentrationsand indicatorsof

Page25 of 32 I

emba).rnenthealth (dissolved oxygen, phytoplankton densities, water clarity, sediment a type and carbon concentrations,macroalgae, eelgrass and benthic communities).Two

Table 7: BuzzardsBay Project Eutrophication Index etrdpoints 0 Points: 100Points: Summer0/o Dissolved Oxygen saturation 40% 90o/o o (meanlowest 1/3) Secchidepth,(m) 0.6 3.0 Dissolvedinorganic nitrogen (DIIrf , (uM) 10.00 1.00 Chlorophyll-a(ug/l) 10.0 3.0 a Total organic nitrogen (TOIli), (mg/l) 0.60 0.28

significant results ofthe MA work are that mean chlorophyll levels of 10 ug/l and DIN of 10 uM (0.14mgll) appearto representthe thresholdbetween suitable and impaired O waters. Table 8 summarizesthreshold TN concenhationsard the resulting obsewations of embaynenthealth. The 2X casemeets the mean chlorophyll a concentrationof 10 ug/l (Figure10) target established by Massachusetts.

Table 8:MA for TN andenvironmental health Condition Threshold Nitrogen Observations o Concentrations Excellent <0.30 Good 0.30-0.39 Eelgrassbeds present, benthic animal diversity and shellfishproductivity high, oxygendepletions to <4 mq/L arerare, chlorophyll 3 to 5 ug/L. Moderate 0.39-0.50 Above this TN range,loss ofdiverse animal a Quality communitiesand replacement by smaller,shorter-lived animalsof intermediateburrowing capabilities, and shellfisheriesmay shift to moreresistant species. Oxygenlevels do not generallyfall below 4 or 5 mg/L, phytoplanktonblooms raise chlorophyll at levelsto around10 us/L. Mafio-algaemav be Dresent. o Significant 0.50-0.70 Largephytoplankton blooms, chlorophyll a of Impairment approximately20 rng/L. ShessfiI oxygenconditions, majorphfoplanklon blooms,complete loss of eelgrass, periodicfish kills, macro-algalaccumulations and aesthetic(odor) problems are observed. Stress tolerant sDecresDefslst, o Severe >0.70 Completeor nearcomplete loss of oxygenperiodically Degradation in bottomwaters, Macro-algalaccumulations and fish kills areobserved periodically. Drift algae,lift-off matsand near complete loss ofbenthic animal communities occurs during a portion of the sufinnel. O

Page26 of 32 o Our summaryof this analysisis that considerablereductions of existingloads to the Providenceand SeekonkRivers arc needed.In the context ofexisting information on water quality conditionsneeded to supportState water quality standardsand the designateduses of the area,a loading scenarioconsistent with the 2X-4X condition representsthe goal for the area.The WWTF scenariothat produces loads consistent with this goalwould require WWTFs in thewatershed to implementreductions to the limit of technology.DEM's interpretationof this limit is the TN:3 scenario,with plant flows at 90% ofpresent design values.

PhasedImplementation of NitrogenConhols

Basedupon the MERL enrichmentgradient experiment,minimum DO levels of approximately3.0 and2.7mll areanticipated from the no treatmentplant andLOT cases, respectively.Lower valuesare expected for the ProvidenceRiver sinceit is stratifiedand the MERL experimentwas conductedunder unstratified conditions.This analysisindicates that the limit of technology is requiredbut will not fully meet existing water quality standards (minimumof 5.0mg/l "exceptas naturally occurs") and may not meetEPA guidelines recentlyrecommended for watersfrom CapeCod to CapeHatteras (EPA 2000).The EPA guidelinesallow instantaneousvalues below 4.8 mg/l providedthe cumulativeexposue to low DO levels do not exceedthe duration criteria establishedto ensurethat the cumulative pefcentageof larvae affected shall not exceeda 50loreduction in larval recruitrnentover the recruihnentseason.

