ARCHIVED REPORTS_XR0007928 - Laserfiche WebLink

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' Ground Water Momtoring and Extraction Events • The ground water remedial alternative originally selected for Former ' Tank Site #1 involved extraction of a fixed volume of hydrocarbon- containing ground water from existing monitoring wells Ground water was extracted from monitoring wells MW-4 and MW-5 during three ' events December 1993/January 1994, May 1994, and September 1994 The ground water extracted during each event was pumped into Baker ' tanks for temporary storage and subsequently transported via vacuum trucks to the City of Stockton Publicly-Owned Treatment Works (POTW) for direct discharge In October 1996, oxygen regenerating compounds ' (ORC) were introduced to the monitoring system to enhance natural biodegradation processes ' Ground water samples were collected routinely from the five wells installed at Site #1 between April 1991 through April 1998 The results of these monitoring events indicate that the gradient varies, probably due to tidal water level fluctuations in the nearby Deep Water Channel However, the overall flow direction over time has been generally ' consistent toward the south-southwest (away from the Channel) The ground water samples were analyzed for purgeable hydrocarbons and benzene, toluene, ethylbenzene, and xylenes (BTEX) constituents as well '. as general water quality parameters Analyses during the earliest monitoring events also included organic and total lead and ethylene dibromide Tables 3-1 and 3-2 present a summary of the quarterly ground ' water sample results for Site #1 The highest concentrations of TPH and BTEX detected since the October ' 1993 excavation were in ground water samples collected at monitoring wells MW-4 and MW-5 However, over time, the results of quarterly ' ground water samples collected from monitoring wells MW-4 and MW-5 have shown a steady decline in the concentrations of TPH (as gasoline and/or gasoline) and BTEX in ground water The last samples collected ' (April 1998) were non-detect for TPH (gasoline and diesel), however, an unknown hydrocarbon mixture, which probably reflects degraded gasoline and/or diesel, was detected at low concentrations TPH ' detections have been less than 1 mg/L at both locations since September 1997 ' Analyses were run in April 1998 for fuel oxygenates (methyl tert-butyl ether, tert-amyl methyl ether, 2-methyl-2-propanol, diisopropyl ether, and ethyl tert-butyl ether) As shown in Table 3-1, these fuel oxygenates were ' not detected in any of the wells at Site #1 3-4