2009-05-22_PERMIT FILE - C1981044A (7)

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which is presently mined at the No. 6 Mine. Stratigraphically, the "P" coal seam lies between the Twentymile Sandstone and the White Sandstone. The "E" and "F" coal seams lie between the Trout Creek Sandstone and the Middle Sandstone. The "E" coal seam underlies the "F" coat seam by approximately 100 fee[. Refer [o Figure 11, Typical Stratigraphic Section. The combined mine discharge from the No. 5 and No. 6 Mines averaged 673 gpm in 1991. A plot of the mine discharge is presented on Figure 21, Discharge from the No. 5 Mine. In their unbroken state, most coals have an intrinsically low permeability. However, where these coals are fractured by naturally occurring stresses, or by induced stresses (associated with extraction of adjacent coals), permeability can be increased substantially. Hydrologic Properties of the coal are inferred from testing of Stratigraphically equivalent coals from a nearby mine. Hydrologic data has been obtained from the Modified Permit Application for Meeker Area Mines and Associated Facilities, Rio Blanco County, Colorado, filed by the Northern Coal Company, June 1980. Testing of two (2) wells in the "G" coal seam at the Northern Coal Property Yielded Petmeabilities of 0.04 and 0.1 gpd/sq. ft. respectively. Northern Coal Company's "G" coal seam is assumed to be equivalent to the "F" coal seam found at EC. Testing of five (5) wells completed in the "FF" coal seam at Northern Coal Company yielded an average permeability of 8.6 gpd/sq. ft and calculated stora[ivity of 0.00095. The "FF" coal seam is assumed to be the equivalent of the "P" coal seam in the EC permit area. Modeling of the mine inflow of the No. 5 and No. 9 Mines yielded a transmissivity of 225 gpd/ft2, permeability of 19 gpd/ft, and storativity of 0.002 for both coals (refer to Section 2.05.6, Mitigation of the Impacts of Mining Operations). Since the "E" coal seam is very similar to the "F" coal seam; its hydrologic properties are most probably similar. Both the No. 5 and the No. 6 Mines are presently kept from being flooded by continuous pumping. When mining is completed, the mine will begin to refill. Based upon the life-of-mine plan and expected inflow rates, the No. 5 and No. 6 Mines will take at least 13 years to fill. Water from the No. 5 and No. 6 Mines may discharge at the surface after completion filling. Mine seals will be used to prevent the direct discharge of mine water to the surface (refer to Section 2.05.4, Reclamation Plan, for details on planned portal seals). Hvdroloev of [he Williams Fork Alluvium Alluvial materials occur on the valley floor of the Williams Fork River. Near the mine site, the valley floor is approximately 800 to 1,000 fee[ wide. The alluvium consists of 10 to 15 feet of poorly sorted clay to cobble-sized materials. The sediments generally become coarser with depth and are mantled by 2 to 4 feet of fine sandy to loamy soil. Underlying bedrock consists of sandstones, siltstones, and shales of the Williams Fork and the Iles Formation. There have been three (3) monitoring wells drilled into the Williams Fork alluvium for the purpose of testing hydrologic properties, collecting ground water samples, and measuring ground water levels. The three (3) wells are: 1) AVF-3, 2) AVF-5, and 3) AVF-6. WellAVF-5 was abandoned in September 1982, and reestablished approximately 100 to 150 feet to the northwest in order to monitor the No. 5 and No. 6 Mine water handling ponds. Historical ground water levels from the three (3) monitoring wells are presented in Figure 22, plot of Water Level Data -Williams Fork Alluvium Wells. The piezometric surface of the Williams Fork Alluvium is presented on the Piezometric Surface -Williams Fork Alluvium Map (Map 17). Water levels have remained relatively constant except for seasonal fluctuations related to river level changes. Hydrologic testing of the alluvial wells yielded an average saturated thickness of 5 to 6 feet, and an average permeability of 13 gpd/ft. Yields of test wells in the Williams Fork Alluvium were very low, less than 1 gpm, and required testing of the wells using the slug-test method or a pump test method. Details of the Williams Fork Alluvium Testing are presented in Exhibit 10, Hydrologic Investigation of Williams Fork and Big Bottom (Yampa) Alluvium, March 1982. Yamoa River Alluvium Alluvial materials occur on the valley floor of the Yampa River. In the Big Bottom area, the valley floor is up to 9,000 feet wide and averages approximately 5,000 feet wide. The valley floor is underlain by approximately 10 to 18 Permit Revision 04-34 2.04-15 Revised 7/2/04