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0 A) Impact on Ground Water Rights <br />Ground water rights within the vicinity of the New Horizon #2 Mine (2 mile radius) are <br />identified in Appendix 2.04.7-1 of the permit. A total of 29 ground water rights have been <br />been identified. All monitoring wells installed by the permittee and domestic wells within the <br />surrounding area are shown on Map 2.04.7-1-A. No wells are within the release area. <br />Of the 29 water rights within the surrounding are, 27 wells have intakes too deep to be <br />affected by the pit pumping induced drawdowns in the overburden aquifer. These wells are <br />installed in the Burro Cantion Formation, which is below the Dakota coals to be mined. <br />Significant shales separate the coals from the strata of the wells. Two righted wells W-009 <br />and W041 have intakes close to the location of the bottom of the mine pit. The wells area <br />located approximately 2,300 feet east of New Horizon #2. At the eastern boundary of New <br />Horizon #2, mining will only extend 10 feet below the water table. Therefore, drawdown <br />impacts to these wells are expected to be small. The wells are righted for irrigation water use. <br />This area has been mined and reclaimed over 10 years ago and there has not been any <br />problem identified with these wells. <br />B) Impact of Spoil Material on Ground Water Flow and Recharge <br />The Phase 3 release areas have been fully reclaimed for approximately 10 years. The potential <br />long term impact on ground water flow and recharge is the change in permeability of the <br />spoil material placed as backfill. The only vertical and horizontal permeability change that <br />will have occurred in the backfill will be of an increase in permeability. This is due to <br />mining techniques. The resaturation time period for ground water will be reduced by the <br />irrigation recharge in the Irrigated Pasture areas and overall by the increased permeability in <br />the backfill. <br />The hydraulic conductivity of the spoil, as measured in well GW-N27, 40 ft/day, which is far <br />greater that any measurement made in the overburden. K values in the overburden generally <br />range from 3.0 to 5.5 ft/day. GW-N27 is located in the old New Horizon #1 Mine northwest <br />of the release area. <br />Based on rainfall data for the site, soil information, and irrigation practices, recharge for the <br />release area has been determined to be 2" from rain and snowmelt, 13" from irrigation, and <br />1" from underburden recharge and overburden recharge at the uphill spoil/overburden contact. <br />Total long-term recharge is therefore 16" per year. The total long-term recharge in the <br />Dryland Pasture areas will be less than 16" since there is no irrigation in those areas. These <br />predications are approximate, but are accurate enough in predicting the behavior of the <br />groundwater in the spoil. <br />Water could build up against the southern mining limit and begin to surface as a spoil spring, <br />since the strata below the mined out area tilts gently to the southwest. As of June 2009, no <br />springs have developed anywhere in this area. Well GW-N40 is located immediately down dip <br />from the release areas, and will show any changes in ground water quality before any spring <br />developed on the surface. <br />0 SL-12 DRAFT 20AUG10.wPd 38