System Development

Pierce County’s collaborative approach to planning and maintenance ensures quality service and cost-effective solutions.
System Development
Pierce County Public Works and Utilities employees Rocky Feller, left, maintenance specialist; James Wilkinson, maintenance worker; and Ryan Hall, maintenance technician, work together to bring debris out of a manhole that they have just cleaned from a sewer line.

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In the early 1970s, local lakes in Pierce County, Wash., began experiencing water-quality problems. The area faced a moratorium on building, but it never reached that point.

The first Utility Local Improvement Districts were put in place across the country in 1970, with funding available through the Clean Water Act. Eventually, ULID 73.1 was passed, which paved the way for the first segments of the municipal sanitary sewer system and a wastewater treatment plant in Pierce County.

“A lot of improvements were made at that time,” says Sewer and Water Utility Maintenance and Operations Manager Terry Soden. “We had some initial systems that were put in. They were constructed as concrete sewer mains, and the flow was actually directed to the City of Tacoma.”

Construction ramped up and carried into the early 1980s. The plant was completed in 1984, and most of the pipe work on the original 300 miles of the system was done in 1986.

Before the early phases of the collections system were completed, local residents were all on private septic systems. Due to local geology — with rocky glacial outwash and areas of till — wastewater from many of these systems eventually made its way to local groundwater-fed lakes, which created the water-quality issues.

Taking shape

The county currently serves a population of over 250,000, with more than 60,000 customer accounts. About 2,700 of those accounts are commercial.

The initial sections of the system were built with concrete pipe, but it wasn’t long before plastics came on the scene and the county shifted to PVC and HDPE pipe. Today, about 80 percent of the system is comprised of those two materials. The rest of the system is concrete, lined ductile iron and some fiberglass pipe.

In the early 1990s, growth management became an issue. Eastern portions of the county were opening up to development, so the county partnered with developers to run a trunk line off the existing collections system and extend it east. It began a trend of continued development stretching the system farther from the treatment plant.

The current plant is permitted for 28.7 mgd, but additional capacity is available through a reciprocal agreement with the City of Tacoma, which allows the county to send excess flow to the city’s treatment plant as well.

In 2006, work began on a satellite system in the Bonney Lake Plateau, which will have a decentralized wastewater treatment plant and will provide infrastructure for additional growth. Work is scheduled for completion by 2016. The plant will be a membrane bioreactor, using reclaimed water and ground discharge instead of discharging into a body of water.

An eye on the system

The county tracks the condition of its collections system with a homegrown asset management system tied to its Computerized Asset Management System from Infor. Currently, about 94 percent of the system is classified as excellent, which Soden partially attributes to its relatively young age. Still, the utility’s collaborative, progressive approach to maintenance and rehabilitation plays a big role.

Maintaining and repairing some of the older interceptors made of unlined concrete pipe has been a big focus for the utility.

“Concrete has been our biggest issue — especially the pipes that have been in since the beginning,” says Karl Imlig, P.E., the utility’s engineering manager. “We’re now going through some aggressive programs to line some of our concrete pipe.”

Seven pump station crews and two line crews regularly clean and maintain the system. Two crews clean parts of the system almost daily. One crew is dedicated to what the utility classifies as “problem lines,” and the other is out working on the rest of the system on a basin-by-basin approach. The process is pretty simple.

“We have two high-velocity trucks, and that’s all they do. We just use sand traps to collect the debris, and then we use basin scoops on poles to pull it out from section to section. It’s just a lot faster,” Soden says, noting his staff helped design the trucks. “They hold 1,500 gallons of water. They have a short wheelbase. They’re very maneuverable in cul-de-sacs.”

Soden says with this type of setup, nozzle selection is really important. He says spinning nozzles have been a big help in lines affected by FOG. They also use standard ferret nozzles in some instances, and rely on larger sled-type nozzles on interceptor lines.

Soden says they take the Goldilocks approach to their cleaning strategy, trying to find just the right cleaning frequency. Currently, crews take about 4 1/2 years to complete a full cleaning cycle through the entire system, moving from one basin to the next as work is completed.

“Our current sanitary sewer overflow rate per 100 miles is less than one, so on average we probably experience about six SSOs per year,” Soden says. “So we’ve demonstrated that we’ve been pretty effective, at least given the numbers that our brethren post around here, sometimes in the double digits per 100 miles.”

The utility collects debris data in its Computerized Maintenance Management System as lines are cleaned, recording the volume of material removed. From there, they can evaluate patterns and try to determine where the debris comes from. They’ve also been testing pole cameras to find one that suits their needs. Soden says that will let them quickly and easily inspect certain lines when necessary and avoid cleaning lines that don’t require it.

“Those are opportunities to optimize what we do,” Soden says. “But clearly the current cleaning method works pretty well, given our blockage rate.”

The county used to use the same basin-by-basin approach with CCTV inspection, but it took too long to get through the system and generate meaningful information. They have since moved toward a criticality-based inspection method.

“As part of our asset management plan we developed a risk model, so we were able to look at the likelihood and consequence of each line segment and get an overall risk score. We call it the ‘level of equivalent risk,’ so we have lines in different categories,” Soden says. “Instead of TVing everything, we decided to TV the lines that are most critical first, and then get that condition assessment information back as well as some additional information. The next phase of this process is taking a look at the rest of the system, and doing more what I would consider analysis on like types of pipe and do a representative sampling. When we get down into the least risky, we’ll just use statistical analysis to assume these like pipes are in the same condition as the rest.”

