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<br />(HJ 1'7 .i;. 3 <br /> <br />Long Hollow Dam and Reservoir Summary Report-Preliminary Draft <br /> <br />The water quality impact assessment completed for the Animas La Plata (ALP) Project found <br />that the project should not adversely affect water quality in the La Plata River basin. This is <br />because incremental divorsions from ALP will be a supplemental source on land that has been <br />irrigated f-or over 80 years. (Comment: May not be relevant now as no new water is coming into <br />the La Plata Basin under ALP except possibly for a rural water system. Not sure yOU can iust <br />change ALP to LHR.) No new land will be irrigated under LHR. Studies completed for the ALP <br />project found that selenium and other metals were readily leached from the soil so that their <br />concentrations in return flows should not be excessive or pose a risk to receiving water quality. <br />The water will be diverted upstream where concentrations of Se and other metals are lower. <br />Return flows accrue to the lower river where concentrations are higher. In addition, the quantity <br />of return flows will be relatively small compared to the flow in the river. Therefore, any effects <br />on concentrations from LHR evaporation will be minimal since evaporation is relatively small. <br />'N atei' will typically be released from the reservoir before it CaR eyaporate. <br /> <br />As a result, concentrations of Se and other metals will not be increased by the project, but will <br />decrease slightly or remain at pre-project concentrations. No significant changes in the frequency <br />or duration of water quality standards exceedances will result from the project. This means that <br />there should not be any adverse impacts on aquatic life because of water quality changes in LHR!. <br />in place. <br /> <br />8.0 INSTITUTIONAL CONSTRAINTS (COMBINE WITH CHAPTER 6 OR CHANGE <br />TITLE <br /> <br />Institutional constraints were evaluated to determine the feasibility of the reservoir project. <br /> <br />8.1 Water Allocation and Reservoir Operations <br /> <br />WWE used a water allocation model (MODSIM) to simulate flow in and diversions from the La <br />Plata River under pre- and post-LHR conditions. The modeled period included the 14 water <br />years (WY), from WY 1989 through WY 2002. This study period was selected because of the <br />availability of the flow data from five stream gauges, including the Long Hollow and Cherry <br /> <br />991-077.115 <br />May 2004 <br /> <br />Wright Water Engineers, Inc. <br /> <br />Page 14 <br />