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S ECOR 7-Eleven Store #32262 d InRemtiOn Work Plan for Additional Site Assessment ,March 19, 2004 C.v �' � Page 7 GROUNDWATER MONITORING AND SAMPLING uarterly and Wells MW-7, MW-8, and MW-9 will be incorporated in the grnto the goundwaterrmonditoatwelhwilltbe taken, program. Prior to sampling, depth to water 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 collectedslowlyuntil transfe ed tolevel laboratory-cleaned level. o 40 mL VOAs, sealed with Tef on1 ned caps, sample will be 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 8260B. 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. FEASIBLITY TESTING AND INTERIM REMEDIATION Feasibility Tests In order to minimize the migration of contaminants offsite, SECOR will conduct separate oxygen injection and groundwater extraction feasibility tests at the site. sc�toior Oxygen injection Feasibility Test � „r 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). Z- Ifv�� Dissolved oxygen (DO) readings will be taken'from S-1, MW-5, and EX-1 with a DO meter equipped botft.."' , with a down hole probe before, immediately following, and approximately one day after the injection ec.%MA � event. During injection, 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