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' Former UnocaUWards <br /> 5400-5606 Pacific Ave., Stockton 2 23 February 2005 <br /> 1 We discussed the results of the BST Report, which showed that Cr6+, detected during the bench scale testing, di <br /> persist in untreated soil (my specific comments to the BST Report and 4Q2004 Report will follow later in a letter)nof <br /> 1 I said that the BST Report provided enough information toconsider writing WDRs to conduct the Ozone Injection <br /> Pilot Study. John said that Unocal had expressed concerns <br /> residual contaminationthat the Ozone Injection would not effectively target the <br /> , because the majority of contamination now lies under Robinhood Drive between the two <br /> 1 commingled sites. Ben explained that they were now beginning to see reductions in concentrations in other portions <br /> of the site as a result of proper operations, maintenance, and upgrades to the SVE/AS G WTS. Ben cautioned that <br /> ' there were not enough quarters of data to eliminate seasonal fluctuations in groundwater as a cause for the reductions. <br /> As an alternative to Ozone Injection, John said ENSR is proposing two additional AS wells, one to the north and one <br /> 1 to the south of Robinhood Drive, to address the residual contamination. I said that conceptually I agreed with ENSR's <br /> rationale for the additional AS wells, but that the Workplan for the new AS wells would need to provide evidence that <br /> AS could reach the contamination under the street. Ben added that, since the piping to the new wells is in place for <br /> the current AS wells, there would be minimal disruption of the businesses operating on Robinhood Drive. I asked for <br /> clarification for the location of the proposed new AS wells, which appeared on plan view to be less than twenty feet <br /> from the existing AS wells. We then viewed two geologic cross section s from the 4Q2004 Report near the proposed <br /> 1 AS wells. Ben explained that the new AS wells would be located in the deeper C-zone, to address TPH-g and <br /> Benzene concentrations that are not declining. Ben added that TPH-g and Benzene concentrations are declining in the <br /> A-and B-zones. I asked for a Workplan to install the AS wells within 60 days, adding that my comment letter to the <br /> ' 4Q2004 Report and BST Report would concur to ENSR's proposal for the AS Wells. <br /> Ben said that the missing Corps of Engineers (COE)Checklists, cited in the Remedial System Evalualion/Comparative <br /> 1 Analysis Of Changes In Contaminant Concentrations(RSE Report) that I received on 4 December 2004, would be <br /> submitted this week. He had previously stated in conversation that ENSR could not submit the Checklists <br /> immediately since they were handwritten and not suitable for publishing. I said that handwritten notes generally are <br /> 1 acceptable for reports, but that I had agreed previously to wait for the typed version of the Checklists. (Subsequently <br /> the COE Checklists were received on 4 February 2005 and I accepted the RSE Report.) I then mentioned that my <br /> 1 23 December 2004 letter comments to the RSE Report had required a report of the proposal to enhance the existing <br /> SVE/AS System by 31 January 2005. However, I said that the request for a 60-day extension appeared reasonable, <br /> since the BST Report stated ENSR would be evaluating additional enhancements, now minus Ozone, for remedial <br /> alternatives to SVE/AS. John agreed to submit an addendum to the RSEReport by 31 March 2005. Ben asked if the <br /> addendum to the RSE Report and Workplan for the additional AS wells could be combined into one document, to <br /> which I replied yes. <br /> 1 John said that ENSR would submit a recommendation to reduce sampling under the CAO Monitoring and Reporting <br /> Program (MRP). I said that any recommendation to reduce the frequency or list of analyses would require a rationale <br /> for the reductions, and must show that water quality would be protected by the reductions. I added that the request <br /> could be submitted in tabular form for individual wells, that the tables should provide the Data Quality Objectives for <br /> sampling of each well, and that I generally would be more inclined to agree with sampling frequency reductions over <br /> ' deletions of specific petroleum hydrocarbon analyses, due to the need to have good post remediation monitoring data <br /> for closure. I added that I would consider all requests for changes to the MRP,which would require my comments to <br /> the recommendation be forwarded for the approval by the Executive Officer of this Regional Board. <br /> California Environmental Protection Agency <br /> 2J Recycled Paper <br />