Austin Water, in Texas' capital city, has begun work on a $1.2 billion project to update and expand its Walnut Creek wastewater treatment facility.
Approved by the Austin City Council in May 2024, construction on the facility began in October 2025 to increase the facility's capacity from 75 million gal. per day to 100 million.
Austin Water photo
Austin, with a rapidly growing population — from 297,000 residents in 1974 when Walnut Creek went into service to 980,000 in 2023 — and facing ncreasingly extreme weather, needs more from its wastewater treatment plants than it did 50 years ago.
In addition to a larger capacity, Walnut Creek will have, among its updates, modern equipment, advanced odor control technologies and improved flood resistance.
MWH is the prime contractor. A U.S. contractor in water, wastewater and industrial water construction projects, MWH was selected after a competitive process, said Austin Water Managing Engineer Lauren King.
The project will be delivered by the construction manager at risk method, or CMAR, King said.
"CMAR has advantages in that it allows the design team and the contractor to work together to achieve a more constructable and efficient final product," she said.
CMAR contracts are broken into individual packages of guaranteed maximum price, or GMPs, she said.
Austin Water photo
Equipment used on the project includes: a tower crane on site; rough terrain cranes and crawler cranes; 150-kilowatt and 45-kilowatt generators; water trucks; street sweepers; skid steers; and lights.
Builders also will use forklifts, front loaders, scissor lifts and side-by-side buggies.
"There will be a lot of concrete," King said.
That include post-tensioned concrete and peak cast concrete for basins and buildings and structures, as well as piping, pumps, control panels, clarifier mechanisms, electrical equipment, motor control centers, programmable logical controllers, different tanks for chemicals and storage, steel, reinforcement and valves.
Project Benefits
Walnut Creek is one of Austin's two wastewater treatment plants. It treats about half of the city's wastewater. Opened in East Austin in 1974, it was most recently expanded in 2000.
The project will benefit Austin in five ways, King said.
Austin Water photo
Greater capacity. 75 million gal. per day will increase to 100 million gal.
"The main way that we're going to accomplish the increase is by building the 25-million-gallon expansion portion of the plant first, thereby increasing our total treatment capacity," King said. "And that will allow us to take portions of the existing plant down to be upgraded and retrofitted for the new treatment technology."
Replacing aging equipment. "We will rebuild and replace aging parts of the existing plant," King said. "So that's various mechanical equipment and electrical systems and control systems; and piping."
In addition, screening machines will remove trash, rags, wipes and other debris from raw sewage to ensure clean water.
Updating wastewater treatment. After the new part of the plant is expanded, the existing plant will be retrofitted to reduce the nutrients that are discharged from the facility, phosphorus and nitrogen being the primary ones, King said.
Those nutrients contribute to algae growth.
"The nutrient removal process requires modifications to our aeration basins. And, so, we will have a more complex microbiology that we maintain to treat the water," King said. "That benefits the ecology of the Colorado River that we discharge into."
Odor control. "We're including improved odor control for our facility as part of the expansion," King said.
Those improvements include biofilters, activated carbon filters and basin covers.
Improving flood resistance. "The plant was not in a floodplain when it was originally built," King said. "But as climate change and urbanization have impacts on our watershed, the new floodplain maps do have the plant in the floodplain."
To bolster the plant's resilience, a flood protection wall will be constructed around the facility.
Cleaning With Ultraviolet
"The Walnut Creek plant and all of our wastewater treatment plants here in Austin require tertiary wastewater treatment, which disinfection is a component of," King said.
Austin Water photo
Walnut Creek disinfects using chlorine, which King said is "a very effective, cost-effective and robust process. It does require that the water be dechlorinated before being discharged into the water body."
As part of the expansion and upgrade, the facility is switching to ultraviolet light disinfection.
"The water is essentially passed over UV light-emitting bulbs — specialized bulbs that kill the pathogens."
UV technology is safer for the staff, as well as the surrounding community and environment.
Construction is expected to be completed in 2031.
Eight construction packages are going out for bidding. Package one includes the head works and the influent lift station.
"We'll start construction in June on package two, which is mobilization and site service, so that's construction trailers and whatnot," King said.
The plant must remain in operation during construction, she added.
"People will keep taking showers and flushing toilets and using sinks," King said. "So, we must keep treating the wastewater.
"And the sequencing of tasks in the construction project, as well as the planning around making it constructable, has been part of the design from the beginning, with the aim of ensuring that our plant is able to meet permit requirements through the construction phase." CEG
