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• Questionable hydrologic feasibility. Data reviewed in the dam operation plan <br />development suggested that stormwater availability may be lower than originally <br />estimated, and sediment may reduce recharge rates substantially. Off -line <br />channels would compensate to some degree the reduction in channel recharge, <br />but total acreage and storage would be small. <br />Absence of partners. —No other agency has offered to provide other source <br />waters, staffing, or funds for operation of the project. <br />Higher- than - anticipated costs. —The foundation for the inflatable dam is expected <br />to cost an additional $300,000 to $400,000; the cost of the pier to which the <br />inflatable dam would be attached has not been estimated. It has been assumed <br />that the sediment for the fuse plugs would be obtained from spur basin <br />excavation. However, spur basin soils may be too fine, and additional costs <br />may be incurred. <br />Competing needs. —At over $1,000,000 for construction of the recharge facilities <br />exclusive of Alamo Wash component, district funds would need to be diverted <br />from other high priority capital improvements. Operational costs are estimated to <br />be $125,000 per year, excluding ALERT system staffing needs. <br />• Limited land availability.— Additional off -site recharge areas would permit <br />higher recharge rates and would minimize dependence on in- channel recharge. <br />However, additional land is very limited. Without expansion capabilities, the site <br />is unattractive to outside partners. <br />Although the inflatable dam will not be constructed, the district will continue to operate <br />stream and precipitation gauge stations at its discretion. The ADWR has removed the <br />water -stage recorders on the Rillito Recharge Project monitoring wells. The district will <br />maintain monitoring wells in their current condition until other needs dictate their <br />abandonment per ADWR standards. Lands purchased for the recharge project will <br />remain in district ownership for future river park construction or potential recharge <br />activities. <br />Rillito Creek does offer potential locations to recharge Tucson's central well field using <br />CAP. Given the limited aquifer storage available upstream of Swan Road, the most <br />effective methods to recharge CAP water would be either in- channel releases or narrow <br />basins located in the south overbank downstream of Swan Road. Additional tests would <br />be needed to confirm the absence of the landfill contaminants in the Columbia Road area. <br />Water Quality <br />Water Quality Data <br />The average total dissolved solids (TDS) content of groundwater from Tucson Water <br />Department's well fields is well below the 500 milligrams per liter (mg /L) maximum <br />recommended concentrations for public water supplies. The TDS concentrations average <br />205 mg /L in the interior well field that includes the Rillito Recharge Project site. The <br />majority of the groundwater in the interior well field is calcium- sodium bicarbonate or <br />12 <br />High Plains States Groundwater Demonstration Program <br />