About the author: Tyler Molatore, P.E., is community systems program manager for Orenco Systems Inc. Molatore can be reached at [email protected] or 800.348.9843 x416.
In the early 1990s, Bethel Heights, Ark., was a community of only about 700 people. With corporate giants such as Wal-Mart and Tyson Foods headquartered nearby, however, the city had the potential for tremendous growth. A major factor limiting such growth was the city’s reliance on individual septic tanks for wastewater treatment, plus a required minimum lot size of ¾ acre.
Then, in 1999, the state of Arkansas passed a law allowing property owners to de-annex from one city and into another if the original city was unable to provide essential utilities, including wastewater services. In a relatively short amount of time, Bethel Heights was faced with a loss of tax revenue from de-annexations that threatened its very existence.
Threatened by De-Annexations
“After the first de-annexation, doing something became a very high priority,” said Fred Jack, former mayor of Bethel Heights.
With so few residents, however, the city was limited financially. If a centralized sewer system using gravity collection and a standard activated sludge plant were installed, the area’s hilly terrain would require numerous expensive lift stations and deep excavations. The dispersed nature of new developments also would add to the upfront cost of a traditional gravity collection system. But, with the threat of more de-annexations looming, there was no time to begin the lengthy process of applying for federal grants and loans.
Instead, Bethel Heights chose to install an Orenco effluent sewer, along with an AdvanTex textile treatment system and subsurface dispersal via drip irrigation.
“From a financial standpoint, we really didn’t have much of a choice,” said Jeff Hutcheson, mayor of Bethel Heights from 2010 to 2014. “We had to do what was best for the city, and I think it was the right option in the end.”
Reaping the Benefits
For small towns like Bethel Heights, effluent sewer has many economic advantages, from minimized initial capital investments to low overall lifecycle costs.
An effluent sewer begins with a wastewater collection system consisting of small-diameter pipe. There is no need for manholes or lift stations. The pipe is installed in shallow trenches that follow the contour of the land, so it was relatively inexpensive to install throughout Bethel Heights, despite the town’s hilly surroundings and the long distances between the treatment system and the city’s far-flung developments.
Next, on-lot interceptor tanks are installed at each home and business on a “just-in-time” basis, deferring upfront costs until the time that new construction actually takes place. These tanks typically run eight to 12 years between pump-outs. They also provide primary treatment of sewage, which translates into lower biochemical oxygen demand (BOD) loads and lower hydraulic loads and, in turn, allows for smaller, less complex, less
expensive treatment plants.
In addition, each on-lot tank is equipped with an Orenco Biotube pumping system that includes a lightweight, energy-efficient pump with an expected life of 20 to 30 years. The tank and the filters in the pump system reduce solids by up to two-thirds before effluent from the tank’s “clear zone” is pumped into the 2-in.-diameter force main. The size and cost of this pipe is minimized, because an effluent sewer’s watertight plumbing essentially is free of inflow and infiltration (I&I), as well as the majority of solids.
Little to no I&I means the treatment facilities in Bethel Heights did not have to be oversized to handle increased flows during wet weather. As a result, the city also saves money on wastewater staffing. Bethel Heights’ full-time wastewater operator, Zack Williams, has one full-time employee who assists him at the city’s two treatment sites, as well as one part-time employee who handles service calls.
The ultimate system capacity at Bethel Heights is sufficient to serve 1,000 equivalent dwelling units; however, should greater capacity be needed, additional treatment equipment can be installed unit by unit, as required.
Low Bond, Fast Payback
To finance the effluent sewer system, the residents of Bethel Heights approved a $1.3 million bond, which paid for two multi-pod AdvanTex treatment plants, all effluent transport lines, the purchase of acreage needed for effluent discharge and an operations facility. That bond was paid off in 2013, some 20 years ahead of schedule.
Low operations and maintenance (O&M) costs contributed to the city’s ability to pay off the bond so quickly. Municipalities such as Bethel Heights routinely handle all on-lot maintenance for effluent sewer systems, but, according to Williams, “There are some of our original houses, going back to 2003, that we’ve never had any service calls on at all.”
Low O&M expenses also allow cities to keep their monthly sewer rates low. Bethel Heights charges its residents $35 per month.
Steve Hesse, P.E., of Earthplan Design Alternatives PA in Springdale, Ark., said the Bethel Heights system was the first one he designed using Orenco equipment. Since that time, he has recommended the technologies for projects in the nearby towns of Lowell and Rose Bud as well.
“I would still recommend an effluent sewer and Orenco’s AdvanTex treatment to other small communities that need a wastewater system but don’t have the funding for traditional, ‘big-pipe,’ gravity sewer,” Hesse said. “From a value standpoint, Bethel Heights made a wise investment in its future by deciding to go with an effluent sewer.”
Accommodating Future Growth
As Bethel Heights grows, its effluent sewer system will allow scattered future developments to be connected as needed. The city currently has 45 AX-100 units, which can handle up to 180,000 gal of total wastewater per day. Effluent test results show typical carbonaceous BOD levels of 6 to 12 mg/L and total suspended solids levels of less than 2 mg/L, well below permit limits of 15 mg/L for each.
Since its installation in 2003, serving just a few dozen residences and small businesses, the Bethel Heights effluent sewer system has undergone the completion of four phases and is approaching 500 connections, including both homes and businesses.
“Bethel Heights’ city government realized growth would not occur for us unless we could provide sewer service,” said Cynthia Black, mayor of Bethel Heights and a long-time resident of the city. “Without Orenco’s system and assistance, we could not have continued to grow and maintain our small city.”
Once a tiny town of just 700 people and at risk of disappearing from the map altogether, Bethel Heights now boasts more than 2,300 residents and is well positioned to handle its future wastewater needs.
Download: Here