2010-07-28_REVISION - M1977300 (2)

Home Browse Search

Response to TR 12 Comments Item 1 The item adequately addresses the issue of Sump Number One water treatment. The Cotter response also references modifications intended to eliminate the need for water treatment. Any such proposals must be addressed through the permit revision process. Cotter plans to present several potential remedial options in a revised Environmental Protection Plan (to be submitted to DRMS by August 1, 2010) that could eliminate the need for treatment of or provide for passive treatment of contaminated groundwater from the valley alluvium and fill. Such options are expected to include source term removal and/or isolation, capture, and passive treatment of groundwater from the alluvium and fill. Several possibilities were proposed in the previous Environmental Protection Plan submittal (April 19, 2010), including a stream isolation barrier, a funnel and permeable reactive barrier gate, and/or a constructed wetlands system. Evaluation of water quality data collected from Ralston Creek and groundwater monitoring wells during active treatment of water reporting to Sump Number One is expected to provide critical information for determination of an optimal approach to a long-term strategy which will ensure continual compliance with water quality standards in Ralston Creek. Cotter proposes to evaluate water quality monitoring data in collaboration with DRMS to assess the beneficial impacts on water quality in the creek and to determine the best approach for a long-term strategy. Once concurrence between DRMS and Cotter is reached on the best long- term remedial approach, Cotter will submit a technical revision request to modify the approved reclamation plan accordingly. Item 2 In addition to the activities proposed, the Division requires Cotter to address the potentially serious problem of the mine pool. Now that the cone of depression that formed due to mine dewatering appears to have recovered (Figure 8-13 in Environmental Protection Plan), the subsequent attainment of static conditions in the water table for a period of time should result in a reversal of the ground water hydraulic gradient back toward the creek. Hydraulic communication from the mine pool to locations downgradient is therefore inevitable, and the operator must prepare for that contingency to prevent or minimize off-site migration of mine pool water. The current chemical condition in the mine pool represents a significant disturbance to the prevailing hydrologic balance and a potential violation of §3432-116(7)(c), (g), (h), and (i) C.R.S. Therefore, the operator shall comply with the requirements of the May 21, 2010 letter. As stated in the May 21, 2010 letter, the operator must reinitiate mine water dewatering and water discharge treatment sufficient to bring the mine water table to a level at least 500 feet below the Steve Level, and sufficient to reestablish a hydraulic gradient away from Ralston Creek. Details of how that will occur must be included in your response to this letter and implementation must occur as soon as possible, but no later than 31 July 2010.