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Extended Site Characterization Report: 7500 West Eleventh Street, Tracy, CA Page 5 3.0 REMOVAL OF UNDERGROUND TANKS AND PIPELINES Following is a summary of the information regarding the environmental condition of the subsurface that was gathered when the underground storage tanks and other infrastructure were removed from the 7500 West EIeventh Street site in December 1998. 3.1 Removal of Tanks Four registered underground tanks that were in use prior to the closing of the Olympian Service Station were removed from Tank Pit No. 1, which was located as shown on Figure 3. They included one 10,000-gal. diesel tank, one 3,500-gal. diesel tank and two 8,000-gal. gasoline tanks. All were in excellent condition and no sources of leaks from the tanks or attached piping were identified(Dietz Irrigation 1999). 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 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. That procedure cleared the groundwater in the tank pit, and it remained free, for a time, of any 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. That floating product was also removed from the subsurface by drawing it into a vacuum truck for off-site disposal. In total, some 2,000 gallons of floating product and affected } = => groundwater were removed from the subsurface by those operations. As the complex piping system was removed from the subsurface, two lines, having f distinct linear routes, were found and removed by trenching. The locations of the trenches, designated Pipe Trench Nos. 1 and 2, are also shown on Figure 3. After the pipes had been removed, Dietz Irrigation began to recover soil samples from along their trench lengths. However, during the course of that work, another underground storage tank was detected. Further exploration revealed a total of four additional 1,000-gal, -__ underground fuel storage tanks in that vicinity, the presence of which was previously unknown. These very old (circa 1930) tanks, the former locations of which are shown on Figure 2, were badly deteriorated. The pit from which they were exhumed was designated yj Tank Pit No. 2. Its location is shown on Figure 3. Their remains were lifted from the j ground, cut up and shipped off-site for disposal. '-_ 3.2 Over-excavation of Dispenser Pit Excavation of the piping (in excess of 6,000 linear feet) from the area around the former pump islands revealed that soil in that vicinity was heavily affected by fuel hydrocarbons =' to a depth at Ieast equal to that of the groundwater table. To remove that heavily affected soil, Dietz Irrigation over-excavated the area and formed a temporary stockpile of that material. For convenience of reference, the area from which that soil was excavated was designated the "Dispenser Pit." See Figure 3 for location. sic