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Posted on: July 6, 2018

Treating Minot's water is a lengthy process

wtp for construction

The Minot Water Treatment Plant is undergoing a $26 million expansion that will more than double the facility's daily treatment capacity. 


Mark Paddock, superintendent at Minot’s water treatment plant, has a simple message when discussing the city’s municipal water supply.

“Our water is very safe to drink,” Paddock said. “We follow every state and federal standard for treatment and every guideline set up by the Environmental Protection Agency. We have a very good system here.”

The Minot facility, capable of treating between 12 million and 13 million gallons of water per day, is staffed and operated 24 hours per day, 7 days per week, 365 days per year. During peak usage times, especially during hot summer weather, users can use nearly as much water as the facility treats every day. That could be problematic if there was a large fire in the city or if the water treatment plant had equipment failures. It’s difficult to keep storage tanks filled when the treatment capacity and daily usage needs are approximately the same at 13 million gallons.

That potential predicament will change in the near future, as the treatment plant is a busy place these days. Construction equipment has taken over the area west of the plant as part of an expansion project.

The $26 million project is on schedule after the first two months of construction, with the new facility expected to be operational by late 2019, according to Assistant Public Works Director Jason Sorenson. The project is part of the Northwest Area Water Supply Project, which will provide clean drinking water to many communities in Northwest and North central North Dakota. The expansion will add another 18 million gallons per day of potential treatment capacity.

“Essentially, we’re adding two more clarifiers to increase our treatment capacity,” Sorenson said. “When this project is completed, the old clarifiers will be rehabbed and eventually downsized to be more efficient. Our ultimate goal is to get to the NAWS design capacity of treating 28 million gallons per day.”

The original Minot Water Treatment plant was built in 1951, and has undergone several expansions and renovations. In 1951, the plant could treat 6 million gallons of water per day.

The treatment process involves several steps to turn raw water from Minot’s wells into the clean, safe water that flows from faucets.

Step 1: Raw water from 15 wells flows into the water treatment plant. In the winter months, about 5.5 million gallons flow into the plant every day. In the summer months, about 11 million gallons flow into the plant daily. About 68% of the raw water comes from the five wells in the Sundre well field southeast of town; 32% comes from the other 10 wells in the Minot aquifer system.

Step 2: The incoming raw water flows through three aerators. “The main purpose of the aerators is to release hydrogen sulfide gas that occurs naturally and to introduce air into the water to oxidize iron and manganese,” Paddock explained.

Step 3: Water flows into the treatment basins. Lime and other coagulants are added. “That raises the pH level of the water and helps draw minerals out of the water that settle to the bottom of the basin,” Paddock said. The minerals settle to the bottom of the treatment basin, carrying much of the dirt and bacteria with them.

Step 4: The water is put through a recarbonation process. “A mixture of carbon dioxide and water is injected into the treated water to bring the pH level down from 11 to 9.3. It also helps maintain a coating of calcium on the inside of lead and copper pipes,” Paddock said. “There are still a lot of old service pipes that are lead and copper. Some are city service lines but a lot of them are residential service lines.”

Step 5: As the water leaves the recarbonation chamber, phosphate (for corrosion control) and fluoride (for dental health) are added. “I don’t know of any city in North Dakota that doesn’t add fluoride to their water,” Paddock said. “If there are any, it’s likely because there’s enough natural fluoride in their water.”

Step 6: A small amount of chlorine is added as a disinfectant, and then the water enters 12 rapid sand gravity filters, which contain 20 inches of anthracite coal and 10 inches of fine sand. “This process absorbs any fine particles that may still be in the water. The water sinks downward through the filters, and nice, clean water comes out of the bottom of the filters,” Paddock said.

Step 7: Water goes into the clear well, which is an underground reservoir. Here, ammonium sulfate is added to form the disinfectant known as chloramine.

Step 8: The treated water flows from the water treatment plant to the pump station located across 16th Street Southwest. “From there, it’s pumped into the Minot system and to all the other users,” Paddock said. Water from the pump station is sent to three 3 million gallon ground storage tanks, then through seven booster stations to three 500,000 gallon elevated tanks and one 1 million gallon elevated tank located throughout the city. Water is also distributed to other towns, including Kenmare, Berthold and other cities as part of NAWS.

How would Paddock describe Minot’s water?

“I would say that Minot’s water could be considered a little on the hard side; 80 parts per million or less is considered soft water. Our water averages between 100 ppm and 150 ppm,” he said.
“Raw well water can have between 500 ppm and 600 ppm, so that shows the effectiveness of our treatment process.”

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