2018-08-22_REVISION - M1977493 (7)

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Eagle Park Reservoir Chemical Loading and Mixing Analysis entire area. Nevertheless, the saturated thickness in this area was conservatively estimated as being 10 feet and the same hydraulic conductivity (1.15 ft/day) was assigned. Bedrock beneath the alluvium in both valleys consists of Minturn Formation, typically shale with minor sandstone and dolomite, interbedded with younger igneous rocks, typically quartz monzonite porphyry or granodiorite. The igneous rocks were intruded along bedding planes in the Minturn Formation and are a few to many tens of feet thick. The Minturn Formation rocks are contact -metamorphosed into schistose rocks adjacent to the igneous intrusions. Permeability in the Minturn and the igneous rocks is limited to fractures. Results from testing of the Minturn Formation and the igneous rocks at relatively shallow depths in the Tenmile and Eagle valleys provide a median hydraulic conductivity value of 0.17 ft/day (Climax Molybdenum Company, 1984; Climax Molybdenum Company, 1985; Kumar, 1994; Titan Environmental, 1995; Wells, 1996; ARCADIS, 2012). Fracture density typically decreases with depth, and the hydraulic conductivity estimated from a well drilled to 590 feet deep in quartz monzonite and Minturn Formation shale and dolomite near the mine offices was about 0.003 ft/day. For estimating groundwater flow through deeper bedrock beneath the alluvium, the median hydraulic conductivity of 0.17 ft/day and a saturated thickness of 45 feet were used. The saturated thickness is based on the screened interval in wells EVMW-1D and EV -MW -004. Table 1. Alluvium/Shallow Bedrock Flowoaths A -A' and B -B' Hvdroeeoloeic Parameters Table 2. Deeper Bedrock Flowoaths A -B' Hvdroeeoloeic Parameters Hydraulic Hydraulic Saturated X -Section X -Section Conductivity (k) A Elevation Length Thickness Width Area Flux (Q) Path ft/day ft ft ft ft ft, acre feet/year A -A 1.15 47.5 776 20.30 415 8,425 4.97 13-13' 1.15 50 1200 10.00 520 5,200 2.09 Table 2. Deeper Bedrock Flowoaths A -B' Hvdroeeoloeic Parameters Eagle Park Reservoir Capacity and Inflows The overall capacity of EPR is approximately 3,150 acre-feet. According to storage records for Eagle Park Reservoir (available through the Colorado Decision Support System), over the past several years, the typical annual change in water storage is on the order of 1,000 acre-feet per year. In comparison, the estimated groundwater inflow represents approximately 1% of this typical recharge volume. The primary source of inflow to the reservoir is surface water run-off from the Chalk Mountain Interceptor and the natural drainage areas to the north and northeast. On an average annual basis, these tributary drainage areas can contribute over 2,100 acre-feet of water to the reservoir. Therefore, even under dry year conditions, the contribution from groundwater is likely to remain a very small portion of the total inflow to the reservoir. Climax Molybdenum Company Page - 3 - Hydraulic Hydraulic Saturated X -Section X -Section Conductivity (k) A Elevation Length Thickness Width Area Flux (Q) ft/day ft ft ft ft ft, acre Path feet/year A -B' 0.17 48.8 988 45.00 1210 54,450 1 3.83 Eagle Park Reservoir Capacity and Inflows The overall capacity of EPR is approximately 3,150 acre-feet. According to storage records for Eagle Park Reservoir (available through the Colorado Decision Support System), over the past several years, the typical annual change in water storage is on the order of 1,000 acre-feet per year. In comparison, the estimated groundwater inflow represents approximately 1% of this typical recharge volume. The primary source of inflow to the reservoir is surface water run-off from the Chalk Mountain Interceptor and the natural drainage areas to the north and northeast. On an average annual basis, these tributary drainage areas can contribute over 2,100 acre-feet of water to the reservoir. Therefore, even under dry year conditions, the contribution from groundwater is likely to remain a very small portion of the total inflow to the reservoir. Climax Molybdenum Company Page - 3 -