Laserfiche WebLink
To: Jared Ebert <br /> Date: December 29. 2017 <br /> Page 18 <br /> The ditches were simulated in the groundwater model. Mine dewatering was projected to <br /> increase ditch losses by a few percent for the Little Cache and Taylor and Gill, <br /> respectively, during mining. After mining, ditch losses are expected to decrease due to <br /> lining of the pits. The results section of the groundwater modeling report provides <br /> estimates on the increased losses due to dewatering. Sections 6 and 7 of the revised <br /> groundwater report provides a monitoring and mitigation plan to measure for and <br /> mitigate excessive ditch losses. <br /> Comment 36 <br /> Given the number of permitted groundwater wells in the area, please provide a <br /> groundwater model showing likely impacts to the groundwater surface <br /> (drawdown/mounding) resulting from the proposed mining activity at the time of <br /> maximum dewatering. <br /> Response 36 <br /> The revised groundwater report will be provided within a few days of this response. The <br /> modeling files can be provided should DRMS wish to recreate the simulations. <br /> Comment 37 <br /> Please submit a groundwater monitoring and impact mitigation plan to DRMS for <br /> approval. This plan should include: all historic water level data available for the site <br /> wells and immediately surrounding area if available, monthly monitoring of water levels <br /> at all existing wells if possible, trigger levels for each well based on historic high and low <br /> water levels for that well, proposed reporting and mitigation plan when groundwater <br /> levels deviate beyond proposed trigger levels to minimize any impact to groundwater <br /> levels and especially off-site impacts. Section 9.1 states LRM may mitigate adverse effects <br /> to existing wells by supplementing water supplies or deepening wells. Due to the <br /> approximately 1,900 feet of Pierre Shale bedrock underlying the area at a depth of 12-30 <br /> feet below ground surface (bgs), deepening the existing wells is unlikely to be a <br /> successful mitigation solution. <br /> Response 37 <br /> Please see Section 7 of the revised groundwater report. Note that deepening of <br /> neighbors' wells is a viable solution as most wells are shallow (less than 10 feet deep <br /> with approximately 5 feet of saturated thickness). The majority use of the wells is for <br /> Response to DRAIS comments T E L E S T <br />