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Now, �! Stantec November 28,2011 Page 4 of 5 On April 27, 2009, Stantec conducted the initial oxygen injection event using the newly installed subsurface conveyance trenching and lines. The initial injection event was observed by Mr. Phil Simmons of the local fire department as required by the City of Stockton Public Works Department. In a letter dated July 17, 2009, the SJCEHD requested the reduction of groundwater monitoring and sampling frequency from quarterly to semi-annually as required under the State Water Resources Control Board (SWRCB) Resolution 2009-0042. However, given that active remediation has been initiated at the site, 7-Eleven will continue to conduct quarterly groundwater monitoring and sampling activities in order to monitor the effectiveness of the remedial approach. MONITORING AND SAMPLING PROCEDURES The depth to water was measured to within 0.01 foot bgs in monitoring wells MW-1 through MW-8 from top of casing (TOC) using a water level indicator. Dissolved oxygen concentrations were also measured in each well using a YSI Model 550A dissolved oxygen meter equipped with a down hole sensor. Well purging and sampling equipment was thoroughly cleaned prior to purging and sampling each well. The sampling procedure for each well included measuring the water level and purging of approximately three casing volumes of water(or to dryness). The equipment and purging methods used for the current sampling event are noted on the field data sheets in Attachment A. During purging, temperature, pH, and electrical conductivity were monitored. After purging, water levels were allowed to recover to at least 80% of the original levels prior to collection of the water sample. Groundwater samples were collected using a disposable Teflon® bailer, placed into appropriate Environmental Protection Agency(EPA)approved containers, labeled, logged onto chain-of-custody documents, and transported on ice to a California state-certified laboratory. Copies of the field notes are presented in Attachment A. GROUNDWATER SAMPLE ANALYSES AND RESULTS The groundwater samples collected from MW-1 through MW-8 were analyzed for TPHg, BTEX, and the fuel oxygenates MtBE, tert-butyl alcohol (TBA), diisopropyl ether (DIPE), ethyl-tert-butyl ether (EtBE), and tert-amyl-methyl ether (TAME) by EPA Method 82608. The certified laboratory analytical report and chain-of-custody documentation are presented as Attachment B. Groundwater analytical results are presented on Figure 3, and are summarized in Tables 1 and 2. Dissolved hydrocarbon and MtBE concentrations have been generally decreasing with some seasonal fluctuations. REMEDIATION The current remediation process is oxygen injection into sparge wells 1-1 through 1-5. Oxygen injection wells 1-2 through 1-5 are connected to subsurface conveyance lines that terminate in a single subsurface vault located on the western edge of the parking lot. On July 13, July 27, August 24, September 8, and September 20, 2011, Stantec field personnel injected oxygen into selected oxygen injection wells. Approximately 300 cubic feet (ft) of oxygen was injected into each well (Table 4). Pre-injection and post-injection DO concentrations were measured in monitoring wells MW-1 through MW-5 and MW-8 (Table 5). The greatest DO increase was observed in MW-1, where DO increased from 2.5 milligrams per liter(mg/L) to 5.8 mg/L during the August 24, 2011 event. Stantec will continue biweekly oxygen injection during the fourth quarter 2011 pending submittal of an evaluation of site closure applicability. Copies of the field notes are shown in Attachment C. 14117 11-3Q Report.doc