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Corrective Action Plan Page 14 <br /> to clay and fine silt particles that become suspended in that water due to the action of the <br /> excavator It would be beneficial in terms of reducing the total load of hydrocarbons in the <br /> subsurface to pump this contaminated water from the excavation and treat it so that it can <br /> be discharged as clean water Aeration in temporary storage tanks and treatment by <br /> activated-carbon adsorption provides a practical means of treating the pumped water if the <br />' rate at which volatile organic compounds are emitted to the air complies with SJVUAPCD <br /> Rule 2020 (Ref 6) and that any discharge to the municipal storm-sewer complies with <br /> CRWQCB Order No 92-150, and NPDES No CA0082929 <br /> It is expected that pumping a volume of water approximately equal to three times the <br /> volume of water that would accumulate in the bottom of an excavation under the action of <br />' gravity would be sufficient to remove the most severely contammated groundwater from <br /> the near field of the excavation as well as the contaminated water that will collect in the pit <br /> bottom as the excavation work progresses Based on the projected dimensions of the <br /> remedial excavation that would amount to some 300,000 gallons <br /> Pumping from an excavation induces significant hydraulic forces that exacerbate any <br /> tendency for the pit bottom to heave or be affected by sand boils Also, inflow through the <br /> walls can cause raveling and piping in non-cohesive soils For these reasons, the total <br /> volume and rate of pumping must also be under the control of an experienced geotechnical <br /> engineer who applies the Observational Method to limit any risks to the stability of the <br /> excavation and surrounding property that may be generated by the groundwater pumping <br /> procedure <br /> The authors of this plan have developed and applied a method for back-filling excavations <br />' when the pit bottom is submerged under a shallow to moderate depth of water The <br /> technique involves placement of uniform layers of clean, single-sieve-size crushed rock <br /> over the bottom of the bottom of the pit until the surface of the rock is just above the <br /> water table The grading and mechanical properties of the crushed rock are selected so <br /> that fines are not generated when the material is compacted, so that is retains its very high <br />' permeability, and so that it will not be susceptible to liquefaction under seismic loading <br /> Back filling by this method can be properly controlled and the rock adequately compacted <br /> when the total depth of rock required to provide dry standing on the bottom of the <br />' excavation is not more than about 3 ft When the rock-filled pit bottom has been <br /> thoroughly compacted, the remaining backfill can be placed and compacted and its density <br /> controlled in the conventional manner Subject to the specific conditions observed by the <br />' responsible geotechnical engineer when the excavation is made, it is expected that this <br /> method would permit an excavation with a total depth of between 10 and 11 ft to be <br /> backfilled at the 152 East 11th Street site in such a manner that the restored ground <br /> would be suitable for construction of conventional commercial buildings <br /> PROPOSED REMEDIATION PROGRAM <br /> Based on the considerations discussed above, including the recently changed <br /> circumstances of the site whereby third-party losses due to demolition of the existing <br />