NAPOLEONVILLE — State highway officials have largely jettisoned three proposed routes for a long-term bypass around the Bayou Corne sinkhole in favor of two other routes, one of which roughly mirrors a route the Assumption Parish Police Jury called for a year and a half ago.
State Department of Transportation and Development officials have been engaged in early planning and design for the bypass and a shorter emergency detour in the event the now 31-acre sinkhole should grow large enough to threaten La. 70 — something state scientists say is unlikely — or if other sinkholes are created from underground salt dome caverns near the sinkhole and La. 70.
State and parish officials were on hand Wednesday at the parish community center in Napoleonville to solicit comments on the two new routes but the two-hour public presentation was very lightly attended.
The detour and bypass are essentially contingency plans that DOTD officials only plan to bring to a certain point in the process before stopping, unless something significant happens to put La. 70 in jeopardy.
Chad Vosburg, DOTD Baton Rouge district administrator, said the hearing Wednesday is a required step for the project’s environmental assessment.
“It’s one less step you’d have to complete if there were a need to complete the bypass,” Vosburg said at the meeting.
Sparked from past salt dome mining by Texas Brine Co. that went awry, the sinkhole emerged in August 2012 in swamp just south of La. 70. The highway is an important connecting route between Napoleonville and parts north and the southern end of Assumption Parish, including Pierre Part. No other short routes, besides La. 70, connect the areas.
But state highway and parish officials have said that regular monitoring of La. 70 has not detected subsidence from the sinkhole while growth of the sinkhole has slowed considerably. Monitoring of other caverns has not indicated emerging problems.
Unlike the earlier bypass routes first proposed by DOTD, which were farther north of La. 70, the two new proposed routes on view Wednesday run north of La. 70 but tie into the highway on each end as Police Jury officials asked DOTD to consider in a Dec. 12, 2013, letter.
Both routes must cross the maze of pipelines emanating from the salt dome complex nearby and anticipate forging through wetlands and need lengthy elevated sections.
The shorter route, Alternative 4, would capitalize on the proposed emergency detour, which would veer north of La. 70 just west of the sinkhole and then tie into La. 69. Under DOTD plans, the detour could be turned into a bypass by extending the detour route farther east from La. 69 so the bypass ties back into La. 70 to the southeast.
Total cost is projected to be nearly $43 million, including $33 million for construction, with about one mile of elevated highway.
The longer route, Alternative 3, which mimics a hand-drawn route parish officials suggested, would run farther north of La. 70 and avoid the entire Napoleonville Salt Dome. That route would require about three miles of elevated highway and has a projected total cost of $222 million, DOTD plans indicate.
Alternative 4 is DOTD’s preferred route, but the agency says it would seek to build Alternative 3 if Alternative 4 were threatened.
Norman Mabile, 76, of Pierre Part, was one of the few residents who attended the hearing Wednesday. In a later telephone interview, Mabile said he went on behalf of his son, who has an ownership interest in the Gator Corner gas station and restaurant at the intersection of La. 70 and La. 69.
Mabile said the longer Alternative 3 would put his son out of business. The shorter Alternative 4, which is closer to the Gator Corner, would still hurt because traffic from Baton Rouge would not run in front of the gas station.
At the same time, Mabile said he understands DOTD has to do what is best for the community. He said he and his son are just waiting and seeing.
“Look, I’m hoping nothing happens. That’d be the best scenario,” he said.
Noel Ardoin, DOTD environmental engineering administrator, said the agency plans to stop bypass planning once federal highway officials approve the environmental assessment, likely at the end of July.
Plans are to bring the detour through 100 percent of the preliminary design before stopping.
Robert Isemann, DOTD project engineer, said from that point, the detour could be built in about two years.
Follow David J. Mitchell on Twitter, @NewsieDave.