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1 <br /> INTERIM SOIL AND GROUNDWATER <br /> • CORRECTIVE ACTION SUMMARY REPORT <br /> 8940 W Walnut Grove Road, Thornton, CA <br /> 4.2 Soil Excavation and Sampling <br /> Ground Zero personnel supervised excavation and confirmation sampling between March 7 and March <br />' 15, 2000 Approximately 2,500 cubic yards of contaminated soil and approximately 650 yards of clean <br /> overburden was initially excavated by Oil Equipment Service within the vicinity of the former USTs <br />' The area excavated was irregular in shape, and roughly measured 85 feet by 127 feet The depth of the <br /> excavation did not exceed 15 feet bgs <br /> Excavation began by removing overburden soil along the northeastern corner of the existing tank pit <br />' The average thickness of overburden was approximately 4 feet Sporadic occurrences of petroleum <br /> hydrocarbon odor and/or soil discoloration were noted within the upper 8 feet of the excavation, but <br />' the primary zone of soil contamination appeared to occur beginning at a depth of approximately 10 feet <br /> bgs <br /> 1 <br /> Soil was excavated both laterally and vertically until lack of odor and significant field meter <br /> readings from a flame ionization detector (FID) indicated that impacted soil had been adequately <br /> removed in all quadrants of the prescribed area Impacted soil appeared to be limited to the upper <br />' 15 feet of soil Field observations indicated that siguficantly impacted soil remained along the <br />' southwestern and eastern boundaries An exploratory trench was then advanced along the <br /> southwestern region in order to estimate lateral and vertical extent to the southwest "Clean" <br /> overburden, "potentially contaminated" soil, and "contaminated" soil were segregated into <br /> separate soil piles Contaminated material was stockpiled on and covered by 6-mil plastic <br /> sheeting <br /> A brief workplan addendum submitted to PHS/EHD on March 14, 2000 recommended excavating the <br /> remaining contaminated soil along the southwestern and eastern portions of the existing pit PHS/EHD <br /> Iconcurred with the recommendation and approved the workplan on March 14, 2000 <br /> Excavation proceeded laterally and vertically until hydrocarbon odor and FID readings indicated that <br /> �) impacted soil had been largely removed Approximately 450 additional cubic yards of clean <br /> overburden and 150 cubic yards of contaminated soil were removed in these areas The soil was <br /> C Oata1GROUNDZEIMANSER\Reportstisodexsum dm 4 <br />