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Site History 14000 Highway 88 Lockeford CA Time Oil Property No 04-049 lithologies encountered at the site SSTLs for benzene were adjusted for California's 0 1 slope factor for carcinogens Based on a review of data collected to date, SECOR determined that the constituents of concern (those that might cause health effects in exposed sensitive receptors) at the subject site include benzene, toluene, ethylbenzene, and xylenes (BTEX) in soil and groundwater, 1,2 dibromoethane in soil, and MTBE in groundwater Since the site is located in a mixed commercial and residential area, site workers and customers, and nearby residents are the most likely populations to be potentially exposed to the hydrocarbons remaining onsite Based on site-specific data, SECOR identified three potentially complete exposure pathways a Onsite workers and customers, nearby offsite residents, and future potential construction workers could be exposed to impacted surficial soils through inhalation, ingestion, andlor dermal contact a Onsite workers and customers and nearby offsite residents could be exposed to hydrocarbon vapors migrating from subsurface soils and groundwater to outdoor air through inhalation • Onsite workers and customers and nearby offsite residents could be exposed to hydrocarbon vapors migrating from subsurface soils and groundwater to indoor air through inhalation Although there is currently no data to which indicates that hydrocarbon impacts are present beneath offsite residences, residential exposure pathways were evaluated to determine protective concentrations Due to the fact that no domestic wells are screened within the zone of impacted groundwater, ingestion of groundwater was not considered to be a complete pathway Results of the RBCA Tier 1 analysis indicate that maximum concentrations of benzene and toluene in subsurface soils and maximum concentrations of benzene in groundwater exceed RSBLs for one or more potential exposure pathways associated with the subject site Results of the Tier 2 evaluation also indicate that maximum concentrations of benzene and toluene in subsurface soils and maximum concentrations of benzene in groundwater exceed SSTLs for one or more potential exposure pathways associated with the subject site A summary of the maximum concentrations which exceed Tier 2 SSTLs follows Rece #mor Exposure Route Max, Conc. Observed SSTL Onsite workers inhalation of vapors from subsurface soils to outdoor air 25 ppm benzene 1 5 ppm benzene Onsite workers inhalation of vapors from subsurface sods to indoor air 25 ppm benzene 0 0074 ppm benzene Onsite workers inhalation of vapors from subsurface sods to indoor air 280 ppm toluene 83 ppm toluene Onsite workers inhalation of vapors from groundwater to indoor air 2,200 ppm benzene 32 ppm benzene Offsite Residential inhalation of vapors from groundwater to indoor air 388 ppm benzene 10 ppm benzene These calculations are based on a 1X10 cancer risk and a chronic hazard quotient of 1 Although the results of the Tier 2 analysis indicate that remediation may be required to reduce benzene and toluene concentrations in soils and groundwater at the subject site, SSTLs may be modified at a later date if additional site-specific data becomes available Evaluation of Appropnate Remediation Altematives Based on values calculated in the RBCA evaluation, it appears as though soil and groundwater remediation is needed reduce hydrocarbon concentrations beneath the subject site In order to determine the most appropriate remediation technology, SECOR evaluated three options which could address both sod and groundwater impacts associated with the subject site 19