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A& e e Mr . Russell F. Chapin October 31, 1990 Page 2 groundwater surface. Borings not converted into monitoring wells will be backfilled with bentonite-cement slurry . Soil samples will be collected at 5-foot intervals and at lithologic contacts using a California-modified split spoon sampler fitted with clean brass sleeves . A photoionizing hydrocarbon vapor detector will be used to quantify semiquantitatively the potential hydrocarbon concentrations in the soil samples. Selected soil samples will be analyzed for total petroleum hydrocarbons as gasoline (TPH(g) ) , and for the gasoline constituents benzene, toluene, ethylbenzene, and xylene isomers (BTEX) , and for organic lead using EPA Methods 8015 (modified) , 8020 , and methods recommended by the California Department of Health Services. Monitoring wells will be constructed in four of the borings using flush-jointed, 4-inch inner diameter, Schedule 40 polyvinyl chloride (PVC) casing. No chemical cements , glues , or solvents will be used in well construction. The screened portion of the wells will consist of factory- perforated casing with 0 . 020-inch-wide slots . The well screen will be set through the augers and will extend from the total depth of each well to approximately 5 feet above the groundwater surface at the time the wells will be installed. This would allow sampling near the air/water interface in the formation during seasonal fluctuation of groundwater levels . The base of each well will be fitted with a threaded PVC plug, and the top of each well will be fitted with a watertight locking cap. The annular space of the well will be packed with sorted sand to a point approximately even with the top of the perforated casing; the sand pack size will be selected based on the grain-size distribution of the ROGER FOOTT ASSOCIATES, MC.