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' GEOMATRIX ' Grab groundwater data suggest that the residual petroleum present in the soil is not providing a significant source of dissolved petroleum constituents to groundwater. These results and con- clusions were reported by Geomatrix on behalf of ChevronTexaco in the report, "Soil and Groundwater Investigation and Site Status Report"dated August 1998, submitted to the San Joaquin County Public Health Service—Environmental Health Department(SJCPHS-EHD). ' At the request of SJCPHS,monitoring wells TW-1 and TW-2 (Figure 2)were installed and sampled in September 1998 to further assess dissolved petroleum hydrocarbons in site ground- water. A sheen was observed on groundwater from monitoring well TW-2. Monitoring well TW-1 was sampled again in October 1998. Because dissolved petroleum hydrocarbons were ' not detected at concentrations above the State of California Regional Water Quality Control Board, Central Valley Region(RWQCB)water quality objectives (WQOs) downgradient of ' affected soil, Geomatrix, on behalf of ChevronTexaco,prepared'and submitted the report "Supplemental Groundwater Investigation Report and Request for Site Closure"dated Janu- ary 21, 1999. The SJCPHS-EHD referred the case to the RWQCB. At the request of the RWQCB, a third ' monitoring well (TW-3; Figure 2)was installed in July 1999 and quarterly groundwater monitoring activities were initiated and conducted through April 2000. The property sur- rounding TW-2 was subsequently developed as a residence and, per a November 8, 1999 letter from the RWQCB to ChevronTexaco, monitoring well TW-2 was destroyed. The well destruction was performed as detailed in the December 29, 1999 well destruction work plan submitted to the RWQCB. A summary of the analytical results for groundwater samples col- lected from the monitoring wells is presented in Table 3. In summary, investigations conducted at the site indicate that petroleum hydrocarbon affected ' soil, specifically degraded crude oil or Bunker C oil, was encountered between depths of 4.5 and 13.5 feet below ground surface (bgs). The lateral extent of residual petroleum in soil on ' the property is shown on Figure 2. Groundwater occurs at a depth of approximately 5 to 7 feet bgs and flows generally toward the north-northwest. Groundwater monitoring data show that the residual petroleum in soil is not providing a significant source of dissolved petroleum con- stituents to groundwater. 3.0 HUMAN HEALTH SCREENING EVALUATION A health risk screening evaluation was conducted to assess the potential human health risks ' associated with residual chemicals detected in soil and groundwater at the site. This evaluation I:\Doc Safe\6000s\6447.007\HRA\Suland HRA.doc 2