2018-09-04_REVISION - C1980007 (11)

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52 In the summer of 1985, MCC submitted an application for PR-3 requesting approval of a permanent lower waste pile to be located adjoining the mouth of Sylvester Gulch. This application originally requested approval to permanently dispose of 1.77 million tons of coal processing waste within the proposed structure. The original design phased the refuse pile into five specific design layouts (Phases I through V), including recompaction and reconfiguration of temporarily stored waste material. The pile was constructed according to this original phased design until the Phase IV configuration. TR-63 was submitted in November 1992, which eliminated Phase V and reduced the pile to 1.2 million tons. The proposed storage volume represents a 15.7 year life. The proposal included the combination of a 28,500 cubic yard topsoil pile during Phases I through III and a maximum of 45,000 cubic yards of non-toxic soil cover (subsoil) stockpile. Topsoil removed for Phase IV will be stored on the 50-foot bench constructed in Phase III. In addition, an access road was constructed in Phase III and a portion of the Sylvester Gulch access road to the main fan portal was relocated. Underdrains have been constructed beneath the pile. Piezometric groundwater monitoring will be conducted. Slopes of the pile will be maintained at 2.5H:1V. The TR-63 application included a thorough slope stability analysis performed in accordance with the prudent state-of-the-art slope analysis for the original design in 1985, and for the redesigned pile in 1992. Material strength values were derived from on-site sample testing and nearby previously reported test results. Piezometer observations, falling head parameter tests and analytical projections were completed in order to predict appropriate phreatic surfaces within the proposed waste structure. Data for the 1992 analysis utilized data collected for the 1985 analysis. The applicant has committed to the installation and quarterly monitoring of three sets of survey monuments to monitor slope stability of the waste structure. One row of monuments has been installed parallel to the state highway adjoining the toe of the waste pile on 100-foot intervals. Two additional rows of monuments have been installed perpendicular to the highway on the facial slope of the pile at 50-foot interval spacing. The operator has also committed to quarterly reporting of visual inspections of the topsoil, non-toxic soil cover stockpiles, and refuse pile. For the LRP, drainage will be controlled by a series of drainage ditches, terraces, and a sedimentation pond. Since the pile will be constructed in phases, the drainage system will also be built in phases. All disturbed area drainage from the topsoil piles, subsoil stockpile and waste pile will be routed to the sedimentation basin at the northwest corner of the lower waste pile (MB-2R). The design incorporates several permanent drainage features into the plan. After final reclamation of the pile, the terraces will be barricaded with rocks or berms to prevent access to the pile. However, the terraces will still function to control runoff from the pile. A hundred-year diversion ditch has been constructed around the perimeter of the pile to permanently collect any runoff from the site and safely route it to the natural drainage system. For a discussion of the hydrologic effects of the waste pile on both surface and groundwater, see the hydrology section in the Probable Hydrologic Consequences section of this findings document.