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MEMORANDUM <br />TD: File <br />FROM: Dave Hallman <br />DATE: January 17, 1990 <br />SUBJECT: SAN LUIS PROJECT, EMBANKMENT MODEL DEVELOPED FOR SENSITIVITY ANALYSIS <br />INCLUDED IN CMLRD RESPONSES <br />For the responses to the Colorado Mined Land Reclamation Division adequacy <br />letter, dated December 18, 1989, pertaining to the proposed amendment to the <br />approved San Luis Project permit, a model of the main tailings impoundment <br />embankment was developed for a slope stability sensitivity analysis. Several <br />conservative assumptions incorporated in the original model used for the <br />stability analyses in the amendment application were eliminated through <br />refinement of the model to more accurately depict the embankment. <br />The model which was developed for the sensitivity analysis is depicted on <br />the attached figure. The main features of the model incorporated the following: <br />• The embankment section analyzed is the maximum height section as per <br />the design drawings. Assumed to be homogeneous with respect to shear <br />strength. <br />• Assumed phreatic surface <br />Conservative, with drainage <br />should actually be lower. <br />as shown on the attached figure. <br />system and free draining beach sands <br />• Foundation sloped at 3% grade as per design drawings. <br />• Foundation shear strength parameters same as embankment fill. Same <br />material and foundation preparation will include stripping and <br />grubbing then compacting surface to 95% of optimum Proctor <br />conditions. <br />The synthetic liner was modeled as a 1 ft thick layer. <br />Impoundment modeled as full of tailings to embankment crest and <br />deposited horizontally. Mill actually be 5 ft below crest when <br />"full" and tailings surface will slope at 1% away from embankment. <br />tjb <br />