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Gi ��J April 22, 1993 Working To Restore Nature ' Fire Engine Company No 2, Stockton, California GROUND-WATER MONITORING On February 24, 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 ground-water flow direction and gradient beneath the site (refer to attached Field Procedures) The ground-water gradient was approximately 0 007 with a flow direction to the southwest (Plate 3) The ground water surface has risen approximately 2 9 feet since the previous monitoring event The direction of ground-water flow has ranged from southeast to northeast Ground-water samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg) and as diesel (TPHd) using EPA Method 8015 (modified for gasoline and diesel) and for benzene, toluene, ethylbenzene, and total xylene isomers using EPA Method 602 These samples were analyzed at RESNA Environmental Laboratories in Fremont, California (California Department of Health Services Hazardous Waste Testing Laboratory Certification No 1211) Copies of the Chain of Custody Records and laboratory analysis reports are attached Results of laboratory analyses indicated dissolved TPHd was not detected in water sampled from the five wells Dissolved TPHg was detected in samples from wells MW-1, MW-2, MW-3, and RW-1 at concentrations ranging from 67 parts per billion (ppb, well MW-3) to 2,300 ppb (well MW-1) Dissolved benzene concentrations in wells MW-1 and RW-1 were 110 ppb and 3 4 ppb, respectively Results of laboratory analyses are summarized in Table 2 SUMMARY AND RECOMMENDATIONS The groundwater flow direction and gradient were generally consistent with those evaluated during previous events Dissolved gasoline hydrocarbons were detected in samples from wells MW-1, MW-2, MW-3, and RW-1, however, dissolved diesel hydrocarbons were not detected during this sampling event Dissolved concentrations of benzene were above maximum contaminant levels The next sampling event has been scheduled for May 1993 We recommend forwarding signed copies of this report to Ms Linda Turkatte of the San Joaquin County Public Health Services, Environmental Health Division, P O Box 2009, Q3181esc 38009-4 2