|
Beacon Station No.474 October 28, 1999
<br /> Stockton California Groundwater Monitoring Repo
<br /> total xylenes (BTEX); the seven oxygenated fuel additive compounds methyl tertiary butyl
<br /> ether (MTBE), di-isopropyl ether (DIPE), ethyl tertiary butyl ether (ETBE), tertiary amyl
<br /> methyl ether (TAME), tertiary butyl alcohol (TBA), methanol and ethanol; and the lead
<br /> scavenger compounds 1,2-dichloroethane (ethylene dichloride or EDC) and 1,2-
<br /> dibromoethane (ethylene dibromide or EDB) utilizing Environmental Protection Agency
<br /> (EPA) Method 8260B. Laboratory analytical results are summarized in Tables 1 and 1 a.
<br /> Copies of the laboratory reports and chain-of-custody are included as Attachment C.
<br /> Conclusions
<br /> Water-level data collected by Doulos on August 30, 1999 was used to construct the
<br /> Groundwater Contour Map (Figure 2). Deeper monitoring wells with submerged well
<br /> screens (wells MW-1, 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 56.68 feet below
<br /> surface grade (bsg). Water levels have decreased approximately 2.18 feet since the last
<br /> monitoring in June 1999. The flow direction at the time of this sampling was generally
<br /> toward the south beneath the site, with an average gradient of 0.003 foot/foot. The flow
<br /> direction beneath East Main Street at the time of sampling was toward the north from a
<br /> groundwater"high" along the northern site boundary.
<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-7, and MW-9. Detectable
<br /> concentrations of benzene were reported in water samples collected from wells MW-2,
<br /> MW-5, MW-6, MW-8, VW-1, and VW-4. Dissolved benzene concentrations have
<br /> decreased in wells MW-6 and VW-4, while increasing in wells MW-2, MW-5, MW-8, and
<br /> VW-1 since the June 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-3, MW-5, MW-7, MW-8, MW-9, and VW-1. Detectable concentrations of MTBE
<br /> were reported in water samples collected from wells MW-2, MW-6, and VW-4. A
<br /> detectable concentration of DIPE was reported in the water sample collected from MW-2.
<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-5, and MW-8.
<br /> Detectable concentrations of EDC were reported in water samples collected from wells MW-
<br /> D, MW-3, MW-6, MW-7, MW-9, VW-1, and VW-4. Detectable concentrations of EDB
<br /> were reported in water samples collected from wells MW-2, MW-6, VW-1, and VW-4.
<br /> Recommendations
<br /> • Horizon recommends continued quarterly monitoring and to proceed evaluate and report on
<br /> the assessment work performed in October. In addition, Horizon recommends proceeding
<br /> with the remedial testing work at the site.
<br /> QMR99.Q3
<br /> Job No. 1474.42 2 HORIZON ENVIRONMENTAL INC.
<br />
|