2007-11-07_HYDROLOGY - M1977300

• Permit No: M1977300
• IBM Index Class Name: HYDROLOGY
• Doc Date: 11/7/2007
• Doc Name: Hydrologic evaluation of mine closure & reclamation
• From: Whetstone Associates
• To: Cotter Corpoartion
• Media Type: D
• Archive: No

Schwartzwalder Mine -Hydrologic Evaluation of Mine Closure and Reclamation 41
5.3 Evaluation of the Hydraulic Connection Between Ralston Creek and the Mine
Ralston Creek does not appear to be in strong hydraulic connection with the Schwartzwalder Mine based
on stream flow rates, mine pumping rates, and isotopic comparison of mine water and surface water.
5.3.1 Evidence from Stream Flow Data
Stream flow data for Ralston Creek above the reservoir" indicate that the monthly average low flows in the
creek are about 1.6 cfs (Section 3.1), and the creek is often dry above Ralston Reservoir. Near the mine,
however, the creek has seldom (if ever) been dry, even while the mine was pumping at its maximum flow
rate. Shutting off the mine pumps has had no detectable affect on flow rates in Ralston Creek.
5.3.2 Evidence from Mine Pumping Rates
Pumping rates from the underground mine were low, considering the depth of the mine and extent of
workings. The highest inflows occurred as during the sinking of new shafts or rapid development of
stopes. These activities led to increased water flow to the mine (Figure 18), which decreased over time as
the storage in the rock mass was drained. If a strong and direct hydraulic connection with Ralston Creek
existed, inflow to the mine would be lower than the observed inflow rates of 140 to 600 gpm (with an
average of around 190 gpm).
5.3.3 Stable Isotopic Analysis of Mine Water and Ralston Creek
The potential for hydraulic connection between the mine and Ralston Creek was evaluated using the
radioactive isotope of hydrogen, tritium (3H), and stable isotopes of oxygen and hydrogen (160/180, IH/zH).
A total of 6 water samples were collected for this analysis. One sample was collected from Ralston Creek
near the mine. Five samples were collected from various locations in the underground mine. Sample
locations and analytic results are summarized in Table 18.
Table 18. Summary of Isotopic Data for Water Samples
Sample Date Location 'H `°O
'a `H
(T.U.) 0)
(S (SD)
RC-980820 8/20/98 Ralston Creek near mine 12.4 -14.2 -108
779-DH 8/20/98 700 Level -pool 14.5 -16.0 -120
1730 Drift 8/20/98 1,700 Level -drift 14.3 -15.5 -114
19D-DH46 8/20/98 1,900 Level-DH19D-15(Fe) 6.0 -14.7 -110
19D-DH-Mn 8/20/98 1,900 Level - DH19D-16(Mn) 4.2 -14.6 -109
19-JOS-2026 8/20/98 1,900 Level -Johnson Ore Shoot 3.1 -14.5 -108
Analyses of oxygen and hydrogen isotope ratios in water samples can be compared to ratios observed in
meteoric water to identify the probable source of underground water. Isotopic data are typically reported as
5180 and SD which are defined as:
(18O/16O)sample -l'g0/160)standard
8 18p - / x 1000
llg~/16O)standard
8 D . (ZHl'H),•ample -(zH/III )standard x 1000
(ZHl'H)sta„dad
~ ~ The flow is the sum of the flow at the gage above Ralston Reservoir and withdrawals at the Long Lake diversion, which takes
water from Ralston Creek above the Stream gage.
4109B.071116 Whetstone Associates •