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investigations at the Site have only encountered claystone to this point. The formation is approximately 565 feet thick <br />(Colton, 1978). <br />3.4 Regional Geology <br />The model covers approximately 23 squares miles, centered around the approximate one-half of a square mile SW TKO <br />Site as presented in Figure 1. The geologic units surzounding the Site were obtained from geologic mapping (Colton, <br />1978). The units are defined as follows: <br />Piney Creek Alluvium Opc :The Piney Creek Alluvium extends approximately one-half mile on either side of the South <br />Platte River. The alluvium generally consists of dark-gray sand and gravel, containing organic matter. The alluvium <br />generally underlies stream terraces with surfaces approximately 10 to 20 feet above the nearby floodplain. Locally, the <br />deposit includes some post-Piney Creek alluvium (Colton, 1978). <br />Eolian Qe: Eolian deposits (wind blown) of clay and silty sand loess bound the models eastern flanks. These deposits <br />are classified as light brown to reddish brown to olive gray deposits of windblown clay, silt, sand, sand granules mainly <br />as sand dunes. The loess deposit ranges in thickness from 15 feet thick to less than 3 feet thick (Colton, 1978). Refer <br />to Figure 3. <br />3.5 Site Hydraulic Conductivities <br />Hydraulic conductivity is a measure of the soils ability to transmit water within the aquifer. Some factors affecting <br />hydraulic conductivity are: pore size distribution, grain size distribution, void ratio, roughness of mineral particles, and <br />degree of soil saturation (Dos, 1998). The Broadway alluvium, underlying the Site, is generally a clean sandy soil, as <br />described above with an approximate depth of 40 feet. The hydraulic conductivity of the alluvium underlying the Site <br />was evaluated from a 24-hour pump test, as described in the attached memo in Appendix A. The resulting data were <br />evaluated to estimate the hydraulic conductivity of the unit at 165 feet per day. See Appendix A for the resulting data <br />and calculations. <br />Table 1 <br />Site Hydraulic Conductivity <br />Geological Unit Hydraulic Conductivity (ruday) Average Geological Unit <br /> Thickness fl <br />Broadway 165 40 <br />Cfaystone 0.003 565 <br />3.6 Regional Hydraulic Conductivities <br />Literature sources were used to evaluate the appropriate hydraulic conductivities of materials outside of the Site <br />boundaries. In northeastern Colorado, hydraulic conductivity values for alluvium generally range from 20 to 750 feet per <br />day (Hershey and Schneider, 1972). The Broadway deposit should vary between the above values, whereas the wind <br />blown finer grained deposits would tend towards the lower end of the reported range. See Figure 4 for the locations of <br />the assigned hydraulic conductivities. <br />Groundwater Model Report - SW TKO Water Storage Project - 3 - February 2005 <br />