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
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.
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.
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.
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
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.
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.
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).
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
plan service-level goals
Fewer than 1 per 1000 homes per
More than 3 per
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
Responded to 85% of calls
within 4 hours
Responded to 88% of calls
within 4 hours