2013-11-29_HYDROLOGY - M1977493 - Laserfiche WebLink

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Status Report, Robinson Seep Investigation 1.0 INTRODUCTION Climax Molybdenum Company The Climax Molybdenum Mine is located near the summit of Fremont Pass, approximately 12 miles south of 1 -70 at Copper Mountain and 13 miles north of Leadville, Colorado. The portion of the mine site within the Eagle River Watershed, which is the particular focus of this study, is located in the western portion of the Climax Mine property. Established monitoring locations within the Eagle River Watershed are illustrated on Figure 1.1. In early 2013, following routine monitoring in accordance with the Water Quality Monitoring Plan (Tetra Tech, 2011), water quality within monitoring well EVMW -1S indicated an apparent increasing trend in several analytical parameters including dissolved iron, dissolved manganese, sulfate and TDS, as well as dissolved calcium and dissolved magnesium. No increasing trends have been observed in any other water quality parameters or at any of the other wells within the Eagle River Watershed. 1.1 Site Setting Groundwater in the upper Eagle River Watershed occurs primarily in the shallow alluvium above the bedrock. Data from test pits and boring logs northwest of Robinson Lake indicate that groundwater is present close to the ground surface and that alluvium in the valley consists primarily of silts, sands, and gravels. The alluvium overlays bedrock of the Minturn Formation and Tertiary-aged quartz monzonite intrusives. Groundwater quality within the upper Eagle River Valley has historically been monitored quarterly at the EVMW monitoring well, constructed in September 1993, located below the Robinson Lake seepage collection system and above Eagle Park Reservoir (Figure 1.1). EVMW-1S and a deeper, paired well (EVMW-1D), were constructed in October 2011. EVMW- 1S is completed within both unconsolidated alluvium /till material and underlying weathered bedrock and was constructed to replace monitoring well EVMW which had partially filled with silt. EVMW-1D was constructed to monitor groundwater in the deeper, bedrock hydrostratigraphic unit. The Robinson Lake seepage collection system was constructed in 1996. The original construction consisted of a concrete cut -off wall, keyed into bedrock at the base and both ends, and a perforated drainage collection pipe installed in gravel backfill upgradient of the wall and connected to two sumps. Significant modifications to the collection system were completed in 2001, including the following elements designed to improve the performance of the system: • Added a 2' 9" extension to the top of the existing concrete cut -off wall; • Applied a waterproof sealant to the upstream face of the wall; • Excavation of a collection pond immediately Upgradient of the cut -off wall; • Installation of a pump station with redundant submersible, fed directly from the surface pond; and • The installation of a diesel emergency generator. Tetra Tech, Inc November 2013