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the bank of the South Platte River. The units include Nunn loam on 0 to I% and 1 to 3% <br />slopes; Dacono loam on 0 to I% slopes, and terrace escarpment soils. Native surficial <br />soils have been stripped from the existing plant area, which is now variably covered with <br />spilled, reworked and re-graded alluvial sand from stockpiling and truck spillage during <br />nearly 20 years of operation to date. <br />Associated with this amendment, 34 test borings were drilled to assess overburden <br />and minable alluvium thickness, and to collect data on the top of bedrock topography. <br />These data were used to evaluate reserves in the proposed new mining phases and to <br />create a rudimentary 3D CAD terrain model of the expansion area and plant site to more <br />accurately calculate available new mining production as described in Exhibit D - Mining <br />Plan. The test boring data and terrain model were also used to evaluate the earthwork <br />balance for the proposed backfilled cropland to be reclaimed above the 100 year <br />floodplain as described in Exhibit L - Reclamation Costs. <br />The 34 test borings were drilled using conventional solid stem auger rotary <br />drilling methods and logging drill cuttings of the overburden, sand and gravel, and <br />claystone bedrock. General logging descriptions were compiled in accordance with the <br />Unified Soil Classification System (USCS). Bulk samples were collected from the <br />cuttings for possible geotechnical laboratory testing. <br />The locations of the new test borings are shown on Figure I-1, Expansion Area Test <br />Boring Location Plan included in this exhibit. Also included in this exhibit is a <br />spreadsheet summarizing the estimated overburden thickness, sand and gravel reserves <br />thickness, as well as the top of bedrock at each test boring location. These data were <br />input into the AutoCAD Civil 3D software used to generate the mining and reclamation <br />plans included in this permit amendment. <br />Estimated depth to bedrock varied from 17 to 51 ft, and averaged 31 ft at the test <br />boring locations. Estimated thickness of sand and gravel varied from 6 to 45 ft and <br />averaged 24 ft thick based on the new borings. Overburden thickness varied from 0 ft (at <br />the existing plant site) to up to 17 ft thick. <br />Calculated volumes for minable reserves and available overburden for <br />reclamation backfill activities for the proposed expansion area and the plant area (which <br />together comprise the new mining areas in this amendment) are directly from the 3D <br />45