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Long Hollow Dam and Reservoir Phase I Summary Report <br /> • Most of the construction material needed for an earth embankment or RCC dam appear to <br /> be present near the proposed dam site. No source of satisfactory riprap appears to be <br /> present close to the project area. <br /> • Additional geologic and geotechnical engineering studies, including subsurface <br /> exploration and laboratory testing, are needed for design. <br /> In the Phase II feasibility work, a geotechnical evaluation of the site through subsurface <br /> exploration and laboratory testing, would be performed. The findings from this additional work <br /> would be used to evaluate alternative dam and spillway configurations. The design inflow flood <br /> would be calculated and hydraulic issues associated with the dam would be evaluated. <br /> 5.0 GROUNDWATER HYDROLOGY <br /> WWE performed a separate groundwater study of the Red Mesa Aquifer (WWE, November <br /> 2002) to obtain a better understanding of the hydrogeology of the aquifer and its relationship to <br /> surface water flows in Long Hollow and irrigation practices on Red Mesa. <br /> Forty-two wells on and adjacent to Red Mesa were studied based on location and accessibility. <br /> Additionally, some ditches and their diversion practices were incorporated into the study. The <br /> static water levels in the wells were monitored on 14 dates, from April 13, 2001 to October 10, <br /> 2002, a dry period. Groundwater contour maps were generated for the Red Mesa Aquifer in <br /> order to determine groundwater flow paths (see Figure 4). <br /> The study found that the primary source of recharge for the Red Mesa Aquifer is the deep <br /> percolation of irrigation return flows and ditch conveyance losses. Hydrographs for the wells <br /> studied indicate that water table fluctuations in the Red Mesa Aquifer correlate with irrigation <br /> practices. Ditch diversion data were compared with the changes in groundwater levels in some <br /> wells that were part of the monitoring program. The water table near these wells rises shortly <br /> after irrigation begins and continues to rise for a period after irrigation ceases. Low water table <br /> conditions typically occur during the winter and early spring. The amount of groundwater in <br /> 991-077.115 Wright Water Engineers, Inc. Page 8 <br /> July 2004 <br />