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and Prescribed Procedures for Measurement of Radioactivity in Drinking Water (USEPA- <br />600/4-80 -032, August 1980). Samples were sent to the USGS National Water Quality <br />Laboratory in Arvada, Colorado, for all analyses except bacteria (USGS, 1995a). Samples <br />of fecal coliform and streptococci were analyzed in the USGS Tucson, Arizona, laboratory <br />(USGS, 1995a). The USGS sediment laboratory in Vancouver, Washington, analyzed <br />surface water samples for sediment concentration and particle size distribution (USGS, <br />1995, 1995a). <br />Summary of Water Quality Studies <br />The water quality studies conducted by USGS from 1987 -94 confirm that storm runoff <br />supplies surface waters with contaminants such as heavy metals and organochlorine <br />pesticides. However, none of the contaminants that exceeded maximum contaminant <br />levels in surface water were detected in groundwater because of adsorption onto <br />sediment particles and microbial degradation in bottom sediments of the stream channel. <br />Analyses of sampling wells located near the channel before and after large flood events <br />demonstrated that even recently recharged water met drinking water standards. <br />Permits <br />As streamflow for the Rillito Recharge Project would be diverted from the Rillito Creek <br />and Alamo Wash, the district needed to obtain surface water rights from the State of <br />Arizona. The district received permits to appropriate water for the recharge project on <br />March 25, 1994, which will lapse if no project is constructed by March 1999. <br />Project Costs <br />CHZMHiII developed an opinion of construction and operation costs in 1992 as part of the <br />Preliminary Feasibility Report (tables 2 and 3). These cost estimates were revised by <br />further studies and circumstances. For example, erosion from the January 1993 floods <br />widened the channel of Rillito Creek, effectively removing most of the alluvium in the <br />vicinity of the West County basin. Subsequently, the Corps decided to maintain the <br />originally planned alignment for the bank stabilization, which would reduce the <br />excavation costs for West County basin by $45,000. <br />The original report did not include the cost of providing the foundation for the rubber <br />dam and fuse plugs. It was originally assumed that the foundation of the rubber dam <br />and fuse plugs would be a soil - cement invert stabilizer built by the Corps. The 1994 <br />"Invert Stabilizer Scour Analysis" prepared by CHZMHiII found that the additional scour <br />would be created by the narrowing of flows when the dam is deflated and both fuse <br />plugs are in place. The 8.5 feet of additional scour caused by the recharge project would <br />require an additional 3,000 cubic yards of soil cement to be added to the invert stabilizer <br />depth. At a cost of $25 per cubic yard, this would add $75,000 to the structure's cost. <br />A subsequent report entitled Change Order No. 1 Report (CHZMHiII, 1995a) found that <br />additional modifications to the invert stabilizer would be necessary —a cutoff wall and <br />widened top slab were proposed to serve as a foundation for the dam. This would have <br />a <br />High Plains States Groundwater Demonstration Program <br />