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results. Devices used to sample alluvial wells include either bailers or submersible pumps, and <br />either bailers, submersible pumps, or positive displacement pumps are used to sample bedrock • <br />wells. <br />Historic Ground Water Monitoring Program. The Historic Ground Water Monitoring Program is <br />described in Appendix 1 5-1. 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 <br />area extended approximately one and one-half miles south of the southern border of the 1990 <br />permit area. Initial baseline monitoring incorporated this larger area as evident from the <br />locations of the monitoring sites. Wells at Sites 1 through 9 were constructed during the <br />summer of 1979. Wells 10W through 13W were completed during the fall 01 1981 to provide <br />additional baseline ground water level data. A site summary of ground water monitoring wells <br />at Seneca II-W is presented in Table 15-2. Historical information for ground water wells is <br />contained in Table 15-3. <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 IAHR, February 28, 19871, <br />Peabody drilled an additional 12 wells in 1987. These wells were 140V 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-52W-201TC1 and a water level observation well (GW-S2W- <br />200TC1 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 />1991 Ground Water Monitorinp Program. The 1991 Ground Water Monitoring Program is <br />described in Appendix 15-3. Upon approval of PR1 in October, 1991, Peabody incorporated <br />the monitoring program detailed in Appendix IS-3. This revision basically addressed the <br />C~ <br />12 Revised 11/15/95 <br />