2012-09-06_REVISION - M2008070 (25)

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Design and Operations Plan October 24, 2011 Western Gravel E & P Waste Disposal Facility Page 21 of 51 Comparing grading plans for Cell A to existing site conditions during September 2010 following mining, it appears that approximately 25,000 cy of fill and 10,000 cy of excavation will be required to construct Cell A to proposed subgrade elevations, resulting in a fill materials deficit of approximately 15,000 cy. Based on the current Phase 1 mining plan, it is assumed that similar soil deficits of approximately 15,000 cy per cell will occur during subgrade construction of the two future cells to be located within the Phase 1 mining limits. Comparing grading plans for Cell A to original ground surface contours prior to mining, 62,000 cy of excavation and 8,500 cy of embankment fill would have been required to construct this cell to proposed design subgrade elevations if mining had not occurred. The result would have been a surplus of 53,500 cy of soil following construction of the cell. An assumed ratio of excavation to fill (7:1), similar to that shown above in the pre - mining/mined conditions comparison is anticipated to occur when the two future cells are constructed outside of Phase 1 mining limits A stormwater retention pond (Pond 1) that will be constructed west of Cell A will generate approximately 5,000 cy of excess soil that will be available for use to construct Cell A subgrade. Based upon the above assumptions and calculations, it is estimated that approximately 247,000 cy of soil will be required to complete construction and closure of the entire facility, including subgrade construction, interim and daily soil cover, final soil cover /cap, and vegetative layer of all 5 cells. It is estimated that approximately 59,500 cy of soil will be available from Pond 1 and the two cell excavations to be located outside of the Phase 1 mining footprint. This results in a soil deficit of approximately 187,500 cy. In order to address the soil deficit, WG is proposing to import required soils from the 115.44 acre permitted Phase 2 mining area, located approximately 4,000 feet to 7,000 feet to the southwest of the landfill facility and on WG property. Of the 115.44 acres, 111 are considered minable. Based on an average overburden soil thickness of 6 feet across the mined area, approximately 1,074,000 cy of overburden soil could be generated and available for landfill construction purposes. Including cut volumes of Pond 1, two future cells, and Phase 2, a total of approximately 1,134,000 cy of soil is available that results in a net surplus of approximately 887,000 cy of material. It should be noted that less soil will be required for interim daily cover that will result in added surplus material anticipating alternative daily cover (e.g. Posi- she11TM) use is approved by APCD. Calculations details regarding soil availability and requirement are provided in Appendix G. 3.4 CELL CONSTRUCTION AND WASTE MANAGEMENT 3.4.1 Cell Progression Waste cells A through E, ranging from approximately two to four acres, and two stormwater retention ponds will be constructed in a phased approach based upon energy industry waste disposal needs and site constraints. As discussed in Section 1.2 and prior to initiation of each cell development, an SUP amendment by Rio Blanco County must be requested and approved. Each cell will be a stand alone waste containment area consisting of a separate double liner, leak detection (LDS), and leachate collection and removal system (LCRS). Cell construction will begin with Cell A and future cells will be generally constructed to the east and south as mining progresses. Construction level plans shall be provided to CDPHE for approval prior to construction of each phase (e.g. cells, stormwater controls) and sealed by a Professional Engineer certified by the State of Colorado. Construction level plans of Cell A and stormwater retention Pond 1 are included in this D &O Plan. Approximate locations of proposed cells are shown on Figure 3. 3.4.2 Excavations Each cell floor will be constructed with a slope ranging from 2 % to 3 % down to a leachate sump that will be used to collect leachate mainly during filling activities. Following cell closure, the final cover will NWCC, Inc.