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RE: J-2 Contracting Company-DPG Pit-Permit No. M-2019-028 <br /> 112(c)Permit Application <br /> Adequacy Review No. 1 Response 8126119 <br /> -9- <br /> including during reclamation. The flood analysis should quantify the velocity and volume of <br /> flows expected on site from a 100-year flood event, as well as the elevation of the 100- <br /> year base flood event and its relation to the elevation of any proposed spillways and <br /> reservoir embankments. <br /> Response: A floodplain analysis was provided with the materials submitted for the <br /> application showing the existing conditions and the proposed mining and final <br /> reclamation scenarios with the HEC-RAS models provided to us from the CHAMP Study <br /> being performed for this area. The design information for the spillways has been <br /> included in the attached information. The spillways were designed per the Urban <br /> Drainage and Flood Control District's Technical Review Guidelines for Gravel Mining and <br /> Water Storage Activities Within or Adjacent to 100-Year Floodplains. <br /> 37) Please identify all known aquifers in the vicinity of the proposed operation. <br /> Response: The alluvial aquifer in the vicinity of the proposed operation is the South <br /> Platte River and the Cache La Poudre River. <br /> 38) Please provide a site map showing potentiometric elevations for groundwater in the <br /> proposed affected lands and surrounding areas in relation to the existing monitoring wells <br /> and proposed reservoirs. Please be sure to indicate approximate flow direction(s) on the <br /> map. <br /> Response: The groundwater modeling analysis and report from McGrane Engineering <br /> shows the existing and proposed conditions for the operation. The existing conditions <br /> prior to slurry walls being installed and proposed conditions after slurry walls are <br /> installed. This document was sent to the DRMS per your attention on July 11, 2019, <br /> 39) The operator states the operation will impact the South Platte River and the Cache La <br /> Poudre River in the form of depletions due to evaporation and operational losses <br /> associated with mining. Please describe how the operation is expected to impact the local <br /> groundwater regime during operations and during reclamation, including estimated <br /> drawdown, and anticipated areas of mounding and shadowing from slurry wall installation. <br /> This information may be best portrayed on a site map in this Exhibit. Additionally, please <br /> indicate any water resources (e.g., tributary water courses, wells, springs, stock water <br /> ponds, reservoirs, ditches) located on or in the vicinity of the proposed affected lands that <br /> may be impacted by the proposed operation, and describe what type of impacts would be <br /> expected at that resource. <br /> Response: The groundwater modeling analysis and report from McGrane Engineering <br /> shows the existing and proposed conditions for the operation. The existing conditions <br /> prior to slurry walls being installed and proposed conditions after slurry walls are <br /> installed. This document was sent to the DRMS per your attention on July 11, 2019. <br /> 40) Please provide more details on the groundwater monitoring plan, including the sampling <br /> frequency, the frequency of reporting the results to the Division, and the specific criteria <br /> that would require implementation of the groundwater mitigation plan. <br /> Response: The existing monitor wells will be measured once a month to establish a <br /> baseline for the seasonal groundwater elevations underlying the property. The <br /> measurements are typically submitted with the annual report and renewal to the DRMS. <br /> The triggers for implementing a drain to balance the effects of groundwater shadowing <br /> or mounding would be plus or minus 2 feet from what the seasonal groundwater <br /> elevations/measurements have been from the baseline data prior to installation of the <br /> slurry wall(s). <br /> V n 305 Denver Avenue-Suite D•Fort Lupton CO 80621 •Ph: 303-857-6222•Fax:303-857-6224 <br />