Laserfiche WebLink
June 14, 2013 <br />'-"Mr. Michael Cunningham <br />Environmental Protection Specialist <br />Division of Reclamation, Mining and Safety <br />Department of Natural Resources <br />1313 Sherman Street, Room 215 <br />Denver, CO 80203 <br />michael.cunningham @state.co.us <br />W /C16N�Z_ <br />The Union Milling Company <br />P.O. Box 620490 <br />Littleton, CO 80162 -0490 <br />+1.303.947.3499 <br />RECEIVED <br />JUN 14 2013 <br />DIVISION OF RECLAMATION <br />AND <br />RE: Leadville Mill; M1990 -057, TR Y4; Adequacy Review No.1 — Extension Req"9? SAFETY <br />Dear Mr. Cunningham, <br />Union Milling Company (UMC) requests a 30 -day extension to respond to queries presented to <br />us in the Division's correspondence dated 22 May 2013. The delay is due to our getting a better <br />understanding of the perched water encountered during the TSF embankment construction last <br />summer. <br />Following are our work -in- progress responses. <br />The Division has reviewed the Applicant's proposed methods for addressing the <br />perched aquifer which was discovered under the tailings storage facility (TSF). The <br />Divisions' primary concern is with the long -term stability of the TSF and the structural <br />integrity of the composite liner. Two of the proposed methods of remediation temporarily <br />eliminate the inflow of groundwater and allow for installing the geosynthetic clay liner <br />(GCL) without premature hydration. However, since there is not a defined gradient to <br />the groundwater flow, it is not clear where the water will be routed. Saturation of the toe <br />of the TSF could potentially lead to failure of the impoundment. <br />The Division has concluded that the only suitable option for addressing the perched <br />aquifer is to install a sub - surface drain along the seep. Please respond. <br />UMC requests additional time to response to this query. During our spring inspection of <br />the TSF embankment, we observed that water flow from the perched aquifer has <br />significantly diminished. See attached photographs showing flow during September <br />2012 and June 2013. <br />We would like some more time to better understand the situation before responding to <br />this enquiry. <br />2. The Applicant has provided a detail drawing for the sub - surface drain. Specify the <br />average flow of groundwater which has been observed in the seep. In addition, please <br />explain how the dimensions of the sub - surface drain were selected. <br />