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4 On November 21, 1988, six exploratory borings were drilled to depths ranging from 12 to 13 feet below grade at the site. Analyses of soil samples collected from depths of 5 and 10 feet showed detectable concentrations of TPH as diesel (TPH-D) up to 2 , 900 parts per million (ppm) and TPH as gasoline (TPH-G) up to 360 ppm. Ground water was encountered between 11 and 12 feet below grade. In February 1989, additional soil samples were collected at the site from 12 test holes at depths of 5 and 10 feet below grade using a backhoe. Analyses of soil samples detected concentrations of TPH -D of up to 3, 600 ppm and TPH-G up to 170 ppm. Results of the investigative work revealed the presence of diesel-range contamination in the subsurface soil extending to a depth of 10 feet below grade and encompassing an area of approximately 3,700 cubic feet. Soil analytical data from test holes suggests that gasoline-range hydrocarbon contamination is limited to the northern portion of the site. Figure 3 shows the locations of the soil borings and test holes with corresponding TPH concentrations detected in the soil samples. Mobil Oil Corporation contracted Alton Geoscience, Inc . in February 1990 to characterize the extent of hydrocarbons in the soil onsite for potential offsite disposal. The results of the soil profiling were to be used during soil excavation to segregate the soil for disposal at an appropriate offsite facilities . Based on the results of this in-situ soil characterization, approximately 6, 100 cubic yards of soil were excavated and properly disposed of at either the Class II facility of Liquid Waste Management, Inc. or at the Class III Durham Road Landfill. To assess the potential impact of hydrocarbon constituents on the ground water beneath the site, Alton Geoscience installed four ground water monitoring wells onsite on September 1990 . The findings and conclusions from this and past site investigative work, and from the results of laboratory analyses and field observations of the preliminary ground water investigation are presented in the December 1990 report submitted to the appropriate regulatory agencies. Pertinent findings of the preliminary study are summarized below: o The soil excavation activity had effectively removed the hydrocarbon contaminated soil within the confines of the property. It is estimated that adsorbed-phase hydrocarbons remaining onsite, if any, are present only in concentrations of less than 10 ppm as TPH-G and/or TPH-D and are limited to the capillary fringe. It is also most likely that no detectable concentrations of BTEX constituents above laboratory . detection limits are present in the soil onsite.