2018-12-26_REVISION - M2008078 (29)

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RE. Prowers Aggregate Operators, LLC. - West Farm Pit-Permit No. M-2008-078 112c Permit Amendment Application (Revision No. AM-01) Preliminary Adequacy Review Response 12121118 -9- necessary) showing the locations of these two permitted discharge points. Response: PAO has revised the Stormwater Management Plan for the site and removed Outfall #002-A. The maps in the attached revised West Farm Pit Stormwater Management Plan show the location of Outfall#001-A. 29) Please confirm the maximum amount of exposed groundwater on site at any time will be 0.61 acre (for temporary dewatering trenches and settling ponds). Please also confirm the appropriate permitting will be maintained from the DWR for any exposed groundwater. Response: The recent reconfiguration of ditches and sediment ponds on the site has increased the exposed groundwater area to 4.79 acres. The pit is currently covered under a temporary Substitute Water Supply Plan that is renewed annually. Monthly accounting is submitted to the DWR, with LAWMA providing the required augmentation water releases to the river to account for depletions resulting from the mining activities. The temporary Substitute Water Supply Plan is being updated to reflect the increase in exposed groundwater area. The updated Substitute Water Supply Plan will be provided to the Division when it is completed. The current Substitute Water Supply Plan and latest accounting spreadsheet is attached for the Division's records. 30) Please confirm that mining in the South Mining Area will remain above the static groundwater table until the proposed slurry wall has been installed and approved by the DWR. Response: PAO confirms that mining in the South Mining Area will remain above the static groundwater table until the proposed slurry wall has been installed and approved by the DWR. 31) Please provide the Division with a copy of the current Substitute Water Supply Plan for the site. If it has not been approved at this time, please commit to providing this document once approved, and maintaining a current version on file with the Division throughout life of mine. Response: The current Substitute Water Supply Plan is attached. Yearly renewals will be submitted to the Division for your records throughout the life of the mine. 32) Please provide more details on the groundwater monitoring plan, including all groundwater sampling points, the frequency of sampling and reporting to the Division, and the parameters analyzed. Please provide a discussion of the monitoring data collected thus far, including any trends observed. Response: At this time PAO is measuring groundwater levels in the monitoring wells on the site on a monthly basis. Groundwater levels prior to and after the installation of the slurry walls on site have remained at or near their historic levels. Groundwater levels around the site fluctuate seasonally due to the irrigation activities on the surrounding lands, Le they are higher during agricultural irrigation periods, and lower when irrigation is not being conducted. PAO has noted a decrease in the groundwater levels in the monitoring wells after the irrigation methods on the surrounding lands were changed from flood irrigation to center pivot sprinkling system methods. This decrease was expected. Flood irrigation contributes a higher amount of infiltration of irrigation water into the underlying water table. Center pivot sprinkling systems were installed to increase the efficiency of the agricultural activities. Center pivot sprinkling systems contribute a lesser amount of infiltration of irrigation water into the underlying water table than flood irrigation does due to the efficient nature of the V 305 Denver Avenue-Suite D-Fort Lupton CO 80621 -Ph: 303-857-6222-Fax: 303-857-6224