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r readings are noted on the logs The soil is examined and classified according to the Unified Soil Classification System SSoil samples are delivered under chain of custody, laboratory Californiap y, to a la bo tory certified by the Cahforn ' Department of Health Services (DHS) for hazardous materials analyses The samples are analyzed for petroleum hydrocarbons in accordance with Table 2 of the "Tri-Regional Board Staff Recommendations for Preliminary Evaluation and Investigation of Underground Tank Sites" (RWQCB 1990) B.3 WELL INSTALLATION tThe boreholes are completed as groundwater monitoring wells, vapor extraction wells, or air sparging wells The wells are constructed by installing Schedule 40 PVC flush-threaded casing ' through the inner opening of the auger The screened interval consists of slotted casing of the appropriate slot size, placed from 10 feet below the water table to 5 feet above it for groundwater monitoring wells A threaded end plug or a slip cap secured with a stainless steel screw is placed on the bottom of the well A filter pack of clean sand of appropriate size is placed in the annular space around the well ' screen to approximately two feet above the top of the screen The sand is placed through the inner opening of the augurs as they are slowly removed The sand is sealed by adding 1-2 feet of bentonite pellets and hydrating them with deionized water A surface seal is then created by placing a cement grout containing less than 5 percent bentonite from the bentonite spacer to the surface with a tremae pipe or grout pump ' The well is finished at the surface with a slightly raised, 12-inch-diameter traffic-rated, water-tight steel traffic box set in concrete The traffic box is secured against unauthorized entry with a cap that requires a special wrench to open, the casing is further secured with a locking well cap B.4 WELL DEVELOPMENT The wells are developed 2-3 days after completion Development consists of surging the ' screened interval of the well with a 4-inch flapper valve surge block for approximately 15 minutes The well is then purged, with a submersible electric pump, centrifugal pump, air-lift pump, or PVC bailer, of 2--6 casing volumes of water The surging and pumping are repeated until the water is free of silt and apparent turbidity, for a maximum of 4 hours A record of the purging methods and volumes of water purged is maintained All purge water is ' contained on the site in properly labeled 55-gallon drums Purged water is disposed of at an appropriate facility on the basis of the laboratory analytical results B.S WELL SURVEY The elevation of the top of the well casing 3s surveyed relative to an established datum with a Lietz C-3 automatic level and a stadia rod A small notch is cut in the top of the well casing to ' WP61 73942 R01 397 APB I B-2