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08 May 1997 AGE-NC Project No 96-0173 ' Page 3 of 4 3 2 ANALYTICAL RESULTS OF GROUND WATER SAMPLES I Dunn the April 7 _ - g p 1 199 sampling, T'PH-g was detected in samples collected from MW 1 through MW 4 at concentrations as high as 140,000 parts per billion(ppb, reported as microgi azns per liter), TPH- d was detected in samples collected from MW-1 through MW-4 at concentrations as high as 36,000 ppb, however, further laboratory chromatogram review suggested that detection of TPH-d was ' probably the result of gasoline interference BTEX were detected in ground water samples collected from wells MW-1 through MW-4 Benzene was detected in MW-1 through MW-4 at concentrations as high as 17,000 ppb, toluene was detected at concentrations as high as 13,000 ppb, ethylbenzene was detected at concentrations up to 3,700 ppb,xylenes were detected at concentrations as high as 16,000 ppb Analytical z esults of TPH-g and BTE&X in ground water are summarized in Table 2 -Analytical Results of Gi ound Water Samples MTBE was detected in a ground water sample collected at monitoring well MW-4 at a concentration of 56 ppb MTBE was not detected from MW-1 through MW-3 for the third straight quarterly ground water monitoring event The laboratory report (CAL Reference Number 1078) and chain-of- custody forms are presented in Appendix B 4.0 CONCLUSIONS/SUMMARY Based on the results of ground water monitoring in April 1997, AGE has concluded the following • From December 1996 to April 1997, ground water flow direction rotated approximately 85 degrees from northeast to northwest • Laboratory analysis of groundwater samples indicated that from December 1996 to April 1997, petroleum hydrocarbon constituents generally decreased in wells MW-1, MW-2 and MW-4, but generally increased in MW-3 However, because only a limited number of Iquarterly sampling events have been performed to date, a trend can not be discerned • Concentrations of benzene, toluene, ethylbenzene and xylenes detected in MW-3 and MW-4 were above the State of Cahfornaa Maximum Contaminant Levels (MCLs) for drinking water of 1 0 ppb, 150 ppb, 700 ppb and 1750 ppb, respectively Concentrations of benzene, toluene and ethylbenzene were above MCLs in MW-1 while benzene, toluene and xylenes were above MCLs in MW-2 • The greatest concentrations of dissolved petroleum hydrocarbons continues to be in the area of well MW-3, down-gradient of the former UST area • MTBE, detected in MW-4, exceeded the State of California Action Limit (AL) of 35 ppb Therefore, it appears that MTBE could be present at the site above the ALs but have not been