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Working To Restore Nature February 12, 1993 BP Oil Facility No. 11193, Stockton, California. FIELD PROCEDURES ' Drilling_Procedures ' We contacted Underground Service Alert at least 48 hours before drilling to delineate public utility lines at the site. Before drilling, we hand-augered each borehole to 3 to 5 feet below grade. ' A licensed well driller drilled the borings using a truck-mounted drill rig equipped with 7- inch-diameter or hollow-stem augers. The drilling was performed under the guidance of a ' field geologist. The earth materials was logged using visual and manual methods as drilled using the Unified Soil Classification System. A photoionization detector (PTD) was used to evaluate soil samples for gasoline hydrocarbons. Field instruments such as the PID are ' useful for indicating relative levels of gasoline hydrocarbon vapors but do not detect the • concentration of gasoline hydrocarbons present with the same precision as laboratory analyses. Any subjective evidence of gasoline hydrocarbons such as soil discoloration or ' obvious odor was noted. Collecting Soil Samples During drilling, soil samples were collected at 5-foot or other appropriate intervals using a Californiwmodifted, split-spoon sampler equipped with clean brass sleeves. Samples were ' collected by drilling the boring to a point just above the sampling depth and then driving the sampler into the soil through the hollow center of the auger. The sampler was driven 18 inches with a standard 140-pound hammer dropped 30 inches. The number of blows ' required to drive the sampler each successive 6-inch interval was counted and recorded on the field boring log to give an indication of soil consistency. Monitoring Well Construction • Monitoring wells were constructed in the borings with thread-jointed, 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 5 or 10 feet above the groundwater surface. This screened interval allows • sampling at the air-water interface during seasonal fluctuations of the groundwater level. ' The annular space in the well was packed with number 3 sand to approximately 1 to 2 feet above the slotted interval. A 3-foot thick bentonite plug was added above the sand pack to prevent the cement from entering the well pack. The remaining annulus was backfilled to grade with a bentonite cement slurry. • 17051.01