2019-11-12_REVISION - M2004044 (13)

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(5) The Operator/Applicant shall affirmatively state that the OperaforlApplicant has acquired(or has applied for)a National Pollutant Discharge Elimination System(NPDES)permit from the Water Quality Control Division at the Colorado Department of Health, if necessary. Al will apply for an NPDES permit prior to mining or dewatering the site. Potential Mining Impacts Tucson South Resource Groundwater Modeling Study on the Hydrogeologic Effects of Mining, prepared by Tetra Tech RMC dated August 2004 was submitted as a referral response to DRMS August 3, 2004. The study is on record with the original application and attached herein for reference. A groundwater monitoring and mitigation plan was submitted to the Division as part of an adequacy response to Mr. Larry Oehler dated November 22, 2004(in pages 17-19). The plan was reviewed and approved by the Division as part of the original permit for the site. A copy of the approved Groundwater Monitoring and Mitigation Plan is described below. The hydrogeologic conditions have changed since the 2004 report. However, many of the changed conditions were considered in the 2004 model. The Challenger Pit north of the West Area has been reclaimed as a lined storage reservoir. The triangle-shaped parcel north of the East Area has been backfilled with fines. The Greenhouses in the northeast corner of the West Area and the small property located entirely within the East Area are now owned by the City of Aurora and will be mined and reclaimed as part of the water storage reservoir., The 2004 report presented eight hydrogeologic scenarios that address the various conditions and associated groundwater impacts of the for the life of Tucson South Mine. Scenario 6 described on pages 9 and 10, illustrated on Figures 9 and 10, represent the current conditions with two exceptions: 1.The wells at the Greenhouse property, now owned by Aurora,will be removed during mining, and 2.The South Area rather than being wet mine will be dewatered. The changes due to the Aurora property are moot and do not have a material impact on the model simulations. However,the dewatering of the South Mine Area will likely impact wells west of the South Area. Al will implement its Ground Water Mitigation Plan to address potential impacts to these wells. The model indicates that after installation of the slurry wall, groundwater will mound up to approximately six feet along the western and southern edges of the West Area. Given the rise in groundwater level west of the slurry wall, the mining operations will not increase seepage from the Brighton or Brantner ditches. The model also indicates that there will be little to no mounding south of the South Area after reclamation. This is due to the presence of the Brighton Return Ditch that acts like a drain and limits the rise in groundwater level. Similarly,the model indicates that there will be minimal rise in groundwater level south of the East Area. This is due to the proximity of the South Platte River. Todd Creek Farms Metropolitan District#1 (Todd Creek)operates several water supply wells between the South Platte River and the slurry wall of the East Mine Area. Todd Creek is aware of the future slurry wall and has an agreement with Al acknowledging the construction of the slurry wall and potential impacts to well yields. Groundwater flows from south-southwest to north-northeast, roughly parallel to the South Platte River. Consequently, there will be very little if any"shadow effect' (decline in groundwater level) in the Morgan Smith Natural Area. The proximity of the River also minimizes the impacts of groundwater levels in the Morgan Smith Natural Area. The modeling (Scenario 6, Figures 9 and 10) indicates there will be a shadow effect north of the mine in the narrow strip of unmined alluvial aquifer beneath Tucson Street. The drawdown estimated by the model assumes the wells were pumping at the Aurora property Greenhouse and one domestic well north of the mine. Given that the greenhouse wells will not be pumping,the drawdown will likely be less than the of six to eight feet estimated by the Aggregate Industries Tucson South Resource Permit#M-2004-044112 Permit Amendment Page G-5