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0 Dune Sands <br />An unbroken line of dunes, with a maximum relief of 100 feet is evident south of the river from <br />Brush east to Sedgwick. These dunes are actively migrating and their thickness can change <br />considerably over a few years. <br />Typically, the dune sand consists of fine to medium sand but can also include some coarse sand <br />and some silt and clay. <br />The dune sand area provides good infiltration for recharge to the underlying alluvial material. <br />However, wells drilled in the dune sand are primarily stock wells that yield small quantities of <br />water. <br />According to the geologic logs and USGS (1957) thick deposits of clay, brule or shale underlie the <br />alluvium or dune sand deposits. The USGS Water Supply Paper identifies three formations that can <br />form the base of the aquifer in the study area: <br />Brule Formation (Member of White River Group): Silt, containing fine sand and clay, <br />light tan to pink; contains channel deposits of gravel and sand. USGS logs in the <br />Tamarack area identify the Brule as blue to green clay. The Brule formation was <br />deposited during the Oligocene time period <br />Chadron Formation (Member of White River Group): pink, blue and green clan and <br />channel deposits. USGS logs identify the Chadron in the Tamarack area as tan, to light <br />brown clay. The Chardron formation underlies the Brule formation and was deposited <br />during the Oligocene time period. <br />Pierre Formation: Dark shale and silt. Contains a few large limestone concretions and <br />sandstone lenses throughout. USGS logs in the Tamarack area identify the Pierre as gray <br />or black shale. The Pierre formation was deposited during the Cretaceous time period. <br />3.0 DATA COLLECTION <br />Groundwater well information was obtained from the following sources: <br />Luis Garcia's (Director, CSU- Integrated Decision Support) GIS coverage and database for South <br />Platte River Basin wells that pump over 50 gpm. This ARCVIEW database formed the base for the <br />Tamarack Model GIS database. The Tamarack Model GIS database stores the locations and <br />information from all the study wells. <br />• Well permit files at the SEO were researched for the following sections. <br />T2N, R47W: Section 33 <br />TIN, R47W: Sections 4 -11 <br />TIN, R48W: Sections 1 -3, and 8 -21 <br />• TIN, R49W: Sections 13 -16, 20 -31 <br />• Wells from Val Flory's (Engineer, NCWCD) ARCVIEW database were added to the main Tamarack <br />GIS database. These wells were DOW'S Tamarack test and recharge wells. <br />3 <br />