2015-08-18_PERMIT FILE - C1982056A (4)

Home Browse Search

Two monitoring wells were completed in 2014 in the Wadge/Wolf Creek Interburden and the Wolf Creek Seam. Well WC008A was drilled to a depth of 556 feet on the east side of the WCR, between the mine area and the Wolf Creek Seam outcrop /subcrop area. Well WC013A was drilled to a depth of 1,456 feet on the west side of the WCR and near the center of the area in which the Wadge Seam is mined and close to the low point of the Twentymile Park Basin. The well locations are shown on Map 23A. Well WC008A is screened from 511 to 556 feet below ground surface (bgs). The Wadge /Wolf Creels Interburden unit at that location is under confined (artesian) conditions, as evidenced by the water level in WC008A being slightly above the land surface. The well flows at a very low rate, and is estimated to have a static water level not more than about 5 feet above the top of the casing, or approximately 6,780 feet amsl. The flowing condition is not unexpected at that location, considering that the depth to water in nearby Wadge Overburden Well 008 -77 -58 is on the order of 6 feet bgs, and the outcrop /subcrop areas of the Wadge/Wolf Creek Interburden and the Wolf Creek Seam, which are areas of natural recharge, generally occur at higher elevations than those of the Wadge Seam. Well WC013A is screened from 1,411 to 1,456 feet bgs, through an interval containing the Wolf Creek Seam and Wadge /Wolf Creek Interburden. The depth to the static water level is 1,242 feet from the top of the well casing (approximately 1,239 feet bgs), and the static water level elevation is approximately 5,519 feet amsl. That water level elevation is about 100 feet above the Wadge Seam, but it is several hundred feet lower than would have been estimated by projecting the hydraulic gradient from the Wadge Overburden wells south of WC013A. T he low water level elevation suggests two possibilities: 1) The greater consolidation and low permeability of the Wadge /Wolf Creek Interburden strongly limits groundwater flow through the unit in a bedding - parallel direction as well as vertically, thereby hydrologically isolating the Wadge/Wolf Creek Interburden, particularly in the deeper part of the Twentymile Park Basin, and /or 2) Dewatering of the existing Wadge mine workings has lowered hydrostatic pressures in the Wadge Seam and Wadge Overburden, and vertical hydraulic communication has allowed hydrostatic pressures in the Wadge /Wolf Creek Interburden in that area to respond to the lowered pressures in the overlying units. Wells WCOOA8 and WC013A were slug- tested to determine the hydraulic characteristics of the Wolf Creek Seam and Wadge/Wolf Creek Interburden. The WC008A test was conducted by first inserting a slug designed to cause approximately 5.6 feet of water -level change within the 4 -inch diameter well casing, which caused the well to overflow but did not raise the water level since the initial water level was at the top of the casing. The slug was then rapidly removed from the well, suddenly lowering the water level. The water -level recovery over time was measured and recorded with a pressure transducer and data - logger for approximately 100 minutes, then manually until approximately 26 hours after the start of the test. In the first 100 minutes, the water level recovered 0.52 foot and in the first 6 hours approximately 1.4 foot. The WC013A test was conducted by pouring 15 gallons of tap water into the well through 1 -inch diameter polyethylene tubing which had been inserted to slightly below the static water level, which raised the water level approximately 23 feet. The gradual decline of the water level over the subsequent 132 hours was measured and recorded with a pressure transducer and data - logger. The results of the testing are summarized below, and the test data and analysis details are included in Exhibit 9. The hydraulic conductivity determined from analysis of the data from both tests was nearly identical and indicative of rocks with very limited permeability that would typically comprise an aquitard. Wolf Creek Seam and Wadge/Wolf Creek Interburden monitoring Well WC -008A was initially sampled, with sampling results provided for baseline review. A sample could not be obtained from Well WC -013A, however, both wells will be purged and sampled as part of TC's ongoing hydrologic monitoring program. TR13 -83 2.04 -22.1 11/17/14 Hydraulic Saturated Thickness Tare Well ID Test Date Conductivity of Tested Interval feet d (square feet per day) (feet/day) feet WC008 10/01/2014 0.0016 35 0.056 WC013 10/ 0.0015 45 0.067 Wolf Creek Seam and Wadge/Wolf Creek Interburden monitoring Well WC -008A was initially sampled, with sampling results provided for baseline review. A sample could not be obtained from Well WC -013A, however, both wells will be purged and sampled as part of TC's ongoing hydrologic monitoring program. TR13 -83 2.04 -22.1 11/17/14