2011-09-28_REPORT - M1977300 - Laserfiche WebLink

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Mr. Jim Dupler September 28, 2011 Page 2 2. Three new sump /French drain systems (Sump 5, Sump 8 and Sump 9) were constructed to intercept alluvial groundwater for water treatment (conducted under TR -15). Construction and burial of piping systems to deliver alluvial groundwater to the water treatment building for water treatment was also undertaken along with construction of a new discharge outfall location near Sump 1. 3. In the area of the old emergency overflow pond, a previously excavated depression where groundwater was daylighting and had formed a pond was filled in to prevent evaporative losses. A 48 -inch diameter corrugated HDPE pipe was installed near the eastern end of the pond in order to continue monitoring groundwater levels and water quality at this location. A temporary pump and above - ground piping was subsequently installed to pump alluvial groundwater from this location to the water treatment plant. It is currently planned to convert this temporary pumping location into a permanent sump location (Sump 10) under the provisions of TR -15. 4. To date, the alluvial groundwater treatment systems have prevented approximately 1,400 lbs. of uranium from migrating to Ralston Creek. 5. Resumption of surface water sampling at historic monitoring stations SW -BDIS, SW -PL, SW -OS, SW -BOS, and SW -GS began in June 2010. Staff gages at these locations were subsequently refurbished in order to develop rating curves to estimate stream flow rates. (Stream flow data since late December 2010 have been compiled.) 6. Environmental monitoring, including expanded monitoring stations and analytical testing requirements for surface water, groundwater, and treated discharge water was continued. 7. Geotechnical studies were initiated, including the engineering design and complex regulatory approval processes to build a temporary pipeline to convey Ralston Creek past the Mine site and prevent interaction between water from the creek and the alluvial fill. 8. Spatial estimates of primary impacts to Ralston Creek were refined (between monitoring stations SW -OS and SW -BOS). 9. The French drain for Sump 5 was expanded upgradient by 100 ft., and plan to deepen Sump 5 and lower pump assembly. 10. An electrical resistivity study of the alluvial fill and groundwater in the vicinity of Sump 10 and MW -3A was performed. 11. A study was conducted to characterize contaminated source term materials within the alluvial fill for planned removal and to assess the source term material itself with respect to potential disposal options including an evaluation of the potential option of disposal in the Minnesota Adit.