2010-04-20_REVISION - M1977300 (9)

Home Browse Search

Environmental Protection Plan, Schwartzwalder Mine 15-10 • (iii)Source Removal Partial source removal will occur as part of the decommissioning of the radioactive materials license (RML). CDPHE has approved the decommissioning plan for RML termination, which includes (1) decontaminating any remaining interior structures as needed to free release the waste water treatment plant building, (2) demolishing the concrete Barren Ponds and disposing of materials in Minnesota portal, (3) excavating up to 5,000 cubic yards of contaminated alluvial fill in the waste water treatment plant license area (RML area 2) and disposing it in Minnesota portal, and (4) potentially excavating additional contaminated alluvial fill source material within or outside of RML area 2 and disposing it in Minnesota portal. RML area 2 encompasses the water treatment plant and concrete barren ponds, as shown in Figure 2-3. The removal of contaminated soils (3 and 4) is expected to reduce the source of chemical loading to alluvial groundwater, and have a positive impact uranium and molybdenum concentrations in the alluvium over time. (c) Monitoring Well Installation Two additional bedrock monitoring wells are proposed for installation in 2010. The set of paired bedrock monitoring wells would be located in the Schwartz Trend rocks, approximately 930 feet from the mine. The proposed location is along the existing 4WD road near the southeast corner of Cotter's property (Figure 1), between the mine workings and Ralston Creek. Two paired wells are recommended, to identify downward vertical gradients and verify the existence of a groundwater divide between the mine and the creek. The deepest well is expected to be 300 feet deep and the shallower well is expected to be 80 to 120 feet deep. A cross section along the Schwartz Trend, showing the #2 and #3 mine shafts, Ralston Creek, the proposed monitoring wells, the water level elevation of the mine pool, and an approximated potentiometric surface, is shown in Figure 15-3. The primary purpose of these wells is to determine water levels, hydraulic gradient, and groundwater flow directions in bedrock. Water quality sampling could also be performed to determine whether water from the mine pool is migrating along the Schwartz Trend. According to the h, drogeologic conceptual model for the site (Section 8(e)(ii)), water levels in the mine pool may be controlled by the level of Ralston Creek near the mine. Bedrock in the area has extremely low permeability, and very little flow occurs. A slight increase in permeability (or decrease in flowpath length) between the mine and the alluvium would dominate the flow regime in a bedrock system having a background hydraulic conductivity of 2.8x10"' cm/sec. Water in the mine pool may be seeping into the Ralston Creek Alluvium at very low flow rates (less than 2 gpm) through near-surface fractures and collapsed historical exploration boreholes that were drilled into the deposit from the valley floor. The mine pool does not appear to impact Ralston Creek via the Schwartz Trend. The conceptual model would be verified with the drilling of one or two additional bedrock monitoring wells. If the new bedrock wells are sampled for water quality, approved passive sampling methods would be employed (Tedlar bag, diffusion samplers, SNAP samplers, HydraSleeve(R, or other passive methods) because hydraulic conductivities are so low that unnatural gradients may be induced by well purging. • 4109C.100419 Whetstone Associates