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,CATC A S S O C I A T E 5 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 MW-4, respectively. Analytical data indicated the groundwater sample from soil boring SB-12 was impacted with TPHd 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 only in the samples collected between 14 and 16.5 feet bgs. Field observations indicated that the samples at these depths also ; ., exhibited the highest FID measurements. Soil samples 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 nondetect. The September 1999 subsurface investigation activities are detailed in ATC's Summary Report, Subsurface Investigation, dated January 10, 2000. 2.0 PUMPING TEST METHODS AND PROCEDURES A groundwater pumping test was proposed in ATC's Workplan for Pumping Test and Subsurface Investigation at Smiths Canal Pump Plant, Stockton, California, dated July 12, 1999. The goal of the groundwater pumping test was to provide aquifer data necessary to characterize the feasibility of operating a groundwater treatment system at the site by providing the following parameters: r�,rrf� 1J � • Radius of influence of groundwater extraction; • Groundwater drawdown; '' • Hydrogeologic properties of the aquifer; -' • Mass extraction rate of groundwater. The scope of work for the pumping test consisted of the extraction of groundwater from monitoring well MW4 for approximately 24 hours, and monitoring the changes in groundwater level in well MW- j: 4 and observation wells MW-1,MW-2,MW-3,MW-5, and MW-6. 2.1 Aquifer PumpineTest F-N The aquifer test was conducted over a 24-hour period by extracting groundwater at a constant rate from well MW-4. The test was performed to determine the aquifer properties and the radius F- of influence for groundwater pumping. Prior to initiating .groundwater pumping, water levels were measured in each site well. ' Measurements were collected using electronic sounders capable of measuring depths to one- hundredth of a foot (0.01 feet). Water elevations are presented in Table 4 and a groundwater gradient map is shown on Figure 3. Prior to initiating the test, ATC place transducers in the extraction well MW2 and observation wells MW-1, MW-2, MW-3, and MW-5 to measure and V tabulate the depth to water in the wells at frequent intervals. wA62574.02Vrports\M-p"teg►.aw 3