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' Geolo :cal2ecFnus Znc Page 3 <br /> g <br /> Groundwater Monitoring Report <br /> Project No 507 2 <br /> April 14,2000 <br />' 1.3 Laboratory Analyses <br />' The groundwater samples collected on January 27, 2000 were delivered to Sherwood Lab <br /> (Department of Health Services Certification No 1400), of Hilmar, California, for analysts <br />' The eight groundwater samples were analyzed by Sherwood for <br /> • Benzene, Toluene, Ethyl Benzene, and Xylene (BTEX) by EPA method 602 <br /> • Total Petroleum Hydrocarbons as Gasoline (TPH-G) by EPA method 503018015(M) <br />' Additional samples were sent to Entech Anal tical from Sherwood Labs for the analysis of <br /> p Y Y <br />' • MTBE, DIPE, ETBE, TAME and TBA by EPA method 8260 <br /> • Methanol and Ethanol by EPA method 8260 <br />' Analysis results from Entech reflect the March 8 re-sampling that was required because <br /> Entech lost the January samples The detection limits for the above analyses are listed in <br /> Table 2 of Appendix A while the lab analytical results are presented in Appendix B <br /> 1 <br /> 2.0 FINDINGS AND DISCUSSION <br /> The results of the groundwater sample analysis show the following <br /> o There is no evidence of any contamination in MW-1, MW-2 and MW-3 <br /> o MW-4, MW-5 and MW-9 have significant BTEX and TPH-G contamination <br /> o MW-6 and MW-8 have slight BTEX and moderate TPH-G contamination <br />' 0 MW-5 and MW-9 have moderate MTBE contamination MTBE samples from MW-4, <br /> which showed moderate contamination in the previous monitoring event, were too highly <br /> diluted during the laboratory testing to determine how MTBE contamination has evolved <br /> in this event <br /> • TEPH (Diesel), DIPE, ETBE, TAME and TBA are not present in any of the groundwater <br /> samples <br />' • The ORP reading measured during well purging show that all the wells but MW-2 have <br /> depleted oxygen content and low potential for bioremediation activity <br /> • The groundwater gradient is relatively flat and is in the opposite direction as it was in the <br />' April 1999 monitoring event The site is quite close to the San Joaquin River and tidal <br /> fluctuations might be enough to cause the groundwater gradient at the site to change <br />' direction in response to them <br /> The lateral extent of the contamination plume is defined to the east, north-east and south-east <br /> by MW-3, MW-2 and MW-1 The plume has not been laterally defined to the west nor has it <br /> been vertically defined <br /> 1 <br />