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• the Yoast Mine, shown in Figure 1, were analyzed for ambient concentrations of these constituents. <br />Table 6 provides a statistical summary of ambient water quality data for all Yoast Grassy Creek alluvial <br />wells. The ambient cutoff date chosen was 1/31/94, as specified in Reg. 41. Maximum values observed <br />in Tables 5 and 6 are also provided on Table 4. Ambient values were higher than the Reg. 41 standards <br />for iron, lead manganese and sulfates. These values are underlined on Table 4 and will serve as the <br />standard for those parameter. For all other parameters, the more stringent of the Reg. 41 domestic or <br />agricultural standards will serve as the standard. Those values are also underlined on Table 4. Review <br />of Table 4 indicates that the water quality from well GW-S70-A has not exceeded any of the proposed <br />standards from October 2005 to May 2008. <br />Potential contributors to the mineralization of the alluvial water in this region include the underlying <br />Lewis Shale, which is a marine shale with high concentrations of these constituents that underlies <br />portions of the Grassy Creek drainage, and use for agriculture, which can further concentrate the <br />dissolved salts in the water. <br />The final water quality standard to be applied is the Regulation 41 Table 4 standard of 1.25 times the <br />ambient concentration of Total Dissolved Solids (TDS). As can be seen in Table 7, the maximum <br />ambient TDS concentration of 4,030 mg/L occurred in well YGAL15. When multiplied by 1.25, the <br />TDS groundwater standard becomes 5,038 mg/L. The current water quality of monitoring well GW- <br />S70-A is 2,840 mg/L (recent maximum occurring on 10/12/05), which is well below the water quality <br />standard. <br />• Additional alluvial materials adjacent to Yoast Mine include those of the Annand Draw. However, <br />Annand Draw flows into Grassy Creek upstream of well GW-S70-A. Since this well is a proposed point <br />of compliance well, an additional well in the Armand Draw alluvium upstream of this confluence is <br />unnecessary. <br /> <br />TR-39 15-1-3 Revised 1/09