2010-04-20_REVISION - M1977300 (2)

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Whetstone' Associates Technical Memorandum ground water is in direct communication with Ralston Creek which terminates in Ralston Reservoir, a drinking water storage facility. Therefore, the alluvial ground water is ultimately a drinking water source. Additionally, the CDPHE discharge permit criterion was a risk-based value that targeted the ultimate concentration in Ralston Reservoir in the context of usage as drinking water. The CDPHE discharge permit recognized the physical and geochemical processes that occur along the 1.6-mile flowpath between the alluvial groundwater at the Schwartzwalder site and the impounded water at Ralston Reservoir. Notably, mixing occurs when surface water in Ralston Creek interacts with alluvial groundwater. The discharge permit considered mixing, and did not apply drinking water standards directly to the mine discharge water. Significant additional mixing also occurs as water from the Moffat collection system enters Ralston Reservoir and mixes with water from Ralston Creek before being pumped to the Moffat water treatment plant. 11) Pg. 8-37: Was the methodology for collecting the underground Tritium samples the same as that described in Section 9. b. (iv).3 on page 9-48 for the other underground water samples? If not, please provide the procedure describing how the Tritium samples were collected. Six samples were collected in August 1998 and submitted to the Tritium Lab at the University of Miami for low-level (0.1 TU) tritium analysis. One sample was collected in Ralston Creek and five samples were collected from seeps, drips, and pools in the underground mine (Table 1). The underground samples for isotopic analysis (tritium, oxygen-18, and deuterium) were collected in the same manner as other underground water samples. Table 1. Samples Collected for Isotopic Analysis Sample Location 3H (T.U.) 180 (6180) 2H (6D) RC-980820 Ralston Creek at Mine Pool 12.4 -14.2 -108 779-DH Pool on 7 Level 14.5 -16 -120 1730 Drift Mine - 17 Level Drift 14.3 -15.5 414 19D-DH46 Mine - 19 Level DH19D(Fe 6 -14.7 -110 19D-DH-Mn Mine - 19 Level DH19D Mn 4.2 -14.6 -109 19-JOS-2026 Mine - 19 Level Johnson Ore Shoot 3.1 -14.5 -108 12) Table 9-7: Was the Fe3+ analyzed from a filtered or an unfiltered sample. The ferric iron (Fe3+) values represent the unfiltered portion of the sample. The laboratories* analyzed the samples for total iron and ferrous iron (Fe 2) using ICP-AA (EPA Method 200.7). The ferric iron (Fe3+) fraction was calculated by the lab, as total iron minus the ferrous (Fe2+) iron fraction. The portion of the sample analyzed for total iron fraction was unfiltered; the portion of the sample analyzed for ferrous iron was filtered. *Four laboratories have analyzed iron species in samples from the Schwartzwalder Mine over the 10- year period spanned by Table 9-7: Core Labs, Severn Trent Laboratories, Energy Laboratories, and the Cotter laboratory at Canon City. 4109C.100416 7