For many years the Town of Dayton, Virginia (population 1,400) supplied its residents with drinking water from spring fed Silver Lake. The water received limited treatment consisting of chlorination before pumping to the distribution system. In 1994, the Virginia Department of Health determined the raw water source was under the direct influence of surface water and must meet all requirements of the Surface Water Treatment Rule.ARCADIS was hired to determine the most cost-effective solution taking into consideration three distinct raw water sources of varying quality (spring fed Silver Lake and two ground water wells), operational requirements, reliability and expandability.
Various types and configurations of water treatment plants were evaluated. Two small plants were compared to a single, larger plant. Both alternatives were evaluated using conventional treatment consisting of coagulation, flocculation, sedimentation, filtration and disinfection. This was determined to be too costly and operator intensive for the resources available to Dayton. A single water treatment plant utilizing membrane microfiltration technology was recommended after further evaluation.
A new 2.2-MGD microfiltration membrane water treatment plant was designed to meet the Surface Water Treatment Rule. The plant was designed to be easily expanded to 3.3 MGD. Additional facilities include a 50,000-gallon raw water storage tank, raw water pumps, a 2.5-MG clearwell, high service pumps and chlorine and fluoride chemical feed systems.
The automatically controlled plant can be operated from a remote site allowing personnel to work at off site locations while still monitoring plant processes. The plant PLC system monitors all alarms and routes the signals to appropriate locations for proper attention. The plant requires personnel to be present at the site only two hours per day.
Another innovation designed into the plant was a unique clearwell that allows optimal constant rate water production. Large fluctuations in water demand required a "tank within a tank" clearwell design. The inner baffled tank, with a capacity of 500,000 gallons, gives sufficient detention time to meet the required CT values at the ultimate plant capacity. The water levels in the outer tank, with a capacity of 2.0 million gallons, rise and fall with changing demands. Complete isolation of both tanks is possible for easy maintenance.
The Town expanded plant capacity to 3.3 MGD in April 2000 to meet increased demand through the simple addition of a 1.1 MGD treatment unit at a cost of $362,152
