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GeologuaLT'ecFinus Inc Page 4 Groundwater Monitoring Report Project No 724 2 August 20,2001 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 ' 1.3 Laboratory Analyses The groundwater samples collected on June 21, 2001, were delivered to Sherwood Labs of Hilmar, California (certification #1400) for analysis of • Benzene, Toluene, Ethyl Benzene, and Xylene (BTEX) by EPA method 602 ' Y Total Petroleum Hydrocarbons as Gasoline (TPH-G) by EPA method 5030/8015(M) Sherwood also sent the samples to Entech Analytical Labs (certification #2346) for the analysis of o MTBE, DIPS, ETBE, TAME, TBA by EPA Method 8260 ' The detection limits for the above analyses are listed in Table 4 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 ® Wells MW-1, MW-3, MW-5, MW-6, MW-7 and MW-104 did not contain contaminant ' concentrations above the laboratory reporting limits • Wells MW-2 and MW-4 have low to moderate benzene contamination and trace to low concentrations of the other BTEX analytes 0 Wells MW-2 and MW-4 contain low concentrations of TPH-G • Intermediate wells MW-106 and MW-107 contained low BTEX concentrations and low ' to moderate TPH-G • Deep well MW-104 did not contain contaminant concentrations above the laboratory reporting limits for the third consecutive event ' • Gasoline oxygenate MTBE was detected in well MW-106 and MW-107 at 7 6 and 32 �ig/l, respectively The shallow groundwater plume is evident in well MW-4 and defined laterally to the east (down gradient) by MW-5 and MW-6 The presence of contamination in wells MW-106 and MW-107 suggests that a submerged plume is being sourced by residual soil contamination beneath the present water table It is noted that the screened intervals of these wells (55-60 feet bgs) are placed near the elevation of the groundwater table in 1992 — approximately 54 feet bgs 1