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Geo(ogccaCTechnics Inc Groundwater Monitoring Report Project No 724 2 November 13, 2001 Page 4 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 September 17, 2001, were delivered to Sherwood Labs of Hilmar, California (certification #1400) for analysis of • Benzene, Toluene, Ethyl Benzene, and Xylene (BTEX), MTBE by EPA method 602 • Total Petroleum Hydrocarbons as Gasoline (TPH-G) by EPA method 5030/8015(M) 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 -5, MW -6, MW -7 and MW- 104 did not contain contaminant concentrations above the laboratory reporting limits • Wells MW -2 has moderate benzene contamination and trace to low concentrations of the other BTEX analytes • Well MW -3 and MW -4 contain low concentrations of TPH-G or BTEX • 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 fourth consecutive event • TPH-G was not detected in water table wells MW -4 through MW -7 However, benzene was present in well MW -4 • TPH-G was detected in intermediate wells MW -2, MW -3 and MW -107 Figure 5 — Intermediate Well TPH-G Concentrations - illustrates the extent of the TPH-G plume • MTBE was detected in intermediate well MW -2, MW -106 and MW -107 utilizing EPA Method 602 The levels detected are consistent with those detected in past events utilizing EPA Method 8260 The shallow groundwater plume is evident in well MW -4 and defined laterally to the east (down gradient) by MW -5 and MW -6 This situation is illustrated in Figure 6 — Water Table Well Benzene Concentrations Figure 7 — Intermediate Well Benzene Concentrations & Figure 8 — Intermediate Well MTBE Concentrations suggest that a significant plume does not exist below the water table The presence of TPH-G contamination in well MW -106 and MW -107 suggests that a submerged plume is being sourced by residual soil