State regulators say that the Rapid City Regional Airport did not cause a contamination when it dumped approximately 74,000 gallons of sewage on its property last month.

Tests of the airport's septic lagoon found that its contents would have been safe to spread on land had airport officials sought permission to do so, according to the Department of Environment and Natural Resources.

DENR spokesman Brian Walsh said last week that department officials also determined during an investigation last month that "there was no evidence of runoff or impacts to surface water bodies" in places where wastewater was dumped.

Those results were corroborated by a private firm that conducted tests of its own, Walsh said.

The investigation stemmed from an occurrence last month in which the airport spread sewage from the lagoon on the northern end of its property without a permit from the DENR. Airport officials contend that the incident was the result of a miscommunication between themselves and the department.

At the time, airport Executive Director Patrick Dame said that the open-air lagoon was at risk of overflowing following weeks of heavy rainfall. It took less time to dispose of the excess wastewater on-site, he said, than it would have to truck it away.

The airport on Aug. 14 submitted an application for a permit that will allow it to properly "land apply" septage from the lagoon, according to the DENR. Dame said Wednesday that the airport is seeking the permit as it waits for clearance to build a new wastewater system.

Currently, the airport is conducting what Dame called an environmental assessment of the lagoon. Such a study is required by state regulators, he said, before a replacement can be constructed.

"Sometimes having the money to do a project doesn’t matter," he said.

A separate airport study commissioned in 2017 lays out several alternatives to the lagoon that range from replacing it with a larger pond to constructing an on-site water treatment facility. Another option for the airport would be to build a regional sewage collection system that links to the municipal lines already in place and that future developments could tap into. Dame previously said that the city favors this alternative and that engineers estimate it would cost approximately $20 million.

The airport could also build its own sewer line that extends directly to the city Water Reclamation Facility approximately five miles away. Dame has said that such a project would cost slightly less than $2 million to construct.

Even after the airport clears all of the regulatory hurdles ahead of it, Dame said that it may take years to finance and construct a new sewer project. In the meantime, he said that trucking wastewater from the lagoon off-site and disposing of it in-house and as needed will have to do.

"We’re following the prescribed process," he said.

— Contact Matthew Guerry at [email protected]

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