Expanding rapidly to accommodate retiring baby boomers, Camas, Wash., had a stressed, aging sewer infrastructure that required replacement or refurbishment of many sections and substantial investment in new systems. With site limitations thrown into the mix, keeping the sewer system healthy required an innovative solution, which engineers found in a pre-engineered lift-station package.
Many of the new subdivisions are going up in the northwest part of town, where pressure sewers traditionally have been used. Septic tank effluent pump (STEP) pressure sewers are used when the layout of a site prevents effluent from running downhill. STEPs use household septic tanks to settle out solids; specially designed effluent pumps deliver wastewater through small-diameter plastic piping to a treatment site.
“We started with the pressure sewer systems years ago—1500-gallon tanks with submersible pumps,” says city engineer Wes Heigh. Such systems require significant maintenance, and the smaller lot size typical of new developments has prohibited use of pressure sewer systems.
In recent years, the city has been involved heavily in improving and extending its sewers. An intregal part of this effort is the pre-engineered package lift station, provided by Roseburg, Ore.-based Romtec Utilities (see sidebar). As part of its capital improvement program, the city has upgraded five existing stations and installed seven new lift stations in or near new residential developments. The packaged lift stations let Camas quickly get the equipment it needs from one source. “We wanted quality components but did not want to have to deal with multiple vendors,” says city project engineer Jim Hodges.
Standardization within the network is also a concern, particularly since the city does not build the lift stations for new residential areas—developers do, then dedicate them to the city.
The city has installed a series of large fiberglass “community” tanks, with a total capacity of 110,000 gallons. Three 20,000-gallon tanks and two 25,000-gallon tanks were placed upstream of the wet well. The entire sanitary sewer flows into these tanks; solids are stored and liquids routed through the tanks into the inlet pipe in the wet well. The lift station then pumps the liquids into the sanitary sewer system. The pit for the tanks and the wet well, sized to compensate for the area's high ground-water, is 25 feet deep.
“Instead of many individual STEPtanks, we would rather maintain a pump station,” says Heigh. Developers install the lift stations and the city handles maintenance. That arrangement is a big reason why officials have specified the packaged lift stations.
— Megan Monson is a freelance writer based in Myrtle Creek, Ore.
Romtec Utilities' pre-engineered lift stations consist of the following components:
Wet well: Self-cleaning, precast concrete wet wells; they come in diameters of 6 and 8 feet, in overall depths from 10 to 35 feet
Valve vaults, flow metering: Prefabricated, pressure-tested valves and flow meter vaults, with piping diameters from 4 to 10 inches
Submersible pumps: Units from ITT Flygt Corp. from 3 to 105 hp, in duplex or triplex systems
Generator: Cummins standby power in two available configurations: permanent onsite generator with automatic transfer switch, or portable trailer-mounted units
Control panels: A variety of UL-listed units, preassembled and ready for operation
SCADA and alarms: Selection of operating systems, including supervisory control and data acquisition, and less complex radio and auto-dialer systems.