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Scott Mansholt - 2 - 4 December 2003 ChevronTexaco US Can/Welty Road Additionally, volatile organic compounds (VOCs), including among others, trichloroethylene (TCE) were detected in soil near a former drainpipe at the northeastern side of an existing site building. According to the reports, the presence of VOCs in soil and groundwater are likely due to a former can manufacturer at the site. Similarly, concentrations of benzene (1.5 pg/L) and total petroleum hydrocarbons as gasoline (TPH-g, 110 pg/L) reported in groundwater from an off-site boring (GMX-6), north of the site, may be attributable to a former retail gasoline station located at the northeast intersection of State Highway 33 and Welty Road. We have the following comments: 1) The analytical results indicate that the area of petroleum hydrocarbons in soils on-site is generally limited in extent and has been delineated, occurring within two areas along the northeastern property boundary. 2) Based on the reports' findings, it appears that the vertical extent of petroleum-impacted soil on-site has been delineated, defined by boring GMX-8, where TPH as crude oil (TPH-c) was detected at 55 feet but not at 89 feet. 3) Impacted soil has not been delineated off-site, (northeast), where petroleum-impacted soil was observed from 45-50 feet in boring GMX-10. Additional borings are needed off-site to obtain soil samples for analysis to evaluate the lateral extent of TPH-impacted soil. 4) The lateral extent of affected groundwater on-site has generally been delineated, but has not been defined downgradient. Additional downgradient borings are needed to define the lateral extent of TPH in groundwater. Regional Board staff agrees with your consultants observations that the vertical extent of TPH-d concentrations in groundwater exceeding the Water Quality Objective (>100pg/L) generally corresponds to the vertical extent of petroleum-impacted soil. However, additional soil and groundwater sampling and analysis are needed, and additional monitoring wells need to be installed to delineate the extent of groundwater impact. Once TPH-impacted groundwater is defined and additional monitoring wells are installed, a sampling and monitoring plan needs to be implemented. Borings completed during the additional investigation should incorporate areas that require further delineation. In conjunction, a site evaluation needs to include soil sampling that is consistent with the depths and analytical levels required for a human health risk assessment. Additionally, Regional Board staff concurs that a well survey needs to be conducted to identify possible receptors in the area. 1