2009-03-19_PERMIT FILE - C1994082 (6)

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• limey shales, and silty, fine-grained sandstones. Because of the thickness and low permeability of the strata separating the Trout Creek Sandstone from the mining and the upward hydraulic head below the mined strata, it is unlikely that the mining could have any effect on the water quality of this unit. For these reasons, the current coal mining operations at Yoast are unlikely to significantly impact bedrock groundwater offsite, and no point of compliance is warranted for bedrock groundwater. Points of Compliance - Alluvium At Yoast Mine, the flow direction of the reclaimed spoil will be predominantly towards the adjacent western drainage of Sage Creek and tributaries, which have potential to receive direct runoff and groundwater inflow from the mine operation (Figure 1). The impact to the Sage Creek tributary alluvial groundwater would be most noticeable directly downgradient of the spoil. However, as this water mixes and is diluted by the groundwater in the significantly larger Sage Creek alluvial deposits, potential impacts are negligible. Nonetheless, the alluvial material has the highest hydraulic conductivity of the materials downgradient of the mine site and would be most indicative of any offsite impacts. Therefore, the existing well YSAL3 will be designated a compliance well for this monitoring. The well is actively being monitored and will be sufficient to capture any impact to alluvial groundwater quality from the Yoast Mine. Results from recent monitoring can be seen in Table 1. This table also provides the agriculture and domestic use groundwater standards from Regulation 41. • Other monitoring wells in the same drainage show concentrations higher than the standards in the background data (i.e. prior to mining in 2000). Table 2 provides a statistical summary of water quality data for all Yoast Sage Creek alluvial wells prior to mining. The maximum observed values on Table 2 are also provided on Table 1. Background values were higher than the Reg. 41 standards for aluminum, cadmium, iron, lead, manganese and sulfates. These values are underlined on Table 1 and will serve as the standard for those parameters. For all other parameters, the more stringent of the Reg. 41 domestic or agricultural standards will serve as the standard. Those values are also underlined on Table 1. Review of Table 1 indicates that the water quality from Well YSAL3 has not exceeded any of the proposed standards from October 2005 to May 2008. The final water quality standard to be applied is the Regulation 41 Table 4 standard of 1.25 times the background concentration of Total Dissolved Solids (TDS). As can be seen in Table 3, the maximum background TDS concentration of 2,140 mg/L occurred in well YSAL8. When multiplied by 1.25, the TDS groundwater standard becomes 2,675 mg/L. The current water quality of monitoring well YSAL3 is 1,180 mg/L, which is well below the water quality standard. In the Grassy Creek drainage, the well GW-S70-A (SGAL70, located downstream of Seneca II Mine) will be designated a compliance monitoring well. The well should be sufficient to capture any impact to alluvial groundwater quality from both the Seneca II and Yoast Mines. Recent monitoring results from well GW-S70-A are shown in Table 4. Wells along Grassy Creek at the • Seneca II Mine are analyzed for concentrations of ground water compliance parameters. Table 5 provides a statistical summary of ambient water quality data for those wells. Likewise, wells adjacent to TR-39 15-1-2 Revised 1/09