2014-01-29_HYDROLOGY - P2009025 (8)

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Baseline Hydrologic Monitoring Plan — Hansen Project 38 4.2 Monitoring Well Design and Installation A professional engineer or geologist will prepare monitoring well specifications and designs. All new wells will be installed and developed by a licensed water well drilling contractor under the direct supervision of Black Range Minerals or their consultants. Final well depths, screened intervals, filter pack, and other relevant well construction features will be determined in the field by the supervising engineer or geologist. Monitoring well specifications are provided in Appendix E and summarized in the following sections. 4.2.1 Typical Well Specifications for "Shallow to Intermediate" Wells (less than 420 ft) Monitoring wells drilled less than 420 feet deep will be drilled using a mud or air rotary rig. The borehole diameter will be a minimum of 6.5 inches. Injected water, drilling foam, or mud may be used during drilling. The "shallow" monitoring wells will be completed using 2 -inch ID, flush- threaded, Schedule 40 or 80 PVC and 0.02 -inch (20 -slot) factory slotted PVC screen. A 5 -ft sump (blank casing) will be installed below each screen. The annulus of each shallow well will be filled with 10 -20 Colorado silica sand that is tremied into place to at least 10 feet above the screen, followed by at least 10 -ft seal of bentonite chips or coated pellets. The filter pack will be mechanically agitated and settled prior to installing the bentonite pellet plug. A high - solids bentonite or Portland cement grout will be tremied into the annulus from the pellet plug seal to 20 feet below ground surface. The upper 19 feet of annular space will be filled with Portland cement. The surface completion will include a locking steel well cap set in a concrete pad that slopes slightly away from the well. All well locks will be keyed alike using keys provided by Black Range Minerals. Well drilling and construction must follow standard practices for environmental monitoring wells (including non - metallic environmental pipe dope on drill rods and wearing clean latex or nitrile gloves while handling casing). An example well completion diagram for shallow monitoring wells is provided in Figure 13. 4.2.2 Typical Well Specifications for Deep Wells (Greater than 420 ft) Deep monitoring wells will be drilled using a mud or air rotary rig with water, foam, or mud as the drilling fluid. The borehole diameter will be a minimum of nine inches. Deep monitoring wells will be completed using 3 -inch 5 ID, flush threaded, Schedule 80 PVC and 0.02 -inch (20 -slot) factory slotted PVC screen. A 5 -ft sump (blank casing) will be installed below each screen. The annulus will be filled with 8 -12 Colorado silica sand to at least 10 feet above the screen, followed by at least a 10 -ft seal of coated bentonite pellets. The filter pack will be mechanically agitated and settled prior to installing the bentonite pellet plug. A high - solids bentonite or Portland cement grout seal will be installed from the top of the pellet plug seal to 19 feet below ground surface, and a Portland cement seal will be installed from the top of the grout to ground surface. All materials will be placed by tremie pipe, either by gravity or by pumping. Well drilling and construction must follow standard practices for environmental monitoring wells (including non - metallic environmental pipe dope on drill rods and wearing latex gloves while handling casing). An example well completion diagram for deep monitoring wells is provided in Figure 14. 5 Note that the 3 -inch ID casing diameter was selected to be large enough to accommodate either portable sampling pumps or dedicated pumps set in the target horizon, and small enough to minimize the purge volumes and purge water disposal requirements. For comparison, about 10 of the 91 wells completed by Cyprus were 4 -inch diameter and the remainder were 2- inch. 4153A.140129 Whetstone Associates