From high to low

Pierce County is unique because its elevation starts at sea level and then climbs to the highest point in the lower 48 states, the top of Mt. Rainier. The varied terrain requires many pump stations — 101 — but the treatment plant is on Puget Sound, at an elevation of only 30 to 50 feet. This allows the county to maximize gravity flow.

“For the most part our system is gravity from one end to the other,” Soden says. “Most of the pump stations we have are to support other smaller developments that can’t get in with gravity.”

Imlig adds that flow into the plant is gravity-fed, which is an advantage over many municipal systems and helps lower costs.

On one of the county’s current projects, the B Street Interceptor project, about 6,000 feet of 30-inch pipe and 3,000 feet of 8-inch collector pipe will be installed to serve new neighborhoods. This is the third phase of the project, which is currently in the design stage. The pipe will be buried as deep as 25 feet. Installing pipe that deep is a big expense upfront, but Soden notes it will allow gravity flow and reduce costs over time through savings on pump stations and pump station maintenance.

“We try to serve as many of our basins as we can by gravity. By making it that deep we can extend farther — in this case — south, and serve the largest area possible,” Soden says. “One of the things we like to do is base our decisions on least life cycle costing, so that it may not be the cheapest to install, but if you look out 30, 50, 100 years, you have a savings over time. In most of our cases we’re recouping costs within the 20-year time frame.”

Shedding I&I

The county is also looking at a different approach to its inflow and infiltration abatement program, incorporating CCTV to find potential problems.

“First off, most of the time people wait for a leak to avail itself inside an interceptor,” Soden says. “We actually take our grout-packing unit and pump the joint to see if it holds air regardless of whether the joint is actually leaking water that you can see. If it isn’t holding air, more than likely in the high groundwater table time of year it will leak. So we go ahead and grout pack those as needed.

“The other part of the program is our I&I abatement crew that was established in 1996,” he continues. “Those resources were applied just to looking for I&I. We’ve done that through smoke testing and TV inspection, and we found that we weren’t turning up as much work as we used to. So the level of effort, let’s say for smoke testing, wasn’t yielding any inflow connections. So we’re kind of regrouping a little bit, working with our engineering team to take a look at our current placement of flowmeters and looking for opportunities to put a little more granularity in the amount of flowmeters we have out there — a little more strategic — to do a better job of pinpointing it. It’s kind of what I call the tip of the spear approach as opposed to the shotgun blast approach we’ve been using.”

Soden says it costs $175,000 per year to have that crew out working, and they’re not finding the volume of repair work to justify the expense. He says that’s partially a result of the system being in much better shape now than it was when the crew was established.

Imlig also notes that the county has changed its inspection procedures for new residential construction. They do more air testing and vacuum testing of manholes, and inspectors spend more time monitoring construction projects, which has helped improve the way things are done.

“We monitor every connection to our system so hopefully we can catch these things before we have a customer connected to it,” Imlig says.

I&I has also not been a big issue with manholes. About two thirds of the system’s manholes have composite precast bases from Predl Systems. Most are unlined concrete above the base. Some are also lined. Liners are used in areas that are prone to hydrogen sulfide, like in the interceptors. Hydrogen sulfide is a bigger issue in the early years on new interceptors until more connections are added and flow increases.

The precast bases have an incorporated bell and spigot, and the pipes just connect into it, as opposed to the old days where some of the bases were constructed in the field and those field connections had problems.

“I think the fact that we have factory connections in manholes, given the system we chose, has reduced the risk of I&I entering our system,” Imlig says.

The three-legged stool

Soden’s tenure with the county — 28 years — spans almost as much time as the collections system itself. He has seen the system evolve and has a good perspective on what has kept the system functioning smoothly.

“The difference I think that sets us apart, is even if we had an older system, our sewer utility has made a very strong commitment to preservation. We always have,” Soden says, noting that the longevity of the materials being used today is also far better.

“The other piece I would add, is since I’ve been here, we have always used a computerized maintenance management system, not a 3x5 card file index … Not only do we have an inventory, we have work orders, we can track history and usage, we can look at failure modes. I can look at how much corrective maintenance we do over planned maintenance. There’s quite a bit of information we have, and I’m pretty proud of the system we’ve set up. I see a lot of people struggling today in other agencies trying to get a computerized maintenance management system off the ground, and from my vantage point, I don’t get it.”

Soden likens his department’s success to a three-legged stool, where all three legs carry equal weight.

“We’ve got maintenance and operations working with engineering and inspections, all collaborating to try to turn out a good product. If you don’t have a good maintenance plan, kick that leg out from the stool and the stool will not stand,” he says. “On the engineering side, if you don’t design it well and call out the proper specifications, you kick that leg out and nothing good will come of that. And last but not least, if you don’t have a good inspection program with a quality assurance effort, making sure that the specifications are adhered to in the field, you kick that leg out and nothing will stand.

“So I think we have a good culture here where all three groups work together in collaboration with one another. That’s probably the biggest success story over my 28 years of being here.”­­


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