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fluctuation of groundwater in the alluvial fill excavation area. Excavations within this area may <br /> reach a depth of 30 feet, will groundwater be exposed at this depth? Any material to be <br /> excavated should be dewatered to the most practical extent possible. <br /> Response: Cotter has collected measurements of the depth to bed rock in the areas to <br /> be excavated. These measurements indicate that the maximum excavation depth will be <br /> approximately 15 feet. Excavation will occur in the relatively dry months of April to <br /> December, which should minimize the amount of groundwater requiring management <br /> or treatment. Cotter expects to encounter groundwater from rainwater, springs, <br /> overflow from Ralston Creek during periods of high flow, and potentially other sources. <br /> This water will be routed or pumped to the sump collection and water treatment systems <br /> that will be maintained operable during the excavation. <br /> Furthermore, because the alluvial material is coarse, it will drain relatively quickly <br /> during excavation and while the material is being hauled to the WRPs. No other <br /> drainage is practical or necessary <br /> Comment No. 12 - The WRPs were not previously designated as Environmental Protection <br /> Facilities (EPF)because the geotechnical and geochemical characteristics indicated the WRPs <br /> are capped and stable and have a low potential to generate acid. The Division has determined <br /> the addition of alluvial fill to the existing WRP's will require the WRPs to be designated as <br /> Environmental Protection Facilities as defined in Hard Rock Rule 1.1(15). Therefore,the <br /> activities related to reaffecting the WRPs shall be subject to the applicable requirements of <br /> Rule 6.4.21 and Rule 7. <br /> Response: Cotter acknowledges the reclassification of the WRPs as Environmental <br /> Protection Facilities (EPFs). Cotter has revised the July 2010 EPP to state that the WRPs <br /> are EPFs and is providing the information required in Colorado's Hard Rock Rules 6.4.21 <br /> and 7. Sections of the EPP to be revised include 1 through 7, 15, and 18. This revised <br /> EPP is included as Attachment B to this letter. <br /> Comment No. 13 - In the inspection conducted on July 28, 2016, the Division observed a small <br /> seep on top of the northern WRP. The seep was originating from the steep gulch which <br /> terminates on top of the WRP. The seep has the potential to saturate and degrade the stability <br /> of the WRP. The Operator has indicated there may be enough capacity for the excavated <br /> alluvial fill on the south WRP and the north WRP may not be reaffected. The seep must be <br /> routed around the north WRP regardless of whether additional material is added. Please <br /> describe how the Operator intends to keep the seep from coming into contact with the north <br /> WRP. As required by Rule 6.4.21(10),provide design specifications certified by a licensed <br /> professional engineer for any diversion structures which will convey, transport or divert <br /> surface water around or away from acid mine drainage or toxic or acid-forming materials. <br /> Response: <br /> Attachment C contains the plans for the alluvial excavation. These plans, Sheets 21-26, <br /> contain the location of a drainage ditch for the North and South WRPs. Each ditch <br /> 2016-11-07 Response to TR23 Adequacy Review 5 <br />