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In addition to the field investigation,EA recommends collection of any information on other potential sources of petroleum and previous land use in the vicinity of the site. Two offsite wells(Figure 2)are also proposed to define the downgradient extent of the plume that may have moved along a buried stream channel indicated by earlier investigations. Place- ment of downgradient wells was based on output of the computer model BIOPLUME 11 (Rice University 1987)using data from the 15 November 1988 and 14 April 1989 well gauging and sampling rounds(Figure 2). 4. STATUS OF SOIL AND GROUNDWATER REMEDIATION Between 23 and 25 January 1989, five vapor extraction wells were installed in and around the former underground storage tank area,to be used for remediation of petroleum hydrocarbons in soils. Soils were sampled pmTPH were found at 26.5 feet in welling and analyzed for s petroleum V5. T H levels found at 31 ns. Concentra- Bions up to 16,00(1 pp feet in MW4 were 3,300 ppm(see Table 3). On 24 April 1989,four of the five vapor extraction wells were tested to determine design param- eters for a vapor extraction and treatment system at the site. The concentrations measured in vapors from wells V2,V4,and V5 averaged 4,500,50,000,and 16,000 ppm,respectively. On the same day,the vapor transmissivity of the soil was tested. The soil vapor hydrocarbon concentrations and the soil vapor transmissivity measurements indi- cate that the soils beneath former SS 9-1918 are well suited to petroleum vapor extraction. Vapor extraction and treatment will be initiated upon completion and installation of the system and on site(29 October 1990). Groundwater o that hydrocarbons stranded strap ed ins clays and sands by the de- which are now dry will be plumbed to thesystem cline of groundwater can be remediated(Figure 3). Because all wells on the site are dry,EA has developed a work plan for further investigation prior to considering remediation of groundwater. 5. REFERENCES EA (EA Engineering, Science, and Technology). 1990. Proposed Work Plan to Assess Groundwater Contamination,Former Chevron SS 9-1918,Stockton,CA. March. 2 cM/919 f 9fl-9olgtr