2018-01-03_PERMIT FILE - C1981010A (16)

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Similar soluble Se concentrations were found in undisturbed topsoil collected in the PR -7 Mine Expansion Area as discussed in the PR -7 Mine Expansion Area Soils Resource Information, Appendix G. In that report, the fifty-five undisturbed soil horizons all had soluble Se values less than 0.3 ppm. Furthermore, examination of the historic soils data collected from the 1981 Trapper Mine Permit Area shows that 17 soil samples tested for water soluble Se had an average value of 0.028 mg/kg. Thus, the historic soils sampling data from Trapper Mine yields water soluble Se values similar to those obtained from the PR -7 Mine Expansion Area overburden, which averaged 0.064 mg/kg. Based on the results, the probable water soluble Se values of all of the overburden in the PR -7 Mine Expansion Area would lie within the suitable category after mixing during mining and reclamation. Water Soluble Boron (B). Boron plays an essential role in plant growth. It is a unique micronutrient because the range from deficient to toxic concentrations is narrower than any other micronutrient. Carbonaceous soils and rock are an important B source. Overburden water soluble B concentrations ranged from 0.05 to 10.8 mg/kg and averaged 1.50 ± 1.98 mg/kg. These concentrations are generally considered low. Ninety-five percent (or 200 feet) of the overburden samples had water soluble B concentrations less than the WDEQ topsoil and overburden water soluble B suitability criterion of less than 5 ppm. The remaining 5 percent (or 10 feet) of overburden have unsuitable water soluble boron concentrations and exceed the WDEQ criterion of greater than 5 ppm. Three of the five unsuitable B values are associated with coal seams (Sample 11, Sample 21, and Sample 35 which will be mined and hauled to the power plant. This indicates that 7.8 feet or 78.17 percent of the unsuitable water soluble B overburden will be removed by mining. Application of the five -percent dragline mixing rule suggests that all of the unsuitable overburden water soluble B values (0.06 percent or 1.28 feet) will be sufficiently mixed after mining and reclamation so that the materials will have suitable water soluble B concentrations. Verification of this assumption is found in the regraded spoil data found in the 1989 through 2000 Annual Reclamation Reports where the water soluble B concentration in the 110 regraded spoil samples averaged 0.35 ppm, which is less than the average water soluble B concentration of 1.15 mg/kg found in this overburden evaluation. Further evidence of the suitability of the water soluble B concentrations in the reclaimed overburden is found in the undisturbed topsoil data collected in the PR -7 Mine Expansion Area, as discussed in the Soils Resource Information, Appendix G. The reported average water soluble B value of the fifty-five undisturbed soil horizons sampled was 0.17 ± 0.11 ppm. Based on these results, the overburden water soluble B values in the PR -7 Mine Expansion Area will be suitable after mixing during mining and reclamation. Extractable Molybdenum (Mo). Mo is among the elements essential for proper plant and animal metabolism. Interaction of Cu and Mo, as well as sulfide and sulfate, in ruminants can result in the metabolic uptake of Cu resulting in a disease called molybdenosis. All of the overburden extractable Mo values are less than the analytical reporting limit of 1 mg/kg and the WDEQ extractable Mo criterion of less than 1 ppm. These data indicate that all of the PR -7 overburden materials have suitable extractable Mo concentrations. Extractable Arsenic (As). The importance of extractable As in coal mine reclamation relates to its potential contamination of mine spoils and subsequent uptake by plants or leaching to groundwater or 2-391y 71'_ -vision: /,R `N3 Approved: