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<br /> <br />trending N30W and dipping 80 degrees to the southwest. Evidence indicates that this <br />fault extends across the east side of the site, about 180 feet west of the east entrance. <br /> <br />Surface water is present along the north edge of the site, in South St. Vrain Creek, <br />where the 100-year-flood event is expected to inundate the east end of the site. <br />Groundwater is present ponded in low areas and observed as wet areas along the base <br />of the highwall. Groundwater is also anticipated perched above siltstone and shale <br />layers in the Fountain Formation. <br /> <br />Potential geologic hazards or geologic conditions that could adversely impact the site <br />include landslides, rockfall, debris flows and potentially unstable slopes. Seismicity at <br />the site has been characterized by a probabilistic, peak ground acceleration (PGA) of <br />0.1249g with an approximate return period of 2,475 years. The site lies within the <br />Colorado Eastern Mountain seismotectonic province, which has an estimated maximum <br />credible earthquake of Mw 6.75. The nearest identified potentially active fault is the <br />Valmont Fault located approximately 13 miles southeast of the site. <br /> <br />4.0 FIELD INVESTIGATIONS AND LABORATORY TESTING PROGRAMS <br />Field investigations for evaluation of the rock slopes included field logging of existing <br />rock core, geologic mapping and detailed line mapping of the highwall and rock slopes. <br />We performed laboratory testing on rock samples collected from the rock core and line <br />mapping to establish the physical properties of the rock materials. Tests included slake <br />durability, Atterberg limits, uniaxial compressive strength, and direct shear testing on <br />saw-cut joints. <br /> <br />Sirovision software was used with overlapping high-resolution digital photographs and <br />survey control data to produce 3-D outcrop models using principles of close range <br />terrestrial photogrammetry. <br /> <br />Field investigations for evaluation of the fill slopes included field logging of test pits <br />excavated at locations across the existing fill slopes and in-situ density and moisture <br />content testing, using a Nuclear Density Gage, at the locations of the test pits. We <br />performed laboratory testing to establish the physical properties of the fill materials. <br />Tests included Atterberg limits, grain-size distributions, triaxial shear strength testing, <br />and Standard Proctor moisture-density relationships. <br /> <br />86995/DEN8R017 Page 2 of 5 February 2008 <br />Copyright 2008 Kleinfelder West, Inc.