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<br />Studies also show significant increases in dissolved uranium, lithium, iron, strontium, <br />and other trace elements in addition to selenium within this section of the Arkansas <br />River and in the ground water. At times state and EPA standards for maximum <br />contamination levels are approached or occasionally exceeded. Irrigation induced <br />leaching of marine shale derived soils and evaporative concentration has been found <br />to significantly increase concentrations. Extensive irrigation and reuse of irrigation <br />return flows in this watershed elevate concentration levels downstream. In addition a <br />strong positive correlation exists between sodium, magnesium, sulfate, and chloride <br />salts with selenium and nitrates as well as uranium and other trace elements <br />mentioned above. Changes in specific conductance serves as a useful measurement <br />to estimate changes in concentration of each6. Also, it has been found that there is a <br />directly proportional change in concentration of each with any change in deep <br />percolation. <br /> <br />Eight organochlorine pesticides were detected in bird liver samples, eggs, and in fish <br />from the reservoirs. All concentrations were well within the ranges of reported <br />background concentrations and were less than levels of biological concern. <br /> <br />Project action will reduce deep percolation which will improve ground water and <br />Arkansas River water quality. This is achieved through reduced loading of nutrients, <br />trace elements, heavy metals, pesticides, salts, and sediment. <br /> <br />Water Quantity <br /> <br />The economy of the watershed is derived from irrigated agriculture and livestock. <br />Surface irrigation water availability varies considerably from year to year. The <br />irrigation systems in use in the watershed contribute to lower water application <br />effectiveness. <br /> <br />Two major factors greatly impact this issue, available labor and inherent deficiencies <br />in irrigation methodology and equipment. In addition to these factors is the effect of <br />Pueblo Reservoir on the irrigation water. The dam is trapping sediment thus providing <br />cleaner water to irrigators. This has increased the transit losses in the main canals by <br />18% since the 1950s. The clean water has also increased field ditch seepage by 22% <br />since the 1950s. The 1950s data was compared with data from the period 1976 to <br />1985. <br /> <br />The average irrigation requirements for the crop rotation for the project area are about <br />20 inches per acre/year over and above normal precipitation. Crop production <br />reductions occur in the watershed on the water short years. This issue was evaluated <br />in light of the Arkansas River compact and considered in each alternative analysis. It <br />was found that better water management on-farm in order to improve water <br />application effectiveness was the primary need. <br /> <br />S Uranium Waters of Southeastern Colorado: A Function og Geology Climate, and Land Use by Robert <br />A. Zielinski and Sigrud Asher-Bolinder. US Geological Survey, Denver, Colorado. <br />6 Selenium in Agriculture and the Environment, Soil Science Society of America, Special Publication #23, <br />1990. <br /> <br />21 <br />