City of Wentzville demonstrates that you can transform a small, sleepy town into a booming suburb—while decreasing the amount of wastewater you treat a day
Gary Miller, Water/Wastewater Superintendent, City of Wentzville, Missouri
Gary Penrod, Area Account Manager, Insituform Technologies, Inc., Chesterfield, Missouri
Take a look across the United States, and you'll find dozens of Wentzville, Missouri's out there. Not by name, of course, but by circumstance.
Located about 40 miles west of St. Louis, Wentzville is one of many small towns that have gone through a major growth spurt over the past two decades, more than doubling its population of 9,800 people. Between 1998 and 2002 alone, the city added 2,627 new sewer connections.
But Wentzville's story is different from that of many booming communities that struggle with expanding their wastewater infrastructure and treatment capacity to keep up. That's because Wentzville has actually managed to decrease the flow to its wastewater treatment plant by more than 555,500 gallons per day.
This is the story of how Wentzville did it.
A three-pronged approach
In the late 1980s, not long after the city's Water and Wastewater Department started keeping detailed records of flows to the city's wastewater treatment plant, officials noticed something odd. The amount of wastewater accounted for in residents' paid water bills was far less than the metered influent that flowed to the city's wastewater treatment plant. The culprit, they determined, was infiltration.
Soon thereafter, the city took a methodical approach to identify the causes of the accounted-for flows and implemented a multi-pronged attack to reduce them. The seven-year program, which ultimately cost the city approximately $925,000, included a mix of small, spot repairs, manhole lining and water meter change-out effort. Perhaps most significantly, it included the rehabilitation of more than 13,700 feet of city sewers using cured-in-place pipe technology.
Given budgetary restrictions, the city began with the least costly improvements first.
Water and Wastewater Department crews started by repairing lateral clean-outs that had been improperly capped. They conducted visual drive-by inspections of roof drain downspouts that were not discharging to the open air, and repaired low-lying manholes that needed raised to proper grade.
While making these repairs, the department noticed that many homeowners were contributing to the city's problems by piping their sump pump discharges through their basement or laundry drains directly into the sewer system.
To combat this problem, the department divided the city into five sections, which it addressed at a rate of one per year. A questionnaire was mailed to each section's residents to identify those with sump pumps. City workers then inspected the homes of sump pump owners to ensure their discharge was properly connected and did not enter the sewer system. Violators were given 90 days to comply.
Water meter change-out program pays for itself
Next, the department realized it needed a better and more accurate account of the amount of water its customers used. The cost of replacing the old water meters in every home, officials knew, would be expensive. But it was an expense they believed would produce even greater returns, and they were not disappointed.
Over a 48-month period, new, more accurate water meters were installed in more than 2,200 homes, resulting in a 15 percent revenue increase for the water department. Because the city's sewer bills are tied to water usage, the Wastewater Department benefited similarly. Within 15 months, the new meters had paid for themselves.
Sewer rehabilitation program further reduces inflow and infiltration
In 1998, officials again divided the city into five sections and, using a 1980 sewer study, prioritized sewer mains for repair. Virtually all of the deteriorated lines were located beneath existing streets, in backyards or in rough terrain. After reviewing its options, the city chose to rehabilitate the mains using a cured-in-place liner that did not require excavation. It awarded Insituform Technologies, Inc. of Chesterfield, MO, a contract valued at $100,000 per budget year to make the repairs.
Each year for the next five years, the sewers in a given section of the city were televised, with Insituform and city officials prioritizing and making the repairs.
The televising process revealed that a significant portion of the city's infiltration problems could be traced to the original poor installation of sewer mains, laterals and manholes. A department staff member was subsequently appointed to directly oversee construction and inspections of all new water and sewer system installations. A second staff member was later added to keep pace with the community's fast growth.
Meanwhile, Insituform crews went to work on the existing sewers, rehabilitating approximately 13,704 feet of sewers over the five-year period using its Insituform cured-in-place process (CIPP).
Working from manholes, workers used water pressure to insert a flexible liner inside the sewers. Once in place, the liner was then heated and cured into a structurally sound pipe-within-a-pipe with a life span comparable of that to a new sewer.
Between 1993 and 2001, Wentzville had invested more than $700,000 in its infiltration reduction program and reduced the amount of unaccounted-for wastewater from 911,387 gallons per day to just 113,200 gallons per day.
Manholes were the last piece of the city's plan to minimize infiltration.
Back in the 1980s, the city had installed new seal-tight on the faulty manholes identified in the 1980 study. But that was only a small part of the problem. In 1998, the city faced the choice of replacing its manholes or relining them in place. It chose to reline them, keeping the disruption to streets and residents to a minimum. The department's annual budget now includes a $30,000 line item for manhole relining, as prioritized by the wastewater staff.
Is there a lesson to be learned from Wentzville's experience? Yes. In fact there are at least three lessons. First, a community can learn a lot just by keeping detailed records of the flow into its treatment plants. Second, a community can save itself significant cost by taking a proactive approach to its sewer maintenance program. And finally, a community can grow without demanding more capacity at its wastewater treatment plant.
To reach Gary Miller, call (636) 327-4174; to reach Gary Penrod, call (800) 234-2992.