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Procedures used to collect ground water quality samples are dictated by individual well site conditions <br />such as casing diameter, depth to water, casing storage volume, rate of recovery, and pumping • <br />capabilities of sampling equipment. Alluvial and bedrock wells are sampled by purging a minimum <br />volume of water at a constant rate while concurrently measuring field parameters (temperature, pH, <br />and electrical conductivity) for stability, and then collecting the sample once the field parameters have <br />stabilized and the minimum volume of water has been purged. The minimum purge volume, purge rate, <br />and sampling device has been established for each monitoring well based on consideration of well site <br />conditions, field parameter measurements, and evaluation of water quality analytical results. Devices <br />used to sample alluvial wells include either bailers or submersible pumps, and either bailers, <br />submersible pumps, or positive displacement pumps are used to sample bedrock wells. <br />Historic Ground Water Monitoring Program. The Historic Ground Water Monitoring Program is <br />described in Appendix 15-1. In the summer of 1979, Peabody Coal Company initiated a ground <br />water baseline monitoring study of the Seneca II-W Mine. At that time, the proposed permit area <br />extended approximately one and one-half miles south of the southern border of the 1990 permit <br />area. Initial baseline monitoring incorporated this larger area as evident from the locations of the <br />monitoring sites. Wells at Sites 1 through 9 were constructed during the summer of 1979. <br />Wells 10W through 13W were completed during the fall of 1981 to provide additional baseline <br />ground water level data. A site summary of ground water monitoring wells at Seneca II-W is <br />presented in Table 15-2. Historical information for ground water wells is contained in Table 15- • <br />3. <br />Pre-October, 1991 Ground Water Monitoring Program. The Pre-October, 1991 Ground Water <br />Monitoring Program is found in Appendix 15-2. The schedule of water level measurements <br />depended upon when mining was to begin. Since mining began in the summer of 1990, all <br />overburden and coal wells listed in Appendix 15-2 were monitored once very two months, <br />except for the December/January period. This schedule reflected the frequency of water level <br />measurements followed at Peabody's Seneca II Mine. Alluvial wells were monitored monthly <br />except for December through March. <br />As a result of the failure of several of the wells drilled in 1979 (AHR, February 28, 19871, <br />Peabody drilled an additional 12 wells in 1987. These wells were 14OV to 19A. Four new <br />alluvial wells IGW-S2W-20A to 23A) were installed by Peabody in the summer of 1990 in areas <br />of proposed NPDES ponds to provide baseline water level and quality data on a semiannual <br />basis. A production well (GW-S2W-201TC) and a water level observation well (GW-S2W- <br />200TC) was completed in the Trout Creek Sandstone aquifer in order to supply water for <br />domestic and industrial needs at the mine. Locations of the 18 wells are found in Exhibit 7-1 <br />and well descriptions are found in Appendix 7-1. <br /> <br />12 Revised 11/15/95 <br />