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1.0 INTRODUCTION This report presents the results of a preliminary investigation of subs face petroleum contamination conducted by Upgradient Environmental Consultants pgradient Environmental) in August 2001. The investigation was performed at 10848 Copperopolis Road, which is located in a rural area of eastern San Joaquin County, approximately 4 miles east of the City of Stockton(Figure 1). Upgradient Environmei ital was retained by the current property owner, Mr. Philip Henry, in July 2001 under cor tract number 21005. The scope of work was to prepare a Site Investigation Work Plan, perform an initial subsurface drilling investigation to determine whether groundwater, in addition to soil, is contaminated, and prepare this report. The work plan was submitted to the lead , regulatory agency(San Joaquin County Public Health Services, Environmental Health Division [PHS/EHD]) on July 25 and was approved on August 3. D ]ling took place on August 27. 2.0 BACKGROUND The property was operated for many years as a gasoline service station and convenience store known as Countryside Market. According to local residents,th operators ceased selling gasoline approximately 20 years ago,but continued to operate the market until about 1993. It is our understanding that the property has been vacant since early 1993. In March 1993, Stockton Service Station Equipment Co. removed the two 1,000-gallon leaded gasoline tanks and collected four soil samples from beneath the tanks at a depth of , 7.5 feet. Hydrocarbons and lead were detected in all four samples (T ble 1). A two-point composite sample of the excavated soil (approximately 50 yards) als contained low concentrations of gasoline, ethylbenzene, and xylene. The excavated soil was subsequently returned to the excavation, and no investigation was pe rformed. In 1995,the three family trusts that held the first mortgage on the property foreclosed on the previous owner and attempted to initiate an investigation to detel mine the impact to the site. Stockton Mortgage Co., acting as representative of the trust , retained J. J. Hoblitzell and Associates (H&A)to conduct the investigation. H& subsequently retained Upgradient Environmental to submit a work plan to San Jo quin County PHS/EHD. Initially,the plan was to drill four soil borings,,but the plan was revised as a result of further discussions between Stockton Mortgage and PHS/EHD. The revised plan was to excavate and remove the contaminated soil and replace it wit clean backfill. Excavation took place on October 31, 1995. 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 Ch rven of Upgradient Environmental. Near-surface soil was clean, without hydrocarbon o ors, but gasoline odor became evident as excavation proceeded and organic vapor readings measured with a portable photo-ionization detector(PID)began to increase. By mi -afternoon, the depth had reached 13 feet and hydrocarbon concentrations were continuing to increase. 2