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C,eotog"I recluucs Inc Page 3 <br /> Groundwater Monitoring Report <br /> Project No 723 2 <br /> l November 7,2001 <br /> 1 <br /> 1.3 Laboratory Analyses <br /> Theoundwater were delivered to Sherwood <br /> 1� samples p collected on September 12 2001, <br /> ' Labs of Hilmar, California (certification#1400) for analysis of <br /> • Benzene, Toluene, Ethyl Benzene, and Xylene (BTEX), MTBE by method EPA method <br /> 8020 <br /> ' • Total Petroleum Hydrocarbons as Gasoline (TPH-G) by EPA method 5030/8015(M) <br /> The detection limits for the above analyses are listed in Table 2 of Appendix A, while the <br /> ' lab analytical results are presented in Appendix B <br /> 1 20 FINDINGS AND DISCUSSION <br /> ' The results of the groundwater sample analysis show the following <br /> • The concentrations of BTEX and TPH-G continue to fluctuate in individual monitoring <br /> wells from one sampling event to the next However, a significant increase in TPH-G <br /> concentrations was noted in MW-2 from 67,900 to 720,000 ug/l <br /> • Figure 4 illustrates TPH-G and Benzene concentrations versus elevation in well MW-3, <br /> which lies near the core of the plume There appears to be a direct relationship between <br /> ' the water table and the TPH-G concentrations However, Benzene concentrations have <br /> stabilized in the well <br /> a Figure 5 illustrates TPH-G and Benzene concentrations versus elevation in well MW-4, <br /> ' which lies up gradient of the core of the plume The contaminant concentrations have <br /> stabilized in this well <br /> ' • Figure 6 illustrates TPH-G and Benzene concentrations versus elevation in deep well <br /> MW-101, which lies near the core of the plume The concentrations are approaching <br /> stability The steep decline in the initial concentrations suggests that the contaminants <br /> ' detected in the well were initially a drilling artifact The low benzene concentration now <br /> detected (21 ug/1) is probably representative of the lower extent of the groundwater <br /> plume <br /> • Figure 7 illustrates the TPH-G concentrations in the shallow wells The high <br /> concentration in well MW-2 creates a localized node Additional investigation is <br /> needed to gain a more accurate site conceptual model <br /> 1 <br />