2014-05-12_PERMIT FILE - C2010089A (3)

Home Browse Search

New Horizon North Ground Water Monitoring Wells Four holes will be drilled at each of four sites. One of these holes at each site will be drilled as a pilot hole and will be logged with geophysical tools. The other three holes will be constructed as ground water monitoring wells. After reviewing the logs from the pilot holes, the depths for the monitoring wells will be determined. At each site, one monitoring well will be constructed in the overburden above the coal zone, another within the coal zone and the third below the coal zone. All holes will be drilled using a truck- mounted rotary drill rig. The pilot holes will be drilled to a diameter of 5 -1/8" or 5 -5/8" through the Nucla Seam, a thin coaly shale seam found between 15 and 30 feet below the Upper and Lower Dakota seams which are the seams targeted for mining. Each of the four pilot holes will be logged immediately after being drilled. Upon review of these logs, the depths and specific construction details for each monitoring well will be decided. The construction of the monitoring well is subject to the findings of the geophysical logs from the pilot holes but will follow the following general guidelines (see Figure 1). Each well will be drilled to a diameter of approximately 6 -1/2 ". Once drilled, the well will be cased with 4" schedule 40 PVC casing. In the case of the well that will monitor water above the coal zone, the total depth of the hole will be several feet above the Upper Dakota (UD 1) seam. The lower ten feet of casing will be mill - slotted PVC. Above the slotted casing, a soft - formation packer will be placed on the casing and 3/8" bentonite pellets will be poured down the annulus on top of the packer to an elevation of ten feet above the packer. Drill cuttings will then be placed on top of the bentonite pellets to a depth of five feet from the surface. Concrete will be used to grout the surface to the top of the drill cuttings. The wells monitoring ground water within the coal zone will be drilled to the bottom of the Lower Dakota (LDx) seam. Slotted casing will be used from the total depth to the top of the UD1 seam. A soft - formation packer will be installed above the slotted casing and 10 feet of bentonite chips will fill the annulus above the packer. Drill cuttings will be placed in the well to a depth of five feet from the surface. The final five feet will be grouted with concrete. The wells completed below the coal zone will be drilled to a depth of approximately 15 to 30 feet below the LDx seam. Slotted casing will be used from the total depth to just below the bottom of the coal seam. A soft - formation packer will be placed just below the bottom of the lower seam and 3/8" bentonite pellets will be poured to a depth of several feet above the UD 1 seam. Drill cuttings will be placed to a depth of five feet from the surface. The final five feet will be grouted with concrete. The monitoring wells at each site will be spaced approximately 10 to 20 feet from each other. The pilot hole at each site will be plugged and reclaimed in accordance with DRMS regulations (see Figure 2). After the hole is drilled to total depth, bentonite gel will be pumped down the drill pipe to the surface and the hole will be logged with geophysical tools. When logging is complete, each pilot hole will be plugged by pouring two 50 pound bags of 3/8" bentonite chips down the hole. Drill cuttings will fill the hole to ten feet from the surface. The final ten feet will be filled with concrete and a survey cap marking the hole will be set in the concrete at the surface. Map 1 shows monitoring well sites; Figure 1 shows typical monitoring well construction; Figure 2 shows typical pilot hole plugging; Figure 3 is a completion diagram for three new monitoring wells; Table 1 is a list of the locations and estimated depths of the wells at each nest site. Appendix 2.04.7 -1 October 2013 (TR -05) E: \New Horizon \DRMS \NHN Permit \04_Techmcal Revisions TR \TR -05 \Documents from Jason \2.04.7 -1 Appendix -Ground Water Monitoring Data_TR- 05.docx