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E C ® R 7-Eleven Store#19976 Quarterly Groundwater Monitoring and Remediation Progress Report (102003) May 13,2003 Page 4 MONITORING AND SAMPLING PROCEDURES The depth to water was measured in monitoring wells MW-1 through MW-7, MW-1A, MW-4A, and MW-5A from top of casing (TOC) using a water level indicator to within 0 01 feet bgs Dissolved oxygen readings were also collected from each well using a YSI Model 550A dissolved oxygen meter equipped with a down hole sensor i Well purging and sampling equipment is thoroughly cleaned prior to purging and sampling each well The sampling procedure for each well includes 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 are 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 are noted on the field data sheets included in Attachment A During purging, temperature, pH, and electrical conductivity are monitored in order to document that these parameters are stable prior to collecting samples After purging, water levels are allowed to recover to 80% of the original levels prior to collection of the water sample Groundwater samples are 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 have been 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 the presence of TPHg, BTEX, and fuel oxygenates MtBE, tert-butyl alcohol (TBA), diisopropyl ether (DIPE), ethyl-tert-butyl ether (EtBE), and te rt-amyl-m ethyl ether (TAME) using EPA Method 8260B 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 Chemical 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 sparging into SP-1 and SP-1A During the first quarter 2003, mobile SVE was not performed at the site due to a change in environmental consultants for 7-Eleven, Inc, and upgrades to the remediation equipment Mobile SVE will resume during the second quarter 2003 On March 14, 2003, SECOR field personnel performed oxygen injection into site sparge wells SP-1 and SP-1A Approximately 27 pounds of oxygen was injected into each well simultaneously over a = period of approximately one hour (Table 4) Dissolved oxygen concentrations were measured before and after the injection event in each sparge well and in monitoring wells adjacent to the sparge wells The highest D 0 increase was observed in MW-2, located adjacent to SP-1/SP-1A, which saw an increase from 1 8 milligrams per liter (mg/L) to 15 2 mg/L SECOR will continue biweekly oxygen w injection during the second quarter 2003 PURGE AND RINSATE WATER DISPOSAL Water generated during well sampling and equipment cleaning is pumped into a SECOR truck- mounted water tank The water is transferred into properly labeled 55-gallon drums and stored on- site The drummed non-hazardous petroleum hydrocarbon contaminated water is transported quarterly by Belshire Environmental to Demenno Kerdoon in Compton, California, for disposal 19976 03 10 Report SECOR Intematrona!Incorporated