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TETRATECH RMC Mr. Mike Refer <br />May 12, 2004 <br />Page 5 <br />modeled to prevent damage to the property. Due to the slurry wall azound the entire east <br />cell, the azea was assumed to be dewatered. Based on the drilling records, no mud lens <br />appears to be present in this area. The protected "structure" is the property itself and <br />includes an old shed. <br />Scenario 4: South Platte River. The river forms the property line in the northeast corner of <br />the project. The comer was modeled for slope stability; however, it is likely that minimum <br />offset regulations will govern the location of the slurry wall and the extent of the mining. <br />The slope stability model included a slurry wall, no mud lens, and a high groundwater table. <br />Scenario 5: Border to Tucson north cell. The north end of the east cell will butt against the <br />existing Tucson cell. The slope stability of this azea was modeled to determine the effects of <br />the lazge stockpiles placed close to the property line. The setbacks and conclusions for <br />scenario may change depending on the final configuration of the north Tucson cell (extent of <br />mining, stockpile location, etc.). The groundwater was assumed to be slightly lower than in <br />other azeas due to the shadow effect of the slurry wall up gradient. Based on the drilling <br />records, no mud lens appeazs to be present in this azea. The protected "structure" is the <br />stockpile. The calculations were done for the apparent deepest bedrock section of the north <br />border. <br />- Scenario 6: Buildings (Greenhouses) at northeast comer of west cell. These buildings aze <br />not part of the mine and must therefore be protected. Drilling records indicate that the mud <br />lens is quite thick in this area. Water levels behind the slurry wall were taken to be average <br />based on the shadow from the upstream slurry wall but with rechazge from the west. A 3,000 <br />psf surcharge simulates the loading by the buildings. <br />Scenario 7: Gas well in west cell. The cell is noticeably shallower at this end. A mud lens <br />is present and the tank is simulated by a 3,000 psf load. Water levels were assumed to be <br />high due to the Brighton Ditch to the west. The final extent of mining maybe determined <br />by the presence of economically mineable aggregate and future access needs by the gas well <br />owner. The final extents may therefore be farther from the well than the minimum distance <br />listed in Table 2. <br />- Scenario 8: Power lines on west side. The power poles are closest to the mine in the <br />northwest comer of the west cell. The poles appeaz to be at the edge of the claystone <br />bedrock outcrop and the alluvial gravels. The scenario was modeled with the alluvial gravels <br />and mud lens, but this is likely very conservative. The water levels were assumed to be high <br />due to recharge from the Brighton Ditch. The final extent of mining may be determined by <br />the presence of economically mineable aggregate and may therefore be farther from the <br />power lines than the minimum distance listed in Table 2. <br />- Scenario 9: Brighton Ditch. The unlined Brighton Ditch runs along the west side of the <br />mine and is closest at the northwest comer. When it is running, it can be assumed to be <br />locally raising the groundwater table. The mine is relatively shallow in this area and a mud <br />