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October 2, 1990: Alton Geoscience monitored and sampled the newly installed ground water monitoring wells. Analysis of ground water samples collected from AW-3 detected TPH-G at 4,200 ppb, TPH-D at 10,000 ppb, and benzene only in AW-3 at 0.5 ppb (Alton Geoscience 1990). April 30 and May 1, 1991: As part of a supplemental site investigation, Alton Geoscience drilled additional Soil Borings B-1 through B-9 and conducted a qualitative shallow ground water survey to define the extent of the dissolved-phase plume. Based on the results of the qualitative survey, Soil Borings B-2, B-3, B4, and B-9 were completed as ground water Monitoring Wells AW-5, AW-7, AW-6, and AW-8 (Figure 2). TPH-D was detected only in the soil sample collected at 6 and 11 fbg from AW-6 at concentrations of 180 and 5.4 ppm. TPH-G was not detected in any of the soil samples (Alton Geoscience 1991). May 7, 1991: Alton Geoscience performed monitoring and sampling of Wells AW-1 through AW-8. Ground water samples were analyzed for TPH-G, TPH-D, and BTEX. AW-1 and AW-3 were additionally analyzed for fecal coliform. Petroleum hydrocarbons were not detected at or above method detection limits in any of the samples, except AW-3,which had detectable concentrations of TPH-G at 210 ppb, however, the laboratory report indicated the sample chromatogram did not match a typical gasoline pattern. TPH-D was not detected in any of the samples at or above method detection limits (Alton Geoscience 1991a). August 21, 1991: Alton Geoscience conducted quarterly ground water monitoring and sampling of Monitoring Wells AW-1 through AW-8. Detectable concentrations of dissolved- phase petroleum hydrocarbons were reported only in AW-3, for TPH-G at 620 ppb and TPH-D at 22,000 ppb. The laboratory report indicated the samples did not appear to contain either gasoline or diesel (Alton Geoscience 1991b). November 26, 1991: Alton Geoscience monitored and sampled Monitoring Wells AW-1 through AW-8. Analysis for TPH-G detected concentrations above the reported method detection limit only in AW-3 at 610 ppb, however, the May 5, 1992 revised laboratory report indicated the sample did not contain gasoline at or above method detection limits. Although concentrations of TPH-D were reported in all of the ground water samples, the December 16, 1991 revised laboratory report indicated only the sample collected from AW-3 contained diesel. The concentrations reported for the remaining samples were due to several unidentified peaks on the sample chromatogram. Copies of the revised, previously unavailable November 1992 laboratory reports are attached. February 1992: Alton Geoscience conducted quarterly ground water monitoring and sampling of Monitoring Wells AW-1 through AW-8. Dissolved-phase petroleum hydrocarbons were not detected at or above method detection limits in any of the samples collected from the monitoring wells.