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• techniques will increase permeabilities of the material in comparison to the original overburden. <br />Due to truck dumping from the spoil bench, large rock will settle near the bottom of the pit and <br />provide a permeable channel for groundwater flow. The hydraulic conductivity (K) of the spoil, as <br />measured in well GW-N27, is 40 ft/day, which is far greater than any measurement made in the <br />overburden. K values in the overburden generally range from 3.0 to 5.5 ft/day. The New Horizon <br />#1 site has had continued seasonal irrigation from the North Lateral and its secondary ditch which <br />flows immediately north of the New Horizon #1 reclaimed areas. Water from this irrigation and <br />some added precipitation have moved through the spoil and saturated it until it discharges at the <br />low point of the base of the coal which is at the Spoil Spring and the Pond 001 discharge. Flow <br />from this point fluctuates in response to the use of irrigation. It is believed that the spoil in the New <br />Horizon #2 Mine area will remain relatively dry until irrigation is resumed from the West Lateral <br />Ditch. Once this irrigation is resumed, recharge will rapidly infiltrate into the spoil, move to the <br />southwest according to the basal gradient and develop a spring at the low point of the lowwall crest, <br />as was experienced at the New Horizon #1 Mine. This point is expected to be N = 602,530,E _ <br />1,112,350 @ elevation 5580'. Although a large diameter HDPE pipe will be used to carry the ditch <br />water through the permit area, infiltration will begin when the permanent HDPE pipe will be used <br />in re-establishing irrigation in the reclaimed area. This will occur in 2003 for the area east of 2700 <br />Road and will occur after 2010 for the remainder of the mine area west of 2700 Road. It is <br />~ estimated that full irri ation of the reclaimed area will take lace b <br />g p y year 2013. Although the pipe <br />• will be used to carry the ditch flow until the end of its useful life in 30-50 years, its use is not <br />relevant to the prediction of irrigation recharge since this recharge will occur over 99% of the area <br />even when the permanent pipe is in place. <br />From soil information, knowledge of the irrigation practices, discussions with USGS, and the rainfall <br />date for the site, the following recharge data has been calculated: 2" from rain and snowmelt, 13" <br />from irrigation and 1" from underburden recharge and overburden recharge at the uphill <br />spoil/overburden contact. Total long-term recharge is therefore 16" peryear. These predictions are <br />approximate but suffice in predicting the behavior of the groundwater in the spoil. <br />The total affected area is 418 acres. The volume of the reclaim spoil to be recharged below the <br />5580 spoil spring elevation equals 1512 ac.ft. as determined from D.T.M. modeling of the spoil area <br />and the pit bottom. Spoil porosity of 15% is determined for the overburden. This yields a pore <br />volume of (0.15}(1512 ac.ft.) = 227 ac.ft. <br />With a pore volume of 227 ac.ft. and assuming a total recharge of 16" per year from all sources <br />over the 418 acres of spoil, annual recharge equals (16/12)(418) = 557 ac.ft. per year after full <br />irrigation in 2013. It should be noted that a portion of the reclaimed area will be restored to dry land <br />• REVISED MARCH 2006 2.05.6(3)-22 <br />