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Grand River Park Project, M-2006-046 Response to Adequacy Letter of August 1, 2006 6 September 2006 Page 7 embankment as a permanent hydraulic barrier between the basin and the Phase 16 area to be reclaimed as a groundwater lake (see revised Exhibit F). The top width of the embankment will be at least 25 feet. As mining progresses, especially in Phase 16, silt and other fines material may be compacted into the embankment wall if necessary to improve the effectiveness of the clarification or detention process. In Alternative 2, a bulkhead, imported fill, or some other structural solution may substitute for some portion of the land bridge described in Alternative 1. This option would be subject to the future approval of the Division as a Technical Revision. 11. Please inform the Division how the topsoil/overburden screening berms will be protected from the mining operation. If the pit is to be mined to near vertical slopes, the topsoil/overburden berms may cause the mine slopes to become unstable resulting in slope failure if an inadequate buffer distance is not established. The applicant has the following options: • Demonstrate the topsoil/overburden screening berms will be stable under the proposed mining conditions using a slope stability analysis; • Maintain a setback distance of two times the depth of the pit and revise the maps fo reflect this buffer or,~ • Relocate the topsoil/overburden screening berms to a more stable location, and revise the maps accordingly. The applicant will commit to providing a setback between the screening berms and the top of excavation with a setback distance of two times the depth of the pit. Exhibit C-2 has been revised accordingly. Based on standard practices, the applicant reserves the right to provide information in the form of a Technical Revision that would demonstrate the feasibility of other options enumerated above. The amount of soil loading from the topsoil berm shown in cross-section is not large, and, given 2:1 slopes on the berm, the center of this load is offset from the excavation sufficiently to preserve an angle of repose. The applicant also notes that an additional option might be to commit to mining to final slopes in excavated areas adjacent to screening berms, such that subsidence may be presumed to not be an issue in either the mining or post- mining condition. While the applicant will abide by the commitment above, we appreciate feedback from the Division if this latter option may be feasible, Providing an appropriate degree of flexibility in placement of the screening berms will be to the benefit of both the operator and the neighboring property owner.