2009-08-13_PERMIT FILE - C1981019A (4)

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RULE 2 PERMITS Perched bedrock groundwater will be found during mining activities. This has been confirmed by water monitoring during drilling, short-term air lift tests, and an examination of the geophysical logs. This water will contribute to a significant inflow of water during the boxcut and initial mining, but should cease rather rapidly (2 years ±). No artesian groundwater conditions exist above the Km marker bed, a proven regional aquiclude (confining layer), within the proposed mining areas. Groundwater Quantity -Transmissivity of the perched zones of the interburden within the Williams Fork Formation ranged from 79 square feet per day (ft2/d) to 1,930 ft2/d. Corresponding hydraulic conductivity ranged from 3.43 feet per day (ft/d) to 80.4 fUd (CDM, 1985a; Table 2.04.7-26). The range in values is indicative of the variability in the degree of fracturing in the formation. Published transmissivity for the upper Williams Fork Formation is 33 to 95 ft2/d (Robson & Stewart, 1990). The F„b coal seam hydraulic transmissivity was 4.3 to 5.7 ft2/d and the conductivity was measured to be 0.24 to 0.29 ft/d (CDM, 1985a). The Trout Creek Sandstone just south of the Lower Wilson box cut was found to be dry (Well 84-B-TC). Other wells north of the Lower Wilson mine that intersected saturated portions of the Trout Creek closer to the axis of the Collom Syncline had transmissivity that ranged from 2.06 to 4.57 ft2/d and had hydraulic conductivity ranging from 0.086 to 0.29 fUd. All of these values are considered [o be indicative of moderate permeability, and typical of relatively clean and/or fractured sandstone lithologic units (CDM, 1985a). Storativity values for the Williams Fork Formation and Trout Creek Sandstone could not be estimated as part of the CDM studies, however, observations made during drilling and monitoring suggest that the water-bearing intervals are of limited saturated thickness and under confined conditions with significant . artesian pressure (CDM, 1985a). Storativity values (unitless) for the F~ coal seam ranged from 10-3 to 10-', which are indicative of confined conditions. Storativity values for the Trout Creek Sandstone was about 10'2. In addition to the bedrock wells, studies of the alluviaVcolluvial aquifers in the general area have also been conducted. CDM slug-tested the wells to determine the hydraulic characteristics of the shallow aquifers (CDM 1985a). A slug test consists of the introduction or removal of a known volume of water or slug then subsequently measuring the water level through time in the well as the water level declines. For each of the wells, aslug-in and aslug-out test were performed. The results of the slug tests performed on the relevant alluvial wells are presented in Table 2.04.7-27. In 1985, monitoring well A-5 was destroyed by amass-wasting flood event, and the water table which it intersected was substantially lowered, as evidenced by the new wells MW-OS-03A and MW-OS-03B that were installed to bedrock at the confluence of the unnamed drainage leading out of the box-cut area and Wilson Creek (near historic A-5). Both wells were dry at the time of construction, and MW-OS-03A was permanently closed. MW-OS-03B has about ~/z foot of water at the alluvial-bedrock contact. Transmissivity of the alluvium ranged from 1,935 ftZ/day to 10,909 ft2/day. Corresponding hydraulic conductivity ranged from 29.7 fUday to 175 fUday. i• Sough Taylor/Lower Wilson -Rule 2, Page 40 Revision Date: 11 /30/06 Revision No.: PR-02