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0 i Mary Meays Page 4 San Joaquin County Environmental Health Division 22 June 1995 Samples Lift-1 through Lift-6 (Table 3) were collected from stockpiled soil which had been removed from the excavation A number of soil samples were also collected from the excavation sidewalls Figures 3A and 3B show soil sample locations on both the south and east walls of the excavation The analytical results summary indicates that there are elevated concentrations of total extractable petroleum hydrocarbons (TPH-e), toluene, ethylbenzene, and xylenes remaining in the southwest corner of the former excavation that need to be addressed Benzene was not detected in this area, however the minimum detection limit for benzene was elevated due to the dilution factors used for these samples Figure 3B shows the area of soil on the south excavation wall where concentrations of TPH-e are in excess of 1000 mg/kg This area of impacted soil was not removed because the south wall of the 1989 excavation was beginning to undercut the sidewalk and street and the volume of impacted soil was significantly decreasing The four soil samples containing TPH-e concentrations in excess of 1000 mg/kg include 20525, 17S27, 8S18, and 8S27. These samples were collected in July 1989 (Table 3) The lateral extent of this area of petroleum-impacted soil was established to the south by samples 8-S27-8 and 17-S27-8 (Table 3) which were collected by hand augering 8 feet horizontally into the south excavation wall at the 8S18 and 8S27 sample locations The areal locations of these samples are shown on Figure 3 Analytical results from these two 1989 samples (8-S27-8 and 17-S27-8) indicate that TPH-e concentrations in excess of 1000 mg/kg extend less than 8 feet into the south wall of the former excavation Low levels of BTEX were detected in both samples The lateral extent of TPH-e toward the west was established by the non-detect sample results from borehole BH-5 It should be noted that on 5 April 1995 the groundwater elevation in MW-7 was measured at approximately -35 feet relative to mean sea level (msl) or approximately 45 feet below ground surface (bgs) According to the San Joaquin County Flood Control District (oral) seasonal groundwater high during Spring 1986 at the site was approximately -15 feet msl or 25 feet bgs The 9 March 1995 WESTON workplan contains reaps showing the groundwater surface and flow direction at the site AMENDMENTS TO THE WORK PLAN In order to further investigate the vertical extent of the remaining petroleum-impacted soil and to monitor its potential affect on groundwater, WESTON suggests moving the location of the proposed replacement well MW-2A to the location shown on Figure 4 This will place a well over the impacted soil remaining at the southwest corner of the former excavation Soil samples collected during drilling will be used to evaluate the vertical extent of petroleum hydrocarbons in this area The new location for proposed MW-2A will also allow groundwater to be L TROJECr=ANJOQUISBLDG LTR