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Corrective Action Plan Page 25 The accumulated total volume of water treated by the groundwater treatment system is recorded by an integrating flow totalizer (FT-1) situated in the effluent line from the ' carbon adsorption units so that the total flow can be recorded before the clean, treated water is discharged to the storm sewer ' The series arrangement of the pair of GAC units provides for the upstream unit to serve as the primary means of removing any components of gasoline not removed from the water stream in the sparging tanks The quality of water exiting the first unit is monitored by analysis of samples taken from a sampling port (VSP-1) at the mid point of the piping connecting the first unit to the second unit When the adsorption capacity of the first unit ' is exhausted, contaminants break through and are detected in these samples However, no contaminants will be discharged to the environment because water flowing out of the first carbon unit is passed through the, until then, unused carbon in the second unit ' When contaminant breakthrough is observed at the sampling port at the crud-point between the pair of GAC units, arrangements are made to remove the exhausted carbon ' from the upstream unit and replace it with fresh material Both units have the same adsorptive capacity and are sized such that, when breakthrough occurs at the mid-point, the downstream unit captures all detectable contaminants that pass though the system and has sufficient reserve capacity to provide ample time for a new charge of carbon to be procured and placed in the upstream unit The plumbing for the GAC units includes a system of pipes and valves that permit any one of the pair to be upstream of the other After contaminant breakthrough occurs at the mid- point and the exhausted carbon in the upstream unit has been replaced, the valve settings ' are changed so that the unit that was previously on the downstream side of the mid-point is on the upstream side and the one previously downstream is upstream This arrangement permits the GAC vessel having the greatest reserve of adsorptive capacity to operate, at ' all times, as the primary unit and provides maximum redundancy against unexpected failure of any upstream process ' The GAC units are sized such that, when the groundwater treatment system is operating at its design effluent capacity of 45 gpm, breakthrough past any one freshly charged unit ' does not occur for approximately 60 days of continuous operation when the treatment t system is operating normally If all upstream processes were to entirely fail at a time when contaminant concentrations in the influent to the treatment system were at the anticipated ' maximum and, as is extremely unlikely, the upset condition was not detected and the system shut down, breakthrough of a single, freshly charged unit would not occur for 10 days of continuous operation With two GAC units installed in series, even under such ' extreme failure conditions, contaminants would not breakthrough to the discharge to the storm-water sewer before 20 days had elapsed This provides a very large margin of safety given the fact that it is proposed to operate the treatment system only during the normal working day and that only 2 working days notice required to arrange for recharging of the units with fresh carbon �I