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- 45 - <br />will seep from the pile will be 1% or 2% assuming that no evaporation <br />takes place. In our opinion, the rate of evaporation will probably <br />exceed the rate of gravity drainage from the pile. However, since <br />some seepage could conceivably occur beneath the pile, it is <br />recommended that the ground surface in the area utilized for <br />stockpiling the waste rock be lined with 18 inches of reconmpacted <br />on -site clay soils. Material and compaction specifications are <br />presented in the Site Grading section. <br />Based on a production of 3,000 tons per month and an assumed <br />moisture reduction by gravity drainage of 2 %, we calculate that <br />approximately 15,000 gallons per month of fluid could accumulate at <br />the base of the pile. Since the fluid can be re- utilized in the <br />leaching process and removing it from beneath the pile would reduce <br />the potential for seepage into the ground, we recommend that a <br />subsurface drain system be installed beneath the leached rock storage <br />pile area to collect moisture from the pile and return it to the <br />process. <br />The compacted clay lining beneath the leached rock storage pile <br />should be sloped toward a series of drain lines which should consist <br />of perforated drain tile surrounded by a minimum of 12 inches of <br />:lean, free draining gravel. The gravel should contain less than 5% <br />.wing the U.S. No. 200 sieve. The perforated drain lines should be <br />ed to a collection point at the perimeter of the waste rock <br />age pile. A solid drain line should be utilized between the <br />ter of the pile and the processing site. The drain line should <br />.loped a minimum of 1% and should be placed approximately 2 feet <br />