ARM Brief’s State Legislators on Sinkholes in Wake of Recent Street Collapse in Uptown Harrisburg.

At the request of Pennsylvania American Water Company, John Masland, P.E. Vice President of Geotechnical Services at ARM Group Inc., briefed State Representative Patty Kim (103rd District) and State Senator Rob Teplitz (15thDistrict) on the causes of sinkholes within Harrisburg and the surrounding areas.  The briefing occurred in the wake of the January 1st collapse of a section of Fourth Street in uptown Harrisburg, which eventually resulted in the loss of utility services to residents on the 2100 block of Fourth Street.  The collapse expanded in size over the course of several days after it was first disclosed by the street collapsing under the weight of a backhoe that was repairing a depression in the street.   By the time repair work started the collapse had grown to approximately 12 feet in depth and 30 feet in diameter.

The Fourth Street collapse focused attention on the many surface depressions and holes which exist on Harrisburg Streets.  Approximately 40 such depressions and holes are covered by steel plates that have been placed on City streets until repair funds are available.  Many of these problems are the result of soil losses into broken utility lines; the water-bearing pipes in Harrisburg, as well as many other Pennsylvania communities, are typically over 50 years old, and in some cases over 100 years old.   Beyond simply repairing sinkholes after they occur, the City of Harrisburg and state legislators are interested in exploring ways to evaluate the potential for future sinkhole activity, particularly in areas where very old utility lines are still in service.

Mr. Masland spoke to the legislators about the causes of sinkholes, and the common conditions that promote their development.  In addition to naturally occurring sinkholes that result from soil  losses into cavities within underlying limestone bedrock, sinkholes can also occur when soil is washed into sewer lines or similar conduits.  Holes in broken or corroded pipes; or holes created by open joints between pipe segments; can allow enough soil to enter the pipes and be transported by the flowing water within to eventually result in a surface collapse.  The older the piping, the more susceptible it typically is to such problems, and cities with very old utility systems often experience surface collapse that are more related to aging infrastructure than to the underlying geology.  Mr. Masland also spoke to the legislators about the importance of identifying and correcting the root cause of a sinkhole during the repair process, and the importance of proper backfilling and compaction as repairs are made.