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Feasibility Evaluation of the Arkansas Valley Pipeline <br />Water Works! Committee <br />June 2003 <br />3.2.5.1 Background <br />As described in the Status of Water Quality in Colorado, 200?, prepared by the Water <br />Quality Control Division, Colorado Department of Public Health and the Environment, as the <br />Arkansas River leaves the mountains and flows east toward the plains, it crosses several <br />geologic formations that are rich in soluble salts (iron, sulfate, and selenium). With the <br />extensive irrigation in the Lower Arkansas River Basin, these naturally occumng <br />constituents are concentrated in the soil and irrigation return flow. This relatively high total <br />dissolved solids (TDS) concentration lowers the water quality of the lower Arkansas River. <br />The lower Arkansas River from above the Fountain Creek confluence to the Kansas- <br />Colorado state line is listed on Colorado's 303(d) list of impaired waters as only partially <br />supporting its aquatic life beneficial uses because of high concentrations of selenium, iron, <br />manganese and sulfate. The 303(d) document identifies that the whole stream is affected, but <br />"problems increase downstream." Since the publication of the 1998 303(d) list, manganese <br />has been removed as one of the constituents of concern due to a revision of the stream <br />standards for the lower Arkansas to a more site-specific standard. <br />Site-specific standards have also been assigned by the Water Quality Control Division for <br />this segment of the Arkansas River for selenium, iron, and sulfate. The selenium and iron <br />standards were rejected by EPA in 2000. A temporary modification to the standards for these <br />constituents is in place until July 2008, setting the criteria at the 85`h percentile of current <br />water quality levels. <br />3.2.5.2 Lower Arkansas River Water Quality Issues <br />The analysis in this section concerns water quality issues involving interpretation of <br />regulations and laws that are presently in a state of flux. The answers to these issues will not <br />be known with much certainty until the present Denver Water v. Thornton cases are decided. <br />Furthermore, these sections have been prepared without the benefit of legal counsel <br />knowledgeable about these specific matters. <br />A potential objection to the exchange proposed of the 4,300 ac-ft per year to storage in <br />Pueblo Reservoir is that downstream water users may believe that their water rights are being <br />injured due to a decrease in water quality as a result of the exchange. Diverting water to <br />storage in Pueblo Reservoir that is presently diverted from the Arkansas River at, for <br />example, LaJunta can potentially decrease the amount of flow available for dilution of lower <br />quality (i.e., higher TDS) agricultural irrigation return flows. This decrease in flow may <br />result in an increase in certain constituents of concern. <br />23 <br />GEI Consultants, lric. 01284 03-06-30 Feasibility Evaluation Final <br />