What is a paleosink?

A paleo sinkhole can be a technical but important issue that frequently plagues property owners when they receive their engineering report from the insurance company.

The most common presentation of this issue is when the insured is told that “sinkhole activity can be excluded, but that conditions of paleosink or “karst environment have been found.”  Sometimes the reports will state whether or not the property is in a “state of reactivation.”

“Paleo” essentially means “old” in this context.

Sometimes, rather than call these paleosinks, you will see them referred to as “relic sinkholes,” which is a lot easier to understand.  The idea here is that the property was built on a lot where a sinkhole condition had existed some time ago, sometimes even tens or hundreds of thousands of years ago.

After the sinkhole occurred, the area where the surface depression was located filled up with soil and then lithified again into rock.  Oftentimes, because the causes of the sinkhole still exist (for example, a natural spring), the sinkhole is likely to occur again, and is often the reason an insured is filing a sinkhole claim.  The idea of calling a relic sinkhole “reactivated” means that the process of limestone dissolution is again underway.

Limestone in the penetration borings.

The conditions to look for in relic or paleosinks relates to the depth of the limestone in the standard penetration borings.  If, for example, there are two separate borings done on the property, and they both show a great difference in the depth to the limerock, this is a condition often associated with a paleosink.

If you did two standard penetration tests, one hitting limestone at 30 feet, and another hitting it at 42 feet, many engineering firms would call this a paleosinkhole.  If the conditions are then joined with other indicators of sinkhole activity (e.g. loss of drilling fluid, weight of rod, or weight of hammer conditions), it is likely in a state of reactivation.

The difference between a sinkhole and a paleosinkhole is a  complicated, technical issue, but it’s important to know if you have a sinkhole claim that has been denied and these issues are referenced in your engineering report.