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13 October 1998 <br /> AGE-NC Project No. 95-0185 <br />' Page 3 of 4 <br />' MW-4 at concentrations of 6,100 parts per billion: ppb (reported as micrograms per liter), 220 ppb <br /> and 23,000 ppb,respectively.TPH-g was detected in the ground water samples from well MW-1 and <br /> well MW-4 at concentrations of 92 ppb and 230 ppb, respectively. Benzene was detected in the <br />' sample collected from well MW-1 at a concentration of 0.55 ppb. <br /> MTBE and TBA were detected by EPA method 8260m in the samples collected from the monitoring <br /> wells MW-1,MW-2 and MW-4.Tert butanol was detected in the sample collected from wells MW-1 <br /> at a concentration of 7.6 ppb; MTBE was detected in wells MW-2 and MW-4 at concentrations of <br /> 1.7 ppb and 1.1 ppb, respectively. <br /> Analytical results of ground water samples are summarized in Table 2 for analyses by EPA Methods <br /> 8015m and 8020, and in Table 3 for analysis by EPA Method 8260m. The laboratory report (MAI <br /> ' Laboratory I.D. Nos. 90464 to 90467), quality control and quality assurance data and chain-of- <br /> custody form are included in Appendix B. <br /> 4.0. SUMMARY AND CONCLUSIONS <br /> The following conclusions were drawn from the results of this investigation: <br /> ' Ground water elevations have decreased an average 0.64 feet on the site since the last <br /> quarterly monitoring event. <br /> ' Concentrations of TPH-g have fluctuated over a wide range in wells MW-1 and MW-4. <br /> TPH-d concentrations have decreased over the last quarter in well MW-2 to less than <br /> detectable concentrations,but have increased slightly to moderately in well MW-3 and MW- <br /> 4.. <br /> • BTEX concentrations have generally declined in samples collected from wells MWA and <br /> ' MW-4 and were not detected, as usual, in wells MW-2 and MW-3. <br /> • Benzene was detected in only one ground water sample at a concentration of 0.55 ppb and <br /> ' MTBE was detected in two.ground water samples at a maximum concentration-of 1.4 ppb. <br /> These concentrations are less than the current State of California maximum contaminant <br /> level or action level set for these compounds. <br /> • Well MW-2 appears to be located at the southern edge`ofthe dissolved TPH-d plume and-- <br /> monitoring'well MW-3 lies near the western margin of the plume. <br /> Advanced GeoEnvironmental,Inc. <br /> 1 <br />