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• ~i~ iiiiiiiiiii~~ iii STATE OF COLORADO - DEPARTMCNT OF NATURAL RESOURCES MINED LAND RECLAMATION DIVISION CASTLE COP7CRETE COMPANY, R E C E IV E D SNYDER CANTON QUARRY A Colorado Corporation, lpplicant DEC 131989 Permit No. M-77-210 RECOMMENDATION;, FOR MOD[FICATION to the COR^ECTIVE ACT 'ON PLAN C. M. Nagel, Consulting Engineer, requests modification to the applicant's Corrective Action Plan, (CAI'), 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 geotechnica.l consultant recommends a 3:1 slope configurai.ion if water entry into the fill is possible, 2:1 is used in the CAP. Tlie applicant's engineer utilizes a computer program with many assumptions, including a homogeneous soil. In reality the soil is varied and made up of diverse materials. Other alternatives suggested by the applicant's engineer are not evaluated, such as a retaining wall. Recommendations: Area four slide material shall be removed in i.ts nntirety, as is area 2 and 3's. Area 1 shall have interceptor drain:. and/or incorporate other soil improvement methods, such as compaction and retaining gabions, rock anchors, tendons, or mat reinforcement and compaction. tlinimal 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 displacements 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 3oard may anend this order and require additional slope stability improvements to prevent blockage of tho drainage, or to prevent disruption of the revegetation efforts. itie operator's bond for all earth work shall be held until completion of the slope monitoring. Concern 2, Water Impoundrient: "resent 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 teas neither committed to my nor the division's recommendation. Recommendation: Present silt and sludge laden water shall be pwnped andJor transported to an appropriate siltation facility. Concern 3, Culvert 1111-6: Installation of this culvert at ttie presently specified location on ('AP plans is likely to cause downstream erosion, and localized road flooding at the minimum. TV~ere is a strong possibilty water discharge could precipitate a land slide of clay soils, cobbles and boulders onto the adjoining subdivision road. This is an area of a steep road ~:ut in what appears to be marginally stable soils. Recommendation: Select an alternate location in conjunction with the adjacent landowner. Minimal Recommendation: Allow the quarry road to surface drain i:his area, as is the case to date.