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Mining and Reclamation Permit Amend.-M-1988-112 <br /> Groundwater Management Plan Battle Mountain Resources,Inc. <br /> 1.0 INTRODUCTION <br /> Battle Mountain Resources, Inc. (BMRI) operates a groundwater management plan <br /> (GWMP) as prescribed in Technical Revision 26 (TR26) to the Colorado Mined Land <br /> Reclamation Permit M88-112 (BMRI, 1999a) and modified in TR-31 and TR-32, that is <br /> designed to prevent discharge of mine-impacted groundwater from the backfilled West <br /> Pit of the former San Luis Mine into the adjacent Rito Seco drainage. Currently, up to <br /> 200 gallons per minute (gpm) of groundwater is extracted from the West Pit, treated to <br /> appropriate surface water standards at an onsite facility, and then discharged into the Rito <br /> Seco under the Colorado Depart of Public Health and the Environment-Water Quality <br /> Control Division (CDPHE-WQCD) Discharge Permit CO-0045675 (DP CO-0045675). <br /> Brine and sludge generated from the onsite treatment are discharged separately to a <br /> tailings impoundment, approximately one mile southwest of the West Pit. <br /> DP CO-0045675 is issued under the Colorado Discharge Permit System (CDPS) and <br /> serves as both a state discharge permit and a federal National Pollutant Discharge <br /> Elimination System (NPDES) permit. The CDPS permit program is administered in <br /> accordance with the Colorado Water Quality Control Act and the federal Clean Water <br /> Act. <br /> Extraction of groundwater from within the West Pit creates a cone of depression that <br /> draws a substantial portion of groundwater from the alluvial aquifer that is located along <br /> the southern margins of the Pit. BMRI proposes to install a slurry wall around the <br /> southern portions of the West Pit that will act as a hydraulic barrier to prevent the inflow <br /> of groundwater from the adjacent alluvial aquifer (Figure G-1). This will decrease the <br /> volume of water requiring treatment that is extracted from the West Pit. The proposed <br /> installation of the slurry wall meets the objectives of the GWMP, and does not affect the <br /> function of the current pump and treat remedial action. <br /> Major advantages of this proposed remedial action over the current GWMP include the <br /> following: <br /> • The volume of groundwater requiring treatment will be substantially reduced(to a <br /> predicted 10 percent of current rates), <br /> • Interflow between the alluvial aquifer and the Rito Seco will be restored to <br /> conditions similar to pre-mining conditions, and <br /> • A reduction in the production of the brine/sludge generated from the treatment <br /> may allow for different disposal options, if the brine/sludge no longer has to be <br /> discharged to the tailings impoundment, that would allow for eventual closure of <br /> the tailing facility. <br /> 2.0 BACKGROUND <br /> Mining of the West Pit for gold resources commenced in late 1993 using conventional <br /> open pit methods. Pit dewatering was accomplished using a combination of pumping <br /> wells and interceptor trenches and sumps. Extraction operations were terminated by <br /> April 2025 1 Engineering Analytics,Inc. <br />