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DEL-TECH ECH Geotechnicai Support Services Mike Flores August 27, 1993 Stockton Service Station 820 North Union Street / P.O. Box 508 Stockton, CA. 95205 RE: SUMMARY REPORT OF ANGULAR SOIL BORINGS AT PRODUCTION INDUSTRIES / STOCKTON, CA. Mr. Flores, Del-Tech has prepared the following documentation to report the results of the sampling event of July 29, 1993. Two angular soil borings were completed along the facilities southern containment wall of the property. These borings were hand augured at the appropriate angles to investigate the soil surrounding the underground storage tank currently located at the facility. Initial indications have shown signs of a release of petroleum hydrocarbon products. The primary product screened for in the field operations and the laboratory analysis performed was looking for the presence of kerosene. During the cutting of the angular soil borings a Thermodine 580B Photo Ionization Detector was used to detect the presence of Volatile Aromatics at five foot intervals. This screening was also completed to determine the most logical soil samples to submit to the laboratory for analysis. Both of the soil borings completed showed indications that a unknown amount of petroleum based product had been released into the subsurface soils. The depth of the samples submitted for analysis was at approximately ten vertical feet. The overall length of the angular borings was eighteen feet. The attached site map and detailed boring map shows the sampling intervals and field meter reading concentrations. It does appear that the concentrations of volatile aromatics at the bottom of the borings were decreasing dramatically. Upon reviewing the findings from the days monitoring event and the laboratory analysis, it now appears that an additional two vertical borings on the north side of the underground storage tank are now warranted. These two boring would further define the plumes migration in the direction of the facilities main building. Another important factor to consider is that the plume of the soils contamination may have migrated off site and therefore impacted the property adjacent to the underground storage tank. A review of the deeded property boundaries with a current surveying is also necessary to accurately define the site's property boundaries. I have included a amended site sampling map showing were the additional borin�zs would be augured. (SBS-3•& SB-4) Please review th&lattached documents and feel free to contact me if you have any questions. i rely, 10624 Olive Avenue, Oakdale, CA 95361 (209) 847-8757 • Fax (209) 847-7744