Intelligent Planning

The Mesa Water Resources Department optimizes its inspection and rehab program with innovative software that makes it feasible to predict what might break next

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Software that can detect and filter e-mail spam incorporates a library of known spam characteristics, learns from user input and recognizes patterns. It works well.


The City of Mesa, Ariz., has found that the same process can be applied to infrastructure maintenance. In theory, if software can learn to predict spam, it can learn to predict infrastructure failures. This is the reasoning behind the city’s Sewer Cataloging, Retrieval and Prioritization System (SCRAPS).


The Water Resources Department incorporated SCRAPS to help optimize its system rehabilitation and maintenance program. The results to date have been stunning. Hebi Li, the civil engineer in charge of integrating SCRAPS with Water Resources planning, observes, “There have been no surprises since we started using SCRAPS. In fact, we’ve come to trust the program’s judgment when setting up our rehab and inspection schedule.”


SCRAPS automatically sets maintenance schedule priorities based on the likelihood of a problem, the damage that problem could cause and the resources required to prevent it. It takes the guesswork out of planning and recommends the most effective allocation of department resources.


Predictive tool

Mesa’s relatively young sewer system includes 1,632 miles of sewer pipe, 17 lift stations, 19 sulfide control stations, five metering stations and 29 flow diversion structures. Its four wastewater treatment plants process 35 mgd on average.


The city began using SCRAPS in 2009. The software was developed under contract to the Water Environment Research Foundation by the Brown and Caldwell environmental engineering and consulting firm and the University of Washington. It was officially launched in 2001.


The Microsoft Windows-based software is of the genre often called expert systems (see sidebar). The internal model it builds allows it to make statistically sound predictions about where things might next go wrong within a sewer system infrastructure.


Once it assimilated Mesa’s geographic information system (GIS) and started interacting with the staff, it quickly learned to predict the most likely system failures, and that’s where the city focuses its dollars.


When SCRAPS is launched, the user is presented with a series of three input screens requesting data. Those are:

• General and historical information: Includes typical GIS data, such as pipe material, dimensions, slope and age.

• Previous inspection or improvements: Records the pipe’s current rehabilitation and condition status.

• Pipe environment characteristics: Includes pipe depth, type of soil, proximity to bodies of water and street resurfacing costs.


Each screen prompts the user for the appropriate data. Much of it can be assimilated directly from the existing GIS, but that requires proper formatting of the attributes. “It takes a little setup time, and maybe some global editing in the GIS, but then SCRAPS just pulls it all in,” notes Bill Fick, senior civil engineer.


Data output

After crunching all the numbers, and consulting its expert system algorithms, SCRAPS displays its prioritization summary. This is the payoff for all the setup and data entry. With reference to individual pipe numbers, the software lists every pipe in its database, starting at the top with what it has judged to be the highest-priority job, whether repair, rehabilitation or inspection.


The first column on this output report (Need to Inspect) really calls the shots. The Need to Inspect is a number from 100 (do it yesterday) to zero (no problems expected). It effectively sets priorities for work based on a combined assessment (other columns) of the probability of failure, consequences of failure, and structural, operational and material considerations.


Mesa Water Resources has generated a five-year plan for pipe rehabilitation and inspection based on the priorities assigned by SCRAPS. The city is just now completing its cycle of inspections for year 1, and it’s working. “I’ve been amazed by the lack of surprises,” says Fick. “We open up the pipe at the top of the list, and sure enough, it’s a good thing we did.”


About 8 percent of the pipes have been in the ground for more than 50 years. The rest of the collection system has been in place for 40 years (16 percent), 30 years (39 percent), 20 years (63 percent) and 10 years (22 percent). That boom in piping 20 years ago corresponds to Mesa’s transition from a largely agricultural area to a residential and commercial metropolis — it is now the 38th largest city in the country.


Making compensation

SCRAPS was designed to be used in any location, but some locations have unique environments that lie a little too far from the mean design parameters. “The internal weighting factors that assign relative importance to things like pipe material or slope are not user adjustable,” Li observes. “They’re averages. Sometimes we find ourselves questioning these weightings. It would be nice to set them ourselves.”


Fick adds, “So what we find ourselves doing, when we input the database, is mentally compensating for these weighting factors. We adjust up or down based on how we know these weighting factors operate. I’d like to have more control over that.”


For example, attributes such as pipe depth and freeze depth are internally correlated, and the correlation is averaged for use throughout the country. But in central Arizona, where freezing is not an issue, that correlation is higher than it needs to be.


Another attribute is the extent and likely duration of traffic disruption, should excavation be required. In a city with high population density and narrow two-lane streets, this is indeed an important consideration. But in Mesa, with its large open spaces and relatively low population density, and many of its lines under four-lane streets, that factor gets too high of a weighting.


High confidence

Still, both Li and Fick have confidence in the software, as evidenced by their commitment to a five-year plan based on its prioritization schedule. They may revise that schedule as new inspection data is entered and SCRAPS continues to learn and revises its prioritization schedule.


Water Resources farms out all work on pipes 15 inches and larger. The work is generally done by Achen-Gardner Engineering LLC, a general contractor specializing in wet utility, roadway and highway construction. Smaller pipes are handled in-house. “We find that this provides a good balance between operational and capital expenses,” Li says.


The department fields three in-house-built jet-vacuum cleaning trucks, one camera van, and one easement machine for working on off-road rights-of-way. The camera van carries with it an OZII camera and Granite XP software from CUES Inc.


The city’s nominal inspection cycle is set for 10 years, or about 162 miles of pipe each year. SCRAPS has already identified where to inspect for the next five years of that cycle. As more data is acquired, it will do the same for the final five years.


“Typically you would start with the oldest pipe and work your way up based solely on age,” Li says. “But what SCRAPS has shown us is that it’s not always the oldest pipe you need to throw your resources at.”


Fick adds, “Sometimes a newer pipe gets flagged for inspection based on factors other than age, and when we go take a look, we’ll find that, sure enough, we’ve got root intrusion or a corrosion problem.”


The next act

Water Resources is working along a similar track with lift stations, sulfide control stations, metering stations and flow diversion structures. Here the department is using another Brown and Caldwell program, Asset Management Planning System (AMPS).


“AMPS identifies replacement and refurbishment activities and associated costs to ensure the asset attains its expected useful life,” Li says. It’s a work in progress, as crews are still gathering data from field inspections for input to AMPS.


But once done, the software will provide crucial guidance for long-term capital improvement budget planning. Working in concert with SCRAPS, effective and efficient resource allocation is the result. Having an “expert” in the house 24/7 is a powerful tool.


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