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Corrective Action Plan Page 31 �f unit A valve (V-3) allows the pressure in the discharge line to be regulated so as to maintain sufficient differential pressure between that line and the backflush effluent line when upward flow through the filter-media vessels is required for backflushing operations Sand-Bin Operation. The backflush water from the modular, vertical silica-media filter system is discharged to the settling chamber in the Sand-Bin (SB-1) where the detntus settles out When the water rises in the settling chamber, it flows over an internal weir into the second sand-bin chamber which serves as a sump A 114 horse-power, self-priming, submersible pump (P-4) empties the sump by raising it over the top of the bin via a discharge line routed back to recovery well RW-2 Operation of this pump is regulated by a modular, float-switch (FS-1) and controller so that the pump is energized when the water level is within 6 in of the top of the sand bin and de-energizes it when the sump is close to empty, but sufficient water remains to keep the pump submerged The rate at which backflush water is returned to well RW-2 is regulated by a valve (V-2) in the sand-bin discharge line After passing through the vertical silica-media filter system, the recovered groundwater is raised under the action of the discharge head generated by the groundwater recovery pumps into the top of the surge tank (ST-1) which serves to balance the flow to the upstream process units The rate of water flow into this tank is measured by an rotameter-type, flow meter (FI-1) in the tank-influent line is in the surtank provided b a radio-frequency Primary control of water leve surge is P Y admittance type, differential water-level probe (LS-1) and a controller (LC-1) that regulate the 112 horse-power centrifugal pump (P-2) that discharges water from the tank (See System 13 on Figure 10 for pump location) The probe and controller are calibrated so that the booster pump is energized when the water level in the tank is between 1 ft of the bottom and 1 ft of the top When the water level reaches the normal high level, the booster pump is energized and water is pumped from the tank to the upstream process units If the water level falls to within 1 ft of bottom of the tank the booster pump is de-energized and discharge is stopped until the water level in the tank again rises to the normal high level at which time the booster pump is re-energized and discharge from the surge tank to the ir upstream process units resumes t A regulating valve (V-3) is located in the discharge line from pump P-2 so that the rate of discharge from the surge tank can be controlled so as to reduce cycling of this pump to a practicable minimum and perrrut a generally continuous and steady flow of water from the surge tank to the upstream treatment system equipment If, for any reason, the water level in the surge tank should rise above the normal operating � n, level, it is detected by a high-level sensor (LSH-1) connected to a high level alarm/switch (LAH-1) and the groundwater-pump controllers When such an upset condition is detected, all of the well pumps are de-energized so that water ceases to flow into the groundwater treatment system and an alarm lamp mounted on the well-pump control panel r