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Beacon Station No.474 January 10,2000
<br /> Stockton California Groundwater Monitoring Report
<br /> the volatile aromatics benzene, toluene, ethylbenzene and total xylenes (BTEX); the seven
<br /> oxygenated fuel additive compounds methyl tertiary butyl ether (MTBE), di-isopropyl ether
<br /> (DIPS), ethyl tertiary butyl ether (ETBE), tertiary amyl methyl ether (TAME), tertiary butyl
<br /> alcohol (TBA), methanol and ethanol; and the lead scavenger compounds 1,2-dichloroethane
<br /> (ethylene dichloride or EDC) and 1,2-dibromoethane (ethylene dibromide or EDB) utilizing
<br /> Environmental Protection Agency (EPA) Method 8260B. Laboratory analytical results are
<br /> summarized in Tables 1 and 1 a. Copies of the laboratory reports and chain-of-custody are
<br /> included as Attachment C.
<br /> Conclusions
<br /> Water-level data collected by Doulos on December 10, 1999 was used to construct the
<br /> Groundwater Contour Map (Figure 2). Deeper monitoring wells with submerged well
<br /> screens (wells MW-I, MW-2 and MW-3) were not utilized for creating the groundwater
<br /> contour map. The average depth-to-water for the wells was approximately 56.60 feet below
<br /> surface grade (bsg). Water levels have decreased approximately 0.08-foot since the last
<br /> monitoring in August 1999. The flow direction at the time of this sampling was generally
<br /> toward the south-southeast beneath the site, with an average gradient of 0.001 foot / foot.
<br /> The flow direction beneath East Main Street at the time of sampling was toward the north
<br /> from a groundwater"high" beneath the street area.
<br /> . Data collected from this sampling event was used to construct a Benzene Isoconcentration
<br /> Map (Figure 3). Concentrations of benzene were not detected in the groundwater samples
<br /> collected from monitoring wells MW-1, MW-3, MW-5, MW-7, MW-8, and MW-9.
<br /> Detectable concentrations of benzene were reported in water samples collected from wells
<br /> MW-2, MW-6, VW-I, and VW-4. Dissolved benzene concentrations have decreased in
<br /> wells MW-2, MW-5, MW-8, and VW-I, while increasing in wells MW-6 and VW-4 since
<br /> the August 1999 sampling event.
<br /> Concentrations of the fuel oxygenates MTBE, DIPE, ETBE, TAME, TBA, methanol and
<br /> ethanol were not detected in the groundwater samples collected from monitoring wells MW-
<br /> 1, MW-2, MW-3, MW-5, MW-6, MW-9, VW-I and VW-4. Detectable concentrations of
<br /> MTBE were reported in water samples collected from well MW-7. A detectable
<br /> concentration of TBA was reported in the water sample collected from well MW-8.
<br /> Concentrations of the lead scavenger compounds EDC and EDB were not detected in the
<br /> groundwater samples collected from monitoring wells MW-1, MW-2, MW-5, and MW-8.
<br /> Detectable concentrations of EDC were reported in water samples collected from wells
<br /> MW-3, MW-6, MW-7, MW-8, MW-9, VW-1, and VW-4. Detectable concentrations of
<br /> EDB were reported in water samples collected from wells MW-6, VW-1, and VW-4.
<br /> i
<br /> gmr99.Q4
<br /> Job No. 1474.42 2 HORIZON ENVIRONMENTAL INC.
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