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f Corrective Action Plan Page 24 groundwater so that their concentrations will be substantially reduced compared to those in the water in the remedial excavation ' To further purge volatile organic compounds VOCs from P (VOCs) the water, sparging air is forced into the bottom of the tanks via manifolded systems of 0 75 inch diameter, perforated, Schedule 80 PVC pipes that are arranged in parallel, on approximately 18 in centers along the full length of the bottom of the tank The air is supplies by a 125 cubic foot per minute (cfm) capacity, mobile, air compressor The curtain of bubbled air rising ' though the full volume of the tank will sparge any remaining VOCs not removed by aeration ' To provide reserve capacity and for re-circulation and re-treatment in case of a system upset and to enable the total flow through the treatment system to be balanced, two identical sparging tanks (see Units TI on Figure 10) are provided and they are connected together through a system of pipes and valves that permits them to be filled in any order, used singly or in unison and discharged either to the downstream elements of the treatment system or back into the remedial excavation Carbon AdSorPtion Units After passing through the sparging tanks, the water stream is pumped through a pair of granular, activated-carbon, adsorption vessels (Units CAC-1 on Figure 10) which are connected in series Each vessel has a hydraulic capacity of 50 gpm and contains a 1000 lb charge of activated carbon derived from bituminous-coal The purpose of these units is to remove any traces of long carbon-chain components of gasoline that might remain in the water stream after it has been aerated and sparged in the upstream elements of the treatment system They also provide a conservative defense ' against discharge of any water containing impermissible concentrations of fuel hydrocarbons that might pass through the treatment system in the event of an upset ' The plumbing for the carbon adsorption units is arranged such that they are connected in series and a piping manifold with 8 valves (V-1) can be set so that the relative upstream and downstream order of the vessels can be reversed Pressure gauges (PI-1) are located in the inlet and outlet lines of each vessel so that the pressure drops across each unit and across the combined two-vessel array can be monitored ' Sampling ports (VSP-1) provide for recovery of specimens of the influent to the carbon adsorption system, recovery of specimens of water that has passed through the first of the ' senes-connected vessels (i a at the "mid-point") and for recovery specimens of the final effluent from the groundwater treatment system where it flows out of the downstream vessel before it is discharged to the storm-sewer Exhausted carbon is removed and the vessels recharged with fresh carbon through ough ports in the top Drain valves (V-2) at the bottom of each unit permits the carbon vessels to be fully emptied of water before they are disassembled for maintenance I