2014-05-20_REVISION - C1982056 - Laserfiche WebLink

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Wolf Creek Seam, and the intervening low- permeability units, which act as an aquitard to prevent any significant hydrologic communication between the Trout Creek and Wolf Creek members. The geologic units and any groundwater resources which would potentially be affected by the proposed mine development and subsequent mining activities, exist within a closed groundwater basin, with little potential for water movement from these units out of the basin, and no current beneficial uses of groundwater from the potentially affected units. ➢ Relevant geologic and hydrologic monitoring information and studies indicate that the lower members of the Williams Fork Formation (including the Wolf Creek Coal Seam and Wadge /Wolf Creek Interburden) function as a single hydrologic unit in this area, supporting the proposed groundwater monitoring approach of using a single up- gradient and a single down - gradient monitoring well to monitor the Wolf Creek Coal Seam / Interburden system to characterize and evaluate any potential impacts on the "system" (refer to USGS Water Resources Investigation Report 90 -4020, Robson and Stewart, 1990). The conclusions from these previous studies are further supported by recent radio - isotope analysis of groundwater in the area, indicating that the groundwater is over one - million years old, and further that there is little or no groundwater movement or mixing in the lower portion of the formation. 3. Well completion design plans for additional monitoring wells above and within the Wolf Creek Coal Seam were not provided with this submittal. With respect to TR -83, the Division is requesting review of TC's proposed well completion designs. Construction materials and techniques are important considerations for proper abandonment, and should be reviewed prior to approving an installation. Response: Given the characteristics of the groundwater system in the proposed mining area, and somewhat unique situation of developing and mining an additional seam in an area that has been previously mined, TC needed to work closely with the Division to define and develop reasonable groundwater characterization and monitoring plans. As a result of this collaborative effort, TC has developed the well completion and monitoring plans to address this unique situation which accompany these responses for insertion in the PAP. 4. Well completion logs should be provided following completion of any new monitoring wells for incorporation in the PAP. Please also insure that the well completion summary table is updated for the revised groundwater monitoring plan and add any new monitoring well locations to the Hydrologic Monitoring Map, Map 13a. Response: TC will provide copies of the well completion logs for insertion in the PAP on completion of the additional groundwater monitoring wells, and has updated and revised both the Well Completion Summary Table (Table 7) and the Hydrologic Monitoring Map (Map 13a), copies of which accompany these responses. 5. The current Refuse Disposal Area capacity is 20.0 million cubic yards, which includes refuse material fi°om the permitted Peabody Sage Creek Mine. Please provide information to the Division that the RDA is designed to receive in excess of the 20.0 million cubic yards, or that the Wadge seam refuse, Peabody Sage Creek Mine refuse, and the Wolf Creek refuse will not exceed the 20.0 million cubic yard capacity.