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<br />0177 <br /> <br />Selenium concentrations in ground water produced from terrace deposits <br />and from shallow alluvial aquifers north of the Arkansas River alluvium in <br />Crowley and Kiowa Counties, Colo., frequently exceed 10 ~g/L and can be <br />greater than 100 ~g/L (Cain and others, 1980; Mustard and Cain, 1981) even <br />though these areas receive little or no irrigation drainage. Ground-water <br />data from Kansas during 1976-81 are summarized by Spruill (1983). Selenium <br />concentrations in 52 percent of the wells that were sampled in the alluvial <br />aquifer along the Arkansas River exceeded the Kansas drinking-water standard <br />(10 ~g/L). In addition, data from wells in the Ogallala aquifer indicate <br />elevated concentrations of selenium may be present in areas receiving seepage <br />from the Arkansas River. <br /> <br />Sulfate concentrations in four shallow wells (less than 100 ft deep) near <br />Syracuse, Kans., which were sampled during 1897 through 1907, ranged from <br />291 mg/L to 962 mg/L (Parker, 1911). The maximum dissolved-solids concentra- <br />tion was 1,800 mg/L. In 1940, the sulfate concentration in water from a <br />shallow well located in this same area was 2,800 mg/L, and the dissolved <br />solids concentration was 4,600 mg/L (Latta, 1944). Sulfate concentrations in <br />three wells sampled in the same area during 1977-88 were between 1,400 and <br />3,000 mg/L, and dissolved-solids concentrations ranged from 2,250 mg/L to more <br />than 5,000 mg/L (U.S. Geological Survey, 1978-89). Based on these data, <br />concentrations of sulfate and dissolved. solids in the alluvial ground water <br />seem to have increased substantially between 1907 and 1940 and then stabilized. <br />The primary development of irrigated agriculture in the study area also <br />occurred during 1907-40. <br /> <br />w <br /> <br />Seepage from the alluvial aquifer to the deeper Ogallala aquifer is <br />indicated by lateral and vertical trends in sulfate and dissolved-solids <br />concentrations (Latta, 1944). Higher sulfate and dissolved-solids <br />concentrations were detected in deep wells in the Ogallala aquifer near the <br />Arkansas River valley than in wells located north and south of the valley. <br />Within the Arkansas River valley, near Garden City, sulfate and dissolved- <br />solids concentrations in the Ogallala aquifer decreased with depth. <br /> <br />LittYe previous data have been collected on aquatic biota in the study <br />area. Samples of four fish species collected from Pueblo Reservoir in 1985 <br />were analyzed for mercury by the Colorado Division of Wildlife (Rosenlund, <br />1986). Fillet samples contained less than about 0.25 ~g/g of mercury (weight <br />basis not reported). The Kansas Department of Health and Environment, in <br />cooperation with the U.S. Environmental Protection Agency, has monitored as <br />many as 43 selected priority pollutants in common carp (or alternate species) <br />collected at 20 Kansas stations since 1980 (Cringan, 1989). All of the <br />sampling stations, including those on the Arkansas River, are more than 100 mi <br />east of Deerfield, Kans. (fig. 2). Chlordane was the contaminant of greatest <br />environmental and human-health concern. Selenium was not included in the <br />program. <br /> <br />19 <br />