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Shell Oil Products USA
<br /> Former Station, 1267Country Club Blvd, Stockton.
<br /> Page 2 of 3
<br /> EHD notes that approved work plans are guidelines to a site investigation, but that qualified
<br /> professionals in responsible charge of the field work, utilizing good professional judgement,
<br /> may modify the sampling program in response to field conditions to procure meaningful,
<br /> significant data.
<br /> With groundwater contamination present at 60' bgs and the sand roughly between 41 and
<br /> 47 feet bsg uninvestigated, this site investigation is incomplete and neither the lateral nor
<br /> the vertical extent of the groundwater plume can be considered as being defined. Further
<br /> investigation is required.
<br /> Due to operation of the USTs at this site during the time period that lead scavengers were
<br /> in wide use, the impact the release on groundwater with respect to the lead scavengers
<br /> must be fully characterized.
<br /> 1,2-Dichloroethane (1,2-DCA) has only been analyzed in the monitoring well samples for
<br /> one sampling event—the February 11,1999 event. Monitoring well sample "S-1" had
<br /> 4.55 µg/I, "S-2" was less than the 50 µg/I detection limit, and "S-3" contained 34.1 µg/I
<br /> 1,2-DCA as analyzed by EPA Method 8260. Additional 1,2-DCA analyses are required
<br /> from all the wells. SHELL is directed to sample all monitoring wells associated with this
<br /> site for 1,2-DCA on a quarterly basis starting with the next quarterly sampling event.
<br /> By EHD correspondence dated October 11, 1996, SHELL was directed to evaluate the
<br /> impact of the waste oil UST operated by SHELL. EHD required analysis of soil samples for
<br /> the priority metals Cd, Cr (III & VI), Pb, Zn, and Ni (ICRP or AA), oil and grease (Series
<br /> 5520 F, and /or C & D), chlorinated hydrocarbons (EPA 8010 for soil and 601/624 for
<br /> groundwater), and for PCB, PCP, PNA, and Creosote (EPA 8270), and analysis for the
<br /> analytes in groundwater samples if detected in soil. This requirement has not been met.
<br /> Further investigation is required.
<br /> In order to understand the relationship between the release at this site and the
<br /> groundwater impact in the shallow and deeper intervals beneath this site, SHELL is to
<br /> submit a Site Conceptual Model (SCM). As the site investigation progresses, SHELL is to
<br /> update the SCM and submit the revisions to EHD as soon as the data is available.
<br /> Once the subsurface groundwater flow characteristics are better understood and the extent
<br /> of the petroleum impact is defined, EHD can evaluate SHELL's consultant's conclusions
<br /> that "the oxygenates (including MTBE) detected in the site wells most likely originated at
<br /> the TOSCO station, located upgradient of the subject (SHELL) site."This may well be the
<br /> case, but to demonstrate this point, the SCM should show and characterize the TOSCO
<br /> release, the hydrogeological framework and the contaminant migration route(s).
<br /> To prevent any further confusion, EHD will now require this site to return quarterly
<br /> groundwater monitoring and reporting. In addition to 1,2-DCA, all six monitoring wells are
<br /> to have groundwater samples collected quarterly and analyzed for TPH as gasoline and
<br /> diesel, BTEX, Oxygenates (MtBE, TBA, DIPE, EtBE, TAME, methanol, ethanol) and at
<br /> least two consecutive quarters for waste oil constituents identified above. If after two
<br /> consecutive quarterly data indicate a waste oil constituent is not detected at LUFT protocol
<br /> detection limits, SHELL may request that constituent analysis to be discontinued. EHD will
<br /> notify SHELL if approved.
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