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16 August, 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(o)state.co.us <br />The Union Milling Company <br />P.O. Box 620490 <br />Littleton, CO 80162 -0490 <br />+1.303.941.3499 <br />RECEIVE[ <br />AUG 19 2011 <br />DIVISION OF RECLAMATION <br />MINING AND SAFETY <br />RE: Leadville Mill; M1990 -057, TR -4; Adequacy Review No.2 — Response to All Queries <br />Dear Mr. Cunningham, <br />Union Milling Company (UMC) has prepared the following responses to Adequacy Review No.2. <br />This letter addresses all queries in Adequacy Review No. 2. <br />1. The Division has reviewed the Applicant's proposal to install a geonet over the seeps in the <br />tailings storage facility (TSF) in order to control the flow of water and prevent the premature <br />hydration of the geosynthetic clay liner. The Applicant has estimated that the inflow of water <br />from the identified seeps is approximately 8gpm, which is a decreased flow from what was <br />observed during the last construction season in 2012. The rate of inflow is largely dependent on <br />the amount of snow received during the winter and the subsequent melting of the snow pack. <br />The Leadville area has experienced below average snow pack over the past several years. The <br />observed inflow from the seeps could substantially increase during a year where snowpack is <br />average or above average. Furthermore, if inflows are increased the extent (height and width) <br />of the seeps could also be increased. Finally, the geotechnical investigation conducted by CTL <br />Thompson stated that the area encompassed by the TSF is over lower permeability clays. <br />Overview: <br />Work performed by CTL did, in fact, state that the TSF area was encompassed by low <br />permeability clays. Based on this information UMC initially proposed using this clay for the sub <br />liner in the TSF. However, once embankment construction began, it was discovered that the <br />clay identified was confined only in one small lens and that the TSF area consisted <br />predominately of colluvium material. At that point UMC commenced the Technical Revision <br />application to use GCL in lieu of clay. <br />UMC agrees with the Division in that inflows from the perched aquifer are dependent on winter <br />snowfall as well as overall precipitation in the area, and that the reduced inflows we are now <br />experiencing are related to below average snow fall (precipitation). <br />However, UMC has confirmed with CETCO that premature hydration of the geosynthetic clay <br />liner (GCL) is only a concern during installation when the GCL is unconfined. Once installed <br />