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ti GeoStrateg ies August 4, 1997 Mr Ed Ralston Tosco Marketing Company Environmental Compliance Department 2000 Crow Canyon Place, Suite 400 San Ramon, California 94583 Subject: Second Quarter 1997 VES Report, Unocal Station No. 6981, 4707 Pacific Avenue, Stockton, California. Mr Ralston This report summarizes the sampling and operational data for the vapor extraction system (VES) at the subject site from January through March, 1997 Location of the subject site is shown on Figure 1 The current station configuration is shown on Figure 2 First Quarter 1997 Activities Field activities conducted at the subject site dunng the second quarter 1997 are discussed below GeoStrategies (GSI) Field Methods and Procedures are attached Following shutdown during March 1997 for system maintenance and replacement of the flame sensor, flame rod, and oxygen sensor, the VES was restarted on April 1, 1997 Influent and effluent vapor stream samples were collected by Gettler-Ryan Inc (G-R) on April 24, May 31, and June 24, 1997 The samples were analyzed for TPHg and BTEX at Sequoia Analytical in Redwood City, California (FLAP #1210) Copies of the laboratory reports and chain-of-custody documents are attached Between April 1 and June 24, 1997, the VES operated approximately 571 hours (23.8 days), or approximately 28% of the time The VES continued to have problems flaming out Soil vapor was extracted from wells VW-2, VW-4, and VW-5 during the second quarter 1997, as field monitoring indicated these wells had the highest hydrocarbon concentrations. During the second quarter 1997, the VES extracted and treated approximately 290 pounds of TPHg and < 1 pound of benzene VES analytical data for the quarter are summarized in Table 1, and operational data are summarized in Table 2 ii 785120-3 3164 Gold Camp Drive, Suite 240 • Rancho Cordova, CA 95670 (916) 631-1314 • Fax (916) 631-1317