Newberg Wastewater Plant Expansion Estimated at $32 Million, Slated for 2029 Completion

NEWBERG, Ore. — Most residents of any municipality interact with wastewater by pressing the toilet handle and hearing it flushed down the pipes and out of our minds.

But behind the scenes, hundreds of pipes in Newberg are carrying that waste beneath our feet to the Wastewater Treatment Plant. There, it undergoes a nearly three-month purification process that ends with the clean water deposited into the Willamette River and the solids sold back to the public in the form of Grade A compost.

The City of Newberg expects to spend an estimated $32 million expanding its wastewater treatment plant, with construction projected to start around the beginning of 2028 and finish near the end of 2029, according to a city presentation and City Manager Will Worthey.

The expansion is the City of Newberg’s largest capital improvement project, according to Worthey. It is meant to increase the wastewater treatment plant’s overall capacity and its winter flow capacity.

To expand capacity and allow for more development, the city plans to add a third oxidation ditch and an additional secondary clarifier, expand the chlorine contact basins, and switch to 100% aerated static piles for solids handling. The project is calculated to handle winter flows expected in 2037.

Oxidation ditches aerate wastewater so microorganisms can break down waste, secondary clarifiers separate solids from liquids, and chlorine contact basins give chlorine time to treat the water before it is released into the Willamette River. Aerated static piles are a composting method for the plant’s solids.

“This project is not simply replacing old equipment; it is positioning Newberg’s wastewater system for the next several decades,” according to a presentation at the Sept. 21, 2026, Newberg City Council meeting.

The project comes amid a wave of new housing developments in Newberg, including Springbrook Apartments — which opened for rentals in February 2026 — and other developments currently under construction: Collina Housing, West Branch Apartments, and Crestview Crossing. According to a 2024 letter from the Oregon Department of Environmental Quality to the City of Newberg, the wastewater treatment plant was already near or at its winter flow capacity. Worthey said the city’s population is growing by an estimated 1% to 1.5% annually.

From Sitting In The Improvement Pipeline To Biggest Project Yet

According to multiple city documents, improving the wastewater treatment plant to accommodate growth and adjust to additional infrastructure has been an identified capital improvement project for multiple years, including in the 2018 City of Newberg Wastewater Master Plan.

The plan identifies secondary clarifier rerating as a level 1 priority, the highest priority level. Oxidation ditch expansion and chlorine contact basin expansion are listed as level 2 priorities, and adding a fifth secondary clarifier is identified as a level 3 priority, the lowest priority.

According to a motion at the April 20, 2026, Newberg City Council meeting, city staff initially believed the additions were not necessary until around 2034 to 2035.

“It was, however, thought that this [wastewater plant] improvement would need to occur about seven or eight years into the future,” the motion reads. “We assumed that we had sufficient capacity to see us through until that time. We also assumed that we could focus upon the needed city potable water plant during this period and not on wastewater expansion.”

This assumption shifted in May 2024, when the city sent a request to DEQ to approve the addition of the Crestview Green Sanitary Pump Station, according to the motion. The request included a capacity statement, which DEQ indicated was not sufficient for current or future winter flow.

“The submitted capacity statement indicates that the plant has average dry weather flow capacity but is nearing or exceeded (sic) its average wet weather flow capacity,” the DEQ letter reads. “This is likely a result of excess inflow and infiltration entering the system and should be mitigated with a robust inflow and infiltration program. If the problem worsens it may result in future rejection of plans by DEQ.”

Upon receiving the letter, the city was “extremely skeptical of this result, as [they] had assumed that [they] had more time,” according to the April 20 motion, but began conducting studies with engineering firm Keller Associates to determine the current capacity and what improvements would be needed.

“Coming out of the capacity study, we observe that the oxidation ditches are right at capacity based on your current flows,” Eric Roundy, senior process engineer for Keller Associates, said at the April 20 meeting. “In fact, in 2023 and 2024, you’re right at what that peak winter capacity would be. Projecting into the future, it looks like a third oxidation ditch would be required to meet those future flows.”

Worthey said overflow — when the oxidation ditches exceed capacity and partially treated water may be released into the Willamette River — has not happened at the Newberg wastewater plant. The Dundee wastewater plant had an overflow incident in January 2024, when approximately 4.6 million gallons of partially treated water ended up in the Willamette River, according to a Newberg Graphic article.

“We haven’t had any discharges into the river in my time, but we’re at a point where we’re at the risk of reaching capacity now,” Worthey said. “We’re not there, but the DEQ letter was to remind us that we better get on with increasing our capacity as our population keeps growing.”

