2016-09-26_REVISION - M2004031 (4)

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Rationale for Recommendation to Approve Page 14 September 26, 2016 for approval of AM -01, received January 13, 2016, and September 20, 2016. DWR's conditions for approval included requirements for accounting of all inflow and outflow as necessary to demonstrate compliance with Colorado water allocation laws, and requirements to perform a final leak test, after installation of the drain pipes, to verify the integrity of the slurry wall. In a correspondence dated June 21, 2016, the Operator affirmatively stated operations were in compliance and will remain in compliance with DWR requirements. With respect to the second SEO comment expressing concern for the integrity of the approved slurry wall after the proposed drain installation, it is standard practice for the Division to notice the DWR prior to permit release for any lined reservoir. DWR will have an opportunity to object to the release of the permit if they feel that liner integrity issues have not been fully addressed to their satisfaction at that time. Therefore, AM -0I demonstrates compliance with the applicable requirements of Section 34- 32.5-116(4)(h) C.R.S., and Rule 3.1.6(I)(a). 3. Concerns that the permanentground►vater mounding mitigation plait as proposed will not sufficiently redttcegrorrtrdwater mounding and impacts to off-sitepropetty. (Equity Funding LLC— first and second commentperiods) Pursuant to Section 34-32.5-116(4)(h) C.R.S., and Rule 3.1.6(1), the Operator must demonstrate how the mining and reclamation activities will be conducted to minimize disturbances to the prevailing hydrologic balance of the affected land and of the surrounding area and to the quantity and quality of water in surface and groundwater systems. In the February 29, 2016, adequacy letter to the Operator, the Division identified the average pre - slurry wall groundwater elevations for three monitoring wells up -gradient of the slurry wall and proximal to the location of the permanent groundwater mitigation plan activity (MW -2, MW -3, and MW -11 B). These average pre -slurry wall groundwater elevations were calculated from the monthly groundwater level monitoring data collected by the Operator from February 2004 until the slurry wall was completed in June of 2005. Based on this data, prior to the installation of the slurry wall at the site, the average groundwater elevation for monitoring well MW -2 was 5035.96 feet (5.63 feet below ground surface); well MW -3 was 5037.69 feet (10.58 feet below ground surface); and well MW -I IB was 5036.90 feet (2.63 feet below ground surface). The amendment proposes setting the invert (inlet) elevation of the Orr drain (located adjacent to MW -2) at an elevation of 5036.5 feet. This elevation is an additional 2.3 feet below the elevation of the current temporary drain, and is intended to lower groundwater levels in the area to approximate pre -slurry wall levels while still allowing for positive drainage into the completed reservoir at its design high water elevation of 5036.0 feet. The proposed Orr drain invert elevation (5036.5 feet) is below the average pre -mining