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Groundwater Well Installation Work Plan Sharpe Army Depot Lathrop, California Ahtna Environmental, Inc. 10 tremie pipe by a positive displacement method, such as pumping. The tremie pipe will extend from the surface to the bottom of the zone to be grouted. The tremie pipe will be positioned in the hole with the pipe bottom not greater than 5 ft above the bentonite seal, and then directed to discharge to the sides of the borehole (rather than downward). The tremie pipe will be slowly raised as the grout is placed and the drill rod retracted; however, the discharge end of the pipe will be submerged in the grout at all times. Additional grout will be added to maintain the level of the grout at the ground surface as settlement occurs. 3.2.2 Well Development Well development will begin as soon as practicable after well construction, but not sooner than 48 hours after construction is complete. If deemed necessary to remove mud or clay from the well to properly develop the well, non-phosphoric dispersants (such as Johnson Screen’s Nuwell 220 dispersant polymer, or equivalent) may be mixed at the surface, tremied into place, and allowed to activate per the manufacturer's recommendations. Any water and dispersant added during well construction will be removed before development. The development procedure will be accomplished by bailing and swabbing, followed by pumping. A sand bailer will initially be used to remove fine-grained sediments and sand from the well. A surge block will then be used to gently swab the casing to increase flow from the formation into the well. Bailing and swabbing will continue until sediment is less than one teaspoon per bailer load before pumping begins. As necessary, an air isolation tool will then be used to remove water from the well via air displacement. The tool will be fitted with rubber diaphragms that focus the water removal from 5-ft sections of the well screen. Well development with the air isolation tool will continue until the discharge water is visually absent of sediments. Water will then be removed from the well using a submersible pump until field measured water quality parameters have stabilized. If the parameters do not stabilize within what the Field Geologist or technician considers a reasonable amount of time, the Field Geologist or technician will contact senior technical personnel for guidance. Groundwater parameters are considered stable when the following conditions are met after three successive measurements: • ± 3.0°C temperature (minimum of ± 0.2°C) • ± 0.1 pH • ± 3% conductivity • ± 10 mV ORP • ± 10% DO • < 5 nephelometric turbidity units (DTSC, 2014; USEPA, 1986) 3.2.3 Aquifer Pumping Tests Aquifer pumping tests will be performed on each new extraction well to determine the optimum operational parameters. Aquifer pumping tests include a step-drawdown test followed by a constant-rate test. Step-drawdown tests will consist of pumping for one hour at 5 gallons per minute (gpm) for the A Zone well and 40 gpm for the C Zone well), then increasing the pumping rate by a set amount (5 gpm for the A Zone well and 20 gpm for the C Zone well) every hour until four steps are complete. Each well will be