2015-10-16_GENERAL DOCUMENTS - M1999120

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GANSER LUJAN &, ASSOCIATES Hvdrogeological and Environmental Consultants Table 1 HEC -RAS Modeling Results for 5, 10, and 100 Year Flows The water surface elevation corresponding to this change, as shown on Table, l is 4875.81. As previously discussed in GL&A report dated October 4, 2013, the 100 -year flood plain level determined by Weld County for obtaining a Flood Hazard Permit on 5/19/1987 for the Bachofer property was 4874.0 feet. As such, the elevation determined by this modeling for post- mining conditions is well above the previously established FIS 100 -year flood plain elevation. At the request of Weld County, model simulations were also conducted for lower flows that include the 5 and 10 -year events. The 5 -year event (7,900 cfs) approximates flow at the Bachofer property, which has been currently flooding the lower level of his house. The flooding has been occurring since 2004 when L.G. Everist lined their pit with a slurry wall. As can be seen on Table 1, the 5 -year event (4873.91 feet) for current mining conditions is very close to the l 00 -year permitted flood plain elevation of 4874 feet. The model results show the 100 -year pre -mine surface to be 4873.95. -7- Pre-MiningTo o ra h • 2008 Mining Topography Change in Water Cross -Section Profile Q Total Water Surface Energy Grade Water Surface Energy Grade Surface Elevation (cfs) Elevation (11) Elevation (ft) Elevation (ft) Elevation (ft) (ft) 4700.78 PF l 7900 4873.27 4873.34 4874.25 4874.27 0.98 4700.78 PF 2 10000 4873.48 4873.56 4874.58 4874.61 1.1 4700.78 PF 3 29000 4874.85 4874.94 4876.21 4876.26 1.36 4233.11 PF 1 7900 4873 4873.04 4874.14 4874.16 1.14 4233.11 PF 2 10000 4873.22 4873.25 4874.49 4874.5 127 4233.11 PF 3 29000 4874.57 4874.63 4876.1 4876.13 1.53 3193.73 PF 1 7900 4872.43 4872.46 4873.91 4873.94 1.48 3193.73 PF 2 10000 4872.66 4872.69 4874.26 487429 1.6 3193.73 PF 3 29000 4873.95 4874.01 4875.81 4875.86 1.86 2354.37 PF 1 7900 4871.88 4871.92 4873.6 4873.65 1.72 2354.37 PF 2 10000 4872.1 4872.14 4873.97 4874.01 1.87 2354.37 PF 3 29000 4873.38 4873.44 4875.42 4875.49 2.04 1388.01 PF 1 7900 4871.01 4871.11 4871.61 4872.41 0.6 1388.01 PF 2 10000 4871.35 4871.42 4872.17 4872.94 0.82 1388.01 1 PF 3 29000 4872.54 4872.63 1 4874.09 4874.48 1.55 634.85 PF 1 7900 4869.84 4870.2 4870.57 4870.91 0.73 634.85 PF 2 10000 4870.11 4870.57 4871.3 4871.62 1.19 634.85 PF 3 29000 4871.63 4871.85 4873.08 4873.39 1.45 188.69 1 PF 1 1 7900 4868.84 1 4869.32 1 4868.02 4869.74 -0.82 188.69 PF 2 10000 4869.04 4869.54 4868.72 4870.57 -0.32 188.69 PF 3 29000 4869.91 4870.79 4871.88 4872.64 1.97 The water surface elevation corresponding to this change, as shown on Table, l is 4875.81. As previously discussed in GL&A report dated October 4, 2013, the 100 -year flood plain level determined by Weld County for obtaining a Flood Hazard Permit on 5/19/1987 for the Bachofer property was 4874.0 feet. As such, the elevation determined by this modeling for post- mining conditions is well above the previously established FIS 100 -year flood plain elevation. At the request of Weld County, model simulations were also conducted for lower flows that include the 5 and 10 -year events. The 5 -year event (7,900 cfs) approximates flow at the Bachofer property, which has been currently flooding the lower level of his house. The flooding has been occurring since 2004 when L.G. Everist lined their pit with a slurry wall. As can be seen on Table 1, the 5 -year event (4873.91 feet) for current mining conditions is very close to the l 00 -year permitted flood plain elevation of 4874 feet. The model results show the 100 -year pre -mine surface to be 4873.95. -7-