By Kim Smiley

On August 3, 2012, a massive sinkhole appeared in Assumption Parish, Louisiana that continues to grow and evade easy answers.   About 150 homes were evacuated and residents are still displaced more than seven months later.

What caused a sinkhole to form overnight?

That question can be answered by building a Cause Map, a visual root cause analysis.  In the Cause Mapping process, the first step is to fill in an Outline with the background information for an issue as well as how the problem impacts the goals.  In this example, the sinkhole impacts several goals including the environmental goal, the safety goal because there is a potential for injuries, the financial goal because of the costs associated with the emergency response and remediation of the issue, and the customer service goal because 150 homes have been evacuated for an extended time.  Once the Outline is completed, the next step is to ask “why” questions to find the different causes that contributed to the problem being analyzed.

So why did the sinkhole form?  The sinkhole formed when an underground salt mine collapsed.  This happened because there was a salt mine in the area and a wall of the mine failed.  Salt was mined in the area because there was a large deposit of salt underground and salt mining is profitable since it is used in a wide range of industries.  The wall collapsed because it was too thin to support the pressure because the mine was inadvertently located too close to the edge of the salt deposit.  The mine ended up too near the edge because the location of the salt deposit wasn’t accurately known.  It’s difficult to access salt deposits thousands of feet underground and the mine was permitted in 1982, using 1960s maps of the salt deposit, using technology that was limited compared to what is used today.

There is also a potential for injuries associated with the sinkhole both because it continues to grow and because there is a risk of explosion from the natural gas being released.  The sinkhole has given the underground pockets of natural gas a pathway to the surface. Workers are trying to minimize the danger by flaring the gas off and ensuring there isn’t anywhere it can build up.

The financial impacts of this issue are substantial, both to the community and the mining company.  The salt mining company is in negotiations to buy out the displaced residents and has been providing financial support to them during the evacuation.  The costs of the emergency response are also adding up, not to mention the cost of whatever remediation is necessary once the area becomes stable and the full extent of the issue is known.

The final step of the Cause Mapping process is to develop solutions to prevent the problem from reoccurring.  This is still an ongoing issue, but some steps have already been taken to help prevent future sinkholes from forming.  Advances in technology have already improved understanding of underground deposits and will help in locating future mines.  Another possible solution is regulation changes to require mines to be located farther from the edge deposit.

To view an Outline and a high level Cause Map for this issue, click on “Download PDF” above.