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( )in the next sampling event 1992 October The data indicated that the groundwater had .` been impacted by a significant, though unknown, volume of gasoline ' San Joaquin County Public Health Services - Environmental Health Division (PHS/EHD), subsequently required further assessment of the lateral extent of groundwater contamination Comfort Air appealed this request to the San Joaquin County Board of Supervisors, and was granted permission to install a single well northeast of MW-3 to delineate the down-gradient extent of the dissolved-phase contamination plume On October 12, 1993, one soil boring was drilled at the site and completed as groundwater monitoring well MW-4 Hydrocarbon odors were noted in soil samples from 35 to 50 feet Laboratory analysis confirmed the presence of low levels of contamination at 40 and 45 feet (3 10 ppm and 190 ppm TPH as gasoline respectively) On October 19, 1993 and January 25, 1994, all four wells were monitored and samples were collected form MW-4 The gradient was determined to be very flat (0 00057 ft/ft and 0 00099 ft/ft) directed N 660 E to S 800 E. Groundwater flow direction has been consistently easterly TPH as gasoline was detected in the water sample at a concentration of 6,800 ppb to October 3993 and 1,400 ppb in January 1994 After review of these results, the PHS/EHD issued a directive for further investigation (December 17, 1993) 2.3 Purge Water Drum Sampling On January 25, 1994, water samples were also collected from each of the nine water storage drums located on-site One 40-m1 EPA vial was collected from each drum using a disposable plastic bailer These nine samples were composited and analyzed for TPH as gasoline and BTE&X in accordance with EPA methods 8015m and 602, respectively No contamination was detected in the composite water sample collected from the plastic storage drums 3.0 PROCEDURES 3.1 Drilling and Sampling On May 26, 1994, one soil boring was drilled at the site The boring was advanced to a depth of 49 feet and completed as groundwater monitoring well MW-5 Auger returns were placed on plastic sheeting and stored on-site The bonng was drilled using a truck-mounted B-57 drill ng The dnll ng and two-man crew were supplied by Woodward Drilling Co of Rio Vista Dunng dnlling, auger returns were monitored for the presence of organic vapors using a photo-ionization detector (PID Thermo Environmental 580A, 10 0 eV, calibrated to isobutylene) Discrete soil samples were collected ahead of the drill bit using a split-tube sampler loaded GWOF-I Audra 3.11-M lm- A Cu fue MW tut'=S"YIj...199 `'F