Prompton Dam Safety Evaluation

Prompton Dam is a 140-foot-high earthfill embankment dam on the Lackawaxen River in Pennsylvania. Owned and operated by the U.S. Army Corps of Engineers, it is classified as a “high-hazard” dam.

Originