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Success in the sewer

Success in the sewer

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    Top: Inspections showed that nearly all of Reno's large-diameter sewers that were 60 years of age or older were at or near failure. Left: Crew workers weld and install a bypass line that will temporarily carry sewage while the large-diameter interceptor below undergoes rehabilitation using a cured-in-place pipe process.

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    With nearly all of the concrete eaten away and a gaping hole in its side, virtually all that is left of this 60-inch-diameter concrete-reinforced interceptor pipe is its badly corroded rebar.

Like many cities that have experienced significant and sustained growth, Reno, Nev., keeps its public works department busy accommodating its new residents' needs. What makes Reno different from other growing cities, however, is the city's equally strong determination to protect its older collection system assets.

That wasn't always the case. Since 1960, Reno's population has quadrupled to more than 204,000 people today. More than 350,000 people reside in the greater Reno, Sparks, and Washoe County metropolitan area. That growth translates into steady demand for additional sewer connections and requires the construction of miles of new sewer lines. For many years, it also sometimes resulted in “benign neglect” of the wastewater infrastructure in the older parts of town, some of which was as much as 100 years old.

A decade ago, the city's sanitary engineering division began seeing increasing evidence that this neglect wasn't so benign after all. Sewer maintenance personnel were reporting more potential problem areas. In-house closed circuit TV(CCTV) efforts were starting to confirm the problems.

To help stem the tide, the sanitary engineering division stepped in. This division—responsible for planning, design, and construction of improvements to the city's wastewater system—earmarked $2 million annually from existing sewer use fees to fund collection system and lift station rehabilitation and replacement. This was in addition to the sanitary engineering division's existing budget for sewer line and treatment plant operation and maintenance.

This relatively modest stopgap measure worked—for a time. By the city's 2001–2002 fiscal year, however, division officials suspected they had an even bigger problem on their hands.

BUT HOW BIG?

Like most cities, Reno had no way of knowing just how big its problem really was. While the city had scores of videotape and records of its sewers, the early CCTV technology only allowed examination of small-diameter pipe. In addition, the system for cataloging and retrieving this information and using it was cumbersome, inflexible, and incapable of painting a “big picture” of the system's overall condition.

The city developed a geographical information system (GIS) infrastructure to understand the connectivity of the sanitary sewer collection system and to catalog pertinent information that was available or could be developed over time. The goal was to develop the system to the point that meaningful management decisions could be made.

By 2001 the system had matured enough to begin its use as an analysis and decision-making tool provided more data could be accumulated and at a faster pace. The city purchased a new digital CCTV van with bar-code driven defect codes that dramatically improved productivity in the field. A second van and crew were brought online the following year. Since video was now digital and tapes were no longer necessary, the city decided to purchase a mainframe file server to catalog and store imagery on instead of the more common DVDs. An 8-terrabyte server, expandable to 32 terrabytes, was brought online.

With these tools in place, the city initiated a complete structural assessment of the collection system, beginning in fiscal year 2001–2002. Making use of aerial maps of the city, officials hoped to create a system that would provide near-instant access to the age, size, structural condition, and other important information on virtually any sewer line or manhole in its collection system. Their goal: to better understand the scope and severity of the city's problems, and to determine the level of funding needed to fix them.

An engineering consultant was retained to focus on the 65 miles of large-diameter interceptor pipe, much of which was already 50 to 60 years old and accounted for approximately 12% of the collection system. It was believed to pose the greatest risks if failure occurred. An in-house team, meanwhile, undertook a similar study of the small-diameter lines serving the residential and business areas in the older parts of town, as well as all the system's manholes.