A STEP system gets Sandborn sewage under control.
By Bob Whitmore
When the Indiana Department of Environmental Management found E-coli bacteria and other harmful pollutants coursing through the water near Sandborn, Ind., the little town had a problem. A rural community of 225 dwellings in the southwest region of the state, Sandborn needed to clean up its sewage.
Most of the homes in Sandborn were on aging septic systems – a haphazard collection of old tanks feeding into leach fields – many installed in decades past when environmental standards and watertightness were at best an afterthought.
In addition, Sandborn has a high water table, according to John Acree, P.E., an environmental engineer with LAMAC Engineering Co. in Princeton, Ind.
The combination of aging, leaky tanks, leach fields and a high water table may have also had an effect on the town’s drinking water, which comes from wells. The EPA rated water quality in Sandborn 25 on a scale of 100 (higher is better). The national average is 55.
Constructing a full-blown sewage system and water treatment plant was one option. But Acree had a better solution in mind: a Septic Tank Effluent Pump system. Originally developed in the Northwest region of the United States, a STEP system provides a viable solution to a full-blown gravity sewer system, especially in smaller communities with sandy soil and high water tables. A conventional septic tank provides pretreatment, removing the solids from the wastewater. Specially designed pumps then force the septic tank effluent under pressure from a series of small-diameter pipes to a treatment plant on the edge of town.
Rather than a series of 225 individual septic tanks draining into backyard leach fields, the STEP system moves the wastewater to the treatment facility where it is sanitized and then distributed to a creek. The STEP system has a number of advantages, not the least of which is the impact on the town, Acree said.
“A conventional sewer system would go in at a depth of anywhere from 5 to 15 feet,” Acree said, “so your entire work would be done in slop because of the high water table. It would be very expensive, and the town would look like it had been hit by a bomb. The cleanup would be tremendous.”
The ongoing benefit for the town is that the new system should help clean up the area’s groundwater and dry up back yards in low-lying areas.
“They use about 50,000 gallons of water a day here in town, so every day you’re dumping 50,000 gallons of water on the town – 365 days a year,” Acree said. “And this town doesn’t drain well.”
Cliff Pemberton, manager of Sandborn’s new sewer department, said the spring rainy season is particularly messy because the ground is constantly saturated.
“In the low-lying places it’s just like a lake down here,” Pemberton said. “The water does run off eventually, but it takes awhile.”
While the STEP system has caught on in Oregon and Michigan, it has been slow to gain acceptance by regulators throughout the country. Acree helped develop the first project in Illinois 10 year ago in Browns, a rural town with a population of 175 in the southeastern corner of the state.
The Browns project has proven successful and a few additional STEP systems have been installed in Illinois. The Sandborn project is the first to be approved in Indiana.
“The state was afraid that it would be too expensive – that we would be way over budget,” Acree said. The project, funded by a combination of federal and state grants and loans, has a budget of $3.3 million. Acree estimated that it would come in about $700,000 under budget.
It was a no-brainer to specify precast concrete septic tanks for the project, as far as Acree is concerned. “You’re not even comparing apples to apples,” he said. “I just don’t see that a plastic tank can in any way compare to the structural integrity of a precast concrete tank. A lot of these tanks are going to be placed near the road or in the road.” In addition, the buoyant effect of the high water table may have created problems with the installations of lightweight plastic or fiberglass tanks and could have meant additional problems down the road when the tanks were serviced and emptied out. A 4-ton precast tank sits down – and stays down – a lot better than a 100-pound plastic tank.
Working with a precaster at the start of the project to fine-tune the specification helped create a better product for the homeowners. One of Acree’s big concerns was that the tanks remain watertight for the long term.
Mark Bolander, president of Rex Vault Service Inc. in nearby Newton, Ill., supplied the septic tanks for Acree’s Browns project. He planned to bid on the Sandborn project, but offered to help design the perfect tank in the pre-bid stage.
Rex Vault manufactures a mid-seam septic tank with a tongue-and-groove joint. The joint is made watertight with an industrial sealant, but Bolander suggested an additional wrap sealant around the joint and also suggested changing the pipe seals from plastic to rubber.
“They had also specified a coating on the outside to further guarantee watertightness,” Bolander said. “We tested the coating and it wasn’t durable. So we suggested an internal coating that would not only add to the watertightness factor, it also protects the tank from methane gas that is prevalent in the septic tanks,” he said.
“When all was said and done, we actually built one and installed it on our property just to make sure it did everything the engineer wanted,” Bolander said. “We found a couple little things that didn’t make sense, tried some things, found what would work and went back to the engineer before it was too late.”
That was all done before the bids were let. “We still had to convince the contractor to use our product. It wasn’t a slam dunk for us,” Bolander said. The precaster’s work paid off when the contractor, Kieffer Brothers Construction of Mt. Carmel, Ill., chose his product for its portion of the contract.
Construction of the treatment plant ran concurrently with the house-by-house work under contractor Thieneman Construction. The treatment facility consists of two 33,000 gallon cast-in-place tanks and a variety of precast structures supplied by Thorn-Orwick (Division of Oldcastle), from Corydon, Ind.
Scheduled for completion in October, the Sandborn project will start paying dividends almost immediately. Acree expects the soggy backyards to start drying up and the groundwater to start clearing up soon after the STEP system comes online. That’s good news for the town of Sandborn and good news for the environment.
How it works
In the Sandborn, Ind., project, 225 individual precast concrete septic tanks are connected to a closed system that conveys the wastewater to a treatment plant located at the northwest edge of town. Precast manufacturer Rex Vault Service Inc. manufactured 1,000 gallon and 1,500 gallon mid-seam vacuum-tested septic tanks, which were staged at the treatment plant and ready for delivery to each individual excavation site. The larger tanks are for public facilities like the community center, churches and a convenience store.
Unlike a conventional sewer installation, where open excavations are common, the STEP system makes it easy to coordinate the delivery of a septic tank at the time of excavation, which keeps the footprint of the project much smaller.
In Sandborn, the backhoe operator performs the excavation, and a Rex Vault employee drops and levels the tank. The above-grade access is installed and the tank is buried. A shallow excavation is then needed to route a 1-inch diameter pipe to the street, where it is connected to the system. The treatment plant consists of two 33,000 gallon concrete tanks with a recirculating filtering media that provides secondary treatment, disinfects the wastewater and discharges it to a creek.
Once all the tanks are installed, the system will be brought online with connections made at each house and control boxes installed on the outside of each home. The town of Sandborn will be responsible for maintenance on the septic tanks. Homeowners pay for a portion of the project through monthly sewer fees paid to Sandborn based on the amount of water they use.
Bob Whitmore is NPCA’s director of Communication.