2010-09-14_ENFORCEMENT - M1977300 ‎(2)‎

• Permit No: M1977300
• IBM Index Class Name: ENFORCEMENT
• Doc Date: 9/14/2010
• Doc Name: Reply of Cotter Corporation/ Petition for Reconsideration.
• From: Holme Roberts & Owen LLP
• To: DRMS
• Email Name: DB2
• Media Type: D
• Archive: No

Schwartzwalder Mine
by Susan A. Wyman, P. E., P. G., Whetstone Associates
September 13, 2010
TREATMENT SYSTEM EFFECTIVENESS, CAPTURE, AND LAG TIME
Groundwater in the alluvium is being collected at Sump 1, Sump 4, and monitoring well 9 (MW9)
and piped to the water treatment plant (WTP). The pumping system is designed to collect
groundwater in the alluvium and fill that would have flowed to Ralston Creek, had it not been
intercepted. Pumping began at Sump 1 on July 2, 2010 (the 50 gallon per minute [gpm] system).
The 100-gpm system went online July 30, and the system was expanded to include Sump. 4 on
August 16 and MW9 on August 19.
Groundwater that flowed past Sump 1, Sump 4, or MW9 before pumping began would not be
captured by the pumping system. The pumping system is designed to intercept groundwater, not
necessarily to pump back water that had already flowed past each collection point. The concept of
"interception" versus "pumpback" is important to understanding the lag time in the effectiveness
of the water treatment system on water quality in Ralston Creek. Of course, some groundwater on
the downgradient (east/southeast) side of the sumps is captured within the cone of depression and
pulled into the pumps. However significant pumpback is not expected. Most of the captured
groundwater is derived from areas of the aquifer located upgradient (north and west) of the pumps.
Clearly, the water treatment system has had a positive effect on water quality in Ralston Creek.
Uranium concentrations on August 10, 2010 were reduced to 16% of the concentrations in August
2009 (0.259 mg/L in 2010 vs. 1.64 mg/L in 2009). The treatment system has removed significant
quantities of uranium from groundwater: 89 pounds(l) of uranium were removed from July 2
through September 5. On average, the 100 gpm system is removing 2.9 pounds of uranium per
day when Sump 1, Sump 4 and MW9 are contributing water to the treatment system.
However, the concentration in the creek on August 10 still exceeded the water quality standard of
0.03 mg/L because the pumping system had not intercepted all of the contaminated water in the
alluvium before it flowed into the creek. The reasons for incomplete hydraulic capture are three-
fold:
(1) Some of that groundwater had already flowed past the collection point and was not
pumped back, so a lag time exists in seeing the effectiveness of the interceptor system.
Based on aquifer velocities of 4.05 ft/day to 6.67 ft/day (EPP page 15-10) and a
distance of 200 feet to 610 feet along different flow paths from Sump 1 to Ralston
Creek, the travel for groundwater from Sump 1 to Ralston Creek ranges from 30 days
to 151 days. Groundwater that was traveling toward the creek before the pump was
turned on at Sump 1 would likely take 30 to 15.1 days to reach the creek. This water,
The 50 gpm system operated from July 2 to approximately July 30 and removed about 23 pounds of uranium. The 100 gpm
system removed approximately 66 pounds of uranium from July 31 through September 5.
Whetstone Associates, Inc.
243 N. Main St. ? Gunnison, Colorado 81230 6 Phone [phone] ? Fax [phone]