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Site Characterization Report: 7500 West Eleventh Street, Tracy, CA. Page 3 `rf 2.0 REMOVAL OF UNDERGROUND TANKS A report of tank removal that documented the removal and disposal of the underground tanks from the site and the results of analyses of samples of soil and groundwater recovered from the tank pits, the pipeline trenches and the stockpiles of over-excavated { soil was submitted to the SJCPHS on January 16, 1999. (Dietz Irrigation, 1999a.) The locations of the pump islands, tank pits and pipeline routes are shown on Figure 3. Following is a summary of the information regarding the environmental condition of the subsurface gathered when the underground storage tanks and other infrastructure were removed from the property. 2.1 Removal of Registered Tanks The four registered underground tanks that were in use prior to the closing of the Olympian Service Station were removed from Tank Pit No. 1. They included one 10,000- gal. diesel tank, one 3,500-gal. diesel.tank and two $,000-gal. gasoline tanks. All were in excellent condition and no sources of leaks from the tanks or attached piping were identified. When Tank Pit No 1 was excavated, it was necessary to penetrate below the groundwater table to effect the tank removal. When the water in the pit bottom came to a state of quiescence, a floating scum of aged fuel hydrocarbons covered the water surface. That a ) floating product was skimmed from the water surface using a vacuum truck and shipped under control of a hazardous waste manifest for disposal at a permitted facility. This procedure cleared the groundwater in the tank pit, and it remained free, for a time, of any r: obvious presence of fuel hydrocarbons. However, over the next several hours, additional floating product seeped into the groundwater from the southwestern corner of the pit. This floating product was also removed from the subsurface by drawing it into a vacuum truck for off-site disposal. As floating product flowed into the tank pit from its western side, it was continually skimmed away until the flow of product into the pit ceased completely. A total of some 2,000 gallons of floating product and affected groundwater was removed from the subsurface by those operations. 2.2 Removal of Piping and Pump Islands Following removal of the registered tanks from Tank Pit No. 1, operations were begun to remove their associated piping. That work revealed an unusually complex maze of piping centered beneath the former location of the pump islands, with branches extending to other locations on the property. When the removal operation was complete, the total piping amounted to 6,000 linear feet, which is an extraordinary quantity compared to that normally found at the common type of service station. The extensive excavation necessary to remove the maze of pipelines revealed that there were at least three distinct layers of concrete and bituminous macadam paving and of l other service station'infrastructure laid down on the site at different times. It appears that, sic