A sinkhole is a depression formed as the underlying bedrock is dissolved by groundwater (usually limestone). Sometimes, surface water entering a crevice in the bedrock may be the cause. Thus, sinkholes may form in low-lying areas where water is ponding. A hole will form, at the top of the underground cavern that is dissolved, and the earth above the hole will collapse into the hole.

Thus, a sinkhole often appears as a column when looking down the hole. This is the "throat" of the sinkhole above the collapsed roof of the cavern. While most people think of sinkholes as being huge obvious holes that can be seen by the news helicopter, most are only a couple feet across and deep. The method of repair involves plugging the throat with larger stones or a lean concrete mixture called "flowable fill". Once the throat is plugged, the hole is filled in with smaller stone and earth.

We have provided a typical construction detail for repairing sinkholes. This information was taken from the Cumberland County Cooperative Extension website. This is only meant as a guide, and not all components included may be necessary. We have provided a list of contractors below who may be able to help you in devising a solution to repair your sinkhole.

You may wish to contact your homeowner's insurance to see if you have a claim, especially if the sinkhole appears near a foundation or structure. Sinkhole insurance is also available through most homeowner's insurance providers.

Brian P. O'Neill, PE
Township Engineer