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' Pombo Property <br /> Corrective Action Plan <br /> Page: $ <br />' 4.6 Cost Estimates <br />' Cost Estimates for each of the mitigation scenarios are presented in Table 5. Cost <br /> estimates are based on the SWRCB Underground Storage Tank Clean UP Fund <br /> Cost Guidelines (1995). Unit costs are based on surveyed 1995 rates and do not <br /> reflect current clean up costs. Estimated mitigation costs are presented in Table 5, <br /> Estimated Mitigation Costs. Spreadsheets for the volume and cost of the oxygen <br /> release compound for the enhanced aerobic clean up options are presented in <br /> ' Appendix 3. The cost estimates are only presented for comparison of mitigation <br /> alternatives and are not bids or cost estimates for clean up activities. The cost <br /> estimates do not include preparation of work plans, remedial action plans, site <br /> ' closure reports, or other activity reports. <br /> If the SWRCB low risk closure criteria can be met, the low risk closure is the <br /> most cost-effective closure alternative. Possible concerns with the low risk <br /> closure are BTEX plume stability at 120 feet, no MTBE plume stability at 200 <br /> feet from the point of release and residual groundwater contamination in the <br /> source area of 7700 ug/l. total BTEX and 625 ug/l. MTBE. The estimated cost for <br /> the low risk closure is $1500. <br /> Source removal and aerobic bioremediation have approximately equal clean up <br /> costs. Source removal has projected plume stability at 120 feet (BTEX) and 270 <br /> feet (MTBE) from the point of release with out a projected residual contamination <br /> 10 in the source area. The estimated cost for the source removal closure is $47,585. <br /> Aerobic bioremediation has projected plume stability at 40 feet (BTEX) and 160 <br /> ' feet (MTBE) from the point of release with a projected residual contamination of <br /> 4978 ug/l BTEX and 625 ug/l MTBE in the source area. The estimated cost for <br /> ' the aerobic bioremediation closure is $47,000. <br /> Source removal with aerobic bioremediation have the highest estimated cost but <br /> ' provides predicted BTEX plume stability at 60 feet and MTBE plume stability at <br /> 160 feet from the source without predicted residual contamination in the source <br /> area. The estimated cost for the aerobic bioremediation closure is $65,585. <br /> 5.0 CONCLUSIONS AND RECOMMENDATIONS <br /> ' If the SWRCB low risk closure criteria can be met, the low risk closure is the <br /> appropriate. Clean up alternative. If the SWRCB low risk closure criteria cannot <br /> be achieved than the source removal with aerobic bioremediation is the <br /> ' appropriate clean up alternative. Although of slightly greater cost, the limited <br /> plume extent and rapid plume degradation provide will allow for a rapid clean <br /> closure. <br /> 1 <br />