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3.2 Lateral Extent of Contamination Working from the ramp on the north wall, the excavator excavated the east wall throughout the day of November 17 Initial PID readings at the base of the wall(depth 33 feet)were 15-20 ppm, but readings in the 500-2000 ppm range were measured at depths of 10-20 feet Therefore, Upgradient directed the operator to move the protective fencing back 8-10 feet along the east side of the excavation to allow further excavation on that wall Excavation of the east wall continued on Saturday, November 18 By early afternoon, the wall had been cut back approximately 10 feet to the edge of the sidewalk To avoid damaging the sidewalk or endangering the large Exxon station sign located in the sidewalk, excavation of the ea_-* wall .,�as terminated Excavation of the south wall began on November 20 Strong odors were again evident, and PID readings reached 1300 ppm at 9 15 a m at a depth of 18 feet By 9 30, readings had decreased to 150 ppm at a depth of 26 feet in gray, silty clay Therefore, Upgradient directed the operator to begin digging back (south)at this depth The operator ramped down 3 feet in order to accomplish this Excavation of the south wall continued through the afternoon of November 20 When excavation was terminated at 3 30, this wall had been cut back approximately 30 feet from its position on November 17 PID readings ranged from 35 ppm at 15 feet to 50 ppm at 26 feet Excavation of the west wall took place on November 21 To avoid endangering the building, excavation began 8 feet from the building and the sidewall was sloped at a gradual angle The south half of this wag was reached from the ramp on the south wall, and the north half of the wall was reached from the ramp on the north wall (Figure 4) 4.0 COLLECTION OF CONFIRMATORY SOIL SAMPLES Figure 4 shows the final dimensions of the excavation Upgrachent measured the excavation on the morning of November 22 and laid out sampling stations at 20-foot intervals along each wall Eleven stations were marked, with 2 sample locations at some stations where the height of the sidewalls exceeded 30 feet Because of the very large size of the excavation, several of the sample locations were beyond the reach of the excavator bucket Therefore, with the mutual consent of all parties, the samples were collected by lowering the Upgradient geologist into the excavation with a truck-mounted crane equipped with a slung seat Figures 5A and B are photographs of this procedure Sampling began on the south end of the west wall at approximately 1145 a m and proceeded clockwise around the excavation The general procedure was to log the walls from bottom to top A detailed log was made at each sampling station, and a tape measure was used to measure the depth of important features such as bedding contacts and sample points Mr Knoll arrived at the site at approximately 12 00 p m, and at his suggestion, samples were 3