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<br /> Site Background Information: California Stop
<br /> Page 6 of 7
<br /> 32 feet bsg in boring CPT-1. Fine-grained material (silt, clayey silt, silty clay, and sandy silt)
<br /> was generally identified from 32 feet bsg to approximately 72 feet bsg, where an
<br /> approximately 5-foot thick layer of sandy material (sand, silty sand, and sandy silt) was
<br /> encountered. From 77 feet bsg to the total depth of CPT-1 (100 feet bsg), fine-grained
<br /> material was encountered.
<br /> HYDROCARBON IMPACTED SOIL
<br /> Since 2002, approximately 65 soil samples were collected from the site for analyses of
<br /> various fuel oxygenate and petroleum hydrocarbon constituents. The highest
<br /> concentrations of MTBE(340 mg/kg),TPH-g(10,000 mg/kg), and compounds benzene(17
<br /> mg/kg), toluene (340 mg/kg), ethylbenzene (230 mg/kg) and xylenes (1,300 mg/kg)
<br /> (BTEX) detected at the site were reported in the 2002 dispenser upgrade soil samples
<br /> collected at shallow depths of between 0.5 feet and 2.5 feet bsg.
<br /> The lateral extent of soil contamination appears to be defined on site as there were no
<br /> target analytes detected in borings B7 through B9 located up-gradient, across the street
<br /> from the former UST area, or in borings MW4, MW6, and MW7 located east of the former
<br /> UST area.
<br /> The vertical extent of soil contamination may not be defined in the area directly surrounding
<br /> the UST and dispensers, as contamination is present in the location of 131 through B3 at
<br /> a depth of 25 feet bsg and in B4 at a depth of 20 feet bsg. The vertical extent of impacted
<br /> soil should be further evaluated near the dispenser area.
<br /> HYDROCARBON IMPACTED GROUNDWATER
<br /> Between August 2006 and February 2008, the most impacted groundwater monitoring well
<br /> at the site was well MW-1. During this time period, constituents MTBE, TPH-g, benzene,
<br /> TAME, and 1,2-DCAwere reported at maximum concentrations of 910,000 pg/I, 1,200,000
<br /> pg/I, 580 pg/I, 720 pg/I and 16 pg/l, respectively, in groundwater samples collected from
<br /> well MW-1.
<br /> Between March 2008 and October 2008, TBA began to be reported in groundwater
<br /> samples and the magnitude of the groundwater plume appeared to shift from wells MW-1,
<br /> MW-2 and MW-6 (wells located south-southeast of the dispensers)to wells MW-3, MW-7
<br /> and, most significantly, to well MW-8. During this time period, constituents MTBE, TBA,
<br /> TPH-g, benzene,TAME and 1,2-DCA were reported as high as 400,000 pg/I, 210,000 pg/I,
<br /> 490,000 pg/l, 300 pg/l, 1,100 pg/I, and 7.5 pg/l, respectively, in groundwater samples
<br /> collected from well MW-8. At the time of the September 2009 groundwater sampling
<br /> events, the magnitude of the groundwater plume again shifted to well MW-1, as well as,
<br /> fidnmiced CeoLnvironrnental,Inc.
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