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i After the various non soil fill materials were removed from the excavation spoil pile, R.G. Trucking, 716 Mary Lane, Manteca, California, hauled a total of 468 cubic yards of soil i on May 12 and 90 cubic yards of soil on June 15, 1994, to Forward Inc. Landfill located at 9999 South Austin Road, Manteca, California. EXHIBIT D includes the manifest tickets showing the disposition of the removed soil. i CONCLUSIONS The major amounts of contamination found after removal of the diesel storage tanks were under the product line and in the eastern part of the excavation that underlaid tank #1. The over excavation work done on May 9 and 210, 1994, either removed a majority of the contaminated soil or else the lighter fractions of BETX had volatized during the time from tank removal to over excavation. In this case the lateral and vertical extent of contamination was confined to a shallow and limited area beyond the original excavation. It appears that the concrete layer found at a depth of approximately 14 feet throughout the base of the excavation was probably an effective seal against vertical migration of any contamination except in the southeast corner: of the pit. Soil samples taken after the initial over excavation work reported no detectable levels of BETX, but found some TPH-Diesel contamination. Therefore, additional excavating was doneFto remove the remaining C contaminated soil. Resampling after this additional work found minor contamination of TPH-Diesel only at the base of the southern end of the piping trench (PL12S). A leaching potential analysis work sheet for diesel (TABLE 2-2) indicates that the reported TPH- Diesel (170 ppm) can be left in place without threatening the groundwater. Concrete, Inc. has willingly attempted to improve the environmental conditions at their facility by removing the underground storage tanks which were assumed to be the source of contamination and to use what was considered to be the best as well as economical method to remove and dispose of the contamination. In addition, they have constructed concrete wash pits to contain the rinsate and concrete materials that are washed daily from the ready mix trucks. Previously, the wash areas were unsealed. It is not known nor been determined as to the areal extent of the fill materials encountered. The fill debris, not being composed of consistent and competent materials, allows pathways for migration of fluids and semi fluids. In the pit excavation area, it was observed that thin and thick layers of solidified cement and concrete were dispersed in the fill and aided in locally sealing the pathways for migration. It is further concluded that the Mormon Slough, which is located immediately north and runs east-west along the northern boundary of `the property,, is another uncontained tdrainage feature which can allow contaminants to both enter and exit the site. The excavated tank pit is'located in the truck and equipment parking area which was t, covered and sealed with asphalt, but presently is open. It is believed the sooner the 7