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TETRA TECH RMC Mr. Mike Refer May 12, 2004 Page 6 lens is locally present. The final extent of mining may be determined by the presence of economically mineable aggregate and may therefore be farther from the ditch than the minimum distance listed in Table 2. Scenario 10: Highway 7 (160th Avenue) north side, including pavement and utilities. A 500 psf surchazge was used to simulate the live traffic load on the road. A mud lens is present. Two distinguishing features of this scenario aze the height of the highway embanlanent, about seven feet at the eastern edge of the property, and the high water table. The water table was assumed to rise to three feet below the surface due to water "piling up" on the upstream side of the slurry wall. The calculations have assumed a 30-foot offset from the property line to the slurry wall. However, there is an approximately 20-foot wide flat section within the CDOT right-of--way before the highway embanlanent starts. If it is possible to obtain a construction easement for the slurry wall construction, the slurry wall could be moved 30 feet from the toe of the highway embanlanent instead of 30 feet from the property line. As shown in Table 2, this would move the edge of mining towazds the property line. - Scenario 11: Highway 7 (160th Avenue) along the southwest cell. The south side of Highway 7 was modeled sepazately due to the different mining methods used on the north and south sides. While the north side of the road will have a slurry wall, the south side will be mined either be dewatering or by dredging. A mud lens and 500 psf live traffic load were used in the stability calculations. - Scenario 12: Ditch return at southwest cell. A return ditch from the Brighton ditch runs along the southern edge of the southwest cell. The bottom of the unlined ditch extends into the upper gravels and can therefore be assumed to chazge the upper gravel when the ditch is running and the southwest mine is being dewatered. Stability calculations took this situation into account. The calculations also included a mud lens and the cross section of the ditch berm. Table 2 shows the minimum setbacks for both a dewatering and dredging mining method. Scenario 13: West side of southwest cell. On the west side of the southwest cell is a building and a gravel road for access to property further south. The building was simulated by a 3,000 psf surcharge while the road was modeled by the weight of the embankment. A mud lens was used in the calculations. Table 2 shows the minimum setbacks for both a dewatering and dredging mining method. - Scenario 14: Southwest cell power lines. On the east side of the southwest cell is a set of power lines. A mud lens was used in the calculations. Table 2 shows the minimum setbacks for both a dewatering and dredging mining method. Note that factors of safety are shown to three decimal places only to aid in comparing the results to the graphical and text XSTABL output in the appendix. Actual values should only be considered accurate to one decimal place.