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Geofogwal ec.Finics Inc Page 3 Groundwater Monitoring Report Project No 425 2 September 22, 1998 A chain of custody document, listing all samples collected and their intended analyses, accompanied the samples from field to the laboratory, thereby providing a means to track their movement and insure their integrity 13 Laboratory Analyses The groundwater samples collected on May 29, 1998 were delivered to Sherwood Lab (Department of Health Services Certification No 1400), of Hilmar, California, for analysis The samples were analyzed using the following methods o EPA method 602 - BTEX o EPA method 602 - MTBE o EPA method 5030/8015(m) - TPH-Gasoline The detection limits for the above analyses are listed in Table 3 of Appendix A and the lab data is presented in Appendix B 2.0 FINDINGS AND DISCUSSION • The laboratory analytical data from this monitoring event shows that gasoline range petroleum hydrocarbons have been detected in the following monitoring wells MW-1, MW- 2, MW-4, MW-5 and MW-8 The results from the latest round of sampling are comparable with the results from the past I monitoring events Concentrations in MW-1 showed a large decrease from the last event and are now non-detect for TPH-G See Figure 3 for graph of Benzene and TPH-G versus time in MW-1 Concentrations in MW-2 showed a significant increase from the past monitoring Ievent Concentrations are the highest seen at the site yet See Figure 4 for graph of Benzene and TPH-G versus time in MW-2 Concentrations in MW-4 stayed relatively consistent with the past monitoring events MW-5 exhibited a slight increase in concentrations since the last Ievent MW-102 showed a significant decrease since the last event and is now non-detect for all constituents MW-8 has been non-detect during the previous three sampling events but is now showing low to moderate concentrations of BTEX and TPH-G MTBE was detected in MW-5,just above detection limits The three domestic wells associated with the site were all non-detect for BTEX, MTBE and TPH-G 1 1 1