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<br /> 13336 East Highway 88 2 1'October 1998
<br /> Lockeford, San County n Joa ui '.'r.
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<br /> concentrations of TPHg and BTEX coustituents"tdi a total'de'ff'of the soil borings. Tlie soil samples"" '
<br /> contained contaminants at concentrations 'up to 3200 mg/Kg (ppm) for TPHg; and 6.7 mglKg for
<br /> benzene. ., _ yj I: !'
<br /> On 29 December 1997, SJCEHD sent a Case Closure Summaryand site°chronology to the Regional
<br /> Board,for the site. Regional Board staff did not concur with the NEAR decision by SJCEHD, and in the
<br /> 13 February.1998 letter, Ms. Anderson requested that the vertical extent of contamination be determined
<br /> belowthe the gasoline#UST-�excavation, and `that a groundwater sample be collected to determine if
<br /> petroleum contamination had impacted groundwater.
<br /> In.orderyto determinetthe'vertical extent. of,soil`contamination, and,to evaluate.;if�site activities'have
<br /> impacted 'groundwater,,one,soil'boring was advanced 100,feet.bgs between 26:Jane--and_.1 July'1995:_
<br /> Sixteen soil samples and one grab groundwater sample were.submitted to a State certified laboratory and
<br /> analyzed for,TPHg; BTEX and the`fuel.oxygenates:" The analytical`results of the soil samples indicate
<br /> ` S - ...F r ..,,t c ^! .". mow. .i '� �. ,I '1 e. -,NT ,
<br /> that soil contamination, in the area of the UST excavation, extends to approximately 45 feet bgs for
<br /> TPHg,and.to'60 feet.bgs for benzene.`The highest concentrations of TPHg and benzene'detected'at the .
<br /> site to date, 3;300 mg/Kg', and 13 rn respectively;'were detected in'this boring at approximately 40'
<br /> feet 7bgs.- k Samples'were analyzed bye Toxicity Characteristic Leaching'Procedureµ(TCLP)''with the '
<br /> highest: leacMbleg'benzene concentration' of 460�'gg/L— detected- -in'_the' sample collected 'from
<br /> approximately 39;to 40 feet bgs:"The single groundwater sample was analyzed and is reported to contain
<br /> 210µglL(ppb) TPHg,4:3 gg/L benzene and 16.0 µg/L toluene
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<br /> The 13 July '1998 report,'Excavation For One Soil Boring, -prepared by Geo$ g- included a map
<br /> presenting the regional groundwater gradient and flow direction and one boring log depicting the
<br /> geology underlying the site. The calculated hydraulic gradient and groundwater flow direction are
<br /> derived from Department of Water Resources DWR well records for three domestic/supply wells located
<br /> 3000 feet or more east of the site. The information provided is not valid,,because the depth to water
<br /> measurements'for each'1 .well.,aretfrom"'three ,different years.(December 1970, November`1975, and
<br /> November 1986).'This,inforrriation is not acceptable'to"determine the groundwater gradient and flow
<br /> direction. The boringlog, however, is'useful,by providing data for site geology.
<br /> The highest,concentrations of soil'contamination are present. in clayey sand and`silty sand, between
<br /> 22 and 42,feet bgs."Between 42-and 60'fee tbgs, sandy and silt are present;with silty sand'and`clayey'
<br /> .sand logged between"'60 feet and approximately 871feet bgs. First groundwater was:encountered'in the'
<br /> boring,B7 in'sandy'silt, at 96.4'feet bgs on`1'July 1998
<br /> ..a fi�..tr Fr,� r.:s+7��.yr.:I'�.�dti �.,.,v ...w:". ,.. .. ,.. K"v. - -. # ...y. a,.r. '.-..,. ' •..ten, t. .�.� .r.JC� � �
<br /> Soil contamination is adequately defined in the vicinity of:the former waste oil tank.-with the bulk of the'
<br /> contamination remaining in the soil`between 7.5 and 9 feet beneath the former UST. Some leaching
<br /> of cantaminants�has occurred,`with:lowconcentrations of ethylbenzene�andxylenes adsorbed to soil at`
<br /> '. Vii-
<br /> 16 feet bgs. ,
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<br /> Soil contamination is defined laterally to approximately 20 feet bgs°in-the vicinity of the former gasoline
<br /> USTs.,Below 20 feet bgs, the .lateral extent of soil contamination is not defined. The soil sample
<br /> collected xbetween 25;and 26 feet bgs from.boring'B'1,contained,TPHg and BTEX contamination. TNN
<br /> total depth sof B 1,is 30 feet bgs,4howe ver',ho soilasample 'W"as submitted for analysis below'26 feet bgs,
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