SINKHOLES IN THE BUSHKILL CREEK, NORTHAMPTON COUNTY, PENNSYLVANIA: A CHRONICLE OF ASSESSMENT AND REMEDIATION

Beginning in fall of 2000, a major sinkhole situation developed in Northampton County, eastern Pennsylvania, involving a cement quarry, a residential neighborhood and farmed land, streams, roadways and railroad bridges. In October 2000, a two-lane roadway (SR 2017) bridge over the Bushkill Creek was closed when sinkholes at the foundation caused it to settle and crack. Additional sinkholes affected the northern approach to the bridge, the adjacent fields and a private residence to the south. Several state and local agencies become involved. A hydrogeological investigation by the PA Department of Environmental Protection (PA DEP) to determine the potential cause was complicated by several factors – the suspected overlap of three active quarries' zones of influence, the length of time the quarries had been operating, the changes made to the Bushkill Creek streambed during construction of the nearby PA State Route 33 in 1970, and lack of historical groundwater data for the area. A direct structural connection between pumping at the nearest quarry and the current sinkhole situation could not be established with the information available. Sinkholes continued to appear (and reactivate) throughout the next three years.

Interest and concern escalated suddenly in early 2004 when one of the twin bridges of SR 33, a major transportation structure spanning Bushkill creek, failed when the foundation was compromised by sinkhole activity. A task force was formed by the various governmental entities in order to share information and attempt to understand the geology, hydrology and engineering aspects of this complicated problem and propose remediation suitable to all parties. The SR 33 bridges were reconstructed at an estimated cost of 10 million dollars. The new structures, constructed on micropiles, immediately experienced settlement and movement, necessitating additional remediation measures, monitoring systems and extensive exploratory drilling. In 2006, the situation is not stable and sinkholes continue to plague the community, the PA Department of Transportation, the PA DEP and the nearby quarry company. Remediation for the bridges and the stream is ongoing. The various participants can learn from this situation in order to improve the planning, response and permitting procedures within Pennsylvania's karst areas.