ASSESSMENT OF SINKHOLE DEVELOPMENT RELATED TO SURFACE MINING IN NEW HOPE, PA

Sinkholes are a naturally occurring phenomenon that can pose serious risk to property and human life. This study aims to identify causal mechanisms of sinkhole development in response to quarry operations. The Buckingham Valley region of Bucks County, Pennsylvania is underlain with carbonate bedrock of the Cambro-Ordovician Allentown, Beekmantown, and Leithsville Formations. These formations are susceptible to sinkhole development but also serve as great extractable resources for aggregate mining. Though sinkholes are naturally-occurring, we hypothesize that significant drawdown produced by surface mining operations in karstic bedrock can increase the risk of sinkhole development. Understanding the physical dynamics of this system is important to quantify sinkhole risk assessment, propose sinkhole mitigation strategies, and identify land use best management practices.

This study examines spatiotemporal relationships between the hydrologic zone of influence and sinkhole development using groundwater modeling techniques for a site in New Hope, Pennsylvania. The New Hope Crushed Stone quarry, permitted in 1976, spans 35 hectares with a sump elevation 30 meters below sea level before ending operation in 2014. Between 1989 and 2014, 37 sinkholes opened on properties adjacent to the quarry. A MODFLOW-USG groundwater model was created to simulate hydrologic conditions between 1989 and 2014 using groundwater elevation data collected from 24 nearby wells. Reported sinkholes occurred exclusively within the hydrologic zone of influence. The correlation between the model-simulated cone of depression and sinkhole occurrence reveals that a spatiotemporal relationship exists. This study suggests that the physical dynamics at the New Hope site may be used to reduce sinkhole risk adjacent to mining operations here and elsewhere.