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Atlantic Richfield Company(ARCO) 6 ARCO Station #4932 16 E Harding Way Stockton CA January 15,2002 • Groundwater Extraction Well Installation. One 4-inch diameter groundwater extraction well will be installed with a 10-inch hollow-stem auger to a depth of approximately 50 feet bgs The well will be screened from approximately 25 to 50 feet bgs This well will be installed near boring S13-2 (Figure 2), where the highest concentrations of MtBE in groundwater have been reported • Soil Selection and Analysis. Soil samples will be collected at 5-foot intervals and will be sent under chain-of-custody procedures to a California State-certified laboratory Selected soil samples will be analyzed for TPHd, and TPHg using modified EPA Method 8015, BTEX using EPA Method 8020, and for MtBE, DIPE, TAME,EtBE, TBA, 1,2-DCA, and EDB by EPA Method 8260A i • Extraction Well Development and Sampling. After installation, the extraction well will be developed by rigorously surging the well over the length of the screen interval and by purging approximately 10 casing volumes of water After well development, groundwater samples will be collected and sent under standard chain-of-custody procedures to a California State-certified laboratory The groundwater samples will be analyzed for TPHg and TPHd using modified EPA Method 8015, and BTEX using EPA Method 8020, and fuel oxygenates by EPA 8260A • Well Surveying. Upon completion of well construction,the groundwater extraction well will be surveyed to a local benchmark relative to mean sea level . Field and laboratory procedures are included as Attachment C GROUNDWATER EXTRACTION FEASIBILITY TESTING SECOR will conduct a three-day GWE feasibility test at the site The test will utilize the proposed groundwater extraction well to conduct a hydraulic step-drawdown test in order to further evaluate hydrogeologic conditions beneath the site The data collected from the test will serve to evaluate groundwater extraction as a viable remedial technique at the site A 3-inch diameter electric submersible groundwater pump with controller will be installed in the groundwater extraction well approximately 4 feet from the bottom of the well A valve and flow meter connected in-line with the discharge hose will be used to control and measure flowrate Water levels in the groundwater extraction well and observation wells (MW-1, MW-3, MW-4,MW-5,MW-6, and MW-7)will be monitored during the test The distance vs response relationship between the extraction well and the observation wells will be calculated, and the constant and optimal pumping rates will be determined upon evaluation of the data Extracted groundwater will be discharged to a holding tank All water generated during the pump test will be transported offsite for proper disposal WKPLAN4932—1-11-02 doc