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1 <br /> Regarding Tank 4, the former aviation fuel tank located at the west end of the District's facility, <br /> TPH-G was not detected in soil samples collected from 8 and 12 feet below grade in boring HP- <br /> 2 However, low concentrations of TPH-D were found in both soil samples. The presence of <br /> TPH-D at this site, even at the low concentrations found, continues to be inconsistent with the <br /> historical use of the tank for aviation fuel It is possible, though speculative, that the traces of <br />' TPH-D found at this tank site (as well as those found at Tank 3) may be an artifact of the tank <br /> removal program. All of the tanks at the site were removed at essentially the same time using <br /> the same excavation equipment While there are no records which show the sequence of the <br />' tank removal, there is the possibility that minor cross contamination between tank areas may <br /> have caused the current anomalous TPH-D findings at the two gasoline tank areas <br />' The groundwater sample taken with the hydropunch tool at the Tank 4 site also showed a very <br /> low concentration of TPH-D (1 3 mg/L) along with a trace of toluene and xylene (5.0 and 2 6 <br /> µglL respectively) The TPH-D results are no doubt related to the soil TPH-D issue discussed <br />' above while the toluene/xylene presence is likely related to the historic use of the tank for <br /> aviation fuel However, in ether case, the concentrations found are far below a level that would <br /> suggest further action The Federal MCL in drinking water for toluene and xylene are 1,000 <br /> and 10,000 µglL respectively while California drinking water standards list an action level for <br /> toluene of 100 µglL and an MCL for xylene of 1,750 mg/L. <br />' Given the low concentrations of hydrocarbon parameters in the area of Tank 4, WESTON <br /> recommends no further investigative or remedial action. <br /> 1 <br /> SM\RPTSWCMVCDI MX <br /> 1 <br /> 1 <br /> 8 ion&%. <br />