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taken from the north end of the tank cavity at concentrations . of 0 . 1 ppm in the northwest corner at 15 fbg and 1. 7 ppm in the northeast corner at 14 . 5 fbg. Organic lead and ethylene dibromide were not detected above reported detection limits in all soil samples. Under the direction of the California Regional Water Quality Control Board, Central Valley Region (RWQCB) , a site investigation was completed by WCC. The objectives of the site investigation were to define the extent of subsurface contamination and identify remedial alternatives. Monitoring Wells MW-1 through MW-4 were dry in March and April 1990. In March and April 1990, five soil borings were drilled and sampled. TPH-G and BTEX were detected in soil samples collected at 31 and 55 fbg from MW-7 at concentrations of up to 20 ppm. The five soil borings were converted into ground water Monitoring Wells MW-5 through MW-9 . In May 1990, the average depth to ground water was determined _ to be approximately 57 . 5 fbg. The approximate ground water gradient across the site at this time was reported by WCC to be 0. 008 foot per foot toward the west. Alton Geoscience's interpretation of WCC's ground water elevation data shows the ground water gradient to have been actually toward the north. Ground water samples obtained on May 4 and 11, 1990, from Monitoring Wells MW-5 through MW-9 were analyzed for TPH-G and BTEX. Samples obtained from PAW-7, MW-8 , and MW-9 contained detectable concentrations of TPH-G and/or BTEX constituents up to 3 , 400 ppb. In March 1991, Alton Geoscience was retained by Caltrans to conduct supplemental ground water monitoring and sampling to determine the status of the existing monitoring wells onsite. In May 1991, Monitoring Wells MW-2 through MW-9 were monitored and MW-7, MW-8 , and MW-9 were sampled for TPH-G and BTEX. Monitoring Wells MW-1 through MW-6 were dry. Depth to ground water in MW-7 through MW-9 averaged approximately 65 fbg. Water samples from MW-9 had detectable concentrations of TPH-G at 2 , 100 ppb and BTEX constituents up to 310 ppb. No TPH-G and BTEX constituents were detected in the water samples from MW-7 and MW-8 . A ground water gradient map is shown as Figure 3 . PROPOSED SCOPE OF WORK Alton Geoscience proposes to perform the supplemental site investigation and remedial planning study in accordance with the requirements of the RWQCB and San Joaquin County Environmental Health Department (SJCEHD) . As required by the + SJCEHD and the RWQCB, the extent of hydrocarbons detected in I� ground water must be defined as part of a sub-surface