2010-08-02_REVISION - M1977300 (28)

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Environmental Protection Plan, Schwartzwalder Mine 14-5 • (i) Modeling Approach Water entering the mine originates from two broad sources with variable water quality including: 1. Groundwater which enters the mine at a level equal to, or below, the mine pool; and, 2. Infiltration of meteoric water into the upper portions of the mine. Although numerous water quality samples were collected from the deeper portions of the mine prior to flooding, the actual chemistry of the groundwater before it enters the mine is not well known. Samples from the deep mine are probably the best approximation of background groundwater geochemistry27 but some samples were subject to chemical loading by the dissolution of soluble minerals and salts from wall rocks that had been exposed to oxidizing conditions in the workings during operation. Comparison of the "average" deep mine water quality in 199928 with the water from the partially flooded mine indicates continued loading during filling and at least a three-fold increase in total dissolved solids, predominantly in the form sulfate, calcium, magnesium, and sodium between 1999 and 2003. Uranium, manganese, and molybdenum also increased during that time by factors of ten, five, and three respectively. However, more recent data from 2005 to 2010 suggests a reversal of some of these trends. Major ions (sulfate, bicarbonate, calcium, sodium, magnesium, chloride and potassium) have remained relatively constant since 2007 and molybdenum and uranium have consistently decreased. Water from the upper workings is impacted by acid rock drainage and is of much poorer quality than water entering the lower workings. Water from the upper levels has widely varying pH (2.7 to 8.2) high total dissolved solids (1,230 to 11,000 mg/L), and elevated concentrations of uranium (29 to 150 mg/L) manganese (0.57 to 27 mg/L) and copper (0.04 to 19 mg/L). Molybdenum and other metals were not analyzed for samples collected from the upper workings, but at low pH, most metals exhibit increased solubility and are expected to be present at elevated concentrations. Water quality data for the upper workings is summarized in Table 14-5. (ii) Mass Balance Mixing Model A preliminary mass balance mixing model was prepared to evaluate whether conservative constituents could be identified in the mine water that could be used to confirm percentage inflows from deep groundwater and the upper workings. Results of the analysis did not identify any constituents that could be used to calculate mixing percentages for the upper and lower inflow sources. For many parameters, concentrations in the flooded mine were lower than reported in either the deep mine water or water from the upper workings (i.e. no combination would provide the correct chemistry). In other cases, the calculated mixing fractions were heavily weighted toward the chemistry of the upper workings and indicated that they provided the majority of inflow to the mine. This condition is known to be incorrect. Based on the inability of the mass balance model to provide reasonable results, the chemistry of the mine water is shown to be controlled by dynamic processes which include precipitation and dissolution of minerals from solution. 27 Samples from core holes drilled into virgin rock may be considered representative of bedrock water quality peripheral to the mine. These samples include: 712, 151313, 19D15(Fe), 19D15(Mn), and 191316. • Zs "Average" deep mine water composition from sample RMW (raw mine water) collected 11/15/99 and from 1955 Decline collected 3/23/99, a pooling location for deep mine water during operation. 4109C.100731 Whetstone Associates