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r�as��a September 28, 1993 Working To Restore Nature Fire Engine Company No 2, Stockton, California GROUNDWATER MONITORING On August 5, 1993, RESNA measured the water levels in wells MW-1 through MW-4 and RW-1 and collected groundwater samples from the wells for subjective and laboratory analyses The field methods used are presented as an attachment to this report Floating Product or product sheen was not noted on samples from the wells (Table 1) The depth to water measurements and the elevations of the well casings (Table 1) were used to evaluate the groundwater flow direction and gradient beneath the site (refer to attached Field Procedures) On August 5, 1993, the groundwater gradient beneath the site was 0 008, with a flow direction toward the northeast (Plate 3). Since the previous monitoring event, the groundwater surface has dropped approximately 0 32 foot. The direction of groundwater flow has ranged from southeast to northeast since groundwater monitoring was initiated in December 1988 Groundwater samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg) using Environmental Protection Agency (EPA) Method 5030/8015 and as diesel (TPHd) using EPA Method 3510/8015 (modified for gasoline and diesel) and for benzene, toluene, ethylbenzene, and total xylene isomers using EPA Method 5030/602. These samples were analyzed at Sequoia Analytical in Sacramento, California (California Department of Health Services Hazardous Waste Testing Laboratory Certification No 1624) Copies of the Chain of Custody Records and laboratory analysis reports are attached Results of laboratory analyses indicated dissolved TPHg was detected in samples from wells MW-1, MW-2, MW-4, and RW-1 at concentrations of 3,500, 130, 84, and 540 parts per billion (ppb), respectively Benzene was also detected in wells MW-1 and RW-1 at 770 and 2 7 ppb, respectively TPHd was detected at concentrations of 63 ppb (well RW-1) and 140 ppb (well MW-1) The laboratory report indicates that the compounds detected in wells MW-1 and RW-1 contained carbon range hydrocarbons less than C12 Results of laboratory analyses are summarized in Table 2. 38009-4 2