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S Ms. Victoria McCartney L.i S E C O R ' June 26, 2003 Page 2 petroleum hydrocarbons as gasoline (TPHg) by EPA Method 8015, benzene, toluene, ethylbenzene, and total xylenes (BTEX), methyl tertiary butyl ether (MtBE), ethyl tertiary butyl ether (EtBE), tertiary butyl alcohol (TBA), tertiary amyl methyl ether (TAME), 1,2-dichloroethane (1,2-DCA), ethylene dibromide (EDB), di-isopropyl ether (DIPE), Methanol, and Ethanol by EPA method 8260. Groundwater analytical reports for the groundwater samples collected from well MW-8 are presented as Attachment 1 and the analytical data is summarized in Table 1. MtBE was detected in the groundwater sample collected prior to the aquifer test at a concentration of 19,000 micrograms per liter (Ng/L). MtBE was detected in the groundwater sample collected at the conclusion of the aquifer test at a concentration of 10,000 pg/L. AQUIFER TESTING To assess aquifer properties beneath the site, a slug injection test and a 24-hour duration constant- discharge pumping test were conducted on well MW-8. The purpose of these tests were to evaluate hydrogeologic conditions beneath the site and to determine whether groundwater extraction from MW-8 is a feasible alternative for remediating dissolved MtBE in groundwater from beneath the site. SLUG TEST A slug injection test was performed on well MW-8 on March 11, 2003. The test was performed by creating a near instantaneous change in water level in the well by inserting a PVC pipe in the well. The hydraulic response in the well was measured using a Hermit 1000C data logger and a pressure 1�1 transducer until the groundwater level had equilibrated to a static condition or until sufficient data 'l,l was obtained for analysis. Slug test data was evaluatedusln a method described by Bouwer and Rice (1976) and Bouwer (1989), incorporating AQTES=9. The slug test was performed to estimate the aquifer parameters of hydraulic conductivity (K) and transmissivity (T) before beginning the pumping test. The results of the slug test, which are summarized in Table 2, indicate a transmissivity of 1,950 gallons per day per foot (gpd/ft) and a hydraulic conductivity of 0.01 " centimeters/second (cm/sec). These results were used to estimate an initial pumping rate for the step-drawdown test described in the next section. PUMPING TEST On March 23, 2003, pressure transducers with built-in data loggers were installed in pumping well MW-8 and observation wells MW-1, MW-2, MW-4, MW-5D, and MW-6D to monitor water levels before, during, and after aquifer testing. The data loggers in the observation wells were programmed to record water level depths at one-minute intervals. The data logger in the pumping well was programmed to collect data at time intervals on a logarithmic scale. I A step-drawdown test was conducted on April,`2003, using the submersible pump in well MW-8. Before the start of the test, water levels in pumping well MW-8 and the observation wells were measured. On April 2, 2003, the constant-discharge pumping test was initiated. The objective of the test was to create hydraulic stress in the aquifer by pumping well MW-8 at a constant pumping rate, while monitoring drawdown in the observation wells. During the constant-discharge pumping test, groundwater was continuously extracted for 1,426 minutes at a rate of 8.5 gallons per minute (gpm), while water levels were monitored in the pumping well and the five observation wells. Extracted groundwater was discharged to a 21,000 gallon-capacity holding tank on-site. The groundwater extraction rate and cumulative volume of groundwater extracted were monitored using I:\Chevron\91452\REPORTSWquifer Test Report and Plan for Interim Remedial Measure.doc