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1 <br />Geotechnical Engineering Report Terracon <br />Proposed Gravel Mine <br />'Terracon Project No. 21995030 <br />'SUBSURFACE CONDITIONS <br />Geology <br />'The site is located within the Colorado Piedmont section of the Great Plains physiographic province. <br />The Colorado Piedmont, formed during Late Tertiary and Earl; quaternary time (approximately <br />'2.000.000 years aao), is a broad. erosional trench which separates the Southern Rocky Mountains <br />from the High Plains. Structurally, the site lies near the axis of the Denver Basin. During the Late <br />Mesozoic and Early Cenozoic Periods (approximately 70,000,000 years ago), intense tectonic activihj <br />~ccurred, causing the uplifting of the Front Range and associated downwarping of the Denver Basin to <br />the east. Relatively flat uplands and broad valleys characterize the present-day topography of the <br />olorado Piedmont in this region. The site is underlain by the Cretaceous Fox Hills Formation. The <br />~ox Hills consists of interbedded sandstone and siltstone units. Holocene (Recent) alluvial deposits <br />overlie the Fox Hills. <br />oil and Bedrock Conditions <br />s presented on the Logs of Boring, surface soils to depths of 2 to 7'/z feet consisted of sandy lean <br />lay and/or clayey sand. Silty sand was encountered below the clay in approximately half the test <br />borings and extended to well graded sand with gravel and cobbles that was encountered at <br />~FFroximately 7 to 8 feet. The well graded sand with gravel extended to the bedroc;< that was <br />ncountered at depths of 11 %2 to 18 feet. <br />~ield Test Results <br />Field test results indicate that the clay soils are medium stiff in consistency. The sand soils vary from <br />~ose to dense in relative density. The bedrock was weathered in hardness. <br />roundwater Conditions <br />roundwater was encountered at approximate depths of 3 to 6 feet in the test borings at the time of <br />~eld exploration and when checked 2 days after the drilling. Groundwater levels can be expected to <br />uctuate with varying seasonal and weather conditions. <br />ENGINEERING ANALYSES AND CONCLUSIONS <br />Based on the average thicknesses of the soils encountered in the test borings and the approximate <br />urface area of the site that can be used for gravel mining operations, the following estimated <br />quantities were obtained: <br />1 3 <br />1 <br /> <br />