2011-01-25_REVISION - M1977300 - Laserfiche WebLink

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Daniel Arnold, Esq. January 25, 2011 Denver Water Page 2 of 21 o 3.4 Mine Pool o 3.5 Bedrock Aquifer o 3.6 Surface Water o 3.7 Mitigation Options • Section 4: Review of DRMS' Comments on the EPP • Section 5: References Sources of data and information that were considered and relied on for this EPP review include: • The EPP and appended electronic data files containing water quality data for monitoring wells, mine pool, and surface water locations (Whetstone Associates Inc. 2010). • Communications with Cotter representatives during a mine site tour performed on November 5, 2010. Notes and photographic documentation from the mine site tour were summarized and submitted to Denver Water as a Technical Memorandum (November 22, 2010). ▪ Follow -up discussions with Cotter representatives on December 22, 2010 relative to the content of the Technical Memorandum for the mine site tour. • Letter from Cotter to DRMS regarding the July 21, 2010 discovery of a buried steel borehole pipe (September 3, 2010). • DRMS' Adequacy Reviews #1 and #2 on the September 16, 2009 EPP (letters to Cotter dated October 21, 2009 and May 19, 2010). • Correspondence transmitting recent analytical results of surface water samples collected in Ralston Creek during April and June through October, 2010, and groundwater samples collected in August 2010. 2.0 SUMMARY OF KEY EPP REVIEW CONCLUSIONS A summary of the key aspects of the EPP review is provided below. • The EPP states that the waste rock piles are not a source of uranium contamination in the creek, but the data necessary to support this are not provided. To the contrary, the data indicate that leachate from the waste rock piles is a source of uranium contamination in the alluvial aquifer and concentrations have been increasing since 2004. Impacts from the leachate are not realized in the creek along the rock piles, but instead impact the water quality of the creek when the groundwater eventually discharges into the creek near the downstream end of the mine. • The constructed valley fill material is a source of uranium to the alluvial groundwater and evidence in the EPP support this. However, there are insufficient data to support the fill being the sole source. • There is a strong connection between the alluvium and the creek and data in the EPP support this finding. However, the magnitude of connection and its implication on past and current mitigation measures is not evaluated in the EPP. Most of the water collected by the sumps is from the creek and the groundwater is diluted by the creek