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TO: Tamarack Modeling Team <br />FROM: Mary Halstead, DOW <br />SUBJECT: DRAFT Geologic Information Summary <br />DATE: June 30, 2003 <br />1.0 EXCUTIVE SUMMARY <br />The geology near the Tamarack SWA' was investigated to provide data and information for the design <br />and construction of a groundwater flow model for the South Platte River alluvial aquifer. Figure 1.1 <br />shows the study area. <br />As part of this investigation, 149 groundwater wells were identified, 88 well logs were reviewed and 10 <br />is cross - sections were constructed. Based on the analysis of this data the following general interpretations <br />were made: <br />• The alluvial aquifer can be divided into two layers; 1) the top layer consists primarily of <br />sands; and 2) the lower layer consists primarily of gravels. <br />• The base of the aquifer is easily identified either as clay, brule or shale on the geologic logs. <br />In picking the base of the aquifer, no distinction was made between the three formations. <br />The following maps were generated: <br />• Well location map highlighting the wells that discharge more than 50 gpm. This map can be <br />used to decide on model boundary locations. <br />• Elevation map of the base of the aquifer. Preliminary contours were generated by hand and a <br />comparison of the topography of the aquifer base was made to the USGS map (1972). This <br />data can be used to generate Layer 2 thickness and model grid information <br />• Elevation map of the base of Layer 1. Preliminary contours were generated by hand. This <br />data can be used to generate Layer 1 thickness and model grid information. <br />Information collected was input into an ARCVIEW GIS database project called: <br />• <br />Tamarack Model.apr <br />1 State Wildlife Area <br />2 ArcView 3.2, 1992 -1999, Environmental Systems Research Institute, Inc, Redlands, CA. <br />GIS —g eographic Information System <br />