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<br /> Mr. Kyle Christie
<br /> October 13, 1989
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<br /> Table 2 summarizes the benzene concentrations for the six quarterly sampling events, May
<br /> 1988 through August 1989. This table shows that
<br /> well over time. Benzene concentrations in wells E benzene concentrations have varied in each
<br /> spring Quarter 1989 (May 30, 31, I989). -S, E-8, and E-I2 have increased since the
<br /> Monitoring well E-10 has shown a decrease in
<br /> benzene concentrations since the spring quarter 1989. Benzene concentrations in wells BHD-1,
<br /> E-2, and E-11 have decreased since the spring quarter 19$9. Benzene concentrations in wells
<br /> E-4. E-7, and E-9 have decreased since they were last sampled in the winter quarter of 1989
<br /> (February 27, 28 and March 2, 1989). A contour crap of August 22, 23, and 24, 1989,
<br /> benzene concentrations in groundwater is shown on Figure 1.
<br /> The concentration of ethylbenzcne is above the DHS MCL in monitoring well BHD-1. The
<br /> concentration of toluene is above the DHS Drinking Vater Action Level in well
<br /> BHri-1 wells
<br /> BHD-1, E-S, and E-10. The concentration of xylene is above DHS MCLS in monitoring well
<br /> E-10, and is approaching the DHS MCL in well E-5.
<br /> Groundwater Flow
<br /> Groundwater levels at the site are Iwing measured in each well on a biweekly basis using an
<br /> electronic water level indicator. The levels are measured relative,:o Mp-of-casing elevations
<br /> in order to determine groundwater elevations and monitor possible changes in flow direction.
<br /> Since Iate April 1988, the groundwater flow direction has been influenced by the recovery
<br /> t ( � system. Sometime in April 1989, the recovery pump stopped operatirg. The malfunction was
<br /> detected in rune 1989, and the recovery system is currently being repaired. Figure 2 is a
<br /> water level contour map for August 22, 1989, The figure shows that
<br /> returned to static conditions. During static conditions, groundwater has almost
<br /> ground�vater flows to she northeast.
<br /> Conclusions fob
<br /> Groundwater samples collected daring thr. sum ter quarter 1989, show that benzene Concentra-
<br /> tions have increased in wells E-S, E-$, and E 12 since the spring quarter I989. This increase could be the result of off-site contamination that was pulled toward the site by the recovery
<br /> system. Though the recovery system has not been operating since April 1989, and
<br /> groundwater has returned to nearly static ccnditions, the groundwater gradient is relatively flat, j-,,; <''" -
<br /> Consegnently, contamination pulled from another source during operation of the recovery 1r�i
<br /> system could stili remain. Also, a Chevron station located north of the site, across Benjamin
<br /> Holt Drive, has a confirmed soil-contamination and suspected groundtivater-contamination /00
<br /> problem and could potentially have affected the site during recovery operations. r'.i c;,.t.�, c G./<<
<br /> Groundwater samples collected during the summer quarter 1989, show that benzene
<br /> concentrations have decreased in wells BHD-1, E-2, E-4, E-7, E-9, and E-10 since the spring
<br /> quarter 1989. This could be the result of two factors: (1) decreased solubilization.of product
<br /> from the soil. Product trapped in pore spaces and adhering to soil particles in the capillary
<br /> fringe zone is not being released to the groundwater as water levels de line and (2) product
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<br /> that was once being pulled inward by the recovery system is now influenced by static
<br /> groundwater flow conditions, and is moving outward.
<br /> BROWN ARID CALDWELL
<br /> 723 S STREET SACRAMENTO•CALIFORNIA 95614'n792•a976114i-0723
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