2011-08-08_REVISION - M1977493 (36)

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Water Quality Monitoring Plan Climax Molybdenum Company Version: R1 Permit No. M- 1977 -493 3.0 CLIMAX DRAINAGE BASINS AND SELECTION OF MONITORING • SITES • • This section provides the rationale for selecting the Point of Compliance (POC) and internal monitoring locations in each drainage, and includes a summary of: • Use classifications for stream segments in each watershed; • Existing and potential future uses of groundwater; • Potential contaminant sources; • Hydrogeologic conditions; and • Monitoring locations. 3.1 Arkansas River Watershed The Arkansas River Watershed is located south of the open pit and mill facilities on the east side of the Continental Divide (Figure 1). 3.1.1 Existing and Potential Future Uses of Groundwater Groundwater in the Arkansas River drainage basin at the Climax Mine flows mainly in a thin lens of alluvium and weathered bedrock that is bounded on all sides by lower permeability bedrock. Raw water for industrial uses in the mill and treatment for potable water is delivered from the Arkansas Pond that was created by former gravel quarry operations in the upper Arkansas River Watershed. The source of this raw water is identified as the Arkansas Well. Unlike groundwater monitoring well ARwell, the Arkansas Well is essentially a surface water intake into a wet well. A submersible pump installed in the wet well delivers water to a clear well at the water treatment building in the mill area. For the purposes of potable water treatment system permitting, this source is identified as groundwater under the influence of surface water. The groundwater also recharges the Arkansas River. 3.1.2 Location and Description of Classified Stream Segments Arkansas River Basin Segment 1 b, is the mainstem of the East Fork of the Arkansas River located from the source to a point immediately above the confluence above Bird's Eye Gulch. Segment 1 b is classified as Aquatic Life Cold 1, Recreation E, and Water Supply. 3.1.3 Potential Contaminant Sources The upper Arkansas River Watershed contains portions of the Climax site that supported the historic underground mining operations. Prior to closure of the underground mine, the entrance to the underground operation at Climax was through 5 -Shaft and the Storke Portal at the Storke Yard just east of the hairpin turn on Highway 91, in the upper Arkansas River Watershed. As described more fully in the EPP, the sources of potential contamination in the Arkansas River Watershed include: • Impacted water from the flooded underground workings; • Run -off and seepage from the Storke Yard; and • Run -off and seepage from road cuts and overburden fill placement for road construction on Ceresco Ridge above the Storke Yard. EPP — Appendix C August, 2011 4