While we believe that the MERL tank results provide an adequaterepresentation of the relationshipbetween nitrogen and oxygen levels in the Providenceand SeekonkRivers, some uncertainty remainsregarding predicted water qualif improvementsand loading reductions necessaryto meetwater quality standards.As notedabove, significantly lower meanDIN concentrationswere observedin the Providenceand SeekonkRivers as comparedto the MERL experimentfor an equivalentloading rate, which may be the result of large differencesbetween the field and experimentalflushing times, uptakeby macroalgaeand denitrification in the bottom waters. Also the MERL experimentDO samplingprotocol does not providesufficient data to fhlly assesscompliance with the recenflyestablished EPA guidelinesregarding cumulative periods oflow dissolvedoxygen. However, it is clearthat the Providenceand SeekonkRivers are impacted by low dissolvedoxygen levels and high phytoplanktonlevels related to excessivenitrogen loadings. For thesereasons, evaluation of phasedimplementation is indicated. Implementationof a phasedapproach is consistentwith the EPA TMDL guidance(EPA 1991)which states:"For certainnon-traditional, problems, if there are not adequatedata and predictive tools to characterizeand analyzethe pollution problem,a phasedapproach may be necessary."

Evaluationof ImplementationAltematives

For the reasonsnoted above, RIDEM hasevaluated implementation costs, analysis of the performanceofavailable technology, and estimatesof waterqualiry improvement to developeda phasedplan for implementationof WWTF improvementswhich maximizesthe DO levelsrelative to imDlementationcost.

Page27 of 32 o

a Nine differentcases, representing various combinations of nitrogenreduction at 3 MA and 7 RI facilitieswere examined. The facilitiesincluded in this analysisare: Upper Blackstone WaterPollution Abatement District ("UBWPAD" or "UB"), locatedin Worcester,MA, North Attleboro("NA"), Attleboro("A"), Woonsocket("W'), Bucklin Point ("8P"), Fields Point ("FP"), EastProvidence, Cranston, West Warwick and Warwick. Estimateswere developedfor capitalcosts, including allowances for planning,design, construction and a administration,to modify a secondarytreahn€nt facility to achievethe target levels on a seasonalbasis. Table 9 lists the altemativesevaluated and the estimatedimplementation costs. Costsshown must be considered"Order-of Maenihrde" cost estimates. since specihc facility characteristicswere not availablefor manyaltematives. The costarc based on estimateswhich were developedfor control ofpoint sourcesin the ChesapeakeBay I watershed(Nutrient Reduction Technology Cost Task Force,2002), with the exceptionofa few facilitiesfor which planningestimates or constructionbid costswere available. A comparisonof th€ cost to water quality benefits arepresented both in terms of the resulting loadinggradient (Figure 2i) and loadinggradient improvement (Figure 22). a Table 9: Estimated costof WWTF nitro reduction alternatives. o BP 5 menrest 8 W. FP, BP 5 rest 8 BP 3.UB. W 5 rest8 FP. BP 5. RestRI 5: RestRl 8: NA. A 95-96lev€ls O

As notedin Figures21 and22, thefollowing WWTF reductionsmaximize the waterquality o improvementsrelative to costs,5 mg/l at UBWPAD, Woonsocket,Bucklin Point andFields Point and 8 mg/l at North Attleboro,Artleboro, East Providence, Cranston, West Warwick andWarwick. Reductionsin loadingare expressed as the mean95-96 summer conditions comparedto conditionsresulting ftom nitrogenloadings at the targetconcentrations dischargedat summerWWTF designflows (90%of approveddesign flows). The anticipated loadingreduction includes estimates ofnitrogen uptake in the tributaryrivers (river o attenuation).If nitrogencontrols are not implemented,loads delivered to the Providence Seekonksystem will increaseby 55 % asWWTFs increaseto their designflows, increasing the existingSeekonk reach loading factor liom 24X to 40X. Using the analysisdescribed above,implementatjon of this first phasewould initially reducethe summerseason WWTF loadingdelivered to the ProvidenceSeekonk system by 68"/odropping to 529/oas WWTF o flows increaseto their approveddesign flows. The correspondingSeekonk reach loading factorswould dropto 6.6 at currentflows and 10X at designflows.

Page28 of 32 o Loading Condition Vs. Capital Gost Of IryWTF upgrades

20.0

x

,€ 1s.o

o El ! 10.0

J

50 100 150 200 250 300 350 CapitalCost ($M) 21; Loading condition versuscapital costof WWTF upgrades

Loading Condltlon lmprovement Vs. Capital Cost Of WWTF Upgrades

p ,""

- 310.0 s

5.0

0 50 100 150 20a 250 300 350 400 CapitalCost (lMl Figure 22: Loading condition improvementversus capital costof WWTF upgrades.

Page29 of 32 o o Evaluationof the Significanceof WWTFs in Massachusetts If the UBWPAD, Attleboro and North Attleboro WWTFs do not implernentnitrogen controls, the summerseason WWTF loading delivered to the ProvidenceSeekonk River systemwill decreasefrom 53%to 30%below curent levels.The impactto the.Seekonk o River is much more significant; a 58o4redustion with fuI1participation (the loading factor is reducedftom 24X to 10X)but only a 9oloreduction (to 22X) if nitrogenloads from theseMA facilitiesare not reduced.

Therehas been a suggestionthat permit limits for nihogenat MA WWTFs shouldnot be pursueduntil after current upgradesare completedand further information is available to o evaluateriver attenuation(e.g. a river deliveryfactor of 85%was computed for the BlackstoneRiver). DEM doesnot believethis is appropriate,since river deliveryfactors would haveto be llYo andTVobefore the UBWPAD at 95-96concentrations and design flov/ would be reducedto the loading resulting from the 5 mg/l dischargeproposed for Bucklin Point andWoonsocket WWTFs andat their designflows. The UBWPAD designflow is a largerelative to the otherWWTFs impactingthe SeekonkRiver: 1.8times larger than Bucklin Pointand 3.5 timeslarger tJran Woonsocket. Furthermore, the UBWPAD is currently planning an upgradeand it would be prudent to considernitrogen removal options while the planningprocess is underway.UBWPAD, North Attleboroand Attleboro WWTFs play a significant role in the ability to improve water quality in the Providenceand Seekonk River system,and efforts to reducetheir nitrogen inputs shouldbe initiated as soonas a possible.RIDEM will be working with Massachusettsand theUS EPA to pursuenitrogen reductionsat thesefacililies.

Implementationof Nitrogen Reductions a As notedearlier, MERL tank experimentssuggest that LOT treatrnentis requiredto meet waterquality standards.However, based on a comparisonof technology,costs and reductions in the nuhient loading factors for the Providenceand SeekonkRiver Systems,RIDEM has establisheda phasedreduction strategy. The first phaseis basedon achievingthe following WWTF ef{luentconcentrations: 5 mg/l at UBW?AD, Woonsocket,Bucklin Point andFields Point and 8 ml at North Attleboro,Attleboro, East Providence, Cmnston, West Warwick a and Warwick.This analysisacknowledges that loadingswill increaseas WWTF flows increaseto their designflows, but follow-upmonitoring and possibly water quality modeling will be neededto determinewhether additional reductions are required. Because LOT treafinentis presentlyindicated, it is DEM's positionthat it is appropriateto expressWWTF permit requirementsas a concentrationlimit, which will enhancethe near-term o environmentalimprovement while plantsare below their designflows. The analysispresented herein evaluatesthe impact of current and future nitrogen loading scenarioson the Providenceand SeekonkRivers using the inputsftom the mostsignificant WWTFs. For example,summer loads measued at themouth of BlackstoneRiver were expressedas loading from the Woonsocketand UBWPAD WWTF inputs,attenuated to a matchloads measured in theriver. UBWPAD is bv far the sinelelareest WWTF in the

Page30 of 32 o BlackstoneRiver Watershed.Attenuation ftom the stateline to the mouth of tlre Blackstone River wasestablished based on the following assumptions:that majority of the loadings duringthe 95-96study period were from the mostsignificant point sources(Woonsocket and UBWPAD), thatWoonsocket is locatedclose to the stateline, thatthe load crossingthe state line and Woonsocket'sloading are equally att€nuatedand adequatelyrepresented by a single deliveryfactor. The first phaseresults in a DIN load at the mouthof the River of403 kg/day or 463 kg/daycombined input from Woonsocketand MA sources.Of this allowableload, 85 kg/dayhas been allocated to Woonsocketand 378 kgldayto MA sources. UpperNartagansett Bay

Areas of Upper Na(agansett Bay are affectedby the WWTFs that impact the Providenceand SeekonkRiver Systems.ln addition, to reduceits impact on GreenwichCove, the East GreenwichWWTF is in the processof constructingmodifications to achievea seasonal nitrogenlimit of 5 mg/l asrequired by its RIPDESpermit. It is DEM's positionthat the point sourcedischarges to the WarrenRiver will alsoneed to reducenihogen to addressimpacts to thePalmer R iver.

Implementationof nitrogenremoval would initially reducethe summerseason nitrogen load dischargedftom theseeleven Rhode Island WWTFs to theUpper Bay by 65%, clroppingto 48% asWWTF flows increaseto their approveddesign flows.

Monitoring Water Quality Improvements

An integral componentofthis phasedimplementation approach is adequatemonitoring ald assessmentofwater qualitychanges to determineif additionalreductions are necessary to meetwater quality standards.Ofparticular concernare the establishment,maintenance and dataprocessing for a systemof continuousdissolved oxygen, chlorophyll, temperature and salinity monitors strategicallylocated throughoutthe Bay. DEM, in parmershipwith NERRS, the NarragansettBay Commission,University of RhodeIsland and Roger Williams University increasedthe NarragansettBay continuouswater quality monitoring systemftom 7 to 9 stationsduring the summerof2004. DEM has obtainedfunding from the federal Bay Window grantto increasethe numberof stationsto at least13by the summerof2005. This monitoring network will provide the datanecessary to evaluatecompliance with water quality standards,particularly temporal detail needed to evaluatecompliance with EPA's dissolvedoxygen guidelines. The United StatesEnvironmental Protection Agency (EPA), Office ofWater's,Office ofScienceand Technology EPA is currentlyseeking a contractorto assistDEM with the developmentof methodsto reviewcontinuous time seriesDO measurementsfor compliancewith EPA'sOctober 2000 recommended ambient water quality criteria. The contractorwill alsoassess monthly hansectsurveys of the bay to determine whether modifications are neededto the existing and plannedmonitoring network basedand providetechnical support to establishguidelines for evaluatingthe responseto changesin nitrosenloads ,

Page31 of 32 a

References Asselin,S. t 991,Flushing times in the ProvidenceRiver based on tracerexperiments. Thesis o (M.S.).University of RhodeIsland.

Chinman,R.A. and S.W.Nixon. 1985.Depth-area-volume relationships in NarragansettBay. NOAA/SeaGrant Marine Technical Report 87. GraduateSchool of Oceanography, Universityof RhodeIsland. o Dennison,W.C., R.J.Orfi, K.A. Moore,J.C. Stevenson, V. Carter,S. Kollar, P.W. Bergshom,and R.A. Batiuk. 1993.Assessing water quality with submersedaquatic vegetation.Bioscience 43 : 86-94.

Environmental ProtectionAgency,2000. Aquatic Life Water Quality Criteia for Dissolved a Oxygen(Saltwater): Cape Cod to CapeHdtteras. EPA-822-R-00-012

EnvironmentalProtection Agency, 1991. Guidance for WaterQuality Based Decisions: The TMDL Process.EPA Office of Water.EPA440/4-91-001

Liberti, A.S.1985.A wasteload allocationfor DO/BOD dymamicsof the PawtuxetRiver o RhodeIsland, Deparhnent of Civil andEnvironmental Engineering, University of Rhode Island,Kingston.

Nixon, S. B. Buckley,S. Granger,and J. Bintz. 2001.Responses ofvery shallowmarine ecosystemsto nutrientenrichment. Human and ecological Risk Assessment.V.7 No.5,pp. o 1457-148r.

Nutrientand BacteriaPollution Panel, 2004. Nutrient and Bacteria Pollution Panel Initial Report,March 3, 2004. http://wwlv.oi.uri.edu/GovC'ornm/Docurnents/PhaseI Rpt/DocsNutrient-Bacteria.pdf o Govemor'sNarragansett Bay andWatershed Plarming Commission. NutrientReduction Technology Cost Task Force, 2002. Nutrient Reduction Technology Cost Estimationsfor Point Sourcesin the ChesapeakeBay Watershed,November 2002. ChesapeakBay Program. a NYDEP and CTDEP.2000. A Total MaximumDaily Load Analysisto AchieveWater Quality Standardsfor DissolvedOxygen in Long IslandSound. h@://www.dec.state.ny.us/website/doilnndllis.pdf.73 pp.

Oviatt, C.A., A.A. Keller, P.A. Sampou,and L.L. Beatty.1986. Patterns of productivity o during eutrophication:a mesocosmexperiment. Mar. Ecol. Prog,.Ser. 28: 69-80. WEF and ASCE. 1992.Design of municipalwastewater treatment plants / preparedby Joint TaskForce of the WaterEnvironment Federation (formerly the WaterPollution Control Federation)and the AmericanSociety of Civil Engineers.WEF FacilitiesDevelopment Subcommifteeof the TechnicalPractice Committee and ASCE EnvironmentalEngineering o Division Committeeon WaterPollution Management . Alexandria, VA : WaterEnvironment Federation;NewYork, NY : AmericanSociety of Civil Engineers.1592pp.

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