2016-05-04_REVISION - M1977300 - Laserfiche WebLink

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Technical Revision 23, Mining Permit M-1977-300 Mr. Robert Noren Disposal of Alluvial Fill Cotter Corporation(N.S.L) 2.0 SCHWARTZWALDER HISTORY Initial development of underground workings at the mine began relatively high up the hillside on the south side of the Ralston Creek valley in the vicinity of the Illinois Fault. As the upper mine workings advanced downwards along various mineralized fault systems, several additional portals were developed until the narrow valley floor forced constraints on the amount of space available for waste rock. As the mine approached the elevation of the valley floor, the Steve Portal (50 feet above the present elevation of Ralston Creek) became the primary access point in support of continued downward mine advancement. Beginning in the late 1970's, two engineered waste rock piles were developed on hillsides above the valley floor to accommodate continued mine development. Material associated with mine disturbance along the valley floor is a mix of mine waste rock and naturally occurring soils, alluvial sands, and gravels. As presented in Amendment 4 (Cotter, 2012) these materials are referred to as Solid Source Term Materials. For the purposes of this report,these materials are collectively referred to as"alluvial fill." Because seasonally varying amounts of groundwater associated with Ralston Creek are in contact with alluvial fill, and some of these materials include mineralized waste rock, water quality in the creek is subject to seasonal uranium concentrations in excess of the applicable stream standard(0.03 mg/L)from this source. The degree of uranium mineralization present in mine waste rock and its location within the alluvial fill may vary depending on original in-situ proximity to highly mineralized veins in the mine, and when during the historic sequence of mine development the material was brought to the surface. Subsequent construction of site facilities and remediation of areas involving the ore sorter and water treatment ponds, likely mixed and redistributed mine waste rock materials within the alluvial fill. Excavation of the contaminated alluvial fill is anticipated to commence in 2016. TR-23 presents a proposed methodology for permanent storage of the excavated alluvial fill. The method will be to store the alluvial fill in the existing permitted waste rock storage locations that have not been fully utilized. December 28, 2015 2 Engineering Analytics, Inc.