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Corrective Action Plan Page 30 <br /> by seasonal fluctuations in the regional and local groundwater flow regime To reduce <br /> on/off cycling of the pump motors to a practicable minimum and to maintain relatively <br /> constant drawdown and steady pumping rates, the discharge from each pump can be <br /> regulated by valves (V-2) in the pump-user lines The depths to water at which the <br /> controllers cause the pumps to be energized and de-energized can also be adjusted to <br /> achieve optimal pumping under varying groundwater flow conditions <br /> l The total volume of groundwater pumped and the instantaneous rate of discharge from <br /> each well is measured by a pulse-type, flow indicator/totalizer meter (FIT-1) in their <br /> discharge risers where they enter the groundwater treatment enclosure Gauges (PI-1) to <br /> measure the pump-discharge line pressure are also located here, as are sampling ports <br /> (VSP-1) that permit samples of the groundwater pumped from each well to be drawn off <br /> for analysis Upstream of the pressure gauges, flow meters and sampling ports, there are <br /> check valves (VC-2), one in each well-discharge line to isolate them from the pipe <br /> manifold where the flow from each well is combined into a single line connected to the <br /> groundwater treatment system The check valves permit the pressure and flow in each <br /> well-discharge line to be independently monitored and prevent reverse-flow when the <br /> well-pumps are de-energized <br /> After passing through the user-pipe manifold, the flow of pumped groundwater passes <br /> through another pulse-type, flow indicator/totalizer (FIT-2) and a sampling port (VSP-1) <br /> so that the combined rate and volume of flow of influent to the treatment system and its <br /> contaminant loading can be measured <br /> Vertical. Silica-Media Filter System The first process unit in the groundwater treatment <br /> system is the vertical silica-media filter system (FS-1) This modular unit incorporates a <br /> pair of filter-media vessels connected in parallel Pumped groundwater enters the top of <br /> the vessels and sand and other suspended solids is removed as it flows down through <br /> them As filtrate accumulates in the filter vessels, differential pressure between the influent <br /> and effluent lines of the system increases and is detected by a differential pressure sensor <br /> (DPS) When the differential pressure reaches a preset level, a controller sequentially <br /> operates two-way, solenoid valves (V-5) so that the direction of flow through each of the <br /> two filter-media vessel is, in turn, revered for a few minutes This reverse flow backflushes <br /> the filter media and carnes the accumulated filtrate through a backflush line to the Sand- <br /> Bin (SBA) <br /> The filter system controller and solenoid valves operate such that, when one vessel is <br /> being backflushed, water continues be filtered by positive flow through the other vessel <br /> When backflushing of the first vessel is complete the order of flow is immediately changed <br /> and positive flow through that vessels is restored while flow through the second vessel is <br /> reversed When the backflush cycle is complete, normal operation of the filter system is <br /> automatically restored <br /> To permit visual observation of the pressure differential across the filter system, pressure <br /> gauges (PIA) are located in the lines downstream and upstream of the modular filtration <br />