Fargo upgrades water treatment plant implementing ozone treatment

FARGO – Workers have been digging a big hole down by the water treatment plant all summer and soon they’ll be driving pilings 100 feet down into more stable ground.

They’re building the first major expansion to the plant at 435 14th Ave. S. since it was built in 1997 when the city’s population was three-quarters of what it is today.

But they’re also building a sort of insurance policy, said Water Utility Supervisor Troy Hall.

Fargo and communities that buy water from the city get their water from the Red River and Sheyenne River, which sometimes have an excess of naturally-occurring sulfate and bromide, salts that affect the taste and odor, and may cause diarrhea.

The water plant’s current coping mechanism is to change the mix, taking in more water from the river with less salt and less water from the river with more.

Hall said it won’t always be able to do that. Flood outlets in Devils Lake are releasing high-sulfate water there into the Sheyenne so the river is brackish more often, which is OK as long as the Red doesn’t run too low or get brackish as well.

“We were kind of nervous a couple of years back because it was pretty dry,” he said.

The expansion will total 65,000 square feet and cost $103.7 million, more than a quarter of which will be paid by the state. The capacity will increase from 30 million gallons a day to 45 million, some of which will be sold to the city of West Fargo to supplement groundwater. The city’s only customer now is the Cass Rural Water District.

Earth is still being removed from the large area on the north side of the Fargo water treatment plant. Dave Wallis / The Forum

Earth is still being removed from the large area on the north side of the Fargo water treatment plant. Dave Wallis / The Forum

Right mix

The level of salts in the Red and Sheyenne tends to fluctuate throughout the year. When snow melts or rain falls, the naturally brackish water is diluted. When water from Devils Lake enters the Sheyenne or when high water in Lake Traverse prompts the U.S. Army Corps of Engineers to release the water into the Bois De Sioux River, a tributary of the Red, those rivers become more brackish.

Hall said he prefers it when the corps releases water from Orwell Dam near Fergus Falls, Minn., which has better quality.

The water plant was built when the water didn’t get brackish that often, so it wasn’t designed to remove salts. Now, when river water enters the plant, it’s softened with lime, treated with ozone to kill microorganisms and filtered. Hall and his team have managed the mix of Sheyenne and Red water such that residents can rarely tell that the taste of their tap water has changed. They don’t use the Sheyenne half of the year when the salts and other minerals are at their highest.

The water plant has done pretty well so far. In October, Fargo water was named the best in the state at the annual American Water Works Association convention in Fargo. Moorhead also won the state contest in Minnesota.

In Fargo’s new treatment system, the water is filtered of small particles and then forced under high pressure through a membrane, which has pores so small that large molecules cannot pass, only water molecules. Plant staff will still need to mix water from the ozone system with the membrane system to achieve the right taste; earlier tests showed the ozone-treated water tends to clog up the membrane, so it has to work separately. With the two systems working together, the plant has much more flexibility.

Hall said it wasn’t very long ago, 1988 and 1989, when the Red River just stopped flowing and the city had to rely on the Sheyenne River alone, and at that time the Sheyenne wasn’t getting any water from Devils Lake.

If the city had to rely only on the Sheyenne now, tap water might start to taste a little funny.