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' Geolvyua[Technw_s 2nc _ Page 3 Groundwater Monitoring Report Project No 724 2 October 18,2000 ' 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 ensure their integrity 13 Laboratory Analyses _ ' The groundwater samples collected on September 26, 2000, were delivered to Sherwood Labs of Hilmar, California (certification #1400) for analysis of + Benzene, Toluene, Ethyl Benzene, and Xylene (BTEX) by method EPA method 602 + Total Petroleum Hydrocarbons as Gasoline (TPH-G) by EPA method 5030/8015(M) • MTBE by method EPA method 602 ' The detection limits for the above analyses are listed in Table 2 of Appendix A, while the lab Y PP analytical results are presented in Appendix B ' 2.0 FINDINGS AND DISCUSSION The results of the groundwater sample analysis show the following M + MW-3 has slight BTEX contamination + MW-2 and MW-4 have moderate to high benzene contamination and slight to low concentrations of the other BTEX analytes ' a MW-1, MW-2, MW-3 and MW-4 have moderate to low TPH-G contamination • Gasoline oxygenate MTBE was detected in well MW-2 at 5 ug/l • Down gradient well MW-5 was non-detect for all analytes for the second consecutive event The contamination plume is defined laterally to the east by MW-5 It is not defined laterally ' in any other direction, nor is it defined vertically ' 3.4 RECOMMENDATIONS ' GTI makes the following recommendations 0 Continue quarterly monitoring • Install additional monitoring wells and/or soil borings to define the plume A work plan for these new wells has been approved by San Joaquin County PHS/EHD and cost pre- approval for reimbursement from the USTCFP has been received The work is in the ' process of being scheduled for completion by December 2000