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Gilcrest/LaSalle Pilot Project <br />Hydrogeologic Characterization Report <br />EXECUTIVE SUMMARY <br />The Gilcrest/LaSalle Hydrogeologic Characterization is a component of the Gilcrest/LaSalle <br />Pilot Project conducted by the Colorado Division of Water Resources (DWR) and funded by <br />the Colorado Water Conservation Board (CWCB). The Gilcrest/LaSalle Pilot Project goal is <br />to evaluate high groundwater conditions in the South Platte alluvial aquifer near Gilcrest and <br />LaSalle, Colorado, as shown in Figures E1 and E2 (Study Area). For this study the Colorado <br />Geological Survey (CGS) compiled, analyzed, and reinterpreted existing hydrogeologic data <br />from previously published regional studies. <br />Through integration of previous investigations with new analysis, CGS has added <br />significantly to the Study Area hydrogeologic characterization, and provided insight into the <br />South Platte alluvial aquifer depositional model, particularly with respect to discontinuous low <br />permeability beds within the central portion of the alluvial aquifer, and lower permeability <br />beds on the aquifer flanks. <br />Specifically, the CGS hydrogeologic characterization presented herein has: <br />1. Developed a hydrograph template to facilitate HydroBase data analysis; <br />2. Refined alluvial aquifer extent mapping; <br />3. Combined surficial geology from different sources to revise surficial mapping; <br />4. Refined the bedrock and alluvial surface geologic mapping; <br />5. Refined the alluvial aquifer lithologic and depositional conceptual models; <br />6. Compiled driller's logs from 448 boreholes into a digital lithologic dataset; <br />7. Developed updated localized time -series water table contour and depth -to - <br />groundwater maps; <br />8. Evaluated groundwater flow in detail; <br />9. Identified local -scale water level data gaps; <br />10. Identified existing candidate wells for additional water level monitoring and aquifer <br />testing. <br />Additionally, this study has determined that, despite a large number and distribution of wells <br />monitored, the overall data set contains significant gaps in data continuity and location. <br />These data gaps limit the ability to analyze detailed long-term groundwater level trends <br />throughout the entire study area and to map detailed water table surfaces across portions of <br />the Study Area during long periods. <br />E1 <br />