2018-04-23_REVISION - C1981020 (3)

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Hydrologic Analysis of Munger Canyon Mine: The following analysis and attachments are based on Munger Canyon Mine's Mining and Reclamation permit #C1981-020 and monitoring data from Munger's Annual Hydrologic Reports. Data submitted is from Surface Water monitoring point SW -8, which is above Munger Creek, SW -4 which is below Munger Creek, and Ground Water Monitoring Point GW -3, which is below Munger Creek. Hydrologically, the Munger Canyon Mine operation is located within the Grand Valley Sub -basin of the upper main stem of the Colorado River Basin. Within the region, high flows typically occur during May and June in response to melting snowpack. Low flows normally occur during the winter months. The Mine site itself is drained by Munger Creek, which then flows into East Salt Creek. Generally, water quality in the area is of poor quality and is of a sodium -sulfate type. In addition, since Munger Creek is an ephemeral channel that only flows in response to precipitation events, there is extreme variability in water quality. Effect of Mining on East Salt Creek Regime Surface Water: Due to the limited disturbance of the mine, there is little chance of significant effect on the quantity or quality of the surface waters of East Salt Creek. As the Division noted in the approval of the Munger Canyon Mine, the total area that will be disturbed for both Munger and McClane amounts to 0.12 percent of the area of the East Salt Creek drainage basin above the mines. Historically, samples collected in East Salt Creek above (SW -8) and below (SW -4) the mine are generally the same for all parameters (see Charts 1-5). This indicates that there has been virtually no effect on the quality of the surface waters near the Munger Canyon Mining operation. Further, sedimentation controls were in place during the mining and reclamation activities and therefore prevented off-site impacts. A sediment pond during operations, which was regulated under a CDPHE discharge permit, and a silt fence in place after reclamation. There were no off-site impacts noted during either stage of mining. Both the sediment pond and other sedimentation control structures performed as designed. When evaluating the water quantity impact, it is important to note, SW -4 is located several miles downstream of the Munger canyon mine, and is downstream of an irrigation diversion structure. Since it is below an irrigated field, and a portion of the water is diverted, data would not provide a meaningful analysis of the effect of the Munger operations on the water quantity of the East Salt Creek Hydrologic Regime. However, given the size of the disturbance associated with the mine, it is not likely Munger had a significant impact on the quantity of the East Salt Creek Regime.