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. City of Stockton TL 394-0074-01 May 4, 1994 Page 10 Upon completion of the drilling and soil sampling, each borehole will be pressure grouted with a six-sack sand-cement slurry with approximately 5 percent bentonite to site grade. Soil I cuttings from the borings will be sealed in United States Department of Transportation (DOT) approved 55-gallon steel drums. The drums will be labeled with information on the source of their contents and stored on site in a location remote from public access. The disposal of the drill cuttings is discussed below. A-2 Groundwater Monitoring Well Installation. Twining is a C-57 licensed water well drilling contractor (Contractor's License No. 506159). The groundwater monitoring wells will be installed under the direction of a California-registered geologist or -certified professional engineer. Soil borings for monitoring wells will be drilled and sampled according to Twining's "Standard Operating Procedures for Drilling and Soil Sampling". Equipment used for drilling, sampling, and constructing wells, and well construction materials will be thoroughly cleaned according to Twining's "Standard Operating Procedures for Equipment Decontamination". Groundwater monitoring wells will be constructed of minimum Schedule 40 polyvinyl chloride (PVC), stainless steel, or other material casing. Screen may be machine-slotted or wire-wrapped. Casing and well screen specifications will depend upon project objectives, site conditions, and project budgets. The well screen and casing sections will be joined by factory-made flush-threaded connections. The well filter pack material will consist of appropriately-sized pre-washed sand. The filter material will be placed in the annulus between the boring wall, from the bottom of the boring to approximately 2 feet above the top of the screen. Subsequent to filter pack emplacement, preliminary development may be performed to provide a uniform filter pack in Approximately three to five feet of bentonite will be laced on the filter about the casing. pp y p pack. The bentonite may consist of 1/4- or 1/2-inch pellets, or may be in the form of a slurry. If pellets are used, they will be hydrated prior to grouting the well,by adding at least one gallon of water for every bucket of pellets. The thickness of the bentonite seal may depend upon local regulatory requirements. The remainder of the well annulus will be sealed with a 6-sack sand-cement, or cement grout slurry containing 3 to 5 percent bentonite. For wells more than 15 feet deep, the seal will be emplaced through the hollow-stem augers, which will extend to within 15 feet of the bentonite seal. If required by the local regulatory agency, the seal will be emplaced by j pumping through a tremie pipe which extends to within 15 feet of the bottom of the boring. The tremie pipe or augers are withdrawn from the boring in 5-foot increments as the boring fills with grout. A watertight well cap will be placed on top of each groundwater monitoring well, and a 3-foot steel standpipe with locking cover or a traffic-rated box will be installed