When demand on its eight groundwater wells threatened to exceed capacity, the City of Wilsonville, Ore., faced a choice: Add more wells or draw from the Willamette River, which flows through town.

On the advice of consulting engineers and its own staff, the city chose the river, despite winter-season turbidity caused by rains and snowmelt. The result is the 15 mgd Willamette River Water Treatment Plant, completed in 2002, built in partnership with the Tualatin Valley Water District and operated by Veolia Water.

Now serving both Wilsonville (population 19,500) and the nearby City of Sherwood (18,200), the plant uses a rapid sedimentation technology as part of its process to deal with turbidity and deliver high-quality drinking water year-round. Its attractive landscaping with water features makes it an excellent fit with a neighboring park.

Supply dilemma

Wilsonville, at the north end of the Willamette Valley, 17 miles south of Portland, is among the fastest-growing cities in Oregon. In the mid- to late 1990s, growth began to stress the city’s drinking water supplies. “We were reaching the point where our need for water was greater than what our wells could produce,” recalls Delora Kerber, Public Works director.

Working with engineering consultants Montgomery Watson Harza, the city looked at new supply alternatives, including additional wells on the south side of the river, before deciding to draw from the river itself.

Other nearby communities were also struggling with water supplies, and Wilsonville explored a variety of potential partnerships before teaming with the Tualatin Valley Water District on a regional treatment facility, fed by a 72-inch intake pipe sized to accommodate future needs.

Although the Tualatin district so far has not drawn water from the treatment plant, it owns 100 mgd of water rights on the river and in 2011 turned over 5 mgd of capacity to Sherwood, just west of Wilsonville. The Willamette Valley plant now delivers up to 6 mgd to Wilsonville and ultimately will provide the 5 mgd to Sherwood.

When plans for the plant were announced, some residents had doubts about the quality of the river water. Some noted that a stretch of the river running through Portland Harbor — well downstream from Wilsonville — had been designated as a Superfund site. Of more immediate concern was runoff from agriculture in the Willamette Valley, potentially containing bacteria and other pollutants.

“There were those who believed the source would be difficult to treat, but it has proven to be quite the opposite,” says Kerber. “It’s a very treatable water source, and the plant was developed with a lot of forethought. The city and the water district used a belt-and-suspenders approach — really taking seriously what people’s concerns were to make sure the finished water would meet or exceed city standards.”

Quick settling

Heading day-to-day plant operations are Veolia assistant project manager Jason Labrie and lead operations and maintenance technician Shane Wyer. Treatment is far more involved than when the city used well water needing only chlorination.

The plant operates two shifts per day, from 8 a.m. to 10 p.m. The most critical challenge is variability in the river water during winter. “We get increasing flows in the river and increasing turbidity from runoff, and that also increases the bacterial load and raises the possibility of other contaminants in the water,” Labrie observes.

The process starts with two T-screens (Johnson Screens) about 30 feet below the river’s surface. The water flows through the intake pipe into a raw water caisson, a stilling well 50 feet in diameter and 80 feet deep. Water drawn out of that structure by Floway vertical turbine pumps (Weir Minerals Floway Pumps) is dosed with aluminum sulfate.

“We also have capability to prechlorinate or add pre-caustic to the system,” Labrie says. “When we see the river turbidity rising, we start to add more alum to optimize the coagulation process. That also depresses the alkalinity. We preemptively start adding pre-caustic when the gauge height and weather predictions tell us the water level will be rising. As long as we keep up on our caustic soda dosing strategy along with alum dosing, we can run quite comfortably at high turbidity.”

The chemically dosed water is fed to an Actiflo rapid sedimentation process (Veolia Water) that is the key to treating seasonal turbidity. The Actiflo process accelerates settling through the addition of microsand ballast. At Wilsonville, it enabled effective turbidity removal within a small footprint.

“We had river turbidity last winter up over 200 NTU, and we were able to knock that down to less than 1 NTU just with the Actiflo, before filtration,” says Labrie. “We use it continuously when we’re operating. We have two identical trains, each sized for 15 mgd, and we run them both unless we’re doing maintenance on one train. Turbidity in the dry season ranges from 2 to 5 NTU going into the plant and from 0.1 to 0.2 NTU coming out of the Actiflo. That’s essentially drinking water quality in terms of turbidity.”

Dual disinfection

Water from the Actiflo process feeds into a common channel that is then divided into two trains of intermediate ozonation (WEDECO – a xylem brand), each with eight ozone contactors. Ozone generators (also WEDECO) bubble ozone through the water in the first two chambers of the contact basin. “After ozonation, we quench the remaining ozone with calcium thiosulfate ahead of the filters,” says Labrie. “We destroy remaining ozone in the headspace with a Carulite filter system (Carus Corporation).”

Ozonation removes dissolved organics that could create taste and odor issues. That process is followed by dual filtration with six feet of granular activated carbon (for further organics removal) and one foot of sand (for polishing). Filtered water collects in an underdrain (Leopold – a xylem brand). After pH adjustment with caustic soda and final chlorination with sodium hypochlorite, the water is pumped to the reservoirs. Finished water quality has a pH of 7.8, 0.88 mg/L chlorine residual, and 0.03 to 0.06 NTU turbidity.

