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3.0 MODEL PARAMETERS <br />3.1 Site Toooaraoh <br />A digital elevation model was built for the Site topography on one-foot intervals using AUTOCAD and was surveyed by <br />Aspen Surveying during 2003 and 2004 (NGVD 88 as vertical datum). The total surface elevation gain from the north to <br />the south is approximately 17 feet. <br />3.1 Regional Toaoaraoh <br />The surrounding topography for the 23 square miles modeled varies from flat slopes immediately west and east of the <br />Site to moderate slopes to the east up to a localized ridge of bedrock outcropping. The surface topography for the area <br />around the Site was taken from USGS digital quadrangle (the Fort Lupton 7.5 minute quadrangle) and adjusted from the <br />NAD 27 datum to the NGVD 88 datum. The regional topography was then tied to the Site topography and a digital <br />elevation model was built using AUTOCAD. <br />3.3 Site Geoloay <br />Subsurface data from earlier aggregate investigations was combined with data from Civil Resources' geotechnical <br />investigation. Geotechnical investigations were completed at the Site by the following consultants: <br />• Ground Engineering (12 borings in Sasaki property in September 2000 and 9 borings around the perimeter of <br />the Watada property in May 2003), <br />• CTL/Thompson (10 borings in the Villano property in September 2003), <br />• Lafarge (4 borings in the Yokcoji property, 3 borings in the Watada property, and 4 borings in Villano property in <br />February 2004), <br />• Civil Resources (7 geotechnical borings completed with piezometers across all properties in June 2004) and <br />• Civil Resources (28 geotechnical borings, two piezometers and one pumping well, September 2004). <br />The earlier investigations were primarily focused on overburden soils and sand and aggregate quality. The boring <br />locations were field approximated. The 35 borings drilled by Civil Resources, obtained insitu claystone bedrock samples <br />in order to obtain geotechnical index and engineering properties and were located by survey. <br />The surficial geology at the Site was also mapped as part of Civil Resources' studies. Geologic mapping and exploratory <br />drilling at the Site identified the major natural geologic strata. The units pertinent to this model are:1) alluvial sand and <br />gravel and 2) claystone bedrock. These units are described more completely as follows: <br />Alluvial Sand & Gravel, Broadway Alluvium Ob: The alluvial deposit underlying the SW TKO Site is primarily composed <br />of the Broadway Alluvium. The alluvium is classified as sand and gravel deposited by the South Platte River and its <br />tributaries. Locally, the unit includes some gravel of Louviers age. The deposit ranges in thickness on the Site between <br />approximately 30 to 50 feet, but averages approximately 40 feet. The deposits extend well above the groundwater table <br />to typically within three feet of the ground surface, creating an unconfined aquifer of relatively homogeneous material <br />(Colton, 1978). <br />Denver and Arapahoe Claystone Tkda: Localized outcroppings of the Denver and Arapahoe formations are located a <br />couple of miles east of the Site on the ridge that generally represents the no-flow boundary of the groundwater model <br />(located near the Fulton Ditch and Brighton Ditch Lateral). These geological formations are classified as olive gray <br />claystone and siltstone interbedded with tuffaceous sandstone and conglomerate. However, the geotechnical <br />Groundwater Model Report - SW TKO Water Storage Project - 2 - February <br />