2013-11-29_HYDROLOGY - M1977493 - Laserfiche WebLink

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Status Report, Robinson Seep Investigation Climax Molybdenum Company Analytical data from the reconnaissance sampling are summarized in Table 3.2. Chemical data from the reconnaissance sampling were plotted on a Piper Diagram and are presented in Figure 3.3 and when combined with historical chemical data (Figure 2.4), describe four water types: • Robinson Lake Type Water — Water from Robinson Lake is a sulfate- calcium type water. This water is comparable to waters from the Robinson Lake Seep, PZ -04 and RL -17 (toe drain piezometers), EVS -007 (toe drain) and EVS -006 (spring). This water is also characterized by having significantly higher EC values than other water types. Pinedale Till Type Water — Waters from EVS -004 (Weir -1) and EVMW-1S are directly comparable based on relative constituent concentrations and ratios and related to saturated flow through the Pinedale Till. These waters are distinguished by their lower sulfate and calcium concentrations, as well as lower EC relative to the Robinson Lake type water. However, the magnitude of constituent concentrations at EVMW -1 S indicate some influence from Robinson Lake type water. • Bedrock A Type Water - This water is distinguished by its higher alkalinity and lower anion (chloride and sulfate) concentrations compared to other waters. Samples that are classified as Bedrock A type water include EVS -005 (old pump house spring) and EVMW -004 (bedrock well near Eagle Park Reservoir). • Bedrock B Type Water — This water is distinguished by its lower concentration of calcium relative to other waters in the catchment. This type of water is distinct from Bedrock A type water and currently described by water quality from EVMW -1 D. Robinson Lake type water is characterized by high TDS, sulfate, and manganese concentrations (Table 3.2), as well as detectable concentrations of zinc and cadmium, not typically observed elsewhere. Additionally, field EC results are generally greater than1,500 pS /cm indicating the potential for EC to be used to further delineate the extent of water from Robinson Lake. This method was adopted in the subsequent field investigations described below. Dissolved iron concentrations were elevated in the two toe drain piezometers PZ -04 (3.7 mg /L) and RL -17 (6.3 mg /L). Dissolved iron concentrations in the toe drain discharge (EVS -007) were an order of magnitude lower than the concentrations in the piezometers, possibly due to the formation of ferrihydrite following oxygenation associated with the discharge. Additionally, the spring to the southeast of Robinson Seep (EVS -006) also has a high dissolved iron concentration (4.8 mg /L). While this flows directly into the Robinson seepage collection system, dissolved iron concentrations in samples collected from the seep collection pond have been consistently low (near the detection limit). This may also be due to precipitation of ferrihydrite in an oxygenated environment within the Robinson seepage collection system. While elevated dissolved iron is present in groundwater immediately downgradient of Robinson Lake (PZ -04 and RL -17), dissolved iron concentrations within Robinson Lake have been observed at a maximum of 0.15 mg /L indicating that the water quality of the lake is not the direct source of dissolved iron. Water seepage through the lake sediments and /or dam embankment and foundation may mobilize dissolved iron through adjustments in water chemistry. In addition, iron bacteria, identified in other locations within the Climax property, may reduce ferric iron (insoluble) to ferrous iron (soluble). Deeper groundwater flow that does not report to the seepage collection system may retain dissolved iron and influence dissolved iron concentrations at EVMW -1 S below the cut -off wall, as a result of limited flow through fractured bedrock. Tetra Tech, Inc November 2013 29