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Phase III - Hydrology Demonstration <br /> A.) Basic Standards Interim Narrative Standard for Ground Water(CWQCC Regulation 41.5(c)(6). <br /> The Yoast Mine Groundwater Points of Compliance (GWPOC)were established in Technical <br /> Revision 39 (TR-39) (see Appendix 15-1 of the C-1994-082 permit package). The two GWPOC <br /> monitoring wells are YSAL3 which is screened within the Sage Creek Alluvium and GW-S70-A <br /> (SGAL70)which is screened within the Grassy Creek Alluvium (see Map IA and 1B). GW-S70- <br /> A (SGAL70) is located downgradient of both the Yoast Mine and adjacent Sage Creek Mine. <br /> GWPOC bedrock wells were deemed unnecessary in TR-39 due to the limited potential for the <br /> mine to negatively impact the quality of bedrock groundwater. The Wadge and Wolf Creek Coal <br /> exhibit low hydraulic conductivity(Wadge Coal: 2.45E-7 to 3.5E-7 cm/sec; Wolf Creek Coal: <br /> 4.55E-6 cm/sec) and will limit mine-impacted groundwater from migrating within these units. <br /> Attenuation and dilution should further limit water quality impacts. Aquifers of regional <br /> significance include the Trout Creek Sandstone and the Twentymile Sandstone. The Twentymile <br /> Sandstone is located approximately 500 ft above the Wadge Coal seam and is not found within <br /> the Yoast permit boundary. Low permeability confining layers of the Williams Fork Formation <br /> isolate the Trout Creek Sandstone from the mine. The Trout Creek Sandstone lies approximately <br /> 300 to 400 feet below the Wadge Coal seam and approximately 60 to 100 feet below the Wolf <br /> Creek Coal Seam. The groundwater in the Trout Creek Sandstone is under confined conditions <br /> and exhibits an upward hydraulic head that further limits the potential for infiltration of mine <br /> affected groundwater into the unit. See Technical Revision 39 (TR-39) located in the Appendix <br /> 15-1 of the Yoast Mine permit package for additional justification for the Groundwater Points of <br /> Compliance. <br /> Tables 12 and 13 include the analytical results for samples collected at wells GW-S70-A <br /> (SGAL70) and YSAL3 over the last five years (2014—2018) and provide a comparison against <br /> the Grassy Creek and Sage Creek Alluvial GWPOC water quality standards established in TR- <br /> 39. The groundwater quality at GW-S70-A (SGAL70) meets the existing water quality standards <br /> for all parameters except for dissolved cadmium and dissolved selenium. The lab detection limit <br /> for three of the dissolved cadmium samples exceeds the cadmium water quality standard.None <br /> of the exceedances were associated with measurable values of cadmium. Water quality samples <br /> at commercial labs are often run in groups that include samples from unrelated locations and the <br /> SL-7 - 34 <br />