$35 mil price tag to expand Williams' wastewater plant

Engineering firm finishes year-long analysis and gives expansion plan to city council

WILLIAMS, Ariz. — The city of Williams is looking at a hefty $35 million tab to expand the city’s wastewater treatment plant, according to Carollo Engineering, who presented the results of a year-long study to the Williams City Council March 24.

The city’s current plant is overcapacity and Carollo Engineering was hired in 2021 to complete a study to help determine the city’s next steps.

In creating an expansion plan, the company looked at historic flows and loading data and analyzed the current residential and tourist populations for the community.

They used projections to determine treatment capacity requirements and evaluated the existing wastewater treatment plant’s ability to treat flows.

After a year-long analysis, Carollo gave a recommendation for the expansion design and developed a construction cost estimate.

“You are at (over) capacity, you crossed that line in the last couple of months,” said Carollo engineer Chad Meyer, who addressed the council. “I know this message is not good, and we do have some breathing room, but this is going to take at least three years to get online and you’re going to be exceeding that capacity the whole time.”

In September 2021, Pat Carpenter, the city’s water and wastewater treatment contractor, and Public Works Director Aaron Anderson advised the Williams City Council that the wastewater treatment plant was nearing capacity.

“Two years ago I would never have imagined we would be maxing out our wastewater treatment plant,” Anderson said at that time. “We are at the point now where we are pushing our limits.”

In 2021, Anderson said the wastewater treatment plant was operating at 65-70 percent capacity.

Based on Anderson’s recommendation, the council approved a $316,600 wastewater treatment plant expansion study with Woodson Engineering and Survey, obtaining sub-consultant services from Carollo Engineering, who specializes in wastewater and water treatment plant design.

Meyer said despite the facility being at capacity, the completed analysis determined that the city’s current treatment facility was in good condition and adequately handled the monthly flows. Their recommendation was to keep the current facility, but duplicate the original design, with a few modifications, to meet future demands.

In December 2022, the plant was at 89 percent capacity. The flow values were around 90 percent, and the strength values were over 100 percent of what the plan was originally designed for, Meyer said.

“In general terms, most of your capacity was being utilized,” he said.

With the record-breaking snowfall this winter, the wastewater treatment plant saw unprecedented flows.

“You can see we were at two to three times the permit level in January,” he said. “We do believe that is an anomaly, the problem is we don’t have the data that goes back 10-20 years to see if this is the worst spike we’ve ever seen. But it’s a pretty terrible spike. It's more flow than the plant operations staff can treat.”

Wastewater was going into the plant and almost directly into the wash.

“The biology does a little work, but treatment is very difficult,” Meyer said.

“Now that you are at capacity, it has to be reported to ADEQ (Arizona Department of Environmental Quality),” he said. “But the good news is that you’re working on it. You’re trying to find a way, and ADEQ likes that. You’re well underway here and trying to solve the problem.”

Although the plant is 16 years old, the engineers said they don’t see many rehabilitation needs other than a few mechanical upgrades.

They feel the most efficient and cost-effective way to expand the plant is to duplicate the existing plant, with a few modifications.

“Your operations are important, so we recommend mirroring the existing plant, so we don’t have to throw new technology at the staff,” said Brian Bernard, another engineer with Carollo Engineering.

Bernard said he recommended the city look at historical flows and population trends when looking at funding options for the expansion.

He said the study found the gallons per capita per day per person in Williams was around 200 gallons, which was unusually high for a residential population.

“This is almost double what we typically see,” he said.

The study took a closer look at tourism lodging to determine how the seasonal population impacted the average usage and the impacts on the wastewater treatment plant. They found that on average, across each day of the year, the population is at or even double the permanent population.

“We said to ourselves ‘Why are the flows where they are at in a city of 3,500 people?’” Bernard said. “And as we started to go through and did a survey of the hotels and RV Parks that were tributary to your collection system, we realized you’re not seeing 3,500 people here, you’re at least double that.”

Bernard said the tourism and permanent population are generating the same amounts of wastewater.

“We can see that in the data,” he said. “Tourism is driving this higher blip. But that’s probably for a discussion that is outside our realm of expertise. We identified some areas of funding assistance, but the take-home message here is that tourism may have to help pay for this. I don’t know the answer to that.”

The engineers said if the city decides to proceed with the expansion, it would be approximately four years for the plant to come online.

The city of Williams is taking the matter to its attorney for recommendations before looking at funding options, said City Manager Tim Pettit.

“This is a large cost burden to put on the citizens of Williams,” Pettit said. “We need to look at options to share the cost with the tourist population.”