2009-03-19_PERMIT FILE - C1982057A

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Procedures used to collect ground water quality samples are dictated by intlividual well site conditions such as casing diameter, depth to water, casing storage volume, rate of recovery, and pumping capabilities of sampling equipment. Alluvial and bedrock wells are sampled by purging sl minimum volume of water at a constant rate while concurrently measuring field parameters (temperature, pH, and electrical conductivity) for stability, and then collecting the sample once the field parameters have stabilized and the minimum volume of water has been purged. The minimum purge volume, purge rate, and sampling device has been established for each monitoring well based on consideration of well Bite conditions, field parameter measurements, and evaluation of water quality analytical results. Devices, used to sample alluvial wells include either bailers or submersible pumps, and either bailers, submersible pumps, or positive displacement pumps are used to sample bedrock wells. Historic Ground Water Monitoring Program. The Historic Ground 1Nater Monitoring Program is described in Appendix 15-1. In the summer of 1979, Peabody Coal Company initiated a ground water baseline monitoring study of the Seneca II-W Mine. At that time, the proposed permit area extended approximately one and one-half miles south of the southern border of the 1990 permit area. Initial baseline monitoring incorporated this larger area as evident from the locations of the monitoring sites. Wells at Sites 1 through 9 were constructed during the summer of 1979. Wells 10W through 13W were completed during the fall of 1981 to provide additional baseline ground water level data. A site summary of ground water monitoring wells at Seneca II-W is presented in Table 15-2. Historical information for ground water wells is contained in Table 15-3. Pre-October. 1991 Ground Water Monitoring Program. The Pre-October, 1991 Ground Water Monitoring Program is found in Appendix 15-2. The schedule of water level measurements depended upon when mining was to begin. Since mining began in the summer of 1990, all overburden and coal wells listed in Appendix 15-2 were monitored once very two months, except for the December/January period. This schedule reflected the frequency of water level measurements followed at Peabody's Seneca II Mine. Alluvial wells were monitored rnonthly except for December through March. As a result of the failure of several of the wells drilled in 1979 (AHR, 1=ebruary 28, 1987), Peabody drilled an additional 12 wells in 1987. These wells were 140V to 19A. Four new alluvial wells (GW- S2W-20A to 23A) were installed by Peabody in the summer of 1990 in areas of proposed NPDES ponds to provide baseline water level and quality data on a semiannual basis. A production well (GW-S2W-201TC) and a water level observation well (GW-S2W-200TC) was completed in the Trout Creek Sandstone aquifer in order to supply water for domestic and industrial needs at the mine. Locations of the 18 wells are found in Exhibit 7-1 and well descriptions are found in Appendix 7-1. 12 Revised 11/15/95