In 2025, Keller Associates ran three studies on the wastewater plant, examining the capacity, secondary clarifier stress limits, and alternative options for solids handling. The firm determined that the improvements, including the third oxidation ditch, fifth secondary clarifier, expanded chlorine contact basin, and additional return activated sludge, or RAS, pumps, which send most solids back into the oxidation ditch, are the necessary and fiscally possible next steps to expand the plant.

An Upgrade All Around

According to Worthey, adding a third oxidation ditch increases flow capacity; the third ditch will double the facility’s capacity serving Newberg’s rising population needs through the 2040s. With the oxidation ditches expanding, though, the clarifiers, basins, and RAS pumps further down the line need to be enlarged as well to handle the increased capacity.

DEQ originally thought two additional secondary clarifiers would be needed to keep up with the doubled flow. However, Keller Associates ran a secondary clarifier stress test in November 2025 to determine whether the stress rating of the current clarifiers could be reevaluated. After completing the test, DEQ verified the results, and the city determined it needed only one additional clarifier to manage the expected capacity, saving the project an estimated $6.5 million.

The project cut an additional estimated $6.8 million from its projected cost by moving the composting system from a compost tunnel reactor to a 100% aerated static piles process. The current compost tunnel reactor operates like a horizontal trash compactor, heating the compost for at least three days at 130 degrees Fahrenheit to kill all leftover bacteria from the oxidation ditches while simultaneously compacting a 3-foot-long portion of the solids into about 2 inches, said to Russ Thomas, the city’s former public works director, in a 2024 video tour on the Living in Newberg YouTube channel.

As the tunnel reactor is already nearing capacity, the city and Keller Associates determined during the design process that moving to 100% aerated static piles, which forces hot air through a pile of compost to accelerate the breakdown process, would be more practical and cost-effective, because the facility already has room for the expansion static piles require.

A Long Road Ahead

The project, which is taking shape after months of planning, still has a long road toward completion. The City of Newberg’s legal team is in contract negotiations with Keller Associates, the design contractor for the project. According to Worthey, the city is in the final negotiation stages of the contract.

Once the contract is completed, Keller Associates will begin engineering work before conducting the basis of design and initiating value engineering to reduce costs where possible. The project is using a Construction Manager/General Contractor, or CM/GC, contract model, which allows Keller Associates to conduct all the design work and then subcontract a general contractor company to complete the construction work while still maintaining control over the project.

“When a project is more complicated, generally you want to do the CM/GC process, and the two partners work together through the whole process for value engineering and cost control,” Worthey said. “It’s also probably safer too, because the engineering firm is always involved till the very last ton of cement goes in. There’s no transfer moment, so I feel like you get better clarity and more quality control.”

According to a presentation at the Sept. 21, 2026, Newberg City Council meeting, the design process will take about a year, starting at the end of 2026 and continuing until near the end of 2027, when Keller will begin the competitive bidding process for the general contracting company. Construction is slated to start around the beginning of 2028 and finish near the end of 2029, with details subject to change because the project is still in its early stages.

Cost and Funding

The project is funded by a combination of System Development Charges, or SDCs, as well as the wastewater reserve fund.

As of November 2026, around $23 million of the project’s funding will come directly from the wastewater reserve fund, which would leave the fund with an estimated $10 million at the end of 2029. The wastewater funds are intended to pay for large projects like this, Worthey said.

SDCs will also contribute an estimated $10 million to the project, leaving the SDC fund around $4.6 million at the end of 2029.

“If we didn’t need to do [improvements like this], we wouldn’t have the reserves in the first place,” Worthey said. “The rate model [the rates committee] votes on has all of the Capital Improvement Project things that need to happen in two, four, or even a 10-year cycle.”

Worthey said that once the project is completed and the city’s remaining debt is retired, wastewater rates can be reduced.

“Everything that is in the rates model, staff, goods and services, and capital projects goes together to make the rate. Now, on the day when this is done, and on the day when our last piece of debt is retired, which should be during my time here, I’ll be able to reduce the rates,” Worthey said. “So we’ll have a little golden time when the wastewater rate won’t go up much, but sometime 15 years after that, the rates are going to have to start going up again to save up money for the next thing. It never ends.”

However, all prices are subject to change, according to Worthey. The $32 million cap holds “barring unexpected discoveries, because you never know what you’re going to find when you remove 50 feet of soil,” Worthey said.

Worthey also said he expects an “extremely competitive” bidding process for the general contractor bid, which could come in below the $27 million construction cost Keller Associates estimates, potentially putting the project under budget.

Regardless of the final cost, Worthey said the city can fund the project using only internal funds. No bonds will be issued to fund the project.

“It is a remarkable thing in Oregon today that a city can afford to cash fund a project like this,” Worthey said. “It is a sign of our high level of fiscal conservatism that we are able to do things like this, as most cities can’t.”