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City of Stockton TL 394-0028-02 <br /> March 10, 1994 Page 8 <br /> A-2 Decontamination: Decontamination procedures will be <br /> implemented to reduce the potential for cross-contamination between <br /> soil borings. <br /> Before, during, and following drilling operations, the augers and <br /> associated drilling and sampling equipment will be thoroughly <br /> cleaned using a high pressure hot water (steam) washer. The hot <br /> water washer has a pressure of approximately 1,200 pounds per <br /> square inch and a water temperature of approximately 100 degrees <br /> Centigrade ( OC) . The sampler and brass sleeves will be washed in <br /> a AlconoxO detergent solution, rinsed with clean tap water, and <br /> air-dried prior to initial use and between each sampling event. <br /> The augers will be steam cleaned prior to the drilling of each soil <br /> boring. <br /> Prior to construction of monitoring wells, all casings will be <br /> cleaned in the same manner as the drilling equipment. <br /> A-3 Soil Gas Probe Installation: Twining is a C-57 licensed water <br /> well drilling contractor (Contractor's License No. 506159) . The <br /> soil gas probes will be installed under the direction of a <br /> California-registered geologist or -certified professional <br /> engineer. <br /> Soil borings for gas probes will be drilled and sampled according <br /> to Twining' s "Standard Operating Procedures for Drilling and Soil <br /> Sampling" . Equipment used for drilling, sampling, and constructing <br /> wells, and well construction materials will be thoroughly cleaned <br /> according to Twining's "Standard Operating Procedures for Equipment <br /> Decontamination" . <br /> Soil gas probes will be constructed of Schedule 80 polyvinyl <br /> chloride (PVC) casing. Screen will be machine-slotted. Rubber <br /> stoppers will be placed at the top of the screened section and at <br /> the top of the casing. TeflonTm tubing will extend from <br /> approximately one foot below the bottom stopper to approximately <br /> one foot above the top stopper for sample collection. Casing and <br /> well screen specifications will depend upon project objectives, <br /> site conditions, and project budgets . The well screen and casing <br /> sections will be joined by factory-made flush-threaded connections. <br /> The well filter pack material will consist of appropriately-sized <br /> pre-washed sand or pea gravel . The filter material will be placed <br /> in the annulus between the boring wall, from the bottom of the <br /> boring to approximately 2 feet above the top of the screen. <br /> Approximately one foot of bentonite will be placed on top of the <br /> sand pack as a seal . The bentonite may consist of 1/4- or 1/2-inch <br /> pellets, or may be in the form of a slurry. If pellets are used, <br /> they will be hydrated prior to grouting the well, by adding at <br />