The City dramatically reduced unaccounted for wastewater after it rehabilitated more than 2.5 miles of city sewers and performed other system maintenance.

Many booming communities struggle with expanding their wastewater infrastructure and treatment capacity to keep up with growing demand.

But not Wentzville, MO. To the contrary, Wentzville has managed to decrease the flow to its wastewater treatment plant by more than 555,500 gallons per day -- even as its population more than doubled over the past two decades.

Between 1998 and 2002 alone, Wentzville, which is located approximately 40 miles west of St. Louis, added 2,627 new sewer connections. But by that time, the City had already embarked on a program to identify the causes of unidentified flows and then implemented a multi-pronged attack to reduce them.

The city’s Water and Wastewater Department first recognized it had a problem when it started keeping detailed records of flows to the city’s wastewater treatment plant in the last 1980s, according to Gary Miller, the City’s Water/Wastewater Superintendent.

“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,” Miller says. “Water was infiltrating the pipes along the way.”

The seven-year program, which ultimately cost the city approximately $925,000, included a mix of small, spot repairs, manhole lining and a water meter change-out effort. Perhaps most significantly, it included the rehabilitation of more than 2.5 miles of city sewers using Insituform Technologies’ cured-in-place pipe technology.

The City began with the least costly improvements first.

Water and Wastewater Department crews started by making simple repairs on improperly capped laterals. They also conducted drive-by inspections of roof drain down spouts that were not discharging to the open air, and repaired low-lying manholes that needed raised to proper grade.

“While making these repairs, we 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,” notes Miller.

To combat this problem, the department divided the city into five sections, which it addressed at a rate of one per year. City workers 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 accounting of the amount of water its customers used. “We knew the cost of replacing the old water meters would be expensive,” says Miller. “But we believed the return on our investment would be substantial, and it was.”

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 I&I
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 back yards 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 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 video-taped so Insituform® and city officials could assess their condition.

“The televising process revealed a significant portion of the city’s infiltration problems could be traced to the original poor installation of sewer mains, laterals and manholes,” says Gary Penrod of Insituform®.

So Insituform® crews went to work on the sewers, rehabilitating approximately 13,704 feet of sewers over the five-year period using its Insituform® cured-in-place process (CIPP).

“Working from manholes, our workers used water pressure to insert a flexible liner inside the sewers,” says Penrod. “Once in place, the liner was then heated and cured into a structurally sound pipe-within-a-pipe with a life span comparable to that of a new sewer. “

Between 1993 and 2001, Wentzville 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 tight seals on faulty manholes. 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,” says Miller. “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.”

Insituform® Technologies, Inc. is a worldwide company specializing in the use of trenchless technologies to rehabilitate, replace, maintain and install underground pipes. Additional information about the company can be obtained at www.insituform.com or by calling 800-234-2992.