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

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water will run off toward Meehan Draw as irrigation return water, some water will be lost to the atmosphere through evaporation, and some water will be lost through plant -take up and evapotranspiration. Flow gain in Meehan Draw through the irrigation water return is about 213 acre -ft /yr which is over 30 percent of the water used for irrigation. The evaporation rate is 60 inches per year (NOAA 1997, evaporation, semi and climates) of which the majority occurs during the warmer drier months that coincide with the irrigation season. WFC estimates that evaporation during the irrigation season could result in loss of 2.5 ac- ft/ac. The evapotranspiration rate for the permit area is estimated at 2.1 ft/year (see Section 2.04.7, Evapotranspiration). These loss figures, added together, would result in very little water being available for infiltration at the Garvey parcel. Adding the loss values for the Meehan parcel would result in negative values. Percolation and infiltration rates into the reclaimed soil is estimated to be moderate (0.6 to 2.0 inches per hour) suggesting that the reclaimed soil will be more acceptable to infiltration than the original soil which should reduce the runoff return flow. The New Horizon 2 Area Permit predicts that 13 inches /yr of irrigation water will infiltrate (recharge) the backfill. Therefore, with a total of 75 irrigated acres in backfill about 81 acre -ft of recharge to the reclaimed backfill would occur per year. As stated earlier, irrigation at NHN Mine could begin as early as the irrigation season of 2015. The backfill material will be relatively dry and will initially absorb moisture. However, channeling of infiltrating irrigation water through more permeable zones will most likely occur. Experience at the New Horizon Mine indicates that the backfill could begin draining irrigation water within a few months of resumption of irrigation on the reclaimed backfill or as early as late summer or early fall of 2015. The flow through the backfill would increase gradually as more of the reclaimed surface is irrigated. At maximum steady state, the backfill flow (at full infiltration rate of 81ac- ft/yr) would average about 0.11 cfs or about 50 gpm. The flow rates through the backfill material will be significantly higher than through the bedrock (hydraulic conductivity of 40 ft/day, versus 2.1 ft/day). Water seeping in from all three sides of the excavated pit is not expected to recharge the bedrock zones as the water will follow the path of least resistance and flow to the south along the pit floor as is now the case at the old Peabody Nucla Mine (New Horizon #1 Area permit ). This water will continue to issue as a spring at Spoil Spring #1(SS# 1) location (see Map 2.04.7 -1). Backfilling of pit walls and continued irrigation adjacent to the permit boundary will allow ground water levels to recover as demonstrated by the 80% recovery of the water levels at GW -N8 in less than 20 years. The ground water from the Dakota bedrock zones has not been used to date because of poor quality and low production potential. Further, the "bedrock" seepage water will continue to flow tributary to Tuttle Draw maintaining the hydrologic balance of the San Miguel River. Infiltrating irrigation water on the reclaimed backfill will also travel the path of least resistance and issue at the SS# 1 location as increased flows tributary to Tuttle Draw and The San Miguel River. The impact of the backfill material on the ground water flow and recharge is therefore minimal. Two quarters (6 months) prior to initiation of mining activity at NHN, flow and water quality monitoring (field parameters) at the SS# 1 location will be resumed in order to detect and Section 2.05.6(3) Page 18 November 2011