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Mr Kyle Christie Project 0805-144 01 February 13, 1995 Page 2 • GROUNDWATER MONITORING; FOURTH QUARTER 1994 Groundwater Technology, Inc , (GTI) of Concord, California., was contracted by ARCO to monitor the groundwater in the monitoring wells previously installed at the site, GTI subsequently forwarded their field notes and the laboratory reports to EMCON EMCON used these data to evaluate dissolved gasoline hydrocarbon concentrations and the flow direction and groundwater gradient On December 1, 1994, a technician from GTI took water level measurements and collected groundwater samples from monitoring wells MW-1 through MW-4 for subjective and laboratory analyses The technician did not observe floating product or product sheen on samples collected from the wells (see Table 1) The surveyed elevations of the top of casing and the depth-to-groundwater measurements (see Table 1) were used to evaluate the potentiometric surface beneath the site On December 1, 1994, the direction of groundwater flow was toward the northwest with a gradient of approximately 0 02 (see Figure 3) The direction of groundwater flow is consistent with previous sampling events. Groundwater elevation decreased approxunately 0 63 feet from the previous sampling event (September 1994) •� Groundwater samples from each well were analyzed for total petroleum hydrocarbons as gasoline (TPHG), and benzene, toluene, ethylbenzene, and total xylene isomers (BTEX) using Environmental Protection Agency (EPA) Methods Modified 8015 and 5030/8020 The samples were analyzed at National Environmental Testing, Inc , in Santa Rosa, California The results of analyses are summarized in Table 1 Copies of the laboratory analysis reports are presented in Attachment A Results of analyses indicated TPHG and BTEX concentrations were below laboratory detection limits in groundwater samples collected from wells MW-1 through MW-4 ACTIVITIES PERFORMED DURING THE FOURTH QUARTER • Performed quarterly groundwater sampling ANTICIPATED WORK ARCO will continue to perform quarterly groundwater monitoring The next sampling event is tentatively scheduled for March 1995 CONCLUSIONS . The groundwater flow direction was to the northwest Gasoline hydrocarbons were not detected in groundwater samples collected from monitoring wells MW-1 through MW-4 Gasoline hydrocarbons have not been detected in the monitoring wells since the morutoring program began, with the exception of MW-3, which contained total xylenes at a concentration of 0 7 ppb during fourth quarter 1993 SAC/P101080S108051440 IBM-94 PAS 3