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a WORK PLAN FOR PRELIMINARY ASSESSMENT _ (former)Countryside Market 10848 Copperopolis Road 1.0 BACKGROUND I The property located at 10848 Copperopolis Road east of Stockton,California(Figure.1)was a- gasoline fueling station and convenience store known as Countryside Market until it was closed . in 1993. Two 1,000-gallon leaded gasoline tanks.were removed from the site'in March of that year by Stockton Service Station Equipment Co. Four soil samples were collected from beneath the tanks at a depth of 7.5 feet(Figure 2), and hydrocarbons and lead were.detected in all four samples(Table 1). A two-point composite sample of the excavated soil (approximately 50 yards) also contained low concentrations.of gasoline, ethylbenzene, and xylene. The excavated soil was subsequently returned to the excavation, and no further investigation was performed. - - t In 1995,the three family trusts that held the first mortgage on the property attempted to initiate an investigation to determine the impact to the site. Stockton Mortgage Co., acting as representative of the trutsts,retained J.J.Hob]itze11 and Associates(H&A)to conduct the investigation. H&A subsequently retained Upgradient Environmental to submit a workplan to San Joaquin County PHS/EHD.The plan was revised.in October 1995 as a result of further discussions between Stockton-Mortgage and PHS/EHD, and the work was performed on October 31, 1995. I H&A supervised the excavation work, which was performed by Stokely Construction using a' backhoe to re-open the excavation and stockpile the contaminated soil.The work was witnessed, by Mr. Steve Sasson of PHS/EHD and Dr.Victor Cherven of Upgradient.Near-surface soil was clean,without hydrocarbon odors, but gasoline odor became evident as excavation proceeded and organic vapor readings measured with a portable photo-ionization detector(PID)began to increase(Figure 3).By mid-afternoon,the depth had reached-13 feet and hydrocarbon lconcentrations were continuing to increase. Therefore, in consultation with Mr. Sasson,H&A terminated the investigation and directed the backhoe operator to obtain a scoop of fresh soil from { the floor of the excavation. After Upgradient Environmental collected a sample from the bucket, y the backhoe filled the excavation with,imported pea gravel and the excavated soil was transported G to REMCO in Richmond,California for treatment. Sample CM-I-13' was transported to Sequoia Analytical and analyzed for TPH-g and BTEX.The laboratory reported weathered gasoline in the Cb-C 12 range,with all analytes present except benzene(Table 1).Upgradient Environmental submitted a report of the investigation to PHS/EHD the following month.No further work was requested by Stockton Mortgage or H&A. 2.0 Proposed Assessment The'new property owner, Mi.Phillip Henry, has been directed by Mr. Marty Hartzell at the Regional Water Quality Control Board to conduct a preliminary drilling investigation of the extent of soil contamination. In further discussion,Mr. Hartzell has recommended drilling one boring to groundwater to determine whether it has been impacted. Figure 2 shows approximate locations of four proposed borings. The first boring will be drilled through the former tank excavation to determine the maximum vertical extent of soil contamination. The estimated depth of this boring is 50 feet, but will depend on visual observations made during drilling. The second and third borings will be located to the west and