How and why Oakdale’s water treatment plant works

The lead and lag tanks at the Oakdale water treatment plant provide a two-step water filtration system. Both tanks are filled up with granular activated carbon, which absorbs perfluorooctane sulfonate and perfluorooctanoic acid, two synthetic chemicals formerly used by 3M Company. Oakdale has five pairs of lead/lag tanks. Aundrea Kinney/Review

After the carbon gets replaced in Oakdale’s water treatment system, a backflow is performed on the system, but the water doesn’t flow backwards to the well. It flows into a special holding tank as seen on the left. According to Brian Bachmeier, Oakdale’s director of public works, this water gets discharged under controlled conditions into the city’s sanitary sewer system. Aundrea Kinney/Review

Water purification may be on the minds of area residents after the Minnesota Department of Health updated its health-based advisory values in May for two industrial chemicals present in some east metro groundwater. 

Although some of the water in supply wells for Oakdale’s public drinking water tests over the new advisory levels, chemical concentrations above the new advisory levels are not reaching area homes thanks to the city’s specialized water treatment facility.

MDH’s updated advisory is for perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), two synthetic chemicals developed by the 3M company for use in products that resist heat, water, oil, grease and stains. 

The advisory affects several private well owners in Lake Elmo and Cottage Grove, as well as supply wells for public drinking water in Cottage Grove, Woodbury and St. Paul Park.

Risks associated with high exposure to the chemicals include low birth weights for babies, accelerated puberty, skeletal variations, some cancers, liver damage, interference with the immune system, thyroid issues and cholesterol changes.

Although six of the eight supply wells for Oakdale water are over the new MDH standards, residents are not drinking water that doesn’t meet the advisory. 

“Two of the six wells ... are connected to the treatment plant,” explained Brain Bachmeier, Oakdale’s director of public works. “We regularly operate the four wells that are below the thresholds, and only use the other wells when necessary. Over 90 percent of the water supplied to our distribution system last year was from the four wells.”


How the water is treated

Oakdale’s 7,000 square-foot water treatment facility is the first full-scale treatment facility for removal of PFOS and PFOA in the country. 

It’s designed to work the same way the granular activated carbon filter systems work in the homes of people with too much PFOS or PFOA in their private well water.

Minnesota Pollution Control Agency educational materials explain that granular activated carbon is made from raw organic materials, like coconut shells or coal that are high in carbon. Heat is then used to activate the surface area of the carbon, which helps the final product remove certain chemicals from the water by trapping the chemicals in the granules. 

In Oakdale, two wells located in Richard Walton Park are piped into the water treatment facility located on the public works campus at a rate of about 2,000 gallons per minute, according to Bachmeier.

Inside the facility the water goes into the first filtration tank, called the lead tank, which is filled with activated carbon granules that absorb the chemicals from the water. Because of the capacity of the two wells, Oakdale has five lead tanks that can be used simultaneously. 

After the water sits in the lead tank for five minutes, it goes to the lag tank, which is also filled with activated carbon granules. The water sits in the lag tank for five minutes to remove any remaining traces of PFOS and PFOA before it goes into the city distribution system.

The water can be tested while it is in any of the five lead or five lag tanks, and the testing helps determine when the carbon granules need to be replaced. However, the used carbon granules don’t make their way to a landfill. 

Oakdale’s water treatment system is made by Calgon Carbon, and according to the company, the spent carbon granules are reactivated through a heating process that removes all of the chemicals the granules absorbed and leaves the carbon granules ready for reuse. 

According to Bachmeier, the carbon granules in Oakdale’s tanks are changed out about every 18 months.


An innovative system

Construction began on Oakdale’s water treatment facility in May 2006, and it became operational in November of that same year. The roughly $2.5 million construction costs were agreed to be paid for by 3M Corporation, and operation costs will continue to be paid for by 3M until the raw water contamination levels drop below MDH-established values for at least two years.

Before the system was selected, 3M conducted research to ensure it would work effectively to remove PFOS and PFOA, and 3M’s methods, research and conclusions were peer reviewed by an independent water quality consultant, Bachmeier said.

Bachmeier added that in addition to removing the chemicals of concern, the water treatment also removes any bad odor or taste the water could have.

“Some communities just put in carbon treatment to address odor and taste, so that’s kind of a coincidence — not that we really had an odor and taste issue before, but it obviously doesn’t hurt it.” Bachmeier said. “It only helped.”

Because Oakdale’s system is the first of its kind in the country, Bachmeier and Oakdale utility superintendent Shawn Nelson explained it’s a point of interest for other communities around the nation that are also looking to treat contaminated water. Bachmeier and Nelson have spoken with consultants from Alaska, Washington, Virginia and Maine in addition to others, but most recently, representatives from a neighboring community came to tour the facility.

Like Oakdale, Cottage Grove has city supply wells affected by the new MDH standards, which resulted in the shutdown of five of the city’s 11 wells. Water from three other affected wells is being blended with water from three unaffected wells, and while the water reaching residents’ homes is safe to drink, there is less of it available, so the city declared a watering ban in late May.


Claim to fame

Cottage Grove communications coordinator Sharon Madsen explained construction is underway of a temporary water treatment facility to filter PFOS and PFOA out of water from two of the city’s wells. 

Bringing just one of the wells back on line, after the treatment facility is in place, will likely ease the watering restrictions, Madsen added.

The temporary facility will be in place for two to five years, giving the city time to design a permanent facility. The temporary facility uses the same type of tanks and piping system as the Oakdale system. Although the design process has not yet begun for the permanent facility, Madsen said it will likely utilize similar technology as well, though it will have to be sized correctly for Cottage Grove.

Nelson said that to his knowledge, Cottage Grove is the first city to proceed with building a comparable treatment facility after touring Oakdale’s. 

And while the water treatment facility may not be the first thing that comes to mind when residents brag about their city, the system’s innovation is an Oakdale claim to fame.


Aundrea Kinney can be reached at 651-748-7822 or

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