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E C 0 R 7-Eleven Store#21756 Quarterly Groundwater Monitoring Report(1Q2004) April 13, 2004 Page 3 �a r A MONITORING AND SAMPLING PROCEDURES The depth to water was measured in four monitoring wells, MW-1 through MW-4, 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 4 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 petroleum (LPH) using 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 R current sampling event are noted on the field data sheets included in Attachment A During purging, temperature, pH, and electrical conductivity were monitored in order 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 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 have been included in Attachment A GROUNDWATER SAMPLE ANALYSES AND RESULTS The groundwater samples collected from four monitoring wells, MWA through MW4, were analyzed for the presence of TPHg, BTEX, and fuel oxygenates MtBE, TBA, dnsopropyl ether (DIPS), ethyl- tert-butyl ether (EtBE), and tert-amyl-methyl ether (TAME) using EPA Method 82606 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 r PURGE AND RINSATE WATER DISPOSAL a Water generated during well sampling and equipment cleaning was pumped into a SECOR truck- mounted water tank The water was transferred into properly labeled 55-gallon drums and stored l` on-site The drummed non-hazardous petroleum hydrocarbon contaminated water Is transported quarterly by Belshire Environmental to Demenno Kerdoon In Compton, California, for disposal ATTACHMENTS " Figures Tables Attachment A—Field Notes Attachment B—Certified Laboratory Analytical Reports and Chain-of-Custody Documentation cc Mr Harlin Knoll, San Joaquin County EHD Mr James Barton, RWQCB, Central Valley Region :I 21756 04-1 Q Report doc SECOR Intemationa!Incorporated I