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Remediation Report - 152 East 11th Street, Tracy, California Page 12 to remove all material that appeared to be affected by components of gasoline as indicated by visual and olfactory indicators unless, in the opinion of the licensed engineer in 1 responsible charge of the work, silty and sandy soils in the walls of the excavation were susceptible to sudden-onset instability In the latter case, excavation in the cell was stopped to ensure the safety of the excavation and the stability of close-by buildings and infrastructure When soil excavated from the bottom floor of a cell was free of visual or olfactory indicators of contamination by gasoline, or the safe limits of excavation had been reached, the floor of the pit in that area was sampled and the samples preserved for laboratory analysis in the manner described in the next section of this report To protect against developing instability of the walls of the excavation or initiation of bottom-heave or quick-sand conditions, after it had reached its maximum depth and had been sampled each cell was immediately backfilled with 4-in to 1 112 in sieve-size, river- run rock containing no fines The excavator was used to distribute the rock over the area of the cell until the surface of the rock was a few inches above the water table Each excavated and backfilled cell could then be used as dry, hard standing for the heavy equipment and from that platform excavation of contaminated soil from beneath the groundwater table could be extended into adjacent cells In this way contaminated soil was removed from the subsurface over the whole area of the 152 East I lth Street property that had been affected by gasoline The areal extent of the remedial excavation, excluding areas excavated in the clean overburden to form access ramps, is shown on Figures 2 and 5 The contaminated soil was trucked to the soil aeration site that had established, as provided for in the CAP, at 475 West Blewett Road in the rural Vernalis district of San Joaquin County on land owned by the Navarras The location of the soil aeration site is shown on Figure 7 Approximately 1,200 cubic yards, as measured in situ, of contaminated soil were removed from the 152 East 11 th Street property and transported to the aeration site for treatment Excavation of contaminated soil beneath the 125 East 1 l th Street property was completed on March 18, 1996 SOIL SAMPLING IN FLOOR AND WALLS OF REMEDIAL EXCAVATION As noted above, when any cell within the remedial excavation reached a depth beneath which there was no visual or olfactory indications of gasoline contamination, or it was necessary for reasons of safety to locally restrict the maximum depth of excavation, soil samples were recovered from the floor of the pit to quantify the success of the remediation Samples were also recovered from the walls of the excavation to investigate the concentrations of components of gasoline in the affected zone of the subsurface that lies beyond the property boundaries