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QUARTERLY STATUS REPORT Texaco Service Station 440 West Charter Way, Stockton, California San Joaquin County Second Quarter 1998 SITE HISTORY The site is an active retail Texaco facility. In October 1988, hydrocarbon-impacted soil was observed at the site after two pump islands were removed in preparation for new construction. Soil beneath the eastern pump island was excavated to a depth of 15 feet below around surface (bgs). Soil samples collected from the bottom of the excavation contained detectable petroleum hydrocarbons (BTEX, TPHg). Between May 1989 and April 1992, twenty soil borings we�� drilled, eleven groundwater monitoring wells were installed(MW-1 through MW-11), and four nested soil vapor extraction(SVE) wells were installed (VE-1 through VE-4). Analytical data indicated that soil samples collected from soil borings SB-1, SB-4, MW-2 through MW-5. and MW-7 through MW-11 did not contain detectable concentrations of TPHg. Soil samples from borings SB-2, SB-3. AB-3, MW-1, and MW-6 contained detectable concentrations of TPHg and benzene. Soil samples were not analyzed from borings VEW-1 through VEW-4 because these borings were drilled adjacent to borings with previous analytical data. To further define the extent of subsurface petroleum hydrocarbons, five soil borings were drilled off site, and monitoring wells were installed in these borings (MW-13 through MW-15), in September 1993' No TPHg was detected in soil samples from borings MW-13, N[W-MW-16, and MW-17. TPHg was detected in selected samples from MW-14 and MW-15. At this time it was estimated that there were approximately 5,600 pounds (896 gallons) of TPHg in the subsurface. 'Groundwater monitoring wells iV1W-1 through MW-5 have been monitored from May 1989 to the present. MW-6 through MW-11 from May 1990 to the present, and MW-13 through MW-17 from September 1993 to the present. Groundwater flow is generally to the east or northeast. Separate phase hydrocarbons (SPH) were historically detected in MW-1, but no measurable SPH has been observed in MW-1 since March 1993. Between May 1989 and December 1989, approximately 45 gallons of SPH was recovered from MW-1. A SVE test was conducted in June 1992 using the four existing nested SVE wells. The radius of influence was approximately 25 feet at a flow rate of approximately 25 cubic feet per minute (cfm). The vapor concentrations of TPHg ranged from 3,300 to 30,000 milligrams per cubic meter. Startup of a SVE system utilizing a 600 cfm thermal oxidizer to extract soil vapor from the four nested SVE wells was conducted at the site on August 28, 1995. Between January 1996 and March 9, 1998, the SVE system removed the equivalent of approximately 6,256 pounds of TPHg. The SVE system was shutdown on vfarch 9, 1998 due to declining influent concentrations ;;'h gh groundwater levels. WORK PERFORMED THIS QUARTER \\ Continued the groundwater monitoring and sampling program. l� MoW�foc LJ 440gsr.982 1 of 2 y ar�ft-A MAUI-��'L J t