The city of Baxter has a looming problem on its hands and city officials don’t have much time to figure it out before April 1.
That was the jist of a Baxter City Council workshop hosted virtually Tuesday, Jan. 19. The council and city staffers discussed the need to repair the city’s water treatment plant — namely, to bring its four water treatment pump filters up to running order, as well as to replace the purifying media (or chemicals and granular substance that filters water), their filter caps, and associated tanks, troughs, retention plates, and more, before summer begins.
In particular, Baxter Public Works Director Trevor Walter said three of the four filters need to be addressed, with No. 1 and No. 3 requiring a routine overhaul of their caps and media after their expected 12-13 year shelf life, while the No. 2 filter presents a head-scratching and concerning problem. Walter said the No. 2 filter cap is failing and leaking media after only two years of use, despite showing no visible structural flaws, corrosion, or stressors on the cap that would explain why it’s failing so quickly and dramatically.
Specifically, Walter said, it is the filter cap itself — the permeable barrier that constrains the media and allows the water to pass through — which is failing, not the components that hold the filter cap in place.
“There's no scientific reason yet that we can come up with for why they're failing,” said Walter, who noted the perplexing status of the second filter first emerged in the back half of 2020 when teams were evaluating the first and third filters. “What's got everybody nervous at the Utilities Commission level is, ‘Are we doing the right thing by replacing the cap with the same plates in filter one as what we did in No. 2 and No.4, but No. 4 has not caused us one problem at all?’”
However, there isn’t much time to make those decisions. Walter said the water treatment plant has to be running at full capacity by April 1, which serves as a cutoff deadline before a substantial and steady increase in water usage by Baxter residents as the summer months approach. This peaks in June, July and August, when the city is using roughly twice as much water as it is now. In the meantime, repairing the filtration system presents a challenge because of the complexity of the parts, some of which may take 12 weeks or more to order and ship to the city of Baxter.
So far, Walter said, it’s been a struggle to find answers regarding the mysterious failure of the second filter cap. The city and its contracting architectural-engineering partners have contacted the filter cap manufacturer, De Nora, regarding the specifications of the caps, and whether or not there’s any history of product failure of this magnitude, but they haven’t received a response in the intervening months. City staffers have also tried to locate or identify any other municipalities with similar water treatment systems and a history with De Nora products to compare notes, but to no avail so far.
There was also a bit of speculation as well — both among staffers, as well as council members. Council members Zach Tabatt and John Ward said they believe the cap is probably the result of some sort of manufacturing error, which may prompt the city to pursue the issue further and possibly take legal action to summon De Nora experts to Baxter and bring them inside the treatment plant to determine what’s happening. On that count, local architectural-engineering firms — such as Widseth and Bolton & Menk — have dissected the filter caps, but found no structural or manufacturing errors that would explain why their cap seals are failing.
It was also noted by Walter that these problems could go as far back as the construction of the current water treatment facility in 2005.
The current facility has four water pump filters, Walter said, when it probably should have eight, but the engineering team at the time decided to build a facility that functions at max capacity on a regular basis. As such, the filtration system is almost always doing the heavy lifting to clean 3.6 million gallons per year, or 2,000 gallons per minute, and store as much as 2.8 million gallons at the plant at any time. Each cap is roughly 1 inch thick, and 18 inches by 36 inches in diameter.
With the watershed containing such a high concentration of arsenic, ammonia and especially iron, Walter said, this means the system needs to backwash — or filter the water through the system for a second time before it can be dispensed to the public — at a much higher rate than typical municipalities. For perspective, a common city water treatment plant of Baxter’s caliber registers roughly 150 backwashers per year. Baxter’s plant registers between 300-400 backwashes per year, which places more stress on the system — although, it’s unclear at this time if this is a contributing factor, especially when only one of the filter caps is experiencing these problems.
Mark Hallan of Widseth said he was optimistic that could possibly explain why this issue is arising — as well as other problems in the facility down the road — but cautioned that a thorough study of the filtration system, such as the No. 1 and No. 3 filters, functioning over the course of weeks needs to be conducted to know for sure.
“If we do find considerable media down in the underdrain system that is caused by some rhyme or reason — pressure differentials and pressures by extreme backwash processes — then we'll determine that you know once we clean that out,” Hallan said. “That's likely the smoking gun, but we don't know that until we get down there and do the investigation.”
In the meantime, the city is installing more fasteners, more sealant, and bolting the retention plates to provide a better seal and expanding the washer area, Walter said, but it’s unknown if that’s a viable long term solution, or whether that would address why the filter cap — not the fasteners holding the filter cap in place — is failing.
During the council meeting Tuesday, the council approved purchase orders for filter media and media retention plates. The cost of the filter media is $48,401.20 and the cost of the new media retention plates is $14,925. According to the city, the estimated construction cost to complete this project — excluding possible additional work in filter No. 3 — is $140,000 to $160,000. Engineering costs are currently estimated at $18,700 for design and another $21,000 for construction administration and observation.
The total cost variance of the project is currently estimated at $243,000 to $263,000.