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a, June 26, 1992 ARCO Service Station No. 549, Stockton, California round- ater Monitoring Well The wells were constructed using clean 4-inch-inner-diameter, thread jointed, Schedule 40 polyvinyl chloride (PVC) casing. No chemicals, glues, or solvents were used in construction of the wells. The screened portion of the monitoring well consists of factory-perforated casing with slots and extends from the total depth of the boring and extends above the depth where water was first encountered. Unperforated casing is set from the top of the screen to several inches below surface grade. The annular space of each well was packed with sorted sand from the total depth of the boring to approximately 2 feet above the top of the screen. A plug of bentonite pellets (approximately 2-feet thick)was placed above the sand to prevent cement from entering the sand pack. This seal reduces the possibility that hydrocarbons migrating downward through the overlying sand will infiltrate the aquifer. The remaining annulus was backfilled to the ground surface with a mixture of water, cement, and.bentonite. The construction details of the individual wells are shown on the Logs of Borings. The wellheads were secured in cast-aluminum utility boxes with PVC aprons. The boxes have watertight seals and were set in concrete approximately flush with the surrounding i ground surface to reduce surface-water infiltration. A special wrench is required to open the box. This design discourages vandalism and reduces the possibility of accidental disturbance to the well. Each wellhead was also fitted with a locking well cage to further protect against unauthorized disturbance of the well. Vapor-Extraction Well Construction S Soil borings chosen for vapor wells were located in soil containing elevated levels of hydrocarbons based on field observations and field screening using a photoionization detector. Soil borings were terminated approximately 1 foot above first encountered ground water, and the vadose wells were constructed in the boring with threadedjointed, 4-inch- inner-diameter,Schedule 40 PVC casing. No chemical cements, glues, or solvents were used in well construction. The screened portion of each well consisted of factory-perforated casing with 0.020-inch-wide slots. The well screen extends from the total depth of the well to approximately 15 feet below grade for wells VW-1 and VW-2, and 10 feet below grade for well VW-3. The screen interval was based on field observations and sediments encountered during_drilling. The annular space in the well was packed with sorted sand to a point approximately 1 foot above the slotted interval. A bentonite plug was added above the sand pack to seal out cement. The remaining annulus was backfilled to grade with a bentonite-cement slurry. The vadose . wells were completed by installing a traffic-rated, cast-aluminum utility box over the well head. MW-4