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' Kyle Christie Project 0805-144 01 Y � November 14, 1994 ' Page 2 GROUNDWATER MONITORING: THIRD QUARTER 1994 ' Groundwater Technology, of Concord California, as contracted b ARCO to monitor Inc ,, (GTI) iiia, Y o ' 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 September 27, 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 September 27, 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 sarrg)hng events Groundwater elevation increased approximately 123 feet from the previous sampling event (June 1994) 1 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 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 I Copies of the laboratory analysis reports are presented in Appendix A Results of analyses indicated TPHG and BTEX concentrations were below laboratory detection hrruts in groundwater samples collected from wells MW-1 through MW-4 WORK IN PROGRESS ' ARCO will continue to perform quarterly groundwater monitoring The next sampling event is tentatively scheduled for December 1994 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 monitoring program began, with the exception of MW-3, which contained total xylenes at a concentration of 0 7 ppb during fourth quarter 1994. SACGPJ"8oW8051440 IAS-94 PAS 5 I