ARCHIVED REPORTS_XR0009463 - Laserfiche WebLink

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--- --- - ------------- 7A Working To Restore Nature reserving enough space to stockpile soil and avoiding utility lines during excavation. Due to the space limitations and the need to keep the site operational, Alternative 1 may need to be completed in two or more phases, which could increase the cost of the project slightly. Alternative 2 has few implementability problems, other than the uncertainty of the remediation timeframe. Criterion 8. Alternative I is a proven remediation method and has been widely accepted by the regulatory agencies and the community on similar projects. Alternative 2 may require significant regulatory oversight due to the addition of nutrients and/or bacteria to the subsurface. Criterion 9. Alternative will have a negligible impact on water conservation since only groundwater in the shallowest water-bearing strata (a non drinking water zone) will be extracted and discharged. Alternative 2 will have no impact on water conservation. 5.0 RECOMMENDED INTERIM REMEDIAL ACTION Based on a comparison of remedial alternatives utilizing the criteria listed above, RESNA proposes interim remediation of hydrocarbon-bearing soil and groundwater beneath the site by excavating contaminated soils both above and below the zone of saturation and extracting f. groundwater and floating free product, if present, from the open excavation. Quarterly groundwater monitoring and sampling activities will continue. This method of remediation, once implemented, should be the most timely, effective and cost- efficient alternative. Soil excavation in conjunction with groundwater extraction and treatment should substantially reduce levels of contaminants in the subsurface. Future remediation needs will be evaluated upon completion of soil excavation, remediation, and subsequent backfilling of the excavation. 6.0 INTERIM REMEDIATION WORKPLAN To prevent the remaining impacted soil from acting as a potential source of groundwater fs degradation, RESNA proposes the following scope of work. Field tasks proposed in this workplan will be performed according to the Quality Assurance/Quality Control Plan on file with PHS/EHD and the Site Safety and Health Plan (Appendix A). 6.1 Soil Excavation Suspected hydrocarbon impacted soil will be excavated by a licensed California contractor employing a backhoe tractor or tracked excavator. A front end loader will be used to stockpile the soil on site. It is estimated, based on data collected to date, that 1500 to 2400 cubic yards of soil (700 cubic yards of which may be impacted) will require excavation. Due to site space limitations for stockpiled soils and the need to maintain accessibility to the pumping plant, it may W0365%REPORTS\CAP0294.FNL 7