Federal regulators have decided the consequences of a failure of the Rapidan Dam are worse than previously thought, and Blue Earth County will pay for additional studies.

The Federal Energy Regulatory Commission, or FERC, has raised the hazard potential classification of the dam from “low” to “significant.”

The classification does not reflect the condition of the county-owned dam, only what would happen were it to fail.

If the dam breaks, all the farm chemicals — fertilizer, pesticides and herbicides — that have accumulated over the decades would flow downstream and pose an ecological hazard, FERC said, according to County Engineer Al Forsberg.

Eleven million cubic yards of sediment has accumulated behind the dam since it was built in 1910, he said.

The “significant” rating means that failure of the dam could cause economic or environmental damage but wouldn’t pose a risk to human life.

The one caveat is the county-owned Rapidan Dam Park, but Forsberg said it could be evacuated, which it was last summer after a hole was discovered in the area supporting the dam.

The regulatory change necessitates a pair of studies; one will review the technical aspects of the dam and the risk of its failure and another to update an emergency plan in case of failure.

Forsberg estimated the cost of both studies to total $60,000, with the county paying half and dam operator North American Hydro paying half. That estimate is likely more than what the studies will actually cost, he said.

“It’s going to cost money, but I think they’ll also be useful over the long run,” Forsberg said of the studies.

The county has not updated its emergency plan for the dam since 1989, and the other report will help consolidate other studies done over the years, he said.

The new regulations come in the midst of a multi-year study by the U.S. Army Corps of Engineers that will give the County Board information to help them make a long-term decision about the dam’s future.