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<br />MEMORANDUM <br />STEFF~OBERTSON AND KIRSTEN <br />TO: Andre Douchane -Battle Mountain Resources <br />I ~1 <br />FROM: Rob Dor~! ffen Robertson~nd Kirsten (U.S.), Inc. (SRK} <br />DATE: June 3, 1992 <br />RE: San Luis Project Tailings Impoundment Seepage Analysis (SRK Project No. 14714) <br />1.0 INTRODUCTION <br />Mr. Allen Sorenson of the CMLRD has requested information regarding the calculations, <br />supporting assumptions, and data used in the design of the containment system for the San Luis <br />Project's, Costilla County tailings impoundment facility. The containment system for the facility <br />consists of a composite liner system and incorporates a drainage layer. The drainage layer is <br />designed to allow consolidation of the tailings directly overlying the containment system. The <br />composite liner consists of a continuous plastic geomembrane overlying a compacted low <br />permeability soil layer and is designed to limit the potential seepage from the system to deminimus <br />levels. <br />This memorandum reviews the design of the components of the containment system and specifically <br />addresses items raised by Mr. Sorenson during a telephone conversation of April 20, 1992 to Mr. <br />Rob Dorey of SRR <br />These items are in regard to the assumptions made and used to calculate potential seepage rates <br />through the containment system, the design of the drainage layer, and drainage collection pipe <br />system. Relevant design data and construction data available in the 112 Permit Application and <br />its amendment submitted in September 1989 and the "San Luis Tailings Impoundment Construction <br />Report", SRK Report No. 14711, July 1991 are referenced herein. <br />2.0 DRAINAGE SYSTEM DESIGN <br />The drainage system overlying the composite liner system consists of a minimum 2-foot thick layer <br />of silty sandy gravel containing a network of perforated drain pipes. This system is designed to <br />