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Mr. Jim Levy - 2 - 20 November 2006 UPRR Tracy Facility Rebound and Product Removal 2. UPRR must revise the Workplan to identify an appropriate analytical method that will be used to quantify both halogenated and aromatic VOCs in the soil vapor samples. If the concentrations are expected to be high, the analytical method used should be EPA Method 8260B. If the concentrations are expected to be low, the analytical method used should be TO-14A or TO-15. The Workplan should also identify the laboratory reporting limits for the target analytes and ensure that the reporting limits are at or below the CHHSL and ESL values. 3. The Workplan indicates UPRR will assess all potential exposure pathways at the site, but does not state how this assessment will be accomplished. The Workplan should be revised to state the soil vapor data will be compared to CHHSLs and ESLs and potential exposure pathways will be assessed in accordance with Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air(Department of Toxic Substances Control, February 2005). Proposal Comments: 1. UPRR may choose to proceed with the low vacuum soil vapor extraction (SVE) technology and free product skimming discussed in the Proposal; however, UPRR should have a contingency plan to terminate this remedial alternative and implement one of the more aggressive remedial alternatives discussed in the Proposal if low vacuum SVE proves to be ineffective during the initial 6 months of operation. Before proceeding with the low vacuum SVE and free-phase product skimming, the Proposal should contain a detailed design plan for Regional Water Board staff review and concurrence. 2. Please revise the Proposal to include an estimate of the time to complete removal of free-phase product using low vacuum SVE and free-phase product skimming in groundwater monitoring wells MW-06A, PZ-01, and TW-01. 3. Before implementing low vacuum SVE to enhance free product removal from site groundwater, Regional Water Board staff recommends completing the assessment of residual soil vapor concentrations as described in the January 2006 Workplan and as per our comments on the Workplan. If the soil vapor sampling indicates VOCs are still present at high concentrations, aggressive SVE and/or dual-phase extraction may be a more appropriate remedial alternative for the source area. General Comments: Based on a review of the existing remedial system use and performance data, the Regional Board staff finds that extraction wells EW-1 through EW-21 are no longer needed and therefore should be either appropriately abandoned or monitored as part of the existing monitoring and reporting program. If not being monitored, these wells currently pose an unnecessary risk to groundwater as an open conduit from the surface. Please include a proposal to either abandon or monitor these wells in the revised Workplan.