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Only 3 wells appear to be downgradient of the site, the closest being approximately 1, 300 feet downgadient. Also, based on an inspection of the excavation sidewalls, LH concluded that Balbi & Chang incorrectly determined the locations of the former USTs. LH placed the location of the former USTs 10 feet farther south and east than Balbi and Chang estimated (Leedshill-Herkenhoff, Inc. January 1990, see Figure 1) . In August 1990, LH drilled three additional soil borings (SB21 through SB23) near TB-5, located in the northwest corner of the site, in order to evaluate the lateral and vertical extent of petroleum hydrocarbons detected in soil samples collected from TB-5 during the previous phase of the investigation. A 4-inch inner diameter monitoring well (MW-6) was installed in soil boring SB21 to a depth of approximately 76 feet in order to replace nearby well MW-1, which had gone dry. Results of this phase of the investigation indicated the lateral extent of petroleum hydrocarbons in soil to the north and south of soil boring TB-5 has been defined. Elevated concentrations of TPHg and BTEX were detected in soil samples collected from boring SB-22 to a depth of ` approximately 15 feet bgs. Low concentrations of petroleum hydrocarbons were detected in soil samples collected from boring SB-22 from a depth of 25 to 60 feet bgs. This data indicates that petroleum hydrocarbons detected beneath the northwest corner of the site are largely limited to the vicinity of TB-5 to a depth of approximately 25 feet bgs (Leedshill Herkenhoff, Inc. September 1990) . The groundwater gradient in August of 1990 was to the northeast at approximately . 005 ft/ft. By September of 1990 all wells on-site, with the exception of MW-6 were dry. On September 24 1992, Kennedy/Jenks Consultants (Kennedy/Jenks) collected four sidewall samples from the former gasoline UST excavation, approximately 2 feet bgs near the center of the excavation sidewall face. Concentrations of TPHg ranged from below laboratory detection limits to a maximum of 4 . 0 ppm. Trace levels r of toluene and total xylenes were detected in the sidewall samples. Samples from the floor of the former UST excavation were not collected. Based on these and previous sample results, Kennedy/Jenks prepared a remediation workplan for uncontrolled aeration of the excavated soil on-site (except for soil from soil boring SB22 and TB5) , and backfilling the excavation using the E aerated soil. Kennedy/Jenks also included a water disposal plan in the workplan. Based on The City of Stockton, Department of Municipal Utilities, Environmental Control Division sanitary sewer groundwater discharge guidelines at the time (maximum concentrations of TPH-100 mg/L and total toxic organics-4 .57 mg/L) Kennedy/Jenks recommended discharging water purged from monitoring wells MW1, MW3, MW4, and MW6 into the sanitary sewer. Kennedy/Jenks also recommended resampling drummed groundwater from wells MW2 and MW5 to evaluate disposal options (Kennedy/Jenks, October 1992) . 3