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' GTeofogtcafTerahmcs Inc Page 3 Groundwater Monitoring Report Project No 507 2 July 28, 2000 ' Additional samples were sent to Entech Analytical from Sherwood Labs for the analysis of • MTBE, DIPE, ETBE, TAME and TBA by EPA method 8260 The results and detection limits for the above analyses are listed in Table 2 of Appendix A while the lab analytical results are presented in Appendix B 2,0 FINDINGS AND DISCUSSION The results of the groundwater sample analysis show the following • There continues to be no evidence of any contamination in MW-1, MW-2 and MW-3 ' • MW-4, MW-5 and MW-9 have significant BTEX and TPH-G contamination • MW-6 and MW-8 have slight BTEX and moderate TPH-G contamination ' • MW-5 and MW-9 have moderate MTBE contamination, while gasoline oxygenates DIPE, ETBE, TAME and TBA are not present in any of the groundwater samples • The ORP reading measured during well purging show that all the wells but MW-2 have depleted oxygen content and low potential for bioremediation activity • The groundwater gradient is relatively flat and the direction of groundwater has varied during the course of the investigation The site is quite close to the San Joaquin River and tidal fluctuations might be responsible for the observed changes in groundwater direction The lateral extent of the contamination plume is defined to the east, north-east and south-east by MW-3, MW-2 and MW-1 The plume has not been defined laterally to the west nor has it been defined vertically GTI makes the following recommendations • Continue quarterly groundwater monitoring ' • Perform a receptor survey to determine if there are any domestic or production wells within 2,000 feet of the site (this effort is tentatively scheduled for August, 2000) • Further define the lateral vertical extent of the plume I