2023-07-12_PERMIT FILE - M2022048 (2)

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ENVIRONMENT, INC. PAGE 2 L.G. EVERIST, INC.-WEST FARM RESERVOIR ADEQUACY RESPONSE 02 JULY 10, 2023 pit at least up to the elevation break from the terrace bench on the west side to preserve the slurry wall during potential inflow events. If the applicant does not wish to armor, at least, the entire river facing(east)side of the Phase 1 pit, they may alternatively provide a design for reinforced inlet/outlet structures for Phase 1 designed to safely pass filling and overflow for a 100 year flood event. Please also modify the provided cost estimate as needed for any updates. We have added armoring to the east bank of Phase 1 and modified Table L-1 to included the additional length and cost. EXHIBIT F -Reclamation Plan Map(Rule 6.4.6): 21) The reclamation plan map will need to be modified as necessary... No contour elevations or interval data are provided on the reclamation plan map. Please provide elevation data for the reclamation map contours. A copy of the revised Exhibit F - Reclamation Plan Map is enclosed. The elevation numbers were added to the map and the approximate location of the under drain is shown along the SE section of Phase 1 from the toe of terrace to the east, approximately 1,880 feet.. Also added was the armoring on the east bank of Phase 1. EXHIBIT G -Water Information (Rule 6.4.7): 22) The applicant will need to provide a site characterization and groundwater monitoring plan, including at least five quarters of baseline/background water level and groundwater analytical data, sufficient to demonstrate compliance with the requirements of the "Water Quality Control Commission Regulation No. 41 - The Basic Standards for Groundwater"for the life of the proposed operation. Please note that permanent monitoring wells and Point of Compliance (POC) wells should be placed where they will not be mined through. 23) The Mining Plan as submitted only includes a 15 foot setback from the permit boundary/utility corridor to the slurry wall on the south side of Phase 1, and does not include any provisions such as a French drain, to allow groundwater to flow unimpeded around the proposed slurry wall. No groundwater modeling data has been provided to demonstrate that the construction of this slung wall will not result in excessive groundwater mounding on the adjacent property to the south of Phase 1, or adverse impacts to the irrigation return flows to the South Platte River which currently flow through Phase 1. Please provide a detailed groundwater model illustrating the projected impacts to groundwater levels adjacent to the site after installation of the proposed sluny walls. This should include a groundwater contour map showing projected depths to groundwater and any mounding or shadowing on properties adjacent to the proposed permit area. If the modeling predicts excessive groundwater mounding on adjacent property, the applicant will need to provide a plan to minimize the impacts and maintain the prevailing hydrologic balance during and after mining activity. Based on the historic data available for the site, please propose trigger levels for groundwater level mitigation and where the monitoring points will be located. For example: excessive mounding