2014-05-12_PERMIT FILE - C2010089 (3)

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lowest level (winter conditions, no irrigation flow) and highest level (summer conditions with full irrigation). The gradient of the potentiometric surface varies from about 0.029 ft/ft to about 0.047 ft/ft during the seasonal low levels and 0.033 ft/ft and 0.051 ft/ft during seasonal high levels. The area directly north of the old Peabody highwall has a low seasonal gradient of 0.028 ft/ft and a gradient during the irrigation season of 0.079. Underburden Water Levels Two (GW -N47 and GW -N50) of the three under burden zone monitoring wells that have been monitored since October 10, 2008 clearly show the seasonal effects of surface irrigation (see Appendix 2.04.7 -1 for hydrographs). Similar to the unweathered overburden at well GW -N55, GW -N53 shows very little if any response to surface irrigation. This well produced negligible water during drilling and the recovery from the first water level measurement to the second measurement attests to the low rate of water level recovery at this location. As with the overburden monitor well at this site the GW -N53 monitoring well shows that the rates of vertical and lateral recharge of the under burden is low. Map 2.04.7 -6 and Map 2.04.7 -7, respectively shows the potentiometric surfaces and the direction of flow of the under burden zone at both the lowest level (winter conditions, no irrigation flow) and highest level (summer conditions with full irrigation). The amplitude of the seasonal fluctuation due to irrigation is about 7 feet and 23 feet for wells GW -N47 and GW -N50, respectively. The gradient of the potentiometric surface varies from about 0.029 ft/ft to about 0.046 ft/ft during the seasonal low levels and 0.0396 ft/ft and 0.055 ft/ft during seasonal high levels. The area directly north of the old Peabody highwall has a low seasonal gradient of 0.024 ft/ft and a gradient during the irrigation season of 0.08. The under burden zone at GW -N47 has an artesian head varying from 34 to 40 ft above the zone from winter to summer. The under burden zone artesian head at GW- N50 varies from about 15 feet to about 39 feet above the zone from winter to summer. Backfill Water Levels The NHN permit area encompasses part of the area of the old Peabody Nucla Mine, which ceased production in 1983. Overburden backfill material exists south of the old Peabody high -wall. Four wells (GW -N10, GW -N26, GW -N27 and GW -N28) monitored water levels in this backfill material through the end of 1987. All four of these wells were abandoned and reclaimed in November of 2001. Map 2.04.7 -1 shows the backfill monitor well locations. The backfill is essentially dry with the exception of the area in the vicinity of GW -N27 and GW -N10. At GW -N27 the back fill has approximately 6.4 feet of maximum saturation. At GW -N10 the backfill is dry from time to time with maximum saturation of only slightly more than 1 foot. GW -N27 was installed in August of 1987 and shows seasonal fluctuation of a little over 3.0 feet corresponding with run off from the irrigation flow ( hydrographs for monitor wells GW -10 and GW -27 are contained in the Appendix 2.04.7 -1 of this section). Recharge and Hydrologic Boundaries The predominate source of recharge to the shallow bedrock zones at the NHN permit area is direct leakage from the 2rid Park Lateral irrigation ditch where it crosses the outcrop of each of the respective zones (overburden, coal and underburden) and infiltration of excess flood irrigation waters into the weathered overburden. Minor recharge also results from infiltration of precipitation. Discharge is down dip to the outcrops and old Peabody high -wall (see Map 2.04.5 -1 of this application). Although exploration drilling has indicated the presence of faults (see Map 2.04.6 -2), there is no evidence that the faulting is affecting ground water flow. Section 2.04.7 Page 4 October 2013 (TR -05) E: \New Horizon \DRMS \NHN Permit \04_Technical Revisions TR \TR -05 \Documents from Jason \2.04.7 Hydrology Description_TR- OS.docx