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4.0 ESTIMATED EXTENT OF IMPACTED SOIL f _ Analytical results from the October 1993 soil investigation, presented in Table 4, combined with the findings presented in the McLaren/Hart Preliminary Site Assessment report and the TreaTek tank removal report indicate that the soil an the vadose zone is impacted with TPH-G and BTEX compounds from an approximate minimum depth of 16 feet below grade to the saturated zone at 26 5 feet below grade, as defined at the time of the October 1993 soil investigation The October 1993 soil investigation soil analytical data sheets and chain-of-custody records are - included in Appendix H. The analytical data from the soil investigation performed in October 1993 indicated that the extent of soil contamination outside the source area is concentrated deeper at a depth of approximately 23 to 26 feet below grade which is at, or immediately above, the saturated zone as it was defined at the time of the investigation (October 1993) The sod sampling method used (ramset pushrod samplers) did not provide an adequate soil sample to determine the exact beginning of the saturated zone As a result, the zone of saturation was not always obvious in the field however, the observations noted during soil sampling and the measured static water levels from the existing monitoring wells indicate that groundwater at the site is approximately 26 5 to 27 feet below grade The soil samples collected above 26 5 feet below grade on October 1993 will thus be considered to be unsaturated and representative of the vadose zone The fluctuating groundwater table has likely attributed to contaminants being distributed throughout the historical saturated zone The elevated concentration of contaminants in the . saturated zone is evidenced by analytical data of soil samples collected from below 26 5 feet as presented in Table 4 This distribution pattern is also evidenced by concentrations of TPH-G and BTEX detected in soil samples collected at the 30-foot below grade sample interval during the November 1992 monitor well installation. At the time of the monitor well installations the groundwater elevation was at approximately 32-feet below grade No concentrations of TPH-G or BTEX were present in any of the soil samples collected at the 35-foot below grade sample interval As indicated in the TreaTek, Inc report, the potential source area for TPH-G at the Site was identified within the former excavation At the time of the tank removal, a confirmation soil sample was collected at approximately 17 feet below grade from beneath the southern end of the northernmost former tank (approximately 30 feet south of the north end of the former excavation) The laboratory analysis indicated that the soil sample had a concentration of 785 mg/kg of TPH-G The presence of TPH-G at a concentration of 785 mg/kg at 17 feet below grade (approximately five feet below the bottom of the former tank) indicates that the source of the soil and groundwater contamination at the site may have originated from a leak in the tank The location of the estimated source area is shown on Figure 2 Based on the confirmation soil sample data collected by TreaTek in January 1992 and subsequent McLaren/Hart soil analytical data, collected at boring locations SI-1, SI-6, and MW-3 (Figure 2), the source area is defined as a zone of soil centered in the area of the former leak, extending horizontally approximately 15 feet in the east-west direction and is assumed to extend a similar 1110lcd3 11