Study to find detour for La. 70 near sinkhole

PIERRE PART, La. -- A feasibility study has been initiated to identify a possible detour route and cost for La. 70 in Assumption Parish, according to an announcement from the Louisiana Department of Transportation and Development Wednesday.

The detour route would serve as a primary solution for an alternate road to be built as DOTD continues to study options for the La. 70 bypass route. The highway department estimates the average daily traffic near the sinkhole area is 6,900 vehicles.

Questions about the highway began very soon after a sinkhole was observed on Aug. 3, south of the highway. The sinkhole has expanded from a small slurry when it was first observed to nearly 15 acres.

The Louisiana Department of Natural Resources has blamed the sinkhole on the collapse of the salt wall separating an underground cavern from the surrounding natural formations. It occurred on land leased by Texas Brine who mined brine from the Napoleonville salt dome.

An environmental assessment for the alternate detour route has also begun and is expected to be completed within six to eight months. The corridor for the detour route has already been identified, and as the study progresses, DOTD will further refine its alignment.

The temporary detour is being considered in case a permanent reroute for La. 70 becomes necessary, according to Assumption Police Jury president Martin Triche. He said that detour is expected to be along the same general area as the highway but farther north of the sinkhole. That route would have minimal effect on residences and businesses.

The feasibility study continues to determine if a long-term alternate bypass route could be built in the affected area, in the event that the existing roadway is compromised, according to Wednesday’s news release. Multiple alignments are being studied, including alignments around the salt dome cap and alignments around the entire salt dome. The study is expected to be complete in September. The next step is the environmental assessment, which will take another eight months.

“The detour and bypass are two alternatives that are included in the study phase,” Deidra Druilhet, a public information officer for the highway department said this morning. “While both are viable options, the difference is that a detour could be constructed more quickly than a bypass and could serve as a short-term fix if needed.”

She estimated the cost to build one mile of new roadway at $10 million.

“At this time, there is no concern regarding the integrity of La. 70 or the bridge structures,” Druilhet said.

Engineers began monitoring the state road system in the area late last year. They began to measure elevation levels at four locations along La. 70 — one on La. 70 perpendicular to the sinkhole site, and at the Bayou Choupique, Grand Bayou and Bayou Corne bridges.

“DOTD is still continuously monitoring with visual inspection. However, we are finalizing our GPS monitoring which will allow for continuous monitoring remotely,” Druilhet said.

So far, no changes in elevation have been found at these locations, according to Triche.

“We are still in a state of unknown,” Triche said this morning. “As it stands right now the roads and bridges are stable and intact. We don’t know what the future holds.”

The feasibility study is being conducted to ensure the state has a good plan in place in case a future event affects the roadway, according to Druilhet.

“At this time we do not foresee a need to close La. 70,” Druilhet said.

Triche said that the parish government is fully supportive of the state highway department moving forward and exploring the option of building a permanent reroute of the highway. If a permanent reroute of the highway is undertaken, he said it needs to be done in a way that provides for a safe roadway while still servicing existing businesses and residents.

“The effect an alternate route could have on residents and businesses in the area will be determined in the on-going feasibility study,” Druilhet said.

In the event conditions develop that would make the road network unusable or unsafe before the detour or new route is constructed, the highway department has posted the follow detour routes:

—Traffic traveling to Pierre Part and points south will be directed to La. 1 South to La. 398 West, to La. 662 West, to U.S. 90 West to La. 70.

—Traffic traveling from Pierre Part and points south will be directed to U.S. 90 East to La. 662 East, to La. 398 East, to La. 1 north to La. 70.

—Local traffic (passenger vehicles and trucks below the posting of the Bayou Pigeon Bridge) will be able to take La. 997 to La. 75 to La. 404 to La. 69.

If the order is given to close the road, the highway department plans to have crews install trailblazing signs to notify drivers of the detour. The department also plans to install variable message signs at the intersections of La. 70 and La. 1 and the intersection of La. 70 and La. 69 as well as one on La. 70 just north of Morgan City.

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