2014-05-27_REVISION - C1981044 (2)

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Effects of Seepage from No. 9 Portal Backfill The No. 9 Mine portal backfill has a surface area of approximately five acres. Using an infiltration rate of three inches per year, the annual infiltration will be less than 1 gpm. This amount is insignificant and will therefore have no measurable effect on nearby aquifers. Also, the backfill area is stratigraphically separated from the nearest aquifer, the Twentymile Sandstone, by 360 feet of very low permeability interbedded claystones, siltstones, and sandstones. Postmining�or Interim Discharge — No. 5A and No. 6 Mines The No. 5 Mine produced coal from the F Coal Seam from 1985 through 1989. In 1987 through 1989 decline ramps�l, were driven from the No. 5 mine workings down to the E Coal Sea, and mining was initiated in the No. 6 Mine, with mining continuing until 1995, when operations ceased. Both the No. 5 and No. 6 Mines were accessed from the 5A Portals at an elevation of approximately 6,380 feet, with the main entries for both mines driven down -dip to the north. Surface elevations in the portal area are approximately 40 feet higher than the portals. The bottom of the ramp where ; it intercepted the E Seam is at an elevation of approximately 6,280 feet. Both the Middle Sandstone and the Twentymile Sandstone outcrop to the north of the 5A Mine Portals, with portions I of these units overlying the No. 5 and No. 6 mine workings. Piezometic levels for the Middle Sandstone and Twentymile Sandstone range from 6,100 to 6,400 feet, with the hydraulic gradient for the Middle Sandstone trending to the east - northeast, and the gradient for the Twentymile Sandstone trending north - northwest (1995 Annual Hydrology Report, Permit C -81 -044, Figure 12). In the stratigraphic sequence, the F Seam lies about 40 to 100 feet above the E Seam, the Middle Sandstone lies about 200 to 300 feet above the E Seam, and the Twentymile Sandstone l ,^ lies 500 to 600 feet above the E Seam. Historic water levels in these two sandstone units have apparently not been effected by mining in the area, as they have been constant since 1981 (ibid., Figure 10) indicating a limited hydrologic connection between these aquifers and the No. 5 and No. 6 mine workings Because they both outcrop to the north of the 5A Mine portals, are well above both the E and F coal seams, and have not apparently been affected by mining in the area, neither drainage to the mines or interim or postmine filling of the mines are expected to affect either water levels or water quality for the Middle and Twentymile sandstone units. With a maximum piezometric level in the general area of the 5A Mine Portals of 6,100 to 6,400 feet, there is very little potential for the No. 5 and No. 6 mine workings to fill to the level where discharge would potentially occur at the portals or in the portal backfill area (postmining). Water Quality Impacts of Mine Discharge Mine discharge rates were discussed under the subsection Mine Inflows. Plot sof total dissolved solids concentrations versus time for the two discharge points, 5 Mine Discharge and 7 North Angle, are presented in Exhibit 42, Figures 58AE and 58AF, respectively. One apparent trend in the plots is an initial increase in the concentrations of total dissolved solids in the 7 -North Angle discharge. The source of this initial increase in dissolved solids in 7 -North Angle discharge is unknown. Observed Impacts Quarterly data from the Williams Fork River gauging stations (WT-1 and WF -2) were reviewed to identify and asses any actual impacts to the Williams Fork River resulting from mine discharges. Summaries of the water quality data are presented in Tables 26 and 27, in Section 2.04.7, Hydrology Information. Plots of field electrical conductivity measurements for the Williams Fork River are presented in Figure 58d and Exhibit 42, Figures 58AG and 58AH, respectively. The comparisons of the data for the upstream and downstream stations on the Williams Fork River indicate that conductivity levels are nearly identical upstream and downstream of the mine. Likewise, plots of total dissolved solids measurements for the Williams Fork River are presented in Figures 58AI and 58AJ for upstream station WF -1 and downstream station WF -2, respectively. The comparisons of these data indicate that TDS concentrations are quite similar upstream and downstream of the mine. Thus, there is no observable effect of mining on conductivity levels and total dissolved concentrations in the Williams Fork River. As TR14 -36 2.05 -47 Revised 03/20/14