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<br />CI & VA TMDLs <br /> <br />0253 <br /> <br />. <br /> <br />hUp:/Iwww.kdhe.slate.ks.usItmdVuastrearr <br /> <br />. <br /> <br />Current Conditions: Sulfate concentrations have been elevated along the Arkansas River. averaging 1875 <br />mg/l near Garden City over 1987-1999, This high level has long been the norm. sulfate concentrations <br />have averaged 1990 mg/l among samples taken at Coolidge over 1963-1999, Analysis of concentration <br />over time shows a single dip below 1000 mgll, but typical levels remain around 2000 mg/l. Concentrations <br />generally reach an upper bound as the saturation limit for gypsum in the vicinity of 2500 mg/I is <br />approached (Figure 2), Seasonally, average river sulfate concentrations at Piercevillc for March-July. <br />August-October and November-February over 1987-1999 are 1709,1801 and 2111 mg/l. respectively, <br /> <br />Below Garden City, concentrations across flow ranges during 1987-1999 average 1860 mg/I at flow below <br />lOcI's, 2002 mg/l at flows betwcen 10 and 250 cfs, 1702 mg/I bctwccn 250-1000 cfs and 972 mg/l at flows <br />over 1000 cf~ (Figure 3), At the stateline near Coolidge from 1963-1999, sulfate concentrations average <br />over 2000 mg/l consistently at flows between 0-200 cfs while average concentrations below 1300 mgll are <br />seen from 300-1000 cfs. marked by significant concentration decreases between 200-300 cfs and over <br />1000 cfs (Figure 4). <br /> <br />There arc significant changes in hydrology and the resulting water quality of the liver between Coolidge <br />and Garden City, While there is little change in now between Coolidge and Syracuse. the river typically <br />loses flow between Kendall and Garden City. in part because of diversions from the ditch systems in <br />Kearney and Finney counties, However, most of the annual loss in !low in this reach of the river exceeds <br />the total sum of irrigation diversions, There has been a historic naluralloss of !low to the surrounding <br />aquifcr which may be aggrevatcd by the rcgional drawdown of the High Plains Aquifer. Ovcr the long <br />telm, flows over 100 cfs at the stateline are necessary for any substantial flows over 50 cfs to be present at <br />Garden City (Figure 5). <br /> <br />This hydrologic relationship is reflected in sulfate concentrations seen along the ri VeL At the Deerfield <br />station, average sulfate concentrations were 1986 mg/l over 1990-1999, very similar to the Coolidge <br />average, In comparing samples taken at the same time, Coolidge averaged 1969 mgll and Dceltield <br />averaged 1959 mg/!. therefore the river is basically unchanged in Hamilton and Kearny counties, A slight <br />decrease in concentration is noted between Deerfield and Pierceville. with concurrent samples averaging <br />1838 mg/l at Deerfield and 18] 8 mg/I at Piercevi lie, At low flows. the wastewater from Garden City may <br />be the predominant source of !low seen at Pierceville and since the city's sulfate discharge averages under <br />400 mg/!. this may lead to a decrease in concentration compared to upstream sites, <br /> <br />Since the gage at Garden City was re-started in 1987, coinciding with collection of samples at Pierceville. <br />the conditions seen dUling the period 1987-1999 will establish the benchmark for this TMDL. The period <br />between 1987 and 1999 encompasses extremes in hydrologic condition ranging from the drought peliods <br />of 1988-1991, as well as floods from 1993 and 1995, Persistent resumption of flow on the Arkansas River <br />started around June, 1996, Given the dynamic nature of flows seen at Garden City, the more rccent record <br />is presumed to reflect the anticipated flow conditions under the erfective period of this TMDL The period <br />is likely to be wetter than past years. For e,ample. !lows of 200 cfs at Coolidge were exceeded 48% of the <br />time over 19&7 - 1999 and 33% of the time over 1963-1999, Flows of SOO cfs wcre infrequent. exceeded <br />10-15% of the time, As seen in Figure 6, flows al Syracuse are nearly identical 10 those seen at Coolidge, <br />Over 1987-1999, no flow was seen at Garden City about 40% of the time, Flows measured at the Coolidge <br />gage at the same time of sampling over 1963 - 1999 shows a significant dip in !low over the 1970's. <br />followed by recovery over the 1980's and 1990's, This !low pattern coincided with the larger sulfate <br />concentrations seen on average at Coolidge (Figure 7), <br /> <br />Since the sulfate concentration is near-constant over the !low regime seen at Coolidge a majority or the <br />time. the loads of sulfate calculated from sampled data will mirror the flow pattern, The 1970's while <br /> <br />d/l"lml j-O- <br />