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1 <br /> ' 08 November 2002 <br /> AGE-NC Project No 97-0351 <br /> ' Page 3 of 4 <br /> ' • TPH-g was detected in the samples from ground water monitoring wells MW-1 and <br /> MW-UST at concentrations of 4,100 micrograms per liter(µg/1) and 5,600 µg/1 <br /> • BTEX compounds were detected in the sample from monitoring well MW-1 at <br /> concentrations of 270µg/1 benzene,20µg/l toluene, 76µg/1 ethylbenzene and 108 µg/1 total <br /> xylenes BTEX compounds and MTBE were not detected in the samples collected from wells <br /> ' MW-2 through MW-5 and MW-UST <br /> • MTBE was not detected in the samples collected from wells MW- <br /> 1 through MW-5 and MW- <br /> UST <br /> ' Laboratory results of samples analyzed for petroleum hydrocarbons are summarized in Table 2 and <br /> Table 3 The laboratory reports(CTEL Laboratory ID 0209149-1 through-6),quality assurance and <br /> ' quality control (QA/QC)reports and chain-of-custody form is included in Appendix C <br /> 4.0. SUMMARY AND CONCLUSIONS <br /> Based upon the results of this quarterly monitoring event, AGE concludes <br /> • Ground water flow direction was inferred to be north-northeast at a gradient of <br /> approximately 0 0019 ft/ft The close proximity of the western UST area to the Stockton <br /> Deep Water channel may have a significant effect on the local flow direction and gradient <br /> • The highest concentrations of dissolved petroleum hydrocarbons were detected in samples <br /> collected from wells MW-1, near the former UST location <br /> • Benzene concentration in well MW-1 is significantly above the DHS's Maximum <br /> Contaminant Level of 1 0 µg/1 in drinking water <br /> • At the present time,neither the vertical extent nor the northern and western lateral extent of <br /> the dissolved hydrocarbons have been defined <br /> 5.0. RECOMMENDATIONS <br /> ' Based on the results of this investigation, AGE recommends <br /> ' • Continued quarterly ground water monitoring, the next monitoring event is scheduled for <br /> December 2002 <br /> • Conduct a well-head elevation survey as required in California Code of Regulations Title 23 <br /> • Installation of additional ground water monitoring wells for vertical and lateral delineation <br /> • of the dissolved hydrocarbons at the site <br /> Advanced Geo Environmental,Inc <br />