2018-07-02_PERMIT FILE - C2010089A (19)

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Groundwater monitoring well GW -N9 (see Map 2.04.7-1) was installed by Peabody and quarterly analyses were conducted from October 1979 to October 1987. This monitoring well is located within the NHN permit area and is open to both the Overburden and Coal zones. The quality data for this well is reported in the New Horizon 1 Mine Area permit pages 7-4-49 to 7-4- 53. The average TDS for the period was 3785 mg/l and the average SO4 concentration was 2423 mg/1. The values of these two parameters are significantly higher than the Coal Zone values at GW -N51. This indicates that water quality in the Coal Zone (and probably the OB Zone) is also dependent on depth or isolation beneath the weathered zone as well as distance from the recharge area. Therefore, water quality is expected to deteriorate in the down dip direction as well as toward areas with higher overburden thickness. The thickest overburden in the NHN permit area is in the southern one third of the area (see Map 2.04.6-3) Underburden Zone Groundwater Ouality The quarterly underburden groundwater sample analyses from wells GW -N50 and GW -N53 are contained in Appendix 2.04.7-1 along with the hydrographs and water level data. These wells have been monitored and samples collected since October 2008. Review of TDS and SO4 from the wells show that GW -N50 (see Map 2.04.7-1 for well locations) has poorer water quality than the Coal Zone at the other sites; whereas, the underburden zone water quality at well GW -N53 is better than the coal zone quality for that site. The shallow depth of the coal zone at well GW -N50 indicates that weathering has removed (oxidized) at least to some degree the higher sulfur content that is to be expected in the coal zone. Table 2.04.7-3 summarizes the groundwater quality from the analyses of the samples from the underburden monitoring wells. The WQCC (Regulation 41) water quality standards are also included on this table for comparison with the underburden samples. Sulfate exceeds the drinking water standards at all wells while iron and manganese exceed drinking water standards at well GW -N50. Springs and Seeps Three springs were defined in and in close proximity to the southern part of the NHN permit area by Peabody at the old Nucla Mine (see Map 2.04.7-1). Two of these springs were at the toe of the old backfill area while the third was a spring issuing from the high -wall of the Nucla Mine after mining ceased in 1983. These three "springs" were monitored from 1983 through 1987. The water quality and flow data for spoil springs SS #1, SS #2 and SS #3 are contained in the Appendix of Section 2.04.7-2. Spoil Spring SS #1 is located along a reclaimed drainage at the toe of the backfill of the old Nucla Mine. SS #2 was located about 50 yds up -stream and to the west of SS #1. The high -wall spring issued from the base of the overburden zone at or very near to the contact with the coal zone. The flow of all three of these springs appeared to vary with the seasonal irrigation. Flow rate varied from a 16.6 gpm to about 47 gpm during the irrigation season at SS #1 to a rate of 16.6 gpm to 32 gpm during non -irrigation periods. SS #3 had a much lower flow rate estimated at about 0.3 gpm during the fall of 1986. The only quantifiable flow rates from the high -wall (SS #3) were during the irrigation season and were measured at about Section 2.04.7 Page 11 March 2018 (TR -16)