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Corrective Action Plan <br /> Page 25 <br /> contam� <br /> Hants are extracted from the carbon in a permitted re-activation plant and a <br /> certificate of VOC destruction issued so that the material can be recycled in beneficial use <br /> A Waste Generator's Number issued by the California EPA will be obtained to comply <br /> with the applicable regulations that control the off-site disposal of the spent carbon <br /> accumulating in the surge tank and fine particulate <br /> F,ltratnn Systems To prevent sand g <br /> matter clogging the air stripper and reducing the contaminant adsorption capacity of the <br /> GAC units, the groundwater treatment system includes primary and secondary filtration <br /> systems <br /> Groundwater entering the treatment system from the recovery wells passes directly into a <br /> vertical, silica-media filtration unit (System 9 on Figure 10) which removes all but the <br /> finest suspended matter <br /> The vertical, silica-media filtration unit comprises two parallel vessels, each charged with <br /> 4001b of crushed-silica, filter media It has a hydraulic capacity of 60 gpm when charged <br /> with fresh filter media and a minimum capacity of 40 gpm when the filter media is fully <br /> loaded <br /> Influent water enters the top of the unit and flows downward through the filtration vessels <br /> into underdratns and from there into the unit's discharge line As solids accumulate in the <br /> filter media the pressure drop across the vessels increases Thts pressure drop is monutored , <br /> by instruments and when it increases to a predetermined level that indicates that the filters <br /> are becoming blocked, an automatic controller causes the flow through the filter u to be <br /> reversed for a few minutes so that each of the two vessels is backflushed in turn The <br /> accumulation of filtrate solids is discharged with the backflush water via piping included <br /> for that purpose <br /> Backflush water from the vertical, silica-media filter is discharged into a sand bin (System <br /> 10 on Figure 10) The sand bin is a low, rectangular holding tank that is divided into two <br /> compartments In the first compartment, which has a 220 gallon nominal capacity, solids <br /> exhausted from the filtration unit drop out of the backflush water and settle to the bottom <br /> The second compartment of 140 gallons nommal capacity, is separated from the first by a <br /> weir and contains a float-controlled, submersible pump (System 11 on Figure 10) which <br /> discharges the backflush water to recovery well RW 2 via an underground pipe <br /> Immediately it enters the well, this water is returned to the treatment system by the well- <br /> pump that operates continuously throughout the filtration unit backflush cycle <br /> ' The total volume of filtrate solids that accumulates in the sand bin is small They are <br /> periodically shoveled out and held in an open-topped, 50-gallon steel drum until they dry <br /> They are then be aerated to remove any traces of components of gasoline and the treated <br /> material sampled and analyzed When it is free of detectable concentrations of the analytes <br /> of concern, it is be disposed as clean material The total volume of filtrate that has to be <br />