Cutting Flow With Comprehensive Management

Tennessee utility’s comprehensive mitigation plan brings significant flow reductions.

Cutting Flow With Comprehensive Management

CCTV Inspections Completed (2006-2010)

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Before 2003, the Hallsdale-Powell Utility District in Tennessee was doing little to stem rampant inflow and infiltration in its system. When they received a consent order in 2004 from the Environmental Protection Agency, they had to play serious catch-up.

To do so, they started from the ground up, building a comprehensive management plan out of nothing.

First was creating a GIS map and collecting the data to populate it. They managed to do so in only a few years’ time, including flow monitoring and video inspection of high-priority areas.

The key to their success was sticking to a long-term plan, allowing a projected decrease of 33 percent wet-weather volume, and an average daily dry-weather flow decrease of 65 percent.

Preparing the plan

Inspection didn’t begin until 2006, and under their long-term strategy, it would continue at an ongoing rate of 10 percent of the system per year.

Unfortunately, after three years, they struggled to meet that goal, inspecting just 23 percent of the system in that time. They also found that the financial burden was significant, averaging over $700,000 per year (which includes cleaning costs for severely impaired areas).

Despite that, the district persevered and by 2011 had inspected around 50 percent of the mainlines.

They determined that 70 percent of their rainfall-dependent I&I was contained within 33 percent of the monitored area.

Rehabilitating the system

The first round of rehab projects was completed in 2009 — a full gamut of repair, rehabilitation and replacement. Everything from cured-in-place pipe lining, opencut replacement, point repairs, pipe bursting, manhole lining and service lateral repair.

However, 97 percent of the nearly 160,000 linear feet of rehabilitated pipe was completed using trenchless methods. By the end of 2011, the city had spent over $7.5 million on rehabilitation efforts.

“Through a strategic plan of pre-rehabilitation monitoring, a prioritization plan was formulated that encompassed both inspection and rehabilitation activities,” according to a study on the project. “By following this plan, the Hallsdale-Powell Utility District has been able to focus dollars on priority areas of the system while measuring successes and noting parts of the plan that need modification.”

For a suburban area just outside of Knoxville, I&I is an important issue. Having a long-term strategy allows the city to keep in line with the Clean Water Act and minimize further system deterioration.

“Once completed, post-rehabilitation monitoring was conducted to verify rehabilitation effectiveness and reprioritize the collections system for the next round of inspection and rehabilitation projects,” the study says.

A 2011 flow study, with nine permanent flowmeters and 33 temporary meters alongside five rain gauges confirmed the validity of their long-term strategy.

Results speak for themselves

“Despite 2009 being one of the wettest years on record, the lowest observed flows were 741,000 gallons below that measured in 2007 (one of the driest years on record according to the National Climatic Data Center),” the study says. “Additionally, a decrease of 874,000 gallons was observed in average flows from 2009 to 2010, during which the majority of the CIPP projects were completed.”

As with any successful I&I program, both inspection and rehabilitation are ever ongoing. But so far, the results indicate dramatic improvements to the system, all thanks to a comprehensive, long-term approach to monitoring, rehab and I&I management.



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