2007-10-22_PERMIT FILE - C1981014A (4)

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• Thompson Ranch Buildings • Refuse Disposal Area • Powerlines • Florence Waterline All other affected areas would require only minor mitigation, such as traffic control, repair of affected utilities, or regrading to establish roadways and drainageways or to prevent ponding of water. Specific road sections or drainageways which could be affected are those which intersect the area defined by angle-of-draw limits. Liability associated with potential subsidence damage to the Thompson Ranch structures is expressly limited by the deeds to the properly, hence, subsidence control is not required. However, in compliance with CDMG requirements, three (3) monuments have been located and EFCI monitored these monuments on a quarterly basis. Significant subsidence impacts on the coal refuse stockpile would occur only if pillars in the sub-mains under the north pile area were extracted prior to retreat mining of the main entries under the remaining portion of the pile. If retreat mining of the submains occured prior to the retreat of the main entries, resulting subsidence could cause an offset in the primary subdrain extending under the central portion of the refuse pile, blocking drainage flows and allowing abuild-up of hydrostatic pressure within the stockpile. In order to address this potential concern EFCI installed a secondary subdrain in the northern portion of the refuse pile extending down-gradient from the refuse pile toe. The secondary rock drain serves to ensure that any seepage is carried away from the refuse pile foundation area, thereby maintaining the required factor of safety. The only other mitigation required for the coal refuse stockpile was minor regrading of pile surfaces to prevent ponding of water and regrading to eliminate any rills, gullies or minor surface cracks which might develop. TR-36 2.OS.6-64 Revised -October 2003