2013-08-05_HYDROLOGY - M1977306 - Laserfiche WebLink

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1.1.2 Monitoring Well Design, Installation, Development, and Reporting A hydrologist 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 Cotter or its 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 wells will be drilled using an air rotary rig and environmental grade thread lubricant (pipe dope). Injected water or drilling foam may be used during drilling to suspend and remove cuttings from the boring. The borehole diameter will be a minimum of 6.5 inches and the monitoring wells will be completed using two -inch ID, flush - threaded, Schedule 80 PVC and 0.02 -inch (20 -slot) factory slotted PVC screen. A five -foot 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 ten feet above the screen, followed by a ten -foot 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 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 Cotter or their consultants. 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 monitoring well completion diagram is provided in Figure 2. Monitoring wells will be thoroughly developed to remove residual drilling fluids or mud. Well development will be conducted by airlifting from above the screen and surging within the screened zone using a double surge block. The supervising hydrogeologist or geologist will monitor the discharge water during well development. Wells will be developed until field parameters (temperature, pH, and conductivity) are stable and the discharge water is clear and free of sediment. Detailed geologic logs and construction diagrams will be prepared for each new well. The logs will include information on geologic conditions, boring depth, drilling conditions, depth to groundwater, and well construction (depth, screened interval, screen slot size, filter pack type and interval, well seal type and interval, and other pertinent information). All required forms will be submitted to the Colorado Division of Water Resources including Form 51 Notice of Intent to Construct Monitoring Hole(s) and Form 46 Monitoring/Observation Water Well Permit Application with the applicable filing fee per well. 1.1.3 Groundwater Sampling Equipment It is anticipated that a bailer will be sufficient to remove three well volumes and obtain a groundwater sample for the compliance well based on experience with the existing monitoring well. The background well will be approximately 600 feet deeper than the existing well or the proposed compliance well. A bailer will be tried for purging and sampling but it may be necessary to install a submersible sampling pump to obtain reliable water samples. Grunfos pumps are designed for two -inch wells and can used to purge and sample the well or for micro -purge sampling where low flow rates (approx. 100 mL /min) capture ambient flow through the well and eliminate the need for well purging and disposal of purge water.