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s • � EC ® R � a 7-Eleven Store #32262 Work Plan for Additional Site Assessment and Interim Remediation March 19, 2004 Page 7 GROUNDWATER MONITORING AND SAMPLING Wells MW-7, MW-8, and MW-9 will be incorporated into the quarterly groundwater monitoring and sampling program Prior to sampling, depth to water in the groundwater monitor well will be taken Each well will be sampled by purging approximately 3 casing volumes of water using a downhole pump or hand bailer until groundwater parameters of pH, temperature, and conductivity stabilized as measured by portable meters calibrated to a standard buffer and conductivity standard Groundwater samples will then be collected by lowering a clean disposable bailer into the well and collecting a representative sample of the formation water If the well is slow to recover, the sample will not be collected until the water level has reached 80 percent of its initial level The groundwater sample will be slowly transferred to laboratory-cleaned 40 mL VOAs, sealed with Teflon -lined caps, and transferred to cooled storage Groundwater samples will be submitted to Kiff Analytical, a California certified laboratory, for analysis of BTEX, TPHg, MtBE, and, TBA, DIPE, EtBE, and TAME by EPA Method 8260E WASTE HANDLING AND STORAGE During drilling operations, all augers, sampling tools, and down hole equipment will be steam cleaned prior to use All rinsate water, purge water and soil cuttings generated during the drilling operations will be stored in 55-gallon drums at the site pending laboratory analysis for proper disposal FEASIBILITY TESTING AND INTERIM REMEDIATION Feasibility Tests In order to minimize the migration of contaminants offsite, SECOR will conduct separate oxygen infection and groundwater extraction feasibility tests at the site Oxygen Injection Feasibility Test , SECOR proposes to conduct an oxygen injection test using the proposed injection well, S-1 Approximately 150 to 300 cubic feet (ft) of oxygen will be injected into well S-1 (Figure 5) Dissolved oxygen (DO) readings will be taken from S-1, MW-5, and EX-1 with a DO meter equipped with a down hole probe before, immediately following, and approximately one day after the injection event During infection, the oxygen flow rate and injection pressures will be recorded Lower explosive limit (LEL) oxygen readings will also be collected in well MW-5 and EX-1 before and after oxygen injection Data collected during the test will be used to determine the oxygen injection radius of influence SECOR expects to inject oxygen for approximately two hours If DO readings measured in MW-5 and EX-1 show a significant increase from baseline levels, oxygen injection may be used as an interim remedial approach to destroy dissolved MtBE by stimulating biologic activity within the saturated zone Groundwater Extraction Step-Draw Down and Constant Discharge Feasibility Test In preparation for the groundwater extraction test, a 6,900-gallon holding tank will be set at the site adjacent to the extraction well A 3-inch diameter electric submersible groundwater pump, controller, and generator will be used to extract groundwater from EX-1 The pump will be set 1 foot off the bottom of the well and depth to the pump intake from top of casing will be recorded A valve and flow meter connected in-line with the discharge hose will be used to control and measure flow rate 32262 Offsite well install and interim remediation workplan doc SECOR International Incorporated