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Bottom of alluvium elevation point data were gathered from Bjorklund and Brown (1957; see <br />Figure 2). Bjorklund and Brown provided strahgraphic data in tabular format for the alluvium <br />and bedrock from drill logs for wells in the area east of Greeley extending into Nebraska. <br />Bjorklund and Brown reported data for 6481ogs, although not all logs identified the bottom of <br />alluvium and not all logs characterized the alluvium within the SPDSS study area. <br />The drill logs within the SPDSS study area were reviewed, and if the log identified the bottom <br />of alluvium and provided a ground surface elevation, the data were added to an electronic <br />spreadsheet. Additionally, for some drill logs, only a depth to the bottom of alluvium was <br />provided. In selected geographic areas, bottom of alluvium data from these drill logs were <br />added to an electronic spreadsheet. The 30-meter USGS NED (digital land surface elevation) <br />was used to estimate a ground surface elevation for these data, from which the depth to bottom <br />of alluvium was subtracted to calculate the elevation of the bottom of alluvium. Location <br />information for each drill log was reported in Bjorklund and Brown using the Public Land <br />Survey System (PCBs), including township, range, and section (down to quarter-quarter <br />section), and sometimes included the distances from section lines. This information was used to <br />estimate horizontal x and y coordinates that were also added to the electronic spreadsheet. A <br />final set of picks were obtained from Bjorklund and Brown (1957) by digitizing values posted on <br />their contour maps. The digitized picks represent original data not gathered from drill logs in <br />the report. <br />It is presumed Hurr and Schneider (1972) used the data from the Bjorklund and Brown (1957) <br />report to develop their contours, because both studies were conducted by the USGS and cover <br />much of the same study area. A total of 412 bottom of alluvium picks were derived from <br />Bjorklund and Brown (1957). <br />The Colorado Groundwater Basic Data Report 16 (Weist, 1964) was reviewed for drill logs that <br />identified depth to bedrock. One value was obtained from this source. The x and y coordinates <br />were estimated from PLSS information provided by the report, and a ground surface elevation <br />was estimated with the USGS 30-meter NED and used to compute a bottom of alluvium <br />elevation. <br />Another source of alluvial aquifer configuration were obtained from driller's logs included with <br />the well permit images maintained by the DWR. Drill logs were gathered for areas across the <br />South Platte Alluvium Region (see Figure 2). The drill logs were reviewed to identify the depth <br />to bedrock. The x and y coordinates were estimated from PLSS information provided on the <br />drill log, and ground surface elevation was estimated with the USGS 30-meter NED. This <br />information was used to compute a bottom of alluvium elevation. Two-hundred sixty-five <br />bottom of alluvium picks were obtained from DWR well permit image driller's logs. <br />One additional bottom of alluvium pick was available from HydroBase. This pick is identified <br />in HydroBase as TH-DWR and summarized under the DWR data source in Table 1. <br />The sources of data used to define the configuration of the alluvial aquifer are summarized in <br />Table 1 and shown spatially on Figure 2. As noted in the preceding discussion and in Table 1, a <br />majority of the existing data sources provide only contoured surfaces of the bottom of alluvium <br />SPDSS Phase 3 Task 42.3 TM -Final 4 <br />11/30/2006 <br />