Attentive operators

The operations team is experienced and well qualified. Labrie holds a Level 4 (highest) water treatment license with filtration endorsement and has seven years of water plant experience. Wyer holds the same credentials and has 19 years in the industry. The team also includes:

• Gary Simantel, operations and maintenance technician III, Level 4 water treatment with filtration endorsement, 28 years.

• Tyler McCune, operations and maintenance technician II, Level 2 water treatment and Level 2 water distribution, 13 years.

• Phillip Leach, operations and maintenance technician II, Level 3 water treatment, Level 2 water distribution, 26 years.

• Greg Murray, operations and maintenance technician II, Level 3 water treatment, 22 years.

• Tom Hubbard, project manager, Level 4 water treatment distribution and Level 4 water distribution, 23 years.

• Chris Hannan, administrative assistant.

Ongoing training is a high priority. Operators receive monthly training through Veolia Water and attend American Water Works Association subsection events, annual conferences, technical sessions and short schools. Labrie recently completed a utility management seminar offered by the Utility Training Institute. “The people I work with are all top-notch individuals,” says Labrie. “I can’t say enough good things about the team, and I appreciate the attention the city pays to this facility and to water quality.”

Control over dosing

While the plant’s technology is sophisticated, performance depends on close operator attention and sound decision-making. “The plant does not run itself,” Labrie observes. “Everything is operator-driven, and that’s the way it was intended.”

The plant uses flow-paced chemical dosing. The operators have to deliver the necessary dosage, but programmable logic controllers from Allen-Bradley (Rockwell Automation) make the dosage calculations. “We have a process control plan that helps us keeps our dosages low — as low as we can go to properly treat the water without wasting chemicals,” Labrie says.

Wyer adds, “Winter is challenging because of the water-quality changes. We can look at trends on the Internet, so that as the river is starting to come up, we can prepare for it. We have significant redundancy in plant equipment, so if for example a chemical pump goes down or needs to be worked on, we can switch to another one.”

Operator decisions begin with daily plant startup: looking at chemical dosages from the previous day, checking raw water quality, performing jar tests, and making dosing changes to ensure proper chlorine residual and pH adjustment. Operators also decide when to take the filters offline for backwash. A SCADA system from Wonderware (Invensys) with multiple nodes lets operators run the plant from a variety of locations.

Instrumentation includes a BTEX analyzer for raw water (Turner Designs), turbidimeters (Hach), pH meters (Hach and Emerson Process Management), ORP meter and ozone sensors (Emerson Process Management), particle counters (Met One Instruments) and streaming current monitor (Milton Roy).

Always improving

Labrie notes that the team strives constantly to optimize the plant. “If we have to buy equipment, reconfigure something, add a valve here or there, we’ll do it,” he says. One significant improvement was an adjustment to the Actiflo system.

Wyer states, “At the end of the process we have a settling zone where the floc, sand and sludge all settle out. That mixture is then sent to hydrocyclones where the sand is separated and returned to the system and the sludge is diverted to a thickener.

“One thing we discovered was that if the hydrocyclones became plugged, we would lose a lot of sand. We installed vibration switches on the hydrocyclones so that if one of them starts to fill up, it will shake enough to activate the switch, stop the pump and keep us from losing sand. There are two hydrocyclones on each Actiflo train, so if one vibration switch picks up, the other unit’s pump automatically starts, and the process continues to run.”

The plant also has a washwater equilibration basin that collects all backwash, all filtered waste, and all water from the sludge dewatering process. That water is re-injected into the raw water line for treatment. There is zero water discharge from the site.

In case of power failure, a 1 MW standby generator (Caterpillar) can enable the plant to produce 4 mgd for up to two days before refueling.

Attractive setting

Besides delivering quality water, the plant makes a positive visual impression on the community. The plant stands next to a 9.9-acre city park. A water feature abutting the park mimics a river: Willamette River water flows through the site and feeds a fountain. Looking out on the water feature is a conference center with a three-sided glass enclosure, available for city staff meetings as well as for neighborhood groups.

The plant exterior façade includes an arch of wood, stone and metal to appeal to neighbors and park visitors. Along the park side of the plant are windows that look in on plant processes. Interpretive displays tell visitors what is happening at each step.

“On weekends, we see a lot of photographers at the plant taking high school pictures,” says Labrie. “We see wedding pictures taken here. So word has gone around that it’s a great park, and photographers are using it for their businesses. We conduct a lot of public tours. Last year more than 400 people came through the plant. We welcome that. If it’s not me leading a tour, it’s one of the operators.”

Bright future

The Willamette River plant is well prepared for more growth in the coming years. The site includes space reserved for expansion. Labrie expects to extend operations to 24 hours per day in the relatively near future.

“The city and Veolia have formed a true public-private partnership,” says Kerber. “The way the city sees it, we are able to provide top-quality water for our citizens at a very good price.”