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i S E C 0 R 7-Eleven Store#21756 Quarterly Groundwater Monitoring Report(4Q2003) • January 20, 2004 Page 3a° �C b MONITORING AND SAMPLING PROCEDURES The depth to water was measured in one of four monitoring wells, MW-4, from top of casing (TOC) using a water level indicator to within 0 01 feet bgs Dissolved oxygen readings were also collected fiy from each well using a YSI Model 550A dissolved oxygen meter equipped with a down hole sensor 6 MW-1 through MW-3 lacked sufficient water for sample collection ,x 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 petroleum (LPH) using 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 one monitoring well, MW-4, were analyzed for the presence of TPHg, BTEX, and fuel oxygenates MtBE, TBA, dnsopropyl ether (DIPE), ethyl-tert-butyl ether (EtBE), and tert-amyl-methyl ether (TAME) using EPA Method 8260B The certified laboratory analytical report and chain-of-custody documentation are presented as Attachment B s z Groundwater analytical results are presented on Figure 3 and are summarized in Tables 1 and 2 Chemical concentrations in MW-4 were generally consistent with historical data 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 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 21756 03-4Q Report doc SECOR International Incorporated i