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S E C 0 R IConceptual Site Model . Chevron Service Station##9-6171 March 25, 2005 Page 12 5.0 REMEDIATION I Due to the complexity of groundwater contamination beneath the Lincoln Village Shopping Center(LVSC), it is pertinent to consider two different remediation systems and strategies 5.1 Hydrocarbon Remediation To identify the remedial action requirements and to develop remedial objectives, the current site concentrations are compared to established Preliminary Remediation Goals (PRGs)for soil and water quality set forth by the California State Environmental Protection Agency (Cal/EPA) The required PRGs are summarized in Table 7 A review of soil hydrocarbon chemistry data from January 1987 to October 2004 indicates that the petroleum hydrocarbon concentrations in the soil are below the established PRGs for groundwater This would indicate that any vertical residual plume movement to groundwater is negligible The lateral extent of soil contamination is limited to shallow soils between 2 and 17 5 ft bgs (Table 4) In addition, soil contamination occurs at a select few locations onsite B-3, B-5, and WOT-1 (Figure 2) Soil samples collected during well � . installation around the perimeter of the site, MW-12 through MW-14, reported no petroleum hydrocarbon contamination Two soil samples collected from MW-8, at a depth of 38 5, and MW-11D, at a depth of 84 ft bgs, reported low concentrations of MtBE and xylenes At the time of well installation, the soil samples collected were within the saturated zone beneath the site It is possible that the observed petroleum hydrocarbon concentrations are a direct result of soil contamination via product transport through groundwater since the other soil samples collected from shallower depths within these wells reported no detectable concentrations of petroleum hydrocarbons Since natural attenuation mechanisms appear to be stabilizing the plume, there is no need for any additional remediation actions at this time Moreover, TPI-Ig and BTEX compounds have not been detected in any of the soil borings at the site IIn October 1994, the concentrations of petroleum hydrocarbons In the groundwater did not meet the water quality goals established by Cal/EPA (Table 7) Monitoring wells MW-2 and MW-4 contained concentrations of TPI-Ig at 630 ppb and 2,900 ppb, respectively MW-2 contained concentrations of benzene at 150 ppb in light of this, a remediation response plan was established to manage the dissolved hydrocarbon plume and reduce the amount of hydrocarbons in groundwater The best available technologies (BATS) were soil vapor extraction (SVE), air sparging (AS), stimulated monitored natural attenuation through bioreclamation (MNA), vapor phase adsorption using granulated activated carbon (GAC), and catalytic/thermal oxidation (CTO) Natural attenuation in conjunction with quarterly sampling was chosen as the best remedial course of action At shallow depths, MNA controls the migration of the plume and reduces the possibility of deep groundwater N 1FdeslProiectslChevronlRetad149-81711Site Conceptual ModeI1RNAL_CSM doc