2021-09-09_REVISION - M2004044 (10)

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alluvial aquifer. The interbedded siltstone and claystone of the Arapahoe Aquifer and associated very low vertical hydraulic conductivity isolates the Arapahoe aquifer from mine operations and potential releases. Monitoring wells have been installed around the West and East Areas; therefore, in the unlikely event of a release, possible impacts to groundwater can be monitored. Water from the initial dewatering operation and runoff from disturbed areas, piled material, and operating surfaces will be diverted to the settling ponds for detention and cleansing. Settling occurs in the trenches, and if necessary, settling ponds will be constructed at a point prior to discharge. Discharges will be directed to the South Platte River, at various points as designated within a State of Colorado, Division of Water Resources, Colorado Discharge Permit System (CDPS) permit. Monitoring of dewatering will be conducted in accordance with the CDPS discharge permit, which sets forth formal monitoring parameters including weekly visual monitoring for oil and grease. In accordance with the CDPS permit requirements, a Stormwater Management Plan (SWMP) will also be developed for this site. The SWMP identifies potential sources of pollution that may reasonably be expected to affect the quality of stormwater runoff from areas around the site and describes the implementation practices to be used to reduce the pollutants in stormwater discharges associated with the facility. Potential impacts to wells. The slurry walls and underdrain will be constructed prior to mining. The underdrain is designed to mitigate impacts to the hydrologic balance. No excavation will occur along the conveyor alignment other than road crossings under Tucson Street and Baseline. Impacts to neighboring wells are not anticipated. Review of permitted wells on August 4, 2021 indicated seven wells completed in the alluvial aquifer within approximately 600 feet of the mine limit. Other wells are screened in bedrock. The wells screened in the alluvium include wells owned by Aggregate Industries and others to monitor site water levels. Wells owned by others, screened in the alluvium, not used for monitoring purposes, and within approximately 600 feet of the mine limits are described below. In the unlikely case that that impacts to these wells due to mining occur, mitigation measures are described below. Gary A. and Delores R. Baker The Baker well (Permit#10310) is located south of the West Area about 500 feet from the mine limit. It is classified as stock watering only at 15 gpm. This well is upgradient of the site and is unlikely to be affected by the mine due to the presence of the slurry wall. San Martin Caballero, LLC The San Martin Caballero, LLC well (Permit#202569-A) is located approximately 500 feet south of the East Area. It is classified as domestic at 15 gpm. This well is upgradient of the site and is unlikely to be affected by the mine due to the presence of the slurry wall. Jason L. Murphy The Jason L. Murphy well (Permit#254461-A) is located approximately 500 feet south of the East Area. It is classified as domestic and stock at 15 gpm. This well is upgradient of the site and is unlikely to be affected by the mine due to the presence of the slurry wall. Aggregate Industries—Tucson South Amendment—MLRB 112 Permit Application Exhibit G-2