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Third Quarter Groundwater Monitoring Report September 2003 Boyett Petroleum,419 S.Main,Manteca,CA Page 2 INTERIM MONTHLY GROUNDWATER 11IONITORING ACTIVITIES A provisional increase in the groundwater monitoring frequency was instituted in July 2003. For a period of six consecutive months, water levels in monitor wells MW-1 through MW-3 and MW-6 through MW- 9 will be measured on a monthly basis and groundwater samples will be collected for MTBE laboratory analysis. The locations of the monitor wells are shown in Figure 2, attached, and field observations are included on the Groundwater Monitoring Field Forms, attached. JULY 22, 2003 MONTHLY MONITORING EVENT On July 22, 2003, a Condor representative was on site to measure water levels and collect groundwater samples for MTBE laboratory analysis from monitor wells MW-1, MW-2, MW-3, MW-6, MW-7, MW-8, and MW-9. Field observations included water level measurement (Table 1, on the following page), appearance of samples (color, clarity, and presence of petroleum product sheen or phase in samples), and collection of water quality field parameters. No floating product, sheen, or odors associated with petroleum hydrocarbons were observed in the groundwater inspection samples purged from the monitor wells during the July 22, 2003, groundwater monitoring event. Clarity was good in the initial field inspection samples collected from the monitor wells and turned brown with poor clarity with additional volumes purged; with the exception of MW-1, all the site monitor wells contained sandy sediment. Groundwater elevations fluctuated relative to the previous quarterly monitoring event (June 2003). The average groundwater elevation (14.32 feet) decreased with respect to the previous quarterly monitoring event by 1.06 feet. Groundwater elevation data for the July 2003 monitoring event are presented in Table 1, on the following page. The groundwater elevation contours (Figure 3, attached) estimated using depth to water measurements • from monitor wells MW-1, MW-2, MW-3, MW-6, MW-7, and MW-8 and well survey data collected by Condor indicate a relatively steep groundwater gradient to the southwest. An estimated groundwater gradient of 0.0094 ft/ft towards the southwest was calculated using water level data from monitor wells MW-2, MW-6, and MW-8. The southwest gradient calculated for the July 22, 2003 monitoring event is consistent with that reported in the Second Quarter Monitoring Report June 2003 dated July 30, 2003. The groundwater samples were analyzed for MTBE by EPA Method 8260B by Argon Laboratories, Inc. (Argon) of Ceres, California. Laboratory analytical results for the groundwater samples collected at the site on July 22, 2003, indicate that MTBE was detected in the groundwater samples collected from MW- 1, MW-2, MW-7, and MW-9. The laboratory analytical results for the July 2003 monitoring event indicate a decrease in the concentration of MTBE detected in the groundwater sample collected from MW-1 and an increase in the concentration of MTBE detected in MW-2 and MW-9 relative to the previous sampling event conducted in June 2003. Laboratory analytical results indicate that the MTBE concentrations detected in MW-7 did not change relative to the June 2003 monitoring event. The laboratory analytical results for the July 22, 2003, groundwater monitoring event are presented in Table 1, on the following page. A map representing MTBE isoconcentration contours in shallow groundwater is included as Figure 4, attached- 1 a �� CONDOR