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S IEC0R 7-Eleven Store#19976 Quarterly Groundwater Monitoring and Remediation Progress Report (4Q2004) February 15, 2005 I Page 5 ' r� ah r � On June 2, 2004 a 22-hour SVE event was conducted on the shallow and deep segments of well SP-1 and the horizontal tank pit wells Based on soil vapor samples collected during the test it is estimated that approximately 0 10 pound of TPHg was removed in soil vapor during the 22-hour test No recordable amount of benzene or MtBE were removed during the test MONITORING AND SAMPLING PROCEDURES The depth to water was measured to within 0 01 feet bgs in monitoring wells MW-1 through MW-7, MW-1A, MW-4A, and MW-5A from the 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 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 shown in Attachment A During purging, temperature, pH, and electrical conductivity were monitored 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 presented 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) by Environmental Protection Agency (EPA) Method 8260B In addition, annual sampling and analysis for 1-2-dichloroethane, 1,2-dibromoethane, methanol, and ethanol was conducted The certified laboratory analytical report and chain-of-custody (COC) documentation are presented as Attachment B Groundwater analytical results are presented on Figure 3, and are summarized in Tables 1 and 2 Hydrocarbon concentrations were generally consistent with historical data REMEDIATION Remediation conducted during the fourth quarter 2004 was oxygen injection into SP-1 and SP-1A On October 1, October 14, October 25, November 8, December 8, and December 20, 2004, SECOR field personnel conducted oxygen injection into on-site sparge wells SP-1 and SP- r 1A Approximately 150 ft3 of oxygen was injected into each well simultaneously for a period of 0 5 hours (Table 4) Dissolved oxygen concentrations were measured before and after • the injection event in selected onsite monitoring wells (Table 5) The highest DO �F 19976 04-4Q Report doc SECOR International Incorporated � F