June 2013, Vol. 25, No.6

Extra

St. Louis takes an asset-management-based approach to consent decree compliance

Jonathon Sprague and Gene Stinnett

 Maintaining a sewer collection system is a lot like maintaining a car. Both will last longer and operate more reliably if small problems are addressed before they become big ones. An older model typically requires more attention than a newer one. The parts that receive the greatest daily wear and tear take priority — especially when money is tight and the threat of a breakdown is real.   

Every sewer, in other words, need not be treated equally when it comes to maintenance. Rather, the most money-saving and results-producing maintenance programs are those that tailor inspections, cleaning, and repairs to the condition of individual pipes and the risks they pose to the people who depend on them.  

That, in a nutshell, has been the philosophy behind the approach taken by the Metropolitan St. Louis Sewer District (MSD) to maintaining its collection system since 2008. That is the year MSD began using data it had been collecting on inspection results and work-order history to implement a systemwide maintenance program focused on reducing basement backups and overflows, as well as improving customer service. In April 2012, MSD took the program a step farther when it became the first sewer district in the nation to receive U.S. Environmental Protection Agency (EPA) approval to apply this asset-management-based approach to consent decree compliance.  

  

Why an asset management approach?  

The need to set priorities was important to MSD because its collection system is larger than most. MSD is responsible for the operation and maintenance of more than 10,800 km (6700 mi) of sanitary and combined sewers, or roughly the same amount of pipe in Los Angeles’ wastewater system, which has nearly three times the population to support it. MSD “inherited” this pipe, along with hundreds of constructed overflows, when it was formed in 1954 to take the place of 79 individual sewer systems that formerly served the city of St. Louis and most of St. Louis County. It has been removing those overflows ever since. 

The consent decree MSD signed with EPA and the Missouri Coalition for the Environment (St. Louis) sped up the process, setting a 2034 deadline for the $6 billion capital program begun in 2003 to address remaining overflow issues. 

Historically, a consent decree such as this would take a prescriptive approach to compliance. In other words, the decree would outline the specific tasks a utility must perform over a prescribed period of time, offering little or no flexibility in adapting those tasks as water quality goals and other program milestones are met. For sewer inspections and cleaning, for example, the metrics often are simple: Clean each sewer every 5 years, no matter the type, age, or size; and video-inspect them every 3 years.  

Data-driven choices 

By the time MSD entered into its consent decree, however, it had amassed historical data that illustrated that such a “one-size-fits-all” approach was neither cost-effective nor necessary. With 4 years of an inspection and cleaning program under their belts and a new computerized maintenance management system to guide them, MSD managers began to identify patterns. They found that 95% of the basement backups were in clay pipes with diameters of 300 mm (12 in.) or less — which tended to clog more frequently than others. They also could track the sources of these clogs, be they tree roots, grease, or other debris.  

Perhaps more importantly, the managers had proof that a proactive, finely tuned inspection and cleaning program worked. Claims attributed to basement backups dropped from $4.3 million in 2008, when the program began, to $1.1 million in 2012. Average wet weather claims also dropped significantly.  

MSD also had data showing dramatic improvements in customer service. Before 2008, it was “all hands on deck” when a major storm hit, requiring a fully staffed “war room” to answer calls reporting basement backups. Even a 25-mm (1-in.) rain event might take 3 days of around-the-clock work to address. But 5 years later, a comparable storm might produce a few calls, resulting in not only lower cleanup costs but also faster response time and dramatically lower overtime needs. 

  

Service-level approach 

Drawing on these results, MSD proposed a program to EPA that currently requires MSD to clean all pipes smaller than 530 mm (21 in.) in diameter and not made of polyvinyl chloride (PVC) every 5 years; similar-size PVC pipe is cleaned every 10 years. But there is an important caveat: Once specific service levels outlined in the decree were met, MSD would be allowed to determine if the targets should be adjusted; cleaning frequency in certain sewers might be reduced, driving continuous improvement and making the best use of limited resources. The determination of whether the targets should be adjusted will be weighed against many factors, including public input, efficiency of the program, and the other programmatic needs at the time.  

The annual target service levels outlined in the consent decree include 

 

  • fewer than one basement backup per 1000 homes per year,   
  • fewer than 2.5 overflows per 161 km (100 mi) of sewer pipe per year, and   
  • response to 85% of emergency calls within 4 hours.   

 

Sewer-pipe maintenance is not the only component of the consent decree that involves asset management. Manholes, force mains, and pump stations also will be subject to similar inspection and repair programs, the frequency of which ultimately will be determined by their location, size, and criticality to the system.  

Results are promising  

Approximately 1 year after entering the consent decree, MSD has an EPA-approved capacity, maintenance, operation, and management (CMOM) program plan that it is now implementing. The CMOM program plan contains the service-level goals to be met by MSD’s program. Although the plan did not go into effect until April, MSD already had met its goals for basement backups and emergency response time. 

Substantial progress also has been made in meeting the wet weather overflow goal. In 2012, a record-low 0.9 backups occurred per 1000 homes — down from 1.0 in 2011 and more than 3.0 in 2008. Overflows in 2012 dropped to 2.7 per 160 km (100 mi) of pipe, down from 5.5 in 2008 (see table, below). 

Financially, the cleaning program already has more than paid for itself. Over the longer term, MSD anticipates that the success of this program may enable it to reduce the scope of other projects associated with the consent decree. A culture change also has occurred as crews transformed from teams that put out fires to ones that proactively address needs before they become problems. MSD and, by extension, its customers, likewise benefit from having the data needed to make decisions that maximize resources and target funding to the areas where it will achieve the greatest gains. Asset management works. 

  

Capacity, maintenance, operation, and management program
plan service-level goals
 

  

Service-level goal  

2008 results  

2012 results  

Basement backups 

Fewer than 1 per 1000 homes per year  

More than 3 per
1000 homes
 

0.9 per 1000 homes  

Wet weather overflows 

Fewer than 2.5 per 100 mi of pipe per year  

 5.5 per 100 mi of pipe  

2.7 per 100 mi of pipe  

Emergency response time 

Respond to 85% of calls within 4 hours  

Responded to 85% of calls within 4 hours  

Responded to 88% of calls within 4 hours  

 

Jonathon Sprague is director of operations, and Gene Stinnett is assistant director of operations at the Metropolitan St. Louis Sewer District.