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ATTACHMENT 1 <br />Sump Design & Installation <br />Whetstone <br />ssoeiates Technical Memorandum <br />To: John Hamrick, Randy Whicker (Cotter Corporation) 4109C <br />From: Susan Wyman, P.E., P.G. <br />Date: October 1, 2010 <br />Subject: Generic Sump Design, Schwartzwalder Mine <br />Additional sumps are proposed to collect groundwater in the alluvium and fill at the Schwartzwalder <br />Mine. The basic sump installation will include the following tasks: <br />• Excavate sump <br />o Estimated depth to bedrock (based on MW6, MW7, MW9) is shown in Table 1. <br />o Final depth determined based on weathered bedrock <br />o Through gravels and cobbles, dig 12"-18" into weathered bedrock <br />o Disposition of spoils <br />¦ Perform rad screening <br />¦ Clean fraction as backfill <br />• Install 48-inch diameter steel pipe (fiberglass or PVC are not recommended) <br />o Factory perforated (louvered) screen bottom 4 feet above bedrock <br />o Blank (unperforated) from 1 ft above ground to 11 ft below ground <br />o Install vertically and plumb <br />o End of pipe is seated in weathered bedrock, no end cap <br />• Backfill outside of casing with 4-inch well-sorted rock <br />• Excavate two French drains extending from each sump <br />o Average 30-ft long <br />o May be eccentric: longer French drain in NE direction from sump <br />o Approximate depth at level of bedrock <br />o Backfill with 3-inch nominal well-sorted (poorly graded) rock <br />o No perforated drain pipe will be installed - coarse rock only <br />o Place geotextile (filter fabric) in trench over coarse rock backfill to prevent intrusion <br />of fines <br />Table 1. Depth to Bedrock <br />Well Total Depth to Screened <br />ID Depth Bedrock Interval <br /> ft has) ft b s ft <br />MW6 15 13 5-15 <br />MW7 11 8 5-10 <br />MW8 12 10 7-12 <br />MW9 19.2 16 9-19 <br />MW12 17.0 17 12-17 <br />Whetstone Associates, Inc. <br />243 N. Main St. & Gunnison, Colorado 8123046 Phone 970-641-7471 6 Fax 970-641-7431