2009-03-19_PERMIT FILE - C1994082 (7)

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• Yoast Technical Revision 39 (2009) Ground Water Points of Compliance Points of Compliance - Bedrock At Yoast Mine, the Wadge coal and Wolf Creek coal were removed during mining. As the replaced spoil material recharges, it may be possible for groundwater to flow into the adjacent undisturbed strata of the Wadge coal overburden, the Wadge coal, the Wolf Creek coal overburden, and the Wolf Creek coal. As can be seen in Tab 7, the hydraulic conductivities and transmissivities are in the lower range when compared to published studies in the region. Hydraulic conductivities of the Wadge coal ranged from 2.45E-7 cm/s to 3.5E-7 cm/s (Table 7-9). The one test conducted in the Wolf Creek coal showed a conductivity of 4.55E-6 cm/s (Table 7-9). An approximation of groundwater velocity in the Wadge coal can be made using an average hydraulic conductivity of 7.05E-7 cm/s (Table 7-10), a maximum hydraulic gradient of 0.15 (Table 17-1), and a maximum porosity of 6.7% (USGS 1993), resulting in an average linear velocity of 1.63 ft/yr. Velocity through the Wolf Creek coal can also be estimated using a hydraulic conductivity of 4.55E-6 cm/s (Table 7-9), a maximum hydraulic gradient of 0.12 (Table 17-1), and an approximate porosity of 6.7% (Wadge coal USGS 1993), resulting in a velocity of 8.43 ft/yr. Other factors, including attenuation and dilution, should assist in limiting water quality impacts to a close downgradient proximity. Dilution by unaffected groundwater plays an important role in reducing dissolved ion concentrations. Attenuation also reduces dissolved ions and can occur through physical, chemical, physiochemical, and biological mechanisms. Although, attenuation is difficult to quantify, there are some site characteristics that suggest an increased rate of attenuation will occur. These include fine grained silty and clayey soils, low permeability shales and siltstones in the overburden and adjacent lithologies, neutral and alkaline groundwater conditions, and low rainfall and infiltration rates. Transmissivity ranged from 0.015 ft2/day to 0.26 ft2/day in the Wadge coal (excluding the test on well YW2) and was equal to 0.328 ft2/day in the Wolf Creek coal. The groundwater yield is insufficient for irrigation or domestic well use (Table 7-25). Locally, low secondary porosity may also contribute to the minimal yields found in these materials. Aquifers of regional significance include the Trout Creek Sandstone and the Twentymile Sandstone. These are thick beach deposit sandstones that can potentially be used for water supply. However, the Twentymile Sandstone is approximately 500 feet above the Wadge Coal seam and is not found within the Yoast permit boundary. Therefore, the Twentymile Sandstone is not affected by the mining activity at Yoast. The Trout Creek Sandstone of the Illes Formation lies approximately 300 to 400 feet below the Wadge Coal seam and approximately 60 to 100 feet below the Wolf Creek Coal seam. The Trout Creek • sandstone is essentially under confined conditions and is separated from the surface mining by finer grained lithologies of the Williams Fork Formation, which are predominantly gray to black siltstones, TR-39 15-1-1 Revised 1/09