State highway designers have settled on a preferred route for an emergency detour of La. 70 around the Bayou Corne-area sinkhole in Assumption Parish and will seek the public’s input on the proposal Wednesday evening.

The 1.09-mile route would cost $10.2 million and link La. 70 with La. 69 through a route parallel to La. 70 and about 1,000 feet north of it, a new state analysis says.

The state Department of Transportation and Development has been developing the route, as well as a much longer and far more expensive bypass, in case the 37-acre swampland sinkhole continues to grow or spawns other sinkholes that could affect La. 70.

La. 70 is a critical freight, commuter and hurricane evacuation corridor with few other alternatives, and the loss of La. 70 without an alternative could force lengthy reroutes of 44 to 70 miles, the DOTD environmental assessment says.

La. 70 runs just north of the sinkhole, which is visible from the highway. The lakelike hole emerged in early August 2012 after a Texas Brine Co.-operated underground salt dome cavern developed a breach that set in motion the movement of rock and sediment that formed the hole.

Though rock and sediment are expected to slowly fill the failed cavern for years, state estimates say the sinkhole will not reach the highway.

An open house-style public hearing on the emergency detour is planned from 5 p.m. to 7 p.m. Wednesday at the Assumption Community Center, 4910 La. 308, Napoleonville.

DOTD officials said Friday they do not have plans to build the detour or the longer bypass unless La. 70 starts showing signs sinkhole subsidence is compromising the highway.

Chad Winchester, DOTD chief of project development, said highway officials plan to complete the environmental assessment process, choose a route, develop road plans to the 50 percent to 60 percent level and then stop.

That work should take until early 2016, but no wetlands permits will be sought nor rights of way purchased, he said.

“We are just going to be ready just in case,” Winchester said.

He said that from the point the emergency detour project will be stopped, it will take DOTD 18 months to two years to actually build the road.

Winchester said DOTD has set up monitors along La. 70 near the sinkhole and they have not shown any movement of the highway.

“We would take action before there was any imminent threat to the roadway,” he said.

A preliminary feasibility study for the longer bypass says it would have to be largely elevated to avoid wetlands and because of poor soils. The three routes undergoing environmental assessment have been estimated to cost $112.6 million to $210.8 million.

Once that environmental assessment is completed, probably at the end of 2015, and a public hearing on it held in May, the work toward the longer bypass also will come to a stop. Winchester said their intention is not to build the road unless absolutely necessary.

Parish officials had called for some kind of permanent bypass in light of the sinkhole, which briefly forced the closure of La. 70 in the sinkhole’s first days, and two previous industrial incidents since 2003 that had forced La. 70 closures and detours for weeks.

Meanwhile, some are concerned about the impact the smaller emergency detour could have on their businesses, including the popular Gator Corner gas station, restaurant and truck stop casino at La. 70 and La. 69.

Peter Graffagnino, comptroller for Roland J. Robert Distributor Inc. of Gonzales, which owns that gas station and several others in south Louisiana, said the emergency detour would probably deal a blow from which Gator Corner would not recover.

Graffagnino said the gas station would no longer be adjacent to the highway, and if it loses 20 percent of its fuel business, by law, the truck stop would have shut off its video poker machines, too. The loss of both revenue sources could sink the business, he said.

“That’s why we’re hoping the detour never has to come to pass,” Graffagnino said.

The DOTD environmental assessment considered an emergency detour route that would have run closer to the truck stop’s property line.

But the assessment noted that the road would conflict with two natural gas pipelines. Moving the lines would significantly raise the cost and present a major delay in building the emergency detour, the analysis says.

Graffagnino said Gator Corner has benefited from the contractors working on the sinkhole the past 2½ years, but the truck stop also has a state court lawsuit against Texas Brine Co. over the loss of its long-term business prospects. The suit is still pending.

Most residents in the nearby Bayou Corne area have or are accepting buyouts and moving away.

Comments on the emergency detour can be submitted to DOTD through Jan. 2. Letters should be sent to Monica Herrera of Providence, 1201 Main St., Baton Rouge, LA 70802, or via email to monicaherrera@providenceeng.com.

Follow David J. Mitchell on Twitter, @NewsieDave.