2018-11-21_REVISION - M2004044 (21)

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(5) The Operator/Applicant shall affirmatively state that the Operator/Applicant 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 a 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 pages 17-19 of an adequacy response to Mr. Larry Oehler dated November 22, 2004. 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 Conclusions and Recommendations as outlined in the Groundwater Modeling Study are outlined below. Please note that two of the parcels referenced in the model(Greenhouses and the small property located entirely within the east mining area now owned by the City of Aurora and located within the permit boundary), make recommendations regarding mitigation no longer relevant. In addition,the mine phasing with this Amendment was revised so references to the Phase 2 cells are now relevant to the East cell(Phase 3). A finite difference groundwater model was constructed for the proposed Tucson South Mine. The model indicates the groundwater near the mine will be lowered or slightly raised locally during mining in response to dewatering and slurry wall installation. The most widespread drawdown was found to occur during the dewatering of the Challenger Pit, Baseline Mine,and southern portion of the Rogers Pit. The dewatering of the Challenger Pit could potentially draw some water out of the Brighton Ditch (depending on the hydraulic connection between the Brighton Ditch and groundwater table in that area) unless local mitigation steps are taken. The largest local drawdown occurred near the greenhouses at the northeast comer of the Tucson South West cell,after the installation of all slurry walls and slope liners. (Note:the greenhouses are no longer in operation and the property is now included in the permit boundary) Water was found to mound several feet along the upstream (southern and western)edges of the West cell after installation of the slurry wall. Depending on the hydraulic connection between the Brighton Ditch and groundwater table,the ditch could potentially gain over parts of the reach nearest the west cell slurry wall. Simulations run without the presence of the Challenger Pit and Baseline Mine showed that groundwater impacts from only the Tucson South cells was much less compared to the impact of all proposed mines. Specifically,the simulations show that for the isolated Tucson South scenarios,water tends to mound instead of being drawn down. Well impacts in these isolated scenarios are predicted to be minimal. (Note:the greenhouses are no longer in operation and the property is now included in the permit boundary and owned by the City of Aurora. The Area will be mined and included within the reclaimed reservoir—no mitigation is required.) Groundwater flows from south-southwest to north-northeast,and hence no"shadowing effect" in the Morgan Smith Natural Area. The proximity of the River also minimizes the impacts of groundwater levels in the Morgan Smith Natural Area. Scenario 4(Figures 5 and 6),was modeled as dewatering the Tucson South Phase 2A(now East cell, Phase 3)area, dewatering the Challenger mine,and the slurry wall around the Tucson South Phase 2(now East cell, Phase 3) East cell is not yet constructed.The groundwater model predicts a 2-to 3-foot draw-down in the Morgan Smith Natural Area. However,the impact from the Phase 2A(now East cell, Phase 3)area has historically been occurring for the period mining and dewatering has been happening in this area,with no known measured impact. If the trees in this area are impacted,Aggregate can direct dewatering water to the ground surface in this area for irrigation. This draw-down would be temporary until the slurry wall is installed around the Phase 2(now East cell, Phase 3)area. Aggregate Industries Tucson South Resource Permit#M-2004-044112 Permit Amendment Page G-4