ARCHIVED REPORTS XR0009904 - Laserfiche WebLink

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' Corrective Action Plan Page 21 The total number of soil samples recovered from the excavation and analyzed for components of gasoline will be determined by the subsurface conditions as they will be revealed as the work progresses but, as a minimum, one sample will be recovered from points, each of which will be not more than 50 linear feet apart, along the walls of the excavation at a depth corresponding to that where the most severe contamination is found and from each 2500 square feet of the floor of the excavation ' Pumping of Groundwater from Remedial Excavation When the remedial excavation is complete, highly permeable, gap-graded, crushed rock containing no fines will be placed and compacted in the bottom of the pit The surface of the rock fill will be just above the level of standing water in the excavation This will ' stabilize the submerged pit bottom and resist sand boil and bottom heave The procedures to be used to place and compact the crushed rock are detailed later in this plan When the crushed rock is in place, a sump will be formed at a location where the undisturbed pit bottom beneath the rock is stable and free of any propensity to heave or boil A trash pump will be used to pump contaminated groundwater out of the sump into a treatment system so that it can be decontaminated before discharge to the municipal storm-water sewer As detailed later, the treatment system will include aeration, sparging and carbon adsorption of the groundwater pumping and treatment will be to remove contaminated The objective gr P P groundwater that flows into the pit bottom during excavation and to remove an additional ' sizable volume of groundwater from the most severely affected zones in the near field of the site so that the contaminant load in the subsurface will be significantly reduced The reduction in contaminant load will promote natural bioremediation of any soil that is not ' safely accessible to excavation and reduce the time required for the currently low concentrations of hydrocarbons in groundwater in adjacent areas to further decrease to concentrations of little or no regulatory concern Because pumping of groundwater from the remedial excavation will increase the ' propensity for bottom heave or sand boiling and may promote accelerated transport of fines from the strata of loose sands and silts in adjacent areas, all pumping operations, including, determination of allowable draw down, maximum pumping rates, total pumped ' volume and any and all procedures or operating conditions that might affect the stability of the remedial excavation or the surrounding property, will be subject to the control of the California-licensed geotechnical engineer in responsible charge of the work Estimated InIumc of Groundwater to bc Pumped Unless safety concerns restrict the scope of the pumping operations, to provide for removal of contaminated groundwater that flows into the excavation and to flush the most severely contaminated water from surrounding strata it is proposed to pump, treat and