2014-05-12_PERMIT FILE - C2010089 (5)

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the spoil bench and 3) dozing. Following top soil stripping, the top bench or free dig zone (weathered zone, suitable material) is loaded into trucks using a hydraulic excavator and hauled around the pit and placed on the top of unsuitable material (unweathered overburden). After removal of the top bench (free dig), the unweathered material is cast blasted (a majority of this material requires re- handling) across the pit to the bottom of the backfill area. Dozers and the shovel and trucks remove the remaining overburden and clean off the top of coal. This backfilling technique greatly increases the permeability of the backfill material in comparison to the original overburden. Due to truck dumping from the spoil bench, large rock will settle near the bottom of the pit and provides permeable channels for groundwater flow. As an example, the hydraulic conductivity (K) of the backfill, as measured in monitor hole GW -N27, is 40 ft /day, which is far greater than the K value measurement made in the overburden at GW -N9 (see New Horizon 1 Area Permit) of 2.1 ft/day. The old Peabody Nucla Mine site (New Horizon 1 Area) has experienced continued seasonal irrigation and runoff return flow infiltration from the 2nd Park Lateral since the final reclamation (1St Qrt. 1992). Water infiltrating from this irrigation and precipitation have percolated and moved through the bedrock zones and then drained into and through the backfill and saturated it until water discharges at the low point of the base of the coal which is at Spoil Spring #1, (see Map 2.04.7 -1 for location). Flow from this spring fluctuates in response to the use of irrigation from a low of about 17 gpm to a high of about 52 gpm with an average annual flow of around 27gpm (or about 44 acre- ft/yr). This flow represents the bedrock zones discharging and draining through the backfill. The NHN Mine will be analogous to the old Nucla Mine with the exception that unlike the "old" mine (not irrigated) portions of NHN Mine backfill will be irrigated. Irrigation of the surface could begin as early as the Spring of 2015. Once irrigation resumes, surface irrigation water will infiltrate into the backfill and then drain toward the southwest along the floor of coal and issue as a spring in the same vicinity as existing Spring #1. As a matter of clarification, the HDPE pipeline will be moved to the approximate location of the 2 Park Lateral after mining, backfilling and replacement of top soil has progressed far enough north. This is expected to require about 3 to 4 years after mining begins. The HDPE pipeline will be retained to prevent the irrigation water from draining into the very permeable pit backfill. This will also prevent the direct loss of irrigation water along the course (sides and bottom) of 2nd Park Lateral ditch as occurs now. The HDPE pipeline will allow for sprinkler irrigation which is much more efficient method of irrigating than is flood irrigation and will further help limit the loss of water to the backfill by infiltration. The amount of irrigation water that will drain through the backfill is estimated by first considering how much water will be used for irrigation. The Garvey parcel (about 37 acres) north of the 2nd Park Lateral will be irrigated with 27 shares of CCC ditch water, (see Map 2.04.10 -1). The Meehan parcel (about 38 acres) may be irrigated with about 20 shares of CCC ditch water. Each share equates to 0.0308 cfs or about 10.08 acre -ft over the 165 day irrigation season. The Garvey parcel will therefore receive about 272 acre -ft/yr or about 7.15 ac- ft/acre /yr of water while the Meehan parcel receives about 202 ac- ft/acre /yr or about 5.3 ft/acre of water. Section 2.04.10, Vegetation, describes the Meehan "irrigated pasture" and the Garvey "intensely managed irrigated pasture ". Not all of this irrigation water will infiltrate the backfill as some Section 2.05.6(3) Page 16 November 2011