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Phase 1 Task 42.2 Denver Basin Region Aquifer Configuration TM. A summary of the <br />sources of configuration data found in the August 2005 edition of HydroBase is <br />provided below. <br />There are two different categories of aquifer configuration data present in HydroBase, <br />which vary in their reliability and the level of supporting documentation: data from <br />geophysical logs, and data derived from published contour maps. For the first category <br />of aquifer configuration data, aquifer formation elevations are interpreted from <br />geophysical logs. These elevations are referred to in this TM as "picks." These data are <br />considered most reliable due to the nature of the data source and detail with which data <br />are collected. <br />The most significant source of geophysical well log picks in HydroBase was provided by <br />the DWR's Geotechnical Services Branch. Since the 1980s they have collected and <br />analyzed thousands of geophysical logs from oil, gas, and water wells in the Denver <br />Basin. From the logs, they have estimated elevation picks representing the top and <br />bottoms of the aquifers penetrated, and estimated net (cumulative) sand thickness to <br />define the hydrogeologic framework of the Denver Basin aquifers. The net sand <br />thickness, as interpreted by DWR, is the total thickness of sandstone and siltstone <br />lithologies that occur between the top and bottom of each aquifer. Much of DWR's early <br />work on the Denver Basin is documented in the Colorado State Engineer Basic Data <br />Report 1 (Van Slyke et al. 1986). There are 3,9701ogs interpreted by the DWR in the <br />version of HydroBase used for this TM. <br />Additional geophysical well log data in HydroBase was obtained from a U.S. Geological <br />Survey (USGS) study conducted near Deer Trail, Colorado (Yager and Arnold 2003), that <br />is referred to herein simply as the Deer Trail study. The Deer Trail study contained 270 <br />geophysical well logs with picks for the top and bottom of the Laramie-Fox Hills <br />Aquifer. <br />Under the SPDSS Task 36.1 field investigations, geophysical log and drill log data were <br />collected from one bedrock well located just north of the Town of Bennett. The well was <br />drilled through the Denver Aquifer and completed in the Upper Arapahoe Aquifer. The <br />geophysical log and drilling logs are reported in the Task 36.2 TM and the picks for the <br />aquifer surfaces are also contained in HydroBase. <br />The second category of aquifer configuration data found in HydroBase is picks derived <br />from contoured data. Contours of the tops and bottoms for the Arapahoe and Laramie- <br />Fox Hills Aquifers are presented in a series of hydrologic maps in a report published by <br />the USGS (1998), which will be referred to herein as the HA-742 report. The HA-742 <br />report provides maps showing the outcrop boundaries of the aquifers, surface elevation <br />contours, and structural contours along the western edge of the Denver Basin. The USGS <br />interpreted approximately 1,700 oil, gas, coal, and water well logs to develop the <br />outcrop contours of the Laramie-Fox Hills and Arapahoe Aquifers; however, the point <br />data used to create the contours were not made available through the report. Therefore, <br />points were digitized by CDM from these maps where surface elevation contours <br />intersected the outcrop boundaries. Only points in the northwest outcrop area for the <br />SPDSS Phase 2 Task 42.2 TM -Final 3 <br />2/13/06 <br />