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i _,< STATE OF COLORADO - DEPARTMENT OF NATURAL RESOURCES MINED LAND RECLAMATION DIUISION CASTLE CONCRETE COMPANY, SNYDER CANYON pUARRY A Colorado Corporation, Applicant Permit No. M-77-210 RECOMMENDATIONS FOR MODIFICATION to the CORRECTIUE ACTION PLAN G. M. Nagel, Consulting Engineer, requests modification to the applicant's Corrective Action Plan, (CAP), and responses to the division's letter of adequacy on the following grounds: Concern 1, Slope Stability: Neither the applicant nor the division recognize the need for an adequate factor of safety of at least 1.5. The applicant's geotechnical consultant recommends a 3:1 slope configuration if water entry into the Fill is possible, 2:1 is used in the CAP. The applicant's engineer utilizes a computer program with many assumptions, including a homogenedus soil. In reality the soil is varied and made up of diverse materials.. Other alternatives suggested by the pplcant's engineer are not evaluated, (such as a retaining wall. Recommendations: Area four slide material shall be removed in its entirety, as is area 2 and 3's. Area 1 shall have interaeptar drain6 and/or incorporate other soil improvement methods, such as compacti0rt:and retaining gabions, rock anchors, tendons, or mat reinforcement and eompedtion. Minimal Recommendations: Area four slide material shall be removed in its entirety. Area one shall be monitored by survey monuments for a minimum of ten years. Monuments shall be on a 50' x 50' grid with lateral and vertical displacement~•recorded and reported in each years annual report. Over the ten year term, or sooner, if measurements give an indication of slow and sustained slope movement toward the drainage channel the 9oaTd may amend this order end require additional slope stability improvements to prevent blockage of the drainage, or to prevent disruption of the revegetation efforts. The operator's bond for all earth work shall be held until completion of the slope monitoring. Concern 2, Water Impoundment: Present pond is functioning as a siltation pond. It is desirable not to leak silt and sludge downstream onto property owned by others. It is desirable to keep silt and sludge out of the drainage basin. Castle Concrete has neither committed to my nor the division's recommendation. Recommendation: Present silt and sludge laden water shall be pumped and/or transported to an appropriate siltation facility. Concern 3, Culvert I1R-G: Installation of this culvert at the presently specified location on CAP plans is likely to cause downstream erosion, and localized road flooding at the minimum. There is a strong possibilty water discharge could precipitate a land slide of clay soils, cobbles and boulders onto the adjoining subdivision road. This is en area of a steep toed cut in what appears to be marginally stable soils. Recommendation: Select an alternate location in conjunction with the adjacent landowner. Minimal ReCOmmi~gdation: Allow the quarry road to surfaoe drain this area, as is the case to date. - _ ~` -