SITE INFORMATION AND CORRESPONDENCE_PRE 2019

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Stantec April 30, 2010 Page 11 of 14 Reference: First Quarter 2010 Site Status, Groundwater Monitoring and Remedial Summary Report-Stockton Terminals Technical Committee Facilities Review of chemical isoconcentration figures from first quarter (Figures 8 through 27) indicates that in general the dissolved plumes are adequately defined near the terminal areas. Although the plumes are not fully delineated to the north of the BP terminal or west of the former Time Oil terminal, these locations are upgradient to cross-gradient of the terminals and the plumes are unlikely to move in these directions. The plumes south of STTC are not fully defined but are located within the southern lease area, which is the ST Services area of responsibility. 6.0 RECOMMENDATIONS AND PROPOSED ACTIVITIES Based on the results from site monitoring and remediation activities, Stantec recommends the following: • Continue groundwater monitoring and sampling to facilitate ongoing evaluation of dissolved hydrocarbon concentration trends and the effectiveness of remedial efforts. • The RWQCB should require the resurveying of wells within the KMEP area (southeast of the Tesoro Terminal) to enable continued compatibility of groundwater elevation data with the STTC and ST Services well networks resurveyed during October 2008. • Continue O&M on the East and West Systems and monitor groundwater wells in the ozone- injection monitoring program. Stantec will continue to closely monitor the "A" zone and "B" zone trigger wells. • In accordance with Work Plan for Interim Response (dated September 28, 2009), BP/ARCO terminal wells that have had MBAS concentrations greater than the California secondary MCL of 500 pg/L during any of the last four quarters will be overpurged during second quarter 2010. Sample all ARCO/BP wells and selected downgradient Port of Stockton wells for MBAS as requested by the RWQCB. • Continue activities associated with the two-phase HPI pilot study on the Tesoro Terminal. • Continue activities associated with the oxygen injection pilot study taking place on the Tesoro Terminal as modified in the February 19, 2010 Pilot Study Work Plan Addendum. Conduct a helium tracer test during second quarter 2010 to evaluate hydrologic communication in the "D" zone between Tesoro wells TS/MW-3DR and TS/MW-2D. 7.0 LIMITATIONS This report was prepared in accordance with the scope of work outlined in Stantec's contract and with generally accepted professional engineering and environmental consulting practices existing at the time this report was prepared and applicable to the location of the Site. It was prepared for the exclusive use of STTC for the express purpose stated above. Any re-use of this report for a different purpose or by others not identified above shall be at the user's sole risk without liability to Stantec. To the extent that this report is based on information provided to Stantec by third parties, Stantec may have made efforts to verify this third party information, but Stantec cannot guarantee the completeness or accuracy of this information. The opinions expressed and data collected are