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S E C 0 R 7-Eleven Store#19976 Quarterly Groundwater Monitoring and Remediation Progress Report(3Q2004) November 1, 2004 • Page 5 t� 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 was 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 ?fit 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 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 included in Attachment A � r 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), dttsopropyl ether (DIPE), ethyl-tert-butyl ether (EtBE), and tert-amyl-methyl ether (TAME) by Environmental Protection Agency (EPA) Method 82608 The certified laboratory analytical report and chain-of-custody (COC) documentation are presented as Attachment B l Groundwater analytical results are presented on Figure 3, and are summarized to Tables 1 y and 2 Hydrocarbon concentrations were generally consistent with historical data INTERIM REMEDIATION The current interim remediation process includes oxygen injection into SP-1 and SP-1A On July 19, August 2, August 16, August 30, and September 13, 2004, SECOR field personnel conducted oxygen injection into on-site sparge wells SP-1 and SP-1A Approximately 150 W of oxygen was injected into each well simultaneously over a period of 0 5 to 0 8 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 ' concentration increase was observed in MW-2, located adjacent to SP-1 and SP-1A, which _ . showed an increase from 16 milligram per liter (mg/L) to 21 3 mg/L on August 2, 2004 j NLA t 19976 04-30 Report doc SECOR Intemahonal Incorporated z �'t