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<br /> ` Mr .Teff Wong
<br /> July 18, 2001
<br /> • Page 2 of 3
<br /> suggests that the shallow aquifer is being influenced by pumping in the water supply well, or that some
<br /> vertical leakage of the shallow aquifer is occurring through the water supply well Groundwater
<br /> monitoring data are summarized in Table 1 and field data sheets are included in Attachment A
<br /> Prior to sampling, monitoring wells MW 1 through MW9(B) were purged of at least three well casing
<br /> volumes During the purging process the physical parameters of temperature, pH and electrical
<br /> conductivity were measured Samples were collected after the physical parameters stabilized and
<br /> water levels in the wells recovered to at least 80% of their initial levels Purged groundwater was
<br /> contained in appropriately labeled DOT-approved 55-gallon drums, which were stored on-site Purge
<br /> logs are included in Attachment A Purged groundwater was removed by American Valley Waste Oil
<br /> for disposal at Seaport Environmental in Redwood City A copy of the Non-Hazardous Water
<br /> Transportation Form is included in Attachment A
<br /> GROUNDWATER ANALYSES
<br /> Groundwater samples were delivered under chain of custody protocol to Argon Laboratories (FLAP
<br /> #2359) for analysis of TPHg by EPA method 8015M, BTEX by EPA method 8020, and oxygenated
<br /> gasoline additives including methanol, ethanol, EDB and 1,2-DCA, by EPA method 8260B
<br /> Detectable concentrations of dissolved petroleum hydrocarbon constituents were detected in wells
<br /> MW1, MW2, MW3, MW4, MW5, MW6, and MW9(B) TPHg was detected in wells MW1, MW2,
<br /> MW3, MW4, and MW6 at 170,000 parts per billion (ppb), 2,000 ppb, 1,100 ppb, 560 ppb, and 150
<br /> ppb, respectively Benzene was detected in wells MW 1, MW2, MW3, MW4, and MW6 at 6,600
<br /> ppb, 25 ppb, 10 ppb, 34 ppb, and 7 0 ppb, respectively MTBE was detected in wells MW1, MW3,
<br /> MW4, MW5, and MW6 at 18,000 ppb, 1,100 ppb, 26,000 ppb, and 3,700.ppb, respectively No
<br /> petroleum hydrocarbon constituents were detected in shallow monitoring wells MW7 or 1\4W8
<br /> Deep well MW9(B) contained toluene, ethylbenzene, and xylenes at 0 6 ppb, 0 6 ppb, and 1 8 ppb,
<br /> respectively No TPHg, benzene, or MTBE was detected in the well MW9(B) Groundwater
<br /> analytical results are summarized in Table 2 Laboratory reports and chain-of-custody
<br /> documentation are included in Attachment B The estimated extent of benzene and MTBE in the
<br /> shallow aquifer is presented on Figures 3 and 4, respectively
<br /> SUMMARY
<br /> Groundwater levels in the shallow aquifer tell an average of 0 29 feet between February 2001 and
<br /> May 2001 Groundwater flow beneath the site was largely influenced by an apparent groundwater
<br /> depression near well MW4
<br /> Elevated levels of dissolved gasoline constituents are present in wells MW 1, MW2, MW3, MW4, and
<br /> MW6 Time versus concentration plots of constituents of concern (TPHg, benzene, MTBE) in wells
<br /> MW 1 through MW5 are included in Attachment C No TPHg, benzene or MTBE was detected in the
<br /> deeper aquifer well (MW9(B)), although toluene, ethylbenzene, and xylenes were detected at very low
<br /> levels
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