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• <br />DEPARTMENT OF NATURAL RESOURCES <br />David H. Getchea, Executive Director <br />MINED LAND RECLAMATION DIVISION <br />DAVID C. SHELTON, Director <br />Richartl D. Lamm <br />Governor <br />DATE: May 10, 1984 <br />T0: Carol Russell <br />FROM: P.C. Saletta •~ <br />RE: R.A. Mining Company - Gypsum Mine <br />As per your request, I have reviewed a portion of the Reclamation Plan <br />submitted by R.A. Mining Company. The applicant states that final reclaimed <br />topography would be graded to slopes of 2 horizontal to 1 vertical. The <br />primary concern for failure of these slopes is related to the high solubility <br />of gypsum rich materials which would erode and create voids. This is evident <br />in the natural badlands topography which no doubt has slumps and rockslides <br />which are related to either gypsum swell or solubility. It is apparent from <br />the topographic and geomorphic expression of this area that no major <br />landslides related to ground water saturation and material strength have <br />occurred. <br />The primary concern for final reclamation is to avoid saturation of these <br />slopes. This can be achieved through proper and consistent grading of the <br />final slopes. The 2 horizontal to 1 vertical slopes should be stable to a <br />safety factor of 1.5 provided they do not become saturated by either <br />pre-existing ground water or improper surface drainage. <br />If data is available to determine if ground water exists in the pit area this <br />should be taken into consideration. Data from exploration drill holes may be <br />useful if water levels were recorded or could be acquired. In addition if pit <br />inflows occur during mining these should be recorded. Pit inflows should be <br />monitored by recording elevation, flow rate, and duration as the pit advances. <br />If saturation due to surface water infiltration is the primary concern this <br />can be remedied by ensuring positive drainage on the 2:1 slopes. All attempts <br />should be made to avoid any possibilities of creating swales which may cause <br />puddling, infiltration and ultimately saturation. If saturation were to occur <br />it would most likely create near surface slumps and possibly sink holes as the <br />result of gypsum going into solution. This in turn could compound the problem <br />by increasing saturation and creating unstable slope conditions. <br />The applicant should be required to monitor pit inflows during operations and <br />grade or regrade slopes during reclamation to ensure adequate surface drainage. <br />If you have any questions or comments, please contact me. <br />/ep <br />Doc. No. 1346 <br />423 Centennial Building, 1313 Sherman Street Denver, Colorado 80203 Tel. (30'x) 866-3567 <br />• iii iuiiiiiiiiu iii <br />