Treating each flush in Sioux Falls

KELOLAND.com Original
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SIOUX FALLS, S.D. (KELO) — When you flush the toilet at least some form of that water goes into the Big Sioux River watershed.

Gross? It could be without the wastewater treatment plant in Sioux Falls.

The plant treats about 21 million gallons of wastewater a day (MGD). The Environmental Protection Agency says toilets account for an average of 30% of all water used in a home. For Sioux Falls, that’s about 6.3 million gallons a day.

That’s about 33 gallons of toilet water each day per person if each one of Sioux Falls’s 190,750 residents flushes.

The rest of that 21 million gallons comes from showers, washing dishes by hand, dishwashers, washing clothes and similar uses by residents and additional water used in manufacturing and by businesses.

The wastewater plant is the gatekeeper that makes sure sewer water that travels the length of any of the 900 miles of sewer pipes in the city is safe to release in the Big Sioux River.

The plant is doing its job, said Mark Cotter, the director of public works for the city of Sioux Falls.

But, as the number of users increases the plant needs to growth with that demand, Cotter said.

The city of Sioux Falls is planning for a $159 million plant expansion and upgrade to handle wastewater needs for at least 25 years, Cotter said.

A concept plan for the proposed new water reclamation project in Sioux Falls. Plan courtesy of the city of Sioux Falls.

Tuesday night, the council approved terms and conditions of preconstruction and construction phases services provided by McCarthy Building Companies as the construction manager at risk to begin to fine tune a design that will lead to construction. A city already has a $24,000 contract with McCarthy. But, city officials said, while Tuesday’s decision is a step ahead, the city can stop any progress during these next months before construction starts.

At this point, the plant continues to function well enough to meet discharge standards, Cotter said.

“They do a great job in Sioux Falls,” said Chris Schmit of South Dakota State University. Schmit is an environmental engineer whose research interest is the wastewater treatment field.

The Sioux Falls wastewater treatment plant has an excellent history of compliance, said Brian Walsh of the South Dakota Department of Environmental and Natural Resources.

The three year compliance history on the Environmental Protection Agency’s website lists one violation that happened during period from June 1 to Sept. 20, 2018. The issue was called a chlorine total residual issue. Walsh said the DENR’s Surface Water Quality program said heavy rains caused water to flow too quickly in the system and the city was not able to remove all the chlorine before discharging.

The violation was self-reported by the city and occurred over less than a day, Walsh said.

“We are beyond the compliance threshold. We never want to be at the threshold,” Cotter said of compliance with EPA standards for discharge treated wastewater.

While the plant is working properly, it’s showing its age, Cotter said.

“The plant is tired,” Cotter said.

Treating millions of gallons of water a day takes its toll.

The wastewater treatment process is “corrosive by nature,” Cotter said.

The process wears down pipes but also the electrical system, the coding system and similar items, he said.

The plant is also handling more water than what it was designed for.

Cotter said the existing wastewater treatment plant is designed for a rated capacity of 21 million gallons per day with a peak capacity of 35 MGD.

Sioux Falls is also growing and with that growth comes more sewer water.

The existing wastewater treatment system was built from 1980 to 1986. The population of Sioux Falls was about 81,000 in 1980. The population grew to 100,814 in 1990.

The city has had a steady growth of about 2% which is manageable, Cotter said, but it also means that facilities will need to change to keep up with growth.

The existing wastewater plant isn’t going to properly handle an estimated population of 190,750, Cotter said.

The city’s plant also treats sewer water from the Renner Sanitary Sewer District and the Prairie Meadow Sanitary Sewer District. Cotter said wastewater from Tea will be treated in Sioux Falls in three to five years.

The new construction will increase capacity to 30.1 MGD with a peak capacity of 57 MGD.

The city plans to use loans from the state to help pay for the project.

Users will pay for a portion of the project cost through rates paid for water use.

The city has planned for a 6% increase in 2020, 5% in 2021, 4% in 2022 and 3% in 2023. According to the city, the average monthly consumption in gallons is 4,638 or 6.2 in CCF.

The prior monthly charge based on the average residential use is $32.25. The new monthly charges for 2020-2023 are $34.14, $35.88, $37.33, $37.33 and $38.42.

The city has already extended the performance of the wastewater plant by encouraging water users to cut down on use.

The city has offered a toilet rebate that encourages users to replace old toilets made before 1992. The program has been in place for about 15 years.

Toilets manufactured before 1992 use more water per flush than those made after 1992.

“Prior to 1992, most toilets used 3 to 7 gallons a flush,” Cotter said.

The city offers up to a $75 rebate to replace a residential toilet and $50 on non residential toilets for the first replacement. The rebate for residential toilets is $60 for the second toilet and $50 for each additional toilet.

“We’ve kept track from the rebates,” Cotter said. “We’ve saved close to four million gallons a day (over the length of the program) from going through our plant.”

Current federal standards for new toilets are 1.6 gallons per flush but the EPA recommends that even more efficient models classified as WaterSense are available. Those toilets use 1.28 gallons per flush.

Cotter said one way water users can save money is to reduce the amount of water they use and dispose of. By conserving on both ends, their costs will go down, he said.

Copyright 2020 Nexstar Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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