2010-01-21_PERMIT FILE - M2009082 (11)

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'I? Page 10 of II Mr. Jared Ebert January 20, 2010 Adequacy Review #3 Comments and Responses: 1. The Division did not receive copies of the PA04 series of borings. Please submit copies of the boring for Division review. The site plan showing boring information for the PA 04 series borings is the best available information. 2. The screening berm and stockpiles are indicated as 7.5 feet in height in the stability analysis models. The applicant must not construct the stockpile above the indicated height used in the stability analysis during mining activities. The Division will include the stockpile height as a permit condition. We understand that this comment refers to the perimeter screening berms above the mining highwall analyzed in the stability analysis. These screening berms do stockpile soil but they are for screening purposes. We understand that the applicant will need to commit to a maximum height of 7%2 feet for these perimeter screening berms. However, the applicant cannot commit to this limitation for internal stockpiles. 3. The Division does not consider the use of conglomerated data adequate to provide a critical cross section and to determine the setback from critical structures. The applicant must provide stability analysis for each individual boring(s) associated with a critical structure. The Applicant must provide a proposal for a single general setback or multiple setbacks, if applicable for a structure, based on the analysis results. The Division recommends the applicant use the greatest setback distance from a structure if multiple setbacks are indicated by the individual boring analysis. Attached is a revised slope stability exhibit which addresses the setbacks. We have also attached a revised Exhibit S to reflect the setback information contained in the revised slope stability exhibit. Whitney Ditch and WCR 64.5 - Phase IA Example The applicant states a worst case cross section was used to evaluate the set back distances for each phase during mining. In the individual cross sections for each phases of mining, the applicant indicates the location of the worst case scenario for each phase, however the soil profile analyzed for each phase is based on a conglomeration of soil information from various borings not the actual worst case scenario. The applicant states the worst case scenario for Phase 1 A is represented by the north mining highwall of the phase. The applicant used conglomerated data from ET02- BH06, ET02-TP03, ET02-PI05, No. 1, No. 2 and MW-3 to determine the offset for the Whitney Ditch and WCR 64.5. The Division agrees the north highwall is the worst case scenario for Phase IA; however the applicant must perform individual analysis for each boring and propose a setback from the critical structures based on the individual results instead of the conglomerated data results.