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9110 Thomton Road, Stockton, California
<br /> The Southland Corporation November 15, 1993
<br /> Page 2
<br /> Analysis of the groundwater monitoring data indicates that groundwater elevations in the monitoring
<br /> wells at the site have decreased approximately 1 2 feet since the previous quarter's monitoring (June
<br /> ' 30, 1993) As of September 29, 1993, the average groundwater elevation at the site was 32 5 feet
<br /> below mean sea level, and the average DTW at the site was 44 5 feet below grade
<br /> Since the groundwater levels at the site were first monitored in May 1986, the local groundwater
<br /> elevation has fluctuated seasonally and, in general, has steadily declined Groundwater monitoring
<br /> ' wells MW-2 through MW-4 and MW-10 were dry on September 29, 1993 Monitoring wells MW-6
<br /> and MW-12 are no longer in service, and at Southland's direction, monitoring wells MW-11 and
<br /> MW-14 are no longer being monitored or sampled The well completion data and current status of
<br /> ' the monitoring wells at the site are summarized in Table 2
<br /> A potentiometric surface map (Figure 2) was prepared using monitoring data collected on
<br /> ' September 29, 1993 The map indicates a groundwater flow direction generally to the east at a
<br /> gradient of approximately 0 002 foot per foot
<br /> MONITORING WELL SAMPLING AND ANALYTICAL RESULTS
<br /> On September 29, 1993, groundwater samples were collected from monitoring wells MW-9, MW-13,
<br /> MW-16 and MW-17A and on September 30, 1993, groundwater samples were collected from MW-1,
<br /> MW-5, MW-7, MW-8, MW-15A through MW-15C, MW-17B, MW-17C, and MW-18 through MW-20,
<br /> ' former pumping wells PW-1 through PW-3, and former recovery well RW-1
<br /> Samples were collected according to Groundwater Technology's SOPs Before sampling, at least 4
<br /> well-casing volumes of groundwater were removed from each well by hand bailing unless the wells
<br /> purged dry The groundwater was allowed to recover to at least 80 percent of the original static
<br /> water level before sampling The groundwater samples were collected using an Environmental
<br /> Protection Agency (EPA)-approved Teflon® sampler The samples were collected in
<br /> laboratory-supplied containers, preserved, labeled, and stored on ice Samples were transported
<br /> under chain-of-custody protocol to GTEL Environmental Laboratories, Inc , a California-certified
<br /> laboratory in Concord, California However, due to work overload, the samples were shipped from
<br /> Concord to GTEL in Wichita, Kansas Each sample was analyzed for benzene, toluene,
<br />' ethylbenzene, and xylenes (STEX), and total petroleum hydrocarbons-as-gasoline (TPH-G) using
<br /> modified EPA Methods 8020/8015
<br />' With one exception, the analytical results of the samples collected on September 30, 1993, reported
<br /> BTEX and TPH-G concentrations below method detection limits (MDLs) For the groundwater
<br /> sample collected from monitoring well MW-1, reported concentrations of BTEX were 0 6, 22, <1 0,
<br /> and 3 1 parts per billion [ppb], respectively Copies of the analytical laboratory reports are included
<br /> in Attachment 1 The historical TPM-G laboratory results for groundwater samples collected from the
<br /> GROUNDWATER
<br />' TECHNOLOGY
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