2010-06-28_REVISION - M1977300 ‎(2)‎

• Permit No: M1977300
• IBM Index Class Name: REVISION
• Doc Date: 6/28/2010
• Doc Name: Notice of a RTB- TR-12 Adequacy Review
• From: Holme Roberts & Owen LLP, Charlotte L. Neitzel
• To: DRMS
• Type & Sequence: TR12
• Email Name: DB2
• Media Type: D
• Archive: No

June 25, 2010 3 of 15
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Figure 1. Electrical Conductivity and pH Profile of Ralston Creek, November 13, 2008
Subsequent water quality monitoring and gamma surveys conducted. in and along Ralston Creek near the
Schwartz Trend crossing in 2009 indicated no evidence of chemical loading from the mine pool via the
Schwartz Trend. The sampling was conducted during low flow (base flow) conditions in early December,
2009. The results showed no detectable changes in molybdenum and. radium 226 concentrations across the
trend (Table 2, Figure 2). Uranium concentrations decreased downstream across the trend. These results
indicate that the mine pool was not contributing loading to Ralston Creek at this location. DRMS (May 19,
2010) states that "further analysis is required to more thoroughly assess any connection between the mine
pool [and Ralston Creek] ...along the Schwartz Trend" and that "a lack of geochemical evidence for a
connection at present should not be taken as irrefutable evidence that a connection does not or will not exist
in the future under conditions of hydraulic equilibrium." Cotter recognizes that the mine pool may not be
at hydraulic equilibrium, and in fact, "equilibrium" may include normal seasonal fluctuations in water
levels in the mine pool. However, it is speculation to assume that water in the mine pool will migrate to
Ralston Creek along the Schwartz Trend based only on the difference in elevation.
The hydrogeologic conceptual model developed by Cotter's consultants is based on available
hydrogeologic data and does not indicate that groundwater will migrate from the mine pool to Ralston
Creek via the Schwartz Trend. A cone of depression still exists around the mine pool, relative to the pre-
mining water table (or potentiometric surface). Prior to mine dewatering beginning in the 1950's, the water
table was within about 100 feet of ground surface beneath the entire hillside'. During dewatering, the water
level near the mine was drawn down to 2,200 feet below the Steve Level. However, because the
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Although groundwater occurred within 100 feet of ground surface. mine dewatering was not necessary until the shaft was
advanced to 250 feet below ground surface (Soule. 1960) due to the low permeability of the rocks. Small quantities of
groundwater can be managed without pumping, including the fraction that is evaporated by a mine ventilation system.