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Corrective Action Plan Page 13 than an order of magnitude lower than those from samples recovered from close to the water table c ) An excavation with its floor 10 ft beneath the ground surface would probably not penetrate into the extensive stratum of loose sand the top of which is typically 12 ft or more beneath the ground surface, but which is locally somewhat shallower or somewhat deeper (Refer to Figures 7 and 8 ) d ) Excavation to a depth of 10 ft beneath the ground surface would have to be very carefully controlled to limit the risk of the loose, underlying sand heaving or boiling through the bottom of the pit and to limit damage to adjacent property due to any instability that may be encountered due to the presence of lenses of loose silts and sands at higher elevations e ) An excavation with a depth of approximately 10 ft would require the bottom approximate 2 ft depth of backfill to be placed and compacted under water By application of the Observational Method of geotechnical engineering (Ref 3) to control the excavation, it is expected that, when the existing building has been demolished, it would be possible to remove the preponderance of the most severely affected soil from the subsurface beneath the 152 East 11th Street property In the present case, application the Observation Method would involve excavating under the direct supervision of an experienced geotechnical engineer who would observe the changing properties of the soil as the excavation is advanced and evaluate the limiting extent and depth of the pit that could be reached without unacceptable risk that uncontrolled heaving or boiling of sand through the bottom of the pit aught develop, or that the safety of adjacent property or structures might be compromised Excavation over the accessible area of the 152 East 11th Street site would include removal of soil to a depth greater than the depth of the water table over the area beneath and adjacent to the former pump island Thus, any contaminated soil in the shallow zone between the ground surface and the water table in that part of the site will be removed as the work progresses Similarly, any piping that carried gasoline from the underground tanks to the dispensing island or served as vents for the tanks and that were left in the subsurface when the tanks were removed from the site can be removed during the excavation work In this manner, any hydrocarbons affecting shallow soils due to leaks ' from those sources would be eliminated without need for additional borings and soil sampling to delineate their precise extent prior to implementation of the remediation program The excavated soil can be cost effectively remediated and recycled in beneficial use by on- surface aeration under the provisions of SJVUAPCD Rule 4651 (Ref 5) Groundwater water that would flow into a remedial excavation would be affected by moderate concentrations of components of hydrocarbons Contaminants will also adhere