2016-10-12_PERMIT FILE - M2016010

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Rationale for Recommendation to Approve 16 September 29, 2016 All surface water will be diverted around the operation, or routed through sediment ponds to minimize impacts to surface waters. Control of sediment and peak flows will be accomplished through the stormwater management control features. To control peak flows and sediment discharge, a series of sediment ponds and energy dissipation drop structures are included. These structures control the peak outflows and are designed for the 100-year, 24-hour storm event, for not only during active operations, but also during reclamation.As the quarry advances,the stormwater management plan will be periodically reviewed. Modifications to the stormwater management plan will be submitted for Division review and approval through either the Technical Revision or Amendment process prior to implementation. The Applicant further addressed concerns regarding the proposed stormwater management plan in the adequacy response submitted on July 28, 2016. In the July 28th response, the Applicant stated that down drain ditches will discharge to sediment detention basins designed to contain runoff from the 100-year, 24-hour storm event, with all structures designed using the most conservative conditions, typically the greatest disturbance area. Also, a Spill Prevention, Control, and Countermeasure (SPCC) Plan to prevent impacts to water quality will be developed and submitted to the Colorado Department of Public Health and Environment (CDPHE) prior to construction. The engineering evaluation submitted in Exhibit S demonstrates that flooding on Little Turkey Creek Road will not increase due to quarry development. The stormwater management plan is designed to safely collect runoff from the 100-year, 24-hour storm event and convey it to sediment detention basins. There will be multiple detention basins, and each one will discharge to the nearby stream over a period of 72 hours. The majority of the detention basins will be constructed in native granite. Due to the short detention time and strength of the granitic material, there is little potential for a failure. In the July 281h adequacy review response, the Applicant confirmed climate data from Colorado Springs Airport was presented in Exhibit K because it is the most extensive climate data available for the region. These data were included to present long-term precipitation trends in the El Paso County area, and they were not used for design of stormwater management structures. Recurrence interval storm precipitation depths were calculated by the National Oceanic and Atmospheric Administration (NOAA), and the data for the proposed mine site were used for design of stormwater management structures. The application includes a hazardous materials management plan, which was submitted in the adequacy review response on July 28, 2016. This plan describes facility operations, a list of typical hazardous materials to be used and/or stored on site, controlling authorities, containment structures, inspection procedures, spill reporting procedures, and emergency contact information. The geotechnical stability report submitted in Exhibit 6.5 includes stability analyses of the topsoil and fines/overburden stockpiles which demonstrate how the stability of the stockpiles will be maintained to ensure Little Turkey Creek will not be impacted by stockpile failure and/or excessive sedimentation resulting from erosion of the affected lands. The Division determined the application demonstrated surface water will not be adversely impacted by the proposed operation. Regardless, the proposed surface water monitoring plan will verify compliance with C.R.S. 34-32-116(4)(h) and Rules 3.1.5(10) and 3.1.6. OF_CO`\\1313 Shernr3n Street, RDo~ 215. Deliver, CO 802D3 P 303.866 3567 F 3D3.832.8106 h+tp:' n r. ,, a ii stare.Co. John W. Wcke�tlhoaer. Governor t Rooert W. Rand tt, Ex:..- D,rector I Vir:,�va Brannon. Dutctor g7ro