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Memo to Kate Pickford 2 November 17, 2004 <br />Cottonwood Quarry Geotechnical Review File No. M-2004-061 <br />structures will be affected by mining" implies that the operator may develop highwalls in excess of 40 <br />feet if such highwalls aze not "adjacent to any structure." If the Operator wants the flexibility to mine at a <br />configuration other than 40'x 40' benches, a specific plan must be provided showing azeas where <br />highwalls in excess of 40 feet will be developed. The amount of reclamation bond to be required must <br />then include estimated costs for blasting and eazthwork to create the required reclamation benches in the <br />event that the bond were to be forfeit prior to full execution of the mine plan. If the applicant commits to <br />active quarry perimeters that will always be in the 40'x 40' configuration, then this concern is moot. <br />It is likely, but be no means a certainty, that the proposed overall 1:1 slopes created by 40'x 40' benching <br />will be stable. The Revey report states "it would be wise to examine subsurface rock conditions by doing <br />some test excavations and rock borings." The DMG concurs, but will allow for the approval of the pemut <br />application with limitations and conditions on the development of the quarry consistent with observations <br />of the rock that is exposed in the initial stages of development and thereafter, along with the requirement <br />to report rock condifions to the DMG, modify the mining and reclamation plans as necessary based on the <br />observations, and have conditional limits on quarry size and highwall height until written approval from <br />the DMG is provided. DMG has a number of examples where an observational method of quarry <br />development related to highwall stability has been successful with no hindrance to ongoing quarry <br />operations. It is incumbent on the quarry operator to conduct the necessary geotechnical investigations in <br />advance of permit condition milestones to avoid unnecessary shutdowns of the quarry due to potential <br />permit non-compliance. <br />The applicant must provide the DMG with a plan, including enforceable quarry limitations and <br />milestones, where the structural geology and rock mechanics of the highwalls will be investigated, and <br />approval of the DMG will be obtained based on the existing or appropriately modified plan prior to <br />continued operation ofthe quarry beyond the specified limits. The DMG is particulazly interested in <br />structural geology evaluations that will map the presence and orientation of rock discontinuities such as <br />_ _ joints, foliation, faults, bedding planes, etc. and the geotechnical condition_of such discontinuities. Ro_ c_k <br />discontinuities that dip out of proposed highwalls must be further evaluated in terms of the frictional <br />resistance to sliding along the plane of the discontinuity, and mining and reclamation plans modified <br />appropriately to assure that working and final pit slope configurations will be stable. <br />enclosure(s) <br />cc: Karl Mount, DMG (via email and w/o enclosures) <br />c:tacsVAANER MACH[NE\cottonwaod geotech review.doc <br />