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5 1 30 May 1997 AGE-NC Project No 95-0121 Page 3 of 4 32 LABORATORY RESULTS OF GROUND WATER SAMPLES I x ' I TPH-g was detected in water samples collected from wells MW-I,through MW-4, and MW-7 at ' concentrations as high as 11,000 µg11 (micrograms per liter or parts per billion ppb) TPH-d was detected in ground water samples collected from MW-I through MW-9 at concentrations as high as '+ 4,900 ppb However, the laboratory reported that the detection of TPH-d had a non diesel' chromatogram pattern and may have been the result of gasoline interference in wells MW-1 through MW-4, heavier petroleum hydrocarbons (oil) in MW-5, MW-6 and MW-9, and a combination of gasoline and heavier hydrocarbons interference in MW-�7 and MW-8 I � I BTE&X constituents were detected in water samples from wells N4W-1 through MW-4, MW-7, and MW-8 at concentrations as high as 3,500 ppb (benzene, MW-2) MTBE was detected iri'samples from MW-2 and MW-5 at concentrations up to 140 ppb ,1 The analytical results for ground water samples are summarized in Table 2 -Analytical Results of IGround Water Samples The laboratory report (Castle Analytical Laboratory Reference No 1029) and chain-6f-custody forms are presented in Appendix B 4.0 CONCLUSIONS'& RECOMMENDATIONS 9 , 1 41 CONCLUSIONS , I Based upon data collected during the February 1997 monitoring, AGE concludes the following - , 2 • Ground water flow direction and gradient have remained relatively constant at the site over ' the past two years Monitoring wells MW-6 and MW-9 continue to be up-gradient of the former UST area, MAV-8, MW-4 and MW-5 continue to be down-gradient 1 • The greatest concentrations of dissolved petroleum hydrocarbons continues to be in the area - of wells MW-1 through MW-4, near the"core" of hydrocarbon-impacted soil 1 • Concentrations of benzene detected ui wells MW-1 through MW-4, MW-7, and MW-8 were above the State of California Maximum Contaminant Levels (MCLS) for drinking water at 1 0µg11 ' • Concentfations of toluene detected in wells MW-Faizd MW-3 were above the MCL for _ drinking water af.150,ugll , • Concentrations of MTBE were detected in wells MW-2 and MVV-5 MTBE,is a widely used gasoline additive (octane enhancer) that began use in California during the late 1970's and. , early 1980's MTBE is very water soluble, and appears to have very slow biodegradation rates, } in ground water The detection of MTBE 1s suggestiVe that a leak source may have occurred 1' r Y I t r '