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Seneca II-W Technical Revision 63 (2009) Ground Water Points of Compliance <br />Points of Compliance - Bedrock <br />In the northern section of Seneca II-W the overburden and the Wadge Coal seam were disturbed during <br />mining. In the southern section of Seneca II-W the overburden, the Wadge coal seam, the Sage Creek <br />Coal seam, and the Wolf Creek Coal seam were disturbed during mining. As the spoil material <br />recharges and saturates, the spoil water may leak into the undisturbed strata adjacent to the mine. The <br />Wadge underburden at this site has an upward hydraulic head (artesian) and is recharging the spoil <br />material. This makes downward movement of spoil water infeasible (Tab 17, pg. 39). <br />Aquifer tests were conducted on these formations as shown in Tables 7-7 and 7-8. The Wadge Coal <br />ranged from 1.05E-6 cm/s to 3.5E-5 cm/s onsite. The Wolf Creek Coal showed hydraulic conductivity <br />ranging from 3.5E-8 cm/s to 3.5E-6 cm/s. These values are similar to those observed at both Yoast and <br />Seneca II mines. The low hydraulic conductivities of the bedrock should limit any impacts to water <br />quality to the immediate downgradient proximity of the mine. <br />An estimate of travel time in the Wadge Coal can be found using the average hydraulic conductivity of <br />1.06E-5 cm/s (Tab 7), a maximum porosity of approximately 6.7% (USGS 1993), and an average <br />hydraulic gradient of 0.09 (Tab 7), resulting in a groundwater velocity of 14.71 ft/yr. For the Wolf <br />Creek Coal, an estimate of travel time can be found using an average hydraulic conductivity of 1.41E-6 <br />cm/s (Tab7), an average hydraulic gradient of 0.11 (Tab 7), and a maximum porosity of 6.7% (Wadge <br />Coal), resulting in an average linear velocity of 2.40 ft/yr. <br />Other factors, including attenuation and dilution, should assist in limiting water quality impacts to a <br />close downgradient proximity. Dilution by unaffected groundwater plays an important role in reducing <br />dissolved ion concentrations. Attenuation also reduces dissolved ions and can occur through physical, <br />chemical, physiochemical, and biological mechanisms. Although, attenuation is difficult to quantify, <br />there are some site characteristics that suggest an increased rate of attenuation will occur. These include <br />fine grained silty and clayey soils, low permeability shales and siltstones in the overburden and adjacent <br />lithologies, neutral and alkaline groundwater conditions, and low rainfall and infiltration rates. <br />The transmissivities are also at the low end of the ran e of values determined for the region. The <br />transmissivity of the Wadge Coal ranged from 0.03 ft /day to 0.36 ft2/day. The Wolf Creek Coal <br />transmissivity ranged from 0.001 ft2/day to 0.20 ft2/day. The low transmissivities indicate that the <br />bedrock will not yield the necessary volume for irrigation use and would be only marginal for a <br />domestic water supply. <br />Aquifers of regional significance include the Trout Creek Sandstone and the Twentymile Sandstone. <br />These are thick beach deposit sandstones that can potentially be used for water supply. However, the <br />Twentymile Sandstone is approximately 500 feet above the Wadge Coal seam and is not found within <br />the Seneca II-W permit boundary. Therefore, the Twentymile Sandstone is not affected by the mining <br />activity at Seneca II-W. <br />TR-63 7-3b-I Revised 1/09