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sail&x ties Repot 1800 E.FtemM 9.,3aelanri,CA prajea Na 150005.00 PNP 2 In May 1991, Emcon Associates installed one groundwater monitoring well (MW-1) in the approximate center of the backfilled tank pit. Analyses of soil samples collected during well installation are summarized in Table 1. A groundwater sample was collected in June 1991 and was reported to contain 100 parts per billion (ppb) TPHG and 1.6 ppb benzene (Table 2). Groundwater was encountered at 69 feet below grade. Well MW-1 was resampled in September 1991. Duplicate samples were sent to two separate laboratories. An additional duplicate sample was collected by the SJCEHD and submitted to a third laboratory for analysis. Analytical results are summarized in Table 2. The sample collected by the San Joaquin County Environmental Health Division did not contain hydrocarbon constituents above method detection limits. In January 1992, Kleinfelder, Inc. drilled two soil borings through the backfill near the southwest corner and the north-central area of the previous excavation. The locations of borings B-1 and B-2 are shown on Figure 2. Boring B-1 was drilled at a 20° angle to the west in order to partially assess the lateral migration of petroleum hydrocarbons in that direction. No analytes were detected in the samples collected from B-1. In boring B-2, 0.0072 parts per million (ppm) xylenes were reported in the sample from 30 feet below grade and TPHD (1.5 ppm) was detected at a depth of 40 feet., . Groundwater was also monitored and sampled in January 1992. Depth to water was measured at 69 feet below grade, as it was in June 1991. Samples were analyzed for BTEX and TPHG. No analytes were detected. Based on this and previous sampling events, it does not appear that groundwater has been impacted by vertical migration of petroleum hydrocarbons, and that the low levels of petroleum hydrocarbons detected during the first monitoring round may have been due to introduction during well installation. SCOPE OF WORK The following scope of work was based upon the information collected during previous site investigations. The work was designed to remove the remaining impacted soil in the vicinity of the former tanks. All field work was performed under the supervision of RESNA personnel in accordance with the Quality Assurance/Quality Control Plan and with the Site Safety and Health Plan (Attachment 1 & 2, Workplan for Soil Excavation, March 8, 1993). Soil Excavation and Sampling On May 13, 1993 residual petroleum hydrocarbon contaminated soil was excavated from the two remaining areas of impacted soils identified during previous excavation and soil boring activities. One area of concern was located near the center of the former 500 gallon tank location beginning at a depth of approximately 16 feet. A second area was near the southwest corner of the excavated pit (in the vicinity of boring B-1) at a depth of approximately 22 feet and near the former dispenser location. Approximately 150 cubic yards of petroleum hydrocarbon impacted soil was removed from PAR-0593.FNL