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' Work Plan for Extended Site Chc�Ricterization: 7500 West Eleventh Street, Tracy, Crl. Page 5 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. 4.3 Back-filling of Excavations To secure the site, gravel was placed in the bottom of Tank Pit No. 1 until the gravel's surface was just above the water table. It was then compacted by vibration so that the bottom - of the pit was stable and dry. The remainder of the pit was then filled with clean overburden and other material that had covered the tanks. Available material from the excavations of the tank pits was also used to backfill Tank Pit No. 2 and similar material was used to back-fill the Dispenser Pit. 4.4 Disposition of Affected Soil Removed from Excavations At the direction of the SJCPHS, affected soil that had been stockpiled on the site and that amounted to 521.25 tons was disposed off-site at the Forward Landfill, a Class II disposal facility in Manteca, California. 5.4 DISTRIBUTION OF HYDROCARBONS IN THE SUBSURFACE The site characterization program conducted during April and May 2000 included installation of seven groundwater-quality monitoring wells at the locations shown on Figure 2. Evaluation of the results of analyses of samples of groundwater recovered from those wells on May 11, 2000 and analyses of soil samples from the well borings and an array of push- probe borings, together with information regarding groundwater flow directions, sources of leakage of fuel hydrocarbons into the subsurface and other information gathered by the site characterization program yielded an interpretation that the site was affected by a primary plume of diesel and gasoline that affected both soil and groundwater. In addition, a secondary plume of diesel and gasoline as well as dispersed low- concentrations of a variety of hydrocarbons in shallow soils - having sources different from those of the primary and secondary plumes of diesel and gasoline - affected the soil on the 7500 West Eleventh Street property. The latter petroleum hydrocarbons affect wide areas of the shallow subsurface beneath the 7500 Eleventh Street property and nearby land. They have been attributed to minor leaks and spills that had occurred from vehicles over the past decades (The San Joaquin Company 2001 d). Figure 2 shows the interpreted extent of the primary and secondary plumes of diesel and gasoline and the areas in which shallow soils are affected by other dispersed hydrocarbons. Figures 4, 5 and 6 illustrate the distribution of petroleum hydrocarbons along sections A-A', B-B' and C-C', the locations of which are also shown on Figure 2. The interpretations shown on Figures.2, 4, 5 and 6 are supported by results from the three additional rounds of groundwater-quality monitoring that have been conducted through September 11, 2001. sic