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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Both filters are backwashed, one then the other, with down time of about 15 <br />minutes per filter; for a total of 30.35 minutes, Each backwash uses about <br />15,000 gallons/filter, <br /> <br />The surface wash system works well on each filter, Surface wash is served by a <br />4" diameter line, There is no flow meter on this system, Operations and rates <br />were not observed, <br /> <br />Turbidity of water leaving the plant is checked every 4 hours, Raw water <br />turbidity is tested once per day, or more often if needed by operator decision, <br /> <br />Two days in 1993 had 3 backwash cycles per shift, Data pertinent to filter operations is <br />presented in Table 4, Performance is also noted in Table 5. There is a significant deviation <br />from the standard in backwash rates recommended to clean the filter media, To meet the <br />recommended standards, the rate of flow would need to be tripled, Operators have stated that <br />the constraint on backwash rate is capacity of backwash troughs; existing troughs are <br />completely full at current rates, Installing more troughs, or larger ones, may remove this <br />constraint. Inlet piping may be an additional constraint. Existing velocities in the 12" <br />diameter inlet piping already exceeds the state standard of 2,0 feet per second (fps), As for <br />turbidity removal, the data of July 7 in Table 5 suggests that overall removal rate is only (1.50 <br />- 0,39)/1.50, or 74 percent at best during periods of high flow, A removal rate of 90 percent <br />is considered a yardstick for gravity granular media filters, <br /> <br />In summary, the above noted deficiencies in the filtration system can be regarded as minor <br />compared to the deficiencies upstream in the clarifier. No data on filter influent is available to <br />make any determination on removal rates or overall performance, <br /> <br />Disinfection <br /> <br />The addition of cWorine gas, Cl2 is done by induction of the gas (in solution water) <br />into the discharge piping of each filter. This piping in turn enters the clearwell, estimated at <br />9500 gallons capacity, The usable pumped capacity of the clearwell may be only 5200 <br />gallons, Dispersion methods and mixing methods to assure contact with filter effluent waters <br />were not observed, The clearwell which receives filter effluent and C 12 solution acts as a <br />wetwell for the high service pumps, <br /> <br />20 <br />