2016-10-28_PERMIT FILE - C2010089A (27)

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Unlike SS #1, SS #4 does not have an existing analogy to draw on or that has been previously monitored and therefore flow and quality must be projected. The expected highwall seepage rate is calculated by Q = (K, ft/day)(area, ft)(gradient)(365days)/43,560ft3 to get acre -ft per year. Hydraulic conductivity or K is different for each of the bed rock zones: OB = 2. 1, Coal = 0. 19, and UB = 1.61, (see Tables 7-5 and 7-6 in Appendix 2.04.7-2 this application). Height of each of the bedrock zones is also different: OB = 20.3 ft. during irrigation season and 14 ft during non - irrigation season; Coal 6.Oft.; and UB 5.Oft. Gradient is estimated from the draw down (cone of depression) around the old Peabody highwall at 0.053. The maximum highwall length from the north and east high walls is 4005 ft. During irrigation season (165 days) it is projected that maximum seepage into the pit will be: OB = 34.3 ac -re; Coal = 1.07 ac -ft; and UB = 7.77 ac -ft for a total of 43.14 ac -ft, or about 59 gpm. During non -irrigation season (200 days) it is projected that maximum seepage into the pit will be: OB = 28.7; Coal = 1.29; and UB = 9.41 for a total of 39.4 ac -ft or about 44.6 gpm. This is a total of about 82.6 ac -ft per year, not all of which will accumulate to issue as a spoil spring. As noted above (see discussion of seepage into "low wall" on pg. 23), it appears that about 17.7 ac -ft per year will seep into the bedrock zones of the low wall of the pit. Therefore, it is projected that during the irrigation season (165 days) that as much as 35.14 ac -ft (at the rate of 0.104 cfs or about 47 gpm) of spoil water could issue as a spring. During the non -irrigation season a maximum of 29.7 ac -ft (at the rate of 0.075cfs or 33.7 gpm.) of spoil water is expected to issue as a spring. The spoil water is a mixture of the water from the three bed rock zones, (see water quality data for bed rock zone water monitoring holes GW -N47, GW -N48, and GW -N49 Appendix 2.04.7-1 and Tables 2.04.7-1, 2.04.7-2 and 2.04.7-3 in Section 2.04.7). During the irrigation season, about 0.105 cfs of OB water with a TDS of about 725mg/l will mix with 0.0033cfs of Coal water at a TDS of 1440mg/1 and with 0.023cfs of UB water with a TDS of 2714mg/l for a water quality of about 1092mg/l TDS. During the non -irrigation season 0.072 cfs of OB water with 850mg/l will mix with 0.0033cfs of Coal water with a 1440mg/l TDS and 0.023cfs UB water with 2714mg/1 for a water quality of about 1307mg/l. Table 2.05.6(3)-1 on page 22 indicates that the water quality in backfill can be expected to be at a maximum of about 10% higher in TDS than in the bed rock zones. Therefore, the water quality of the projected SS #4 during the irrigation season is projected at about 1200 mg/1 TDS. Likewise, during the non -irrigation season the spoil spring water quality is expected to be about 1440mg/l TDS. In the vicinity of SS #4 (see surface water monitoring station SW -N202 in Appendix 2.04.7-2), Meehan Draw has an irrigation season flow of 1.083cfs with about 990mg/l TDS. During the non -irrigation season the flow rate in Meehan Draw (SW -N202) is about 0.134 cfs with a TDS of about 1660 mg/l. During the irrigation season then, about 0.105 cfs of spoil spring with 1200 mg/1 water will mix with 1.083 cfs of Meehan Draw water at 990 mg/1 for a flow of 1.188 cfs with a TDS of about 1009 mg/l, a difference of about 1.9%. During the non -irrigation season 0.134 cfs of Meehan Draw water at 1660 mg/1 will mix with 0.075 cfs spoil spring water with Section 2.05.6(3) Page 27 April 2016 (PR -01)