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I Q It� j City of Stockton i! TL# 394-0192-01 4 September 16, 1994 Page 10 is III it petroleum product volatilization, and fieldltested for organic vapors with a photoionization detector (PiD) . The operation of the I ' PID is explained below. Upon completion of the drilling and soil Isampling, each borehole will be pressure grouted with a six--sack sand-cement slurry with approximately 5 percent bentonite to site grade. Soil cuttings from the borings will be sealed in United States Department of a 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 fi licensed water well drilling contractor (Contractor's License No. 506159) . The groundwater monitoring wells willl be installed under the direction of a California-registered geologist or -certified ' professional engineer. it Soil borings for monitoring wells will drilled and sampled according to Twining's "Standard Operating Procedures for Drilling and Soil Sampling" . Equipment used for lidriking, sampling, and constructing wells, and well constructionlmaterials will be thoroughly cleaned according to Twining s "Standard Operating Procedures for Equipment Decontamination"". 11 Groundwater monitoring wells will be 1cons;tructed 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 factorylmade flush-threaded connections. l The well filter pack material will consist of:'� appropriately-sized pre-washed sand. The filter material will1(be placed in the annulus between the boring wall, from the bottom .t of the boring to approximately 2 feet above the top of the screen. Subsequent to E filter pack emplacement, preliminary development may be performed to provide a uniform filter pack about the casing. Approximately three to five feet of bentonite will be pfacedron the filter 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 :Oeastkone 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 con 1, 3 to 5 percent i bentonite. For wells more than 15 feet1fdeep, the seal will be �I I I� {