SITE INFORMATION AND CORRESPONDENCE_PRE 2019

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Stantec April 30, 2010 Page 3 of 14 Reference: First Quarter 2010 Site Status, Groundwater Monitoring and Remedial Summary Report-Stockton Terminals Technical Committee Facilities (Section 4.3). Baseline metals samples were collected from monitoring wells TS-4R, TS-5, TS/M-2, and TO/T-3 as part of the HPI pilot study. Well locations are shown on Figures 2 and 3. Pre- and post-purge dissolved oxygen (DO) and oxidation reduction potential (ORP) readings were collected from the evaluation monitoring wells as part of the ozone-injection monitoring program. Groundwater sampling field data sheets are included in Appendix D. Stantec coordinated STTC monitoring and sampling efforts with those in the ST Services southern lease area through their consultant Ash Creek Associates, Inc. Twenty "A" zone wells, six "B" zone wells, eight "C" zone wells, and two "D" zone wells in the ST Services monitoring well network were monitored for depth to water on February 1, 2010 (Appendix E). First quarter purge water was temporarily stored in holding tanks on the Tesoro Terminal, pending removal from the Site. On February 3 and March 2, 2010, Stantec oversaw Instrat Inc. remove approximately 2,800 gallons and 3,700 gallons of purge water, respectively. The water was transported to the Instrat facility in Rio Vista for treatment and disposal. Regular O&M activities and system upgrades were conducted on the two ozone systems throughout first quarter 2010. O&M of the ozone system remains fairly significant, indicating that oxygen injection may present a less O&M intensive, more implementable alternative should the current system need augmentation in the future. As part of Tesoro's OI pilot study, wells TS/MW-3DR and TS/MW-4D were installed and developed during March 2010. Results will be presented under separate cover. Hydrogen peroxide injection and evaluation monitoring commenced during March 2010 as part of Tesoro's two-phase HPI pilot study. 3.0 GROUNDWATER RESULTS Wells gauged and sampled under the MRP during first quarter 2010 are listed in Table 1. Time plots were created for selected wells to evaluate long-term groundwater elevation trends, as well as TPHg, benzene and MTBE concentration trends (Appendix F). Non-detectable results are shown at their method reporting limits (MRLs) on the time plots. 3.1 GROUNDWATER GRADIENTS First quarter 2010 depth-to-water measurements were collected on February 1, 2010. Groundwater elevations, gradients, and flow directions in each of the zones were consistent with historical data (Tables 3 and 4). First quarter groundwater elevation contour maps for the "A", "B", "C", and "D" zones are provided as Figures 4 through 7, respectively. Ground surface elevation at the Site ranges from approximately 1.5 to 6.3 feet above mean seal level (msl). A summary of groundwater gauging and elevation data is presented in the table below.