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CI & VA ThlDLs 025;') . http~/www.kdhe.stale.ks.us/undVuastreaJT . sulfate levels above :!50 mg/l. While this background levels are chieflynatural, they have been aggravated from consumptive use and irrigation return flows within the Arkansas River valley from John Mar1in Reservoir to Garden City, Since there are no direct flow diversions for domestic water supply along the river, allempting to improve the surrounding ground water through reduced loading represents the chief concern of Ihis TMDL. As such some intelim endpoint must be developed under this TMDL to refleet this improvement in the relatively shor1teml, Overall, in this phase of the TMDL an intelim endpoint will be to reduce the long term average sulfate concentration below the current average of 1875 mg/I seen at Pierceville, Attaining this reduction should begin to stahilize the quality of the surrounding ground water. albeit at a level elevated heyond typical standards, Seasonal variation in the endpoint is accounted by examining the data on a seasonal basis relative 10 a long tenn average of 1875 mg/L This TMDL may be expressed as a load duration curve corresponding with an constant average of 1875 mg/l (Figure 9), The long range goal is to see future samples plot below the designated curve, particularly in Spring and Summer. As noted previously, there is some decrease in sulfate between the state line and Garden City. This reduction can bc seen seasonally, ranging from 5-7%. Lowest concentrations are associated with runoff conditions in the Spring. As groundwater intluences become more significant. sulfate concentrations increase, The highest concentrations occur in Winter with its lack of runoff and dominant ground water input to the river. OppOltunities to see reduced sulfate levels probably are during the Spling and Summer in situations where runoff is avai lable, -~---^---_.__. - ----~------- ISeason jjJ<.Jl:S7-1999 Garden City SUlCal!; in my I 1111)87-19119 S\l:lldme Sul(.\\c in mgll IIPet Reduction of Sulfate downslream , , ISpring JI 17 17 mgll 111802 mgll 115% I I ISummer-Fall 111800 mgll 111943 mgll 117% i IWinter 112115 mg/l 112226 mg/I 115 % ! These endpoints might be realized through flows of better quality coming down river over time, Emphasis will be placed on improving quality at the higher tlows since this results in lower overall loads entering the stream-aquifer system, It is unlikely that concentrations will improve at flows below :WO cfs. Due consideration of delivery requirements and administration of the Arkansas River Compact between Kansas and Colorado has to be incorporated in this TMDL and will affect the attainment of these modest endpoints, Additionally, evaluation of the existing criterion has to be made under the guise of the current Surface Water Quality Standards. with possible incorporation of background levels and review of designated uses in subsequent phases of this TMDL., 3. SOURCE INVENTORY AND ASSESSMENT NPDES: There are two NPDES pemlitted wastcwater dischargers located along stream reach I of the Arkansas River in the vicinity of Garden City, r- IlST~EA\' ~L\("H I/SE(;MENT JlllESIUN FLOW IIEXPI~ATION Di\TE jDIS('HAIHiER ~nkn Cil)' M\\'WTi' JIAII.:lflS;lS RIver III II' ,(,W;I) II~OO] , Is~~kr ]lArkansa" Rivl.:T --.J11 1111.477 MGll --!1~OO2 - --, <111 "HO , ".0'