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(.anepa 's Car wash ( Pacific Avenue) Problem :Assessment Rcport and Coireeuve Action Plon Page 14 estimate of less than $3 , 000 . However, the equipment and installation costs are estimated to be $50,000 to $ 100,000 . 7.4 PREFERRED ALTERNATIVE The cost analysis indicates that the evaluated alternatives are all similar in initial equipment and installation costs. However, due to the heterogeneous nature of the soils as noted in Section 7 .2 above, we are concerned that air sparging and ozone injection may not be effective. A pump and treat will provide more comprehensive capture for treatment of contaminated groundwater. By lowering the groundwater, the existing soil vapor extraction system can capture exposed contaminants that are now below the groundwater level . Preliminary calculations indicate that at low pumping rates (on the order of 5 gallons per minute), the capture zone would eventually extend as much as t500 feet. However, the drawdown would only be about 10 feet. This would provide excellent plume capture but would still require some additional in situ treatment to complete remediation in a timely fashion . Consequently, we are proposing: • A pump and treat system with ex situ treatment of the groundwater, to provide for plume capture and remediation of groundwater from near the source area; • Soil vapor extraction to remove those contaminants in the vadose zone exposed by the groundwater drawdown ; and • The further remediation of groundwater, as necessary based on the results of the SVE/pump and treat, by enhanced biodegradation and/or chemical oxidation at injection points within the plume. 8.0 TARGET CLEAN-UP LEVELS The proposed clean-up level for benzene in groundwater at the site is the risk based contaminant levels for benzene at a cancer risk level of one in ten thousand from the ASTM Standard Guide for Risk-Based Corrective Action Applied at Petroleum Release Sites (E 1739-95), Table X2 . 1 Example Tier 1 Risk Based Screening Level (RBSL) Look-up Table. This level provides a significant level of source reduction and is based on minimizing potential for human health risks in the vicinity of the site. The completed contaminant transport pathway isiinhalation of indoor air volatilizing from groundwater In a commercial setting. The proposed clean-up level for benzene is : Groundwater benzene — 73 . 9 pg/L E 1739-95 does not include MTBE in Table X2 . 1 . However, the maximum contaminant limit (MCL) for NITBE is 13 ug/L. As a default, the proposed clean-up level for MTBE is: Groundwater MTBE — 13 ug/L Attainment of the clean-up levels for groundwater will be determined by the highest concentration of benzene and MTBE in extracted groundwater (if a pump and treat system is installed) or in any of the monitoring wells. Once the clean-up levels are achieved, the remediation system should be monitored for at least four quarters to verify that the clean-up goals have been achieved. Site closure may be warranted when it can be demonstrated that water quality goals have been achieved during the time period proposed . 9.0 SUMMARY AND CONCLUSIONS The site contains significant subsurface contamination from hydrocarbon fuels that could create health hazards from toxic vapors in the on-site structure, or by migration off site. The most cost effective remediation strategy involves groundwater pumping for treatment, vapor extraction, and potentially A n Cr1 CONDOR