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S [EcC ® R 7-Eleven Store#19976 Quarterly Groundwater Monitoring and Remediation Progress Report (2Q2004) August 20, 2004 Page 5 level and checking for the presence of liquid-phase hydrocarbons (LPH), using either an electronic indicator and a clear Teflon® bailer or an oil-water interface probe Wells not containing LPH were purged of approximately three casing volumes of water (or to dryness) using a submersible pump or bailer The equipment and purging methods used for the current sampling event were noted on the field data sheets included in Attachment A During purging, temperature, pH, and electrical conductivity were monitored to document that these parameters were stable prior to collecting samples After purging, water levels were allowed to recover to 80% of the original levels prior to collection of the water sample Groundwater samples were collected using a disposable Teflon® bailer, placed into appropriate 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 included in Attachment A GROUNDWATER SAMPLE ANALYSES AND RESULTS The groundwater samples collected from MW-1 through MW-7, MW-1A, MW-4A, and MW- 5A 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) using Environmental Protection Agency (EPA) Method 82608 The certified laboratory analytical report and chain-of-custody (COC) documentation are presented as Attachment B 11 Groundwater analytical results are presented on Figure 3, and are summarized in Tables 1 and 2 Hydrocarbon concentrations were generally consistent with historical data INTERIM REMEDIATION The current interim remediation process includes SVE on the horizontal vent wells, in combination with oxygen injection into SP-1 and SP-1A On April 12, April 23, May 13, May 18, May 24, June 7, and June 21, 2004, SECOR field personnel conducted oxygen injection into on-site sparge wells SP-1 and SP-1A Approximately 150 ft3 of oxygen was injected into each well simultaneously over a period of 0 5 to 1 0 hours (Table 4) -Dissolved oxygen concentrations were measured before and after the injection event in selected onsite monitoring wells (Table 5) The highest D O 1 increase was observed in MW-2, located adjacent to SP-1 and SP-1A, which showed an 4` increase from 0 9 milligram per liter (mg/L) to 46 0 mg/L on April 23, 2004 SECOR will continue biweekly to monthly oxygen injection during the third quarter 2004 Copies of the field notes are included in Attachment C v N On June 2, 2004 an SVE equipment inspection was conducted in accordance with San Joaquin Valley Air Pollution Control District (SJVAPCD) Authority to Construct (ATC) permit number N-5013-1-0 along with a 22-hour SVE event Individual tests were conducted on the shallow and deep segments of well SP-1 and the horizontal tank pit wells During the tests an average vacuum of 75 inches of water was applied to each well with an averaged corresponding flow rate of 52 standard cubic feet per minute (scfm) To facilitate extraction from well SP-1, SECOR personnel connected the influent of the oxidizer to the horizontal tank pit well running to well SP-1 Based on DTW readings collected from the shallow and 19976 04-2Q Report doc SECOR Intematronal Incorporated