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TECHNICAL_ DATA SUMMARY THE SOUTHLAND CORPORATION SOUTHLAND SITE NO.20680 9110 THORNTON ROAD STOCKTON, CALIFORNIA Groundwater Technology, Inc. April 4, 1995 HISTORIC SUMMARY Please refer to the attached illustrated timeline (Figure 1). 1. Assessment/Monitoring Tasks f March 28, 1986 tank testing indicates failure of the unleaded fuel tank system. On April 2, 1986, the unleaded tank and the associated dispensing system were shut down. Assessment between 1986 and 1990 included 24 groundwater monitoring wells, 4 recovery wells, 1 soil boring, and 4 vapor recovery wells (Figure 2, Table 2). Groundwater monitoring confirmed the presence of separate-phase (SP) and dissolved hydrocarbons (Table 1). March 1988:Aquifer Test September 1991:two off-site and one on-site groundwater wells (MW-18, MW-19, and MW-20) installed (Figure 3). September 1992: USTs and product dispensing lines removed. 1986 to 1994: groundwater monitoring wells monitored. Initial high hydrocarbon concentrations and SP presence in some monitoring wells at the site has decreased to nondetectable levels of TAN-G and BTEX concentrations in groundwater samples collected from these wells (Figure 5). 1986 to 1993: off-site private domestic wells sampled monthly. Results of sampling indicated levels of hydrocarbon constituents have been at or below California action levels for drinking water since 1989. January 1994: latest groundwater monitoring sampling, coordinated with County: all samples contained nondetectable benzene, or 1 ppb. 2. Remediation Tasks May 1986 to October 1990: a separate-phase hydrocarbon recovery system and groundwater extraction and treatment system was operated. Approximately 760 gallons of hydrocarbons were recovered. Approximately 1.6 million gallons of groundwater were pumped and treated (Figures 6,7,8). February 1987 to January 1991:soil vapor extraction system removed an equivalent of 576 gallons of hydrocarbons. GROUNDW.ATER �L�❑TECHNOLOGY