SITE INFORMATION AND CORRESPONDENCE

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C PAGE 03 10/22/2003 14:24 209-579-2"^5 MODESTO ATf � 'CVA rc I; I In September 1999, ATC supervised the advancement of soil borings SB-11, SB-12, and SB-13 at locations approximately 15 feet northwest, south, and northeast of well MW4 respectively. Analytical data indicated the groundwater sample from soil boring SB-12 was impacted with TPM at a concentration of 24,000 ppb. The groundwater samples from SB-11 and SB-13 contained very low to nondetectable concentrations of TPHd. Results of laboratory analyses performed on selected soil samples indicate that TPHd was present in only the samples corrected between 14 and 16.5 feet bga 1 Field observations indicated that the samples at these depths also exhibited the i highest FID measurements. Soil sampler SB11-15.5, SB12-16.5, and SB13-14.0 contained detectable concentrations of TPHd at 390 ppm, 290 ppm, and 1,100 ppm, respectively. All the remaining soil samples were not detected. ,The September 1999 subsurface investigation activities are detailed in ATC's Summary Report, Subsurface Investigadon,dated January 10, 2000. A groundwater pumping test was conducted during a 24-hour period starting on July 22, 1999 and ending July 23, 1999. The goal of the groundwater pump test was to provide aquifer data necessary to characterize the feasibility of operating a groundwater treatment system at the site. The radius of influence of groundwater extraction, groundwater drawdown hydrogeologic properties of the aquifer, and the mass extraction rate of groundwater were to be determined by this pumping test. The results of the groundwaterm pu ping test showed the radius of influence for groundwater extraction at the site is greater than 50 feet. Hydrogeologic properties of the aquifer, specifically, hydraulic conductivity (1), transmissivity (T), and the coefficient of storage (S) were measured. The average hydraulic conductivity (K) was calculated to be 0.001 meters/seoond, the average transmissivity (T) was calculated to be 6.79 square feet/minute, the Coefficient of Storage (S)was calculated using Cooper- Jacob solution to be 0.0015. In addition, based on analytical results of samples taken during the groundwater pumping test, 6,000 gallons of groundwater were extracted from the subsurface, and 0.00005 lbs. of TPHd were removed from the subsurface during the twenty-four hour test. The groundwater pumping test activities are detailed in the Summary Report ofPumpb{g Test, dated 1 September 19, 2000, 1 FIELD WORK From April 4 to June 30, 2003, static fluid levels were measured on generally a weekly or bi- weekly basis in monitoring wells MWl through MW7. This occurred during groundwater extraction activities located on the northern adjacent property. On August 12, 2003, after groundwater extraction activities terminated, static fluid levels were again measured after the groundwater table bad a chance to equilibrate. Table 1 summarizes the water level data collected during the reporting period and provides previous data for comparison. A groundwater gradient map was created for,each monitoring event (Figures 2 through 10) using groundwater elevation data from all the wells monitored. Figures 2 through 9 depict a generally north groundwater flow direction at a magnitude of which ranged from 0.04 to 0.07 or 211 to r 370 feet/mile. Figure 10 depicted a generally north groundwater flow direction at a magnitude of i 0.01 or 53 feet/mile, a w:w2574.0quwUy3qw2007.dac 3