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other operating criteria, including how best to achieve acceptable water quality of deliveries. <br />Economic considerations also enter into decisions regarding project operations. <br />The Project has typically been operated such that deliveries to the Rio Grande average between <br />30 and 60 cfs. These flows can be sustained year-round, although flows in the conveyance <br />channel are adjusted for winter operation and maintenance activities. <br />Limitations and Constraints <br />Drawdown Impacts <br />As required in the authorizing legislation, the Project must be operated such that impacts to the <br />unconfined aquifer are controlled. The legislation requires that the Project be operated in a <br />manner that will not cause the water table available for any irrigation or domestic wells in <br />existence outside the Project boundary prior to Project construction to drop more than two feet, <br />and in a manner that will not cause reduction of artesian flows in existence prior to Project <br />construction. As previously noted, numerous observation wells are used to monitor Project <br />impacts, although impact determination has proven somewhat difficult because of natural <br />variations in water levels and the effects caused by other wells in the area. <br />San Luis Lake Recreation Area <br />San Luis Lake is managed as a recreational area by the Colorado Division of Wildlife and the <br />Colorado Division of Parks. The Bureau attempts to maintain a surface water elevation of <br />7,519.3 feet in the Lake, corresponding to a Lake surface area of 890 acres. As noted above, <br />Project water may be delivered into or out of the Lake and provides considerable operational <br />flexibility in managing delivery amounts and water quality. Approximately 2,000 to 3,000 acre- <br />feet are lost from Lake surface evaporation each year. <br />Water Quality Requirements <br />Authorizing legislation of the Project requires that water delivered to the Rio Grande meet <br />minimum water quality standards. Of particular interest is the level of Total Dissolved Solids <br />(TDS), and the Compact requires water delivered from the Project to the New Mexico state line <br />have less than 350 ppm TDS when the sodium ion concentration exceeds 45%. The quality of <br />Project water is measured at the river outlet structure on the conveyance channel. Water quality <br />in the well field can vary between 100 and 9,000 ppm of TDS. Project water from the well field <br />is mixed throughout the system to meet water quality standards at the river outlet structure. The <br />quality of water developed from wells in the southern portion of the Project is typically the best, <br />and those wells in the central area of the Project tend to generate the poorest water quality. The <br />Bureau regularly monitors water quality and actively manages Project operations to achieve <br />acceptable conditions. <br />Project Yield <br />In about 1995, the Bureau began to recognize a reduction in the yields from many of the Project <br />wells. The reductions seem to occur approximately 3 to 4 years after these wells were put into <br />service. The Bureau has studied this situation extensively and have concluded that well screen <br />bio-fouling resulting from the growth of iron and related bacteria results in significant clogging of <br />many of the wells. A variety of remedies have been attempted including treatments with <br />hydrochloric acid and chlorine to destroy the bacteria and clean the wells. These remedies have <br />C:Acdss\CBP.doc Closed Basin Division Interview June 23, 1999 -Page 4 of 5 <br />