ARCHIVED REPORTS PHASE II FIELD INVESTIGATION AND LNAPL MOBILITY EVALUATION REPORT

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Phase II Field ARCA�lS Investigation and LNAPL ' Mobility Evaluation Report Union Pacific Railroad Company Former Maintenance Facility ' Tracy, California northeast and the San Joaquin River and Paradise Cut are located 6-5 miles northeast of the Site. Therefore, the Site does not pose an unacceptable risk to the environment. 7. Conclusions/Recommendations iBased on the available data,the Site is a candidate for closure as a low-risk fuel site as discussed in Section 6 because site conditions meet the six evaluation criteria. The remaining residual LNAPL and dissolved TEPH-d plume appear stable and there is no evidence to suggest migration from their current locations is occurring. Based on the findings of the additional site investigation activities and LNAPL mobility evaluation, no further active remediation is recommended for the Site at this time. ARCADIS recommends completing the following activities to prepare the Site for formal site closure. 1. Continue monitoring select groundwater monitoring wells under the existing Monitoring and Reporting Program requirements. The select wells are proposed to be monitored semiannually for two years.Analytical data from monitoring events will be evaluated to confirm the conclusion that the dissolved TEPH-d plume is stable, not migrating,and will continue to remain within site boundaries.A ' monitoring plan will need to be prepared for approval by the RWQCB that will outline specific wells and parameters. 2. Upon verification that the dissolved TEPH-d plume is stable and not migrating, preparation of a formal site closure request,which includes a work plan for abandoning all site monitoring and remediation wells. 3. Provide assistance to the RWQCB in preparing a land use covenant pursuant to California Civil Code Section 1471 and Health and Safety Code Section 25355.5 limiting the future uses of the Site to commercial/industrial, prohibiting the use of the shallow groundwater, and requiring that institutional controls(i.e.,fences around the TPCA Excavation) be maintained.A boundary survey will be prepared by a licensed land surveyor if necessary for purposes of recording the land use covenant. 4. A soil management plan (SMP)will be prepared to provide requirements for future construction activities in areas where petroleum residuals remain for protection of on-site workers and future construction workers. The SMP will be incorporated into the land use covenant by reference. 1 rpU w4racyAnapfmobilky(11-29-20101.doc 32