MANKATO — Community leaders should know by August how much it’s going to cost to do a federally mandated certification of the flood-control system along the Minnesota River. Sometime after that, residents will find out how it’s going to impact their taxes or utility bills.

The question that might go unanswered for a while is whether the study — which could cost several hundred thousand dollars — will be a one-time expense or one that will be recurring frequently in the decades ahead.

“The real question we’re still trying to find out is how often we have to do this,” said North Mankato Mayor Gary Zellmer.

North Mankato, Mankato and South Bend Township were surprised late last year to receive a letter from the Federal Emergency Management Agency demanding that the local governments sign a contract agreeing to do the study. If they refused, FEMA threatened to redraw maps to show low-lying areas of the cities and township as high-risk areas for flooding, something that would require expensive flood insurance and could impact development.

The governments are now planning to work together to issue a “request for proposals” to engineering firms interested in doing the study. The response by the firms should provide the first solid estimates of the cost of the certification.

Rough estimates have suggested the cost could be high — as much as $240,000 for North Mankato or $200,000 for South Bend Township. That leaves government officials thinking about how to pay the unanticipated expense in the midst of extremely tight local budgets due to state aid cuts.

“That’s the $64,000 question right there,” Zellmer said. “Where’s the money going to come from?”

The North Mankato City Council has talked about using general property taxes, a temporary bump in municipal utility bills or a permanent increase if it’s determined the certification will be required every few years.

Finance Director Steve Mork suggested Monday night a $1 per month increase in storm water fees charged to homeowners and businesses so that funds could begin to be accumulated. That would generate $80,000 a year, an amount city officials expect to be the lowest possible cost of North Mankato’s share of the study.

The council decided to wait until firmer cost estimates are available after engineering firms respond to the request for proposals and a firm is selected — something that should happen by August.

Zellmer prefers a special tax or fee increase that will make clear to taxpayers that this is the result of an unfunded mandate by the federal government that is beyond the control of local officials.

North Mankato City Administrator Wendell Sande hopes that by combining the study of the flood walls and levies in all three communities, the engineering costs might be reduced somewhat.

“It only made sense that we collaborated our efforts if we have to go forward with this thing,” Sande said.

And officials are expecting that they will. They complained about the sudden mandate to Congressman Tim Walz, who has been sympathetic but has been unable to get FEMA — or the overall Homeland Security Department — to budge on the requirement.

“We’ve gotten no response yet from Congressman Walz’s office that they’ve had any luck at all working with Homeland Security,” Zellmer said.

Sande said at a council meeting last month that the motivation for the certification requirement is probably the heavy publicity about failed levies flooding communities in recent years. But those failures were typically earthen levies, not the reinforced concrete walls and rip-rap covered levies along the Minnesota River in the Mankato area.

North Mankato got another surprise from FEMA in May. The original requirement mentioned only the need to have the certification completed within two years. The latest letter stated that maps may be revised to add “flood hazard areas” in the city if a progress report isn’t submitted a year sooner — by April 14, 2010.

“After you’ve signed up, then ‘Oh, by the way, you have the 12-month requirement,’” Sande said.