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Messrs Larson and Trommer January 10, 2014 104 W. Beverly Place, Tracy, CA Page 2 of 4 total petroleum hydrocarbons (TPH). From these findings, the Fund determined that the site meets Policy Criterion 2a by Scenario 3a for vapor intrusion concern. The EHD is of the opinion that other site data override these criteria for vapor intrusion evaluation as discussed below. • Fund staff found the case meets Policy Criterion 3b for direct contact and outdoor air exposure, stating that impacted soil is limited to a thin zone between 6 and 10 feet bsg and that residual hydrocarbons present inthe excavation walls were—not confirmed-in recent samplings conducted in 2003. In a strictly technical sense this is so, but there are limitations to the data. The inferred groundwater flow direction has been predominantly northward. Monitoring well MW-4, directly north of the source area, has consistently been impacted by total petroleum hydrocarbons quantified as gasoline (TPHg) and by benzene, toluene, ethylbenzene and xylenes (BTEX). MW-1 located approximately 25 feet obliquely downgradient of the source area has been intensely impacted, but has cleaned up to non-detectable contaminant concentrations in recent years. The more recently installed MW-8, located approximately 65 feet north of the source area was initially impacted, cleaned up to non-detectable contaminant concentrations, and had rebounding TPHg and BTEX concentrations about the time of the insitu chemical oxidation (ISCO) pilot test. Soil data from the relatively recently installed MW-8 demonstrated significant impact to soil at 7 and 10 feet bsg and more moderate impact from 12 to 22 feet bsg, which may be due in part to cross contamination from shallower impacted soil and groundwater. This suggests at least three vertical feet of significantly impacted soil (and probably 4 feet or more) stretching from the source area at least 65 feet northward that extends under the residence. Analytical data for soil samples collected at 5 feet bsg are relatively sparse, and much of the soil data from that depth was collected upgradient, cross gradient, obliquely downgradient or at great distance from the source area. The only soil sample collected at 5 feet bsg between the suspected source area and the residence downgradient of the sources area is P17-5, which contained 11 mg/kg TPHg. Sample P3-6, collected next to the residence contained 2,800 mg/kg TPHg, but less than 0.3 mg/kg benzene. The EHD considers the data to show that if all soil at 5 feet bsg has less than 100 mg/kg TPH, then the 5-foot bioattenuation zone is certainly no greater than 5 feet and may well be less locally due to the high water table and soil heterogeneity in the area; these are knife-edge differences. The Fund found that impacted soil either met the criterion of Table 1 or is unlikely to be encountered in the future. The EHD has some concern with this finding as soil around the tank over-excavation was found to have benzene concentrations (56 mg/kg) that exceed residential land use soil between 5 and 10 feet bsg, and there is no certainty what actions future owners or residents may conduct on the property, but concedes that the shallow depth to water may naturally limit some potential direct exposure. The greatest concern that the EHD has with closing this site at this time is the potential for vapor intrusion affecting future residents. Even though it can be argued that the site meets the LTCP criterion for this issue, it just barely does so and other data suggest to the EHD that there remains a significant health hazard associated with potential vapor intrusion and hydrocarbon vapor concentrations in the crawl space beneath the residence. 2014 SRS Response CUF Claim No 8502.doc