2010-11-15_ENFORCEMENT - M1977300

• Permit No: M1977300
• IBM Index Class Name: ENFORCEMENT
• Doc Date: 11/15/2010
• Doc Name: Reply of Cotter Corporation
• From: Holme Roberts & Owen LLP
• To: DRMS
• Email Name: DB2
• Media Type: D
• Archive: No

Hydraulic Capture of Groundwater
By Sumps Completed in Ralston Creek Alluvium and Fill
at the Schwartzwalder Mine
by Susan A. Wyman, P. E., P. G., Whetstone Associates
November 12, 2010
Cotter Corporation (N.S.L.) ("Cotter") has undertaken an extensive program to mitigate water
quality impacts to Ralston Creek near the Schwartzwalder Mine. The goal of the mitigation
program is to reduce uranium levels in Ralston Creek to below the water quality standard of 0.03
mg/L, to prevent increases in uranium concentrations in the creek as it flows across the mine site,
and to meet the discharge standards specified in the order issued to Cotter by the Water Quality
Control Division (Order) of the Colorado Department of Public Health and Environment
(CDPHE).
Cotter's water treatment system has removed a significant mass of uranium from alluvial
groundwater, thus preventing it from entering Ralston Creek. From July 2, 2010 to October 31,
2010, the water treatment system had removed 302 lbs of uranium from groundwater. Nearly
eight million gallons (7,778,000 gal) of water had been treated and returned to the flow system as
of October 31, 2010. Since the water treatment system began operation in July 2010, seasonal
uranium concentrations in Ralston Creek have been two to ten times lower in 2010 than in 2009
(Figure 1).
Uranium concentrations in the treatment system discharge have remained in compliance with the
Order throughout system operation. Uranium concentrations have been at or below detection
(<0.0004 mg/L) in 83 of 86 samples (97%) of the treated discharge. The highest uranium detected
in the treated discharge water was 0.0023 mg/L, which is 92% lower than the drinking water
standard of 0.03 mg/L.
Despite the significant decrease in concentration and in mass loading, the water quality in Ralston
Creek has not met the 0.03 mg/L standard. (Water quality standards are based on concentration
only, and do not take into account loading rates.)
To further address water quality in Ralston Creek, the groundwater collection system has been
expanded and optimized since its startup in July, 2010, based on an evolving understanding of
groundwater flow and chemistry in the alluvium and fill. Pumping from Sump 1 began on July 2,
2010. Sump 4 was added on August 16, 2010 and MW9 was added on August 19, 2010. Total
flow from these three extraction points averaged approximately 67 gpm from August 20 to
October 31, 2010. Data collected during the four months of system operation and construction
have provided valuable information that Cotter is using to refine the system and improve hydraulic
capture of alluvial groundwater.
A clearer picture of groundwater flow paths in the alluvium has emerged, leading to a more
thorough understanding of how to intercept specific zones of groundwater in the alluvium and fill
that have elevated uranium concentrations and prevent the water from reaching Ralston Creek.
Areas of gaining and losing streams have been clearly identified. While stream survey data from
Whetstone Associates, Inc.
243 N. Main St. 6 Gunnison, Colorado 81230 6 Phone [phone] Fax [phone]