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KLEINFELDER
<br /> . routes of exposure were improbable or incomplete and requested that SJCEHD
<br /> 1 consider granting closure SJCEHD directed additional site investigation be performed
<br /> in their January 9, 2004 response letter The February 20, 2004 Subsurface
<br /> Investigation Work Plan, which proposed details of site work, was submitted to and
<br /> ' approved by SJCEHD
<br /> ' In June 2004, PSC performed the additional subsurface investigation Continuous soil
<br /> lithology, from ground surface to a depth of 100 feet was evaluated at CPT-A boring
<br /> location using an electronic cone penetrometer system Seven CPT borings (CPT-A, -
<br /> B, -C, -D, -E, -F, and -G) were to the vicinity of the former gasoline USTs Soil samples
<br /> were collected from the borings and were submitted for the analysts The analytical
<br /> parameter list includes benzene, toluene, ethylbenzene, xylenes, (BTEX), total
<br /> petroleum hydrocarbons as gasoline (TPH-G), the oxygenate analytes of tertiary butyl
<br /> ' alcohol (TBA), methyl tertiary butyl ether (MTBE), dt-isopropyl ether (DIPE), ethyl
<br /> tertiary butyl ether (ETBE), and tertiary amyl methyl ether (TAME), 1,2-dichloroethane
<br /> (1,2-DCA), and ethylene dibromide (EDB), using test method SW-846 / 8021/8260B
<br /> Groundwater samples were collected at three of the boring locations and were
<br /> submitted for the same analytical parameters The CPT soil investigation indicated that
<br /> the residual petroleum-hydrocarbon impact that remained after the 1987 excavation was
<br /> ' sufficiently addressed by the soil-vapor-extraction system that operated at the site and
<br /> that the mass-of-impact in the vadose zone was negligible The CPT groundwater
<br /> investigation was used to assess the vertical extent of petroleum impact at the site
<br /> Based on the data obtained, PSC conservatively estimates that the vertical extent is -
<br /> approximately 90 feet bgs Although, the relatively higher petroleum concentrations
<br /> appear to occur at depths shallower than 70 feet bgs PSC reported the results from
<br /> the investigation in the June 2004 Site Investigation Report Additionally, groundwater
<br /> samples were collected from all of the on-site monitoring wells and two nearby private
<br /> wells This groundwater-monitoring event indicated that the lateral extent of impacted
<br /> groundwater is largely contained within the Earthgrain's property boundaries In
<br /> addition, historical and current decreases of petroleum impact to groundwater have
<br /> been observed, which are likely due to natural degradation and the use of air sparging
<br /> as a remedial method Based on the findings of this investigation, PSC recommended
<br /> one more groundwater-monitoring event be performed, to which groundwater samples
<br />' would be collected from wells MW-1, MW-5, MW-7, MW-8, MW-10, MW-11, MW-12,
<br /> SPA , SP-2, SP-4, SP-6, PZ-1 , and PZ-2 Although, the analytical parameter of EDB
<br /> would not be performed, since it was not detected during the investigation Upon
<br /> C23-484517-BOOISAC5R540 Page 4 of 14 August 11, 2005
<br />' Copyright 2005 Weinfelder,Inc
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