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' 22 March 1999 . AGE-NC Project No 95-0144 Page 4 of 5 Twelve volatile organic compounds were detected at the site at concentrations as high as 250 ppb ' (1,2,4-tnmethylbenzene,MW-21A) ' During the February 1999 monitoring event, MTBE was detected by EPA Method 8260m in MW- 12,MW-19A and MW-19B, at concentrations of 10 ppb, 13 ppb and 14 ppb, respectively Other oxygenates were not detected at the site during the February 1999 sampling event. Trichloroethene (TCE)was detected in MW-1, MW-20A, MW-20B, MW-21A and MW-21B at concentrations of 4 0 ppb,2 6 ppb, 9 3 ppb,21 ppb and 7 9 ppb, respectively Tetrachloroethene was detected in MW- 21A at a concentration of 61 ppb. State of Califorrua drinking water Maximum Contaminant Levels ' (MCL) for PCE and TCE have been set at 5 ppb Eleven other constituents,without MCLs were detected by EPA Method 8260 ' Analytical results for volatile organic compounds and oxygenates are summarized on Table 5 The laboratory report(MAI Laboratory I D Nos 98243-98252 and 02766-02780) and chain-of-custody forms are included in Appendix B le 4.0. SUMMARYICONCLUS)IONS I Based upon data collected from the site, AGE concludes 1 Ground water elevation decreased slightly at the site dunng the previous two quarters Ground water remained above the screened interval in nine wells at the site Ground water elevations in wells completed beneath the clay layer were nearly two feet lower than wells completed within first ground water ' • TPH-d continues to be detected in the ground water samples collected from MW-13 at slightly above the laboratory reporting limit of 50 ppb The detected hydrocarbons may represent the down-gradient extent of water impacted from the former UST No 8 • Petroleum hydrocarbons were not detected In water samples collected from MW-4, MW-5, MW-8, MW-11, and MW-18 Hydrocarbons were detected at near the reporting limit in wells MW-1, MW-2, MW-12 and MW-13 • Petroleum hydrocarbons were detected in each of the six new monitoring wells installed near the former UST No 8 location during both monitoring events The highest concentrations of hydrocarbons have remained in MW-21A and MW-21B • Only low concentrations of MTBE or TBA have been detected at the site ' Advanced GeoEnvironmental,Inc