2008-03-31_PERMIT FILE - C1980007A (34)

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West Elk Mine Monitoring wells WR-2 and WR-3 were located irmnediately up-slope and down-slope of the initial waste rock pile in the area that is now the site of West Elk Mine's Maintenance Shop and Warehouse. Monthly water level recordings were initiated in September 1981. Well WR-2 was destroyed in June 1982, during construction of the shop and warehouse bench. A new well WR-2 was completed in November 1982, at a location 49 feet upslope of the original well. The initial waste rock pile was removed in 1985. Consequently, the wells WR-1 and WR-2 were abandoned. Wells GP-3, GP-4, GP-6, and GP-7 were subsequently completed on the east-side of the Lower Refuse Pile. Falling head permeability tests were performed on these wells in order to estimate the permeability of the colluvial soils in this area. Field permeability values were determined to be between 2.1 and 3.9 x 10-6 centimeters per second (2 to 4 feet per year). Permeability tests were also perfonned on two shallow boreholes (10 and 15 feet deep) at the initial waste rock pile to determine the permeability of the upper portion of the colluvial soils. The falling head tests indicated a permeability of approximately 1.0 to 1.2 x 10-6 cnn/sec (1.0 to 1.2 feet per year). Alluvium The alluvium of the North Fork consists of mixed sand, cobbles, and boulders capped by finer sands and silts. In the vicinity of West Elk Mine, the North Fork alluvium is relatively narrow and ranges from 40 to 70 feet in thickness. Alluvial deposits within the coal lease area are generally less than 25 feet thick and are part of the active groundwater regime. Where sufficient saturated thickness can be found, alluvial deposits may yield more abundant groundwater. Well AL-1, completed in the alluvium of the North Fork, has a reported sustained production rate of 17.4 gpm as determined from pumping tests. The resulting transmissivity was estimated to be less than 500 gpd/ft (Table 5). A pumping test conducted by Bear Coal Company on an alluvial well near the site of Bear No. 3 Mine yielded a transmissivity of 806.5 gpd/ft. Pumping tests conducted by Colorado Westmoreland, former operator of the Orchard Valley Mine, indicate that the alluvial deposits of the North Fork tributary of Stevens Gulch were of sufficient thickness to support a pumping rate of about 28 gpm. Transmissivity values and well (SG-1) yields within the alluvium of Sylvester Gulch, another tributary to the North Fork, indicate a sustained production of about 1 gpm and an extremely low transmissivity of about 120 gpd/ft (Table 5). In the South of Divide permit revision area, the Dry Fork of Minnesota Creek represents the most significant alluvial deposit. Three wells, A-1 (AV-1), A-2 (AV-2), and A-3 (AV-3), were completed in the alluvium of Dry Fork of Minnesota Creek in August of 1984 (Exhibit 12). Of the three wells completed in the alluvium of the Dry Fork, only well A-2 showed transmissivity results characteristic of an alluvial aquifer and consistent with results from tests on wells on the North Fork or its tributaries. These wells were monitored for a period of time after the installation, but are not part of the current groundwater monitoring program. Two new alluvial/weathered bedrock wells (Upper Dry Fork and Lower Dry Fork) were constructed in 2003 to obtain additional information on this hydrostratigraphic unit. These wells showed the alluvium to be approximately 25 to 30 feet thick with a saturated interval of approximately 20 feet. A permeability test was not completed in theses wells, however based on observations during well development, the estimated hydraulic conductivity of the alluvium/weathered bedrock is about _10-4 cnn/sec (HydroGeo, 2003). Monitoring of these wells was initiated in fall 2.04-70 Revised June 2005 PRIO, March 2006; Rev. Apri12006 PRIO, Sep. 2007PR12