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feet from the grid, and 50 percent differed by less than 4 feet. This indicates current <br />groundwater level measurements are similar to groundwater levels reported in the historical <br />reports. There were two measurements in the area near Weldona that indicated water level <br />declines of approximately 20 feet since the development of the historical groundwater level <br />contours in that area. This trend is in agreement with the water level mapping and analyses <br />undertaken in Task 44 that indicates there are several areas where alluvial water levels have <br />declined over time. For the purposes of developing a generalized saturated thickness map, the <br />time-averaging of available data was determined to be an appropriate approach. <br />A minimum saturated thickness depth and width criteria will be used in Task 48 to define the <br />alluvial model domain. Task 48 will use the saturated thickness created in this TM based on <br />water level data from multiple historic time periods. This analysis validates the use of historic <br />water levels since they have been found in most areas to be consistent with current water levels, <br />and confirms that the model domain developed in Task 48 will sufficiently represent saturated <br />alluvial areas over a range of time periods. <br />Table 3: Water Level Measurement Time Period for each Source <br /> Time Period <br />B~orklund and Brown (1957) November/December 1949 <br />Duke et al. (1966) Summer 1965 <br />Erker et al. 1967 Sprin 1966 <br />Hurr and Schneider (1972a -1972 March 1968 <br />Hurr and Schneider 1977 Januar 1975 <br />NHPQ (1967) Sprin 1967 <br />Robson (1996) Multiple time periods <br />Robson et al. 2000a - 2000d Multiple time periods <br />Smith et al. (1964) November 1957 <br />SPDSS Task 42 Multiple time periods <br />Willard Owens Associates 1971 March 1971 <br />1.2.9 Development of the Alluvial Extent <br />The extent of the alluvium shown in Figure 1 was developed from multiple sources. A line of <br />saturated thickness was obtained from various historical reports including Bjorklund and <br />Brown (1957), Duke et al. (1966), Erker et al. (1967), Hurr and Schneider (1977, 1972a -1972f), <br />NHPQ (1967). These sources provided a basis for defining the extent of the alluvium for the <br />mainstem of the South Platte River from Greeley to Julesburg, Beaver Creek, Badger Creek, <br />Kiowa and Bijou Creeks, Lost Creek, and the Upper Black Squirrel Creek. <br />In the study areas of Robson, (1996) and Robson et al. (2000a - 2000d) as shown in Figure 2 , a <br />saturated thickness extent was only presented in areas where those authors determined the <br />water table to be well-defined. For the purposes of this TM, a saturated thickness grid was <br />computed as indicated in Section 1.2.5, using the bottom of alluvium and water table data <br />provided in the Robson reports. The saturated thickness contour line of approximately 10 feet, <br />which is the minimum saturated thickness expected to be included in the Task 48 model <br />domain, determined from the grid, was used to define the extent of the alluvium. The saturated <br />thickness contour line of 0 feet produced a very discontinuous and fragmented alluvial extent. <br />SPDSS Phase 3 Task 42.3 TM -Final <br />11/30/2006 <br />