2022-05-13_REVISION - M1977300 - Laserfiche WebLink

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_"NONCOLORADO LEGACY LAND $CHWARTZWALDER MINE materials within the alluvial pad,can be performed.To allow for access to the contaminated soils in the alluvial valley,the water treatment plant was relocated up to the Mesa in 2018. The previous water treatment plant was demolished,and debris were returned to the underground mine in accordance with the Mine Permit (M- 1977-300). EA MITIGATION PLAN FOR SOLID SOURCE TERM MATERIALS Alluvial valley excavation began in 2018 and has progressed seasonally(late spring to early fall)to present day. In accordance with 2013 Mine Plan Amendment 4,contaminated alluvial fill materials excavated to date have been placed in an underground stope known as the"Glory Hole",which is accessed through the Minnesota Adit of the Schwartzwalder Mine on the hillside well above the elevation of Ralston Creek on the southern side of the valley. Because the Glory Hole has recently reached capacity, and in accordance with 2021 Mine Plan Amendment 5,additional contaminated materials have been placed in the open adit for the Black Forest Mine, a nearby former decorative rock mine that was only partially advanced before operations were permanently terminated.The true spatial extent of the alluvial excavation project is not fully known.As the excavation work processes, and in accordance with Technical Revision 14, gamma radiation surveys are completed to guide excavations such that material are efficiently and effectively removed based on real time measurements. Figure E-2 illustrates the potential horizontal extent of contamination from the most recent surface gamma radiation survey(Fall 2021)and shows the location of the Ore Sorter Decommissioning Area (also called RML Area#2). The vertical extent of contamination in this area may extend to bedrock(approximately 15 feet below ground surface or less) in some areas.As indicated in Technical Revision-14: Alluvial materials with Radium-226 concentrations above 7 pCi/g shall be excavated and disposed of in the Minnesota Adit(2013 Mine Plan Amendment 4)or the Black Forest(2021 Mine Plan Amendment 5)to protect water quality in Ralston Creek.Alluvial materials with Radium-226 concentrations below 7 pCi/g are expected to meet the 17.2 mg/kg natural-uranium criterion, which in turn, should ensure that groundwater leachate from contact with alluvial fill materials will not exceed the applicable water quality standard of 0.03 mg/L. These soils may be used a fill materials or growth media for reclaiming the valley. Successful completion of alluvial fill excavation work(i.e.confirmation that all contaminated soils have been removed) shall be verified with soil sampling results and presented in a Final Status Survey Report, which shall be provided under separate over to DRMS and CDPHE to satisfy the following regulatory requirements: • DRMS: Remove soil with the potential to leach uranium to surface water above the Colorado domestic water supply limit for uranium [0.03 mg/L].The objective is to protect water quality in Ralston Creek and satisfy reclamation requirements under the Mine Permit(M-1977-300). • CDPHE WQCD: Eliminate the discharge of uranium and other mine-related pollutants from"the Pad" to alluvial groundwater and surface water in Ralston Creek.The removal of contaminated alluvial fill materials is expected to eliminate the long-term need to operate the sump-capture system and bypass pipeline, and to eliminate the need for monthly monitoring of Ralston Creek as required by the NOV/CDO(CDPHE,2010). • CDPHE Radiation Control Program: Remove soil above CDPHE clean-up requirements for unrestricted release of RML Area #2 (also called the Ore Sorter Decommissioning Area in Exhibit U) from Radioactive Materials License CO-369-06. MAY 2022 12 AMENDMENT 6