The Rapid City Council accepted a $172.3 million bid Monday evening for the second phase of improvements on the city's wastewater treatment plant.

The award made city history as the highest dollar amount awarded for a bid, surpassing a $111.5 million permit issued for work on The Monument's Summit Arena in 2019.

PKG Contracting, Inc. of Fargo, North Dakota was the lowest and only bidder for the second phase of the $207 million project to construct new facilities and renovate the city's 57-year-old wastewater treatment plant. The city estimated the second phase to cost $147 million.

The Water Reclamation Facility South Plant is located at 7903 South Side Drive about nine miles east of Rapid City off Highway 44 near the airport. Originally constructed in 1967 with additions constructed in 2003 and intermittent updates made throughout the years, the plant processes all wastewater out of Rapid City and its satellite communities of Rapid Valley, Black Hawk, and the Northdale Sanitary District. The cleaned water is sent downstream into Rapid Creek and ultimately the Missouri River.

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In April 2022, the City of Rapid City was awarded a $101.5 million Clean Water State Revolving Fund loan and a $43.5 million American Rescue Plan Act (ARPA) grant by the South Dakota Department of Agriculture and Natural Resources and the Board of Water and Natural Resources.

An additional $35 million loan to support the project was secured last month from the Board of Water and Natural Resources. Additional efforts are underway to secure the remaining financing needed for the $207 million project to improve the treatment facility, according to a city press release.

The loan and grant package was the biggest award received by the city. It was part of more than $183.9 million in grants and loans distributed by the state in April 2022 for drinking water and wastewater projects in western South Dakota.

Rapid City Water Reclamation Superintendent David Van Cleave explained the plant first mechanically cleans large debris, such as sand. That's taken to the landfill for disposal. Next, "fine organics" are removed. That includes ammonia and anything that has dissolved into the wastewater.

"That's done with biology. We build components that can house bacteria and those types of things, and the bacteria ultimately do the work of cleaning the wastewater," Van Cleave said. "Once they've utilized the pollution as food, those bacteria, they die, they settle out, and we capture them as sludge."

That sludge is also taken to the landfill for disposal. During certain times of the year, the plant also disinfects the water when the creek is used for recreational purposes.

On a daily basis, the facility removes over 2,000 pounds of ammonia, nearly 18,000 pounds of suspended solids, and over 17,000 pounds of organics.

The improvements will include construction of new treatment facilities and processes at the South Side Drive campus, construction of an additional aeration basin, two additional secondary clarifiers, a dewatering building, a pumping building, and all associated equipment. Various portions of the existing facility will also be renovated and modified.

The water reclamation facility in Rapid City.

"The old facility was just not going to be able to meet what we anticipate the future limits to be," Van Cleave said.

"Limits" refer to the amount of solids, organics and chemicals that can be present in the discharged water.

Van Cleave said the plant can treat about 15 million gallons per day effectively. The updates would increase that to 40 million gallons per day. The amount of flow would not necessarily increase, but the capacity and quality would increase.

"We'll be able to push out a higher quality water product at the end of the plant," said Rapid City Operations Engineering Manager Eduardo Lopez.

One of the notable changes to the plant would improve how the bacteria is used to clean the water. Currently, bacteria is grown on surfaces within units. With the updates, bacteria will free float within chambers where they'll clean the water.

"That's the newest way of treating wastewater..." Van Cleave said. "We can remove ammonia down to lower levels."

Van Cleave explained ammonia is very harmful to fish.

The city also awarded PKG Contracting $13 million two years ago for the first phase of the project, which Lopez is set to complete this summer with a new clarifier and the rehabilitation of an existing clarifier.

"Phase one really just allows us some flexibility as we move into phase two to be able to maintain treatment as the bigger project grows in," Lopez said.

Phase two is expected to begin this spring and complete in winter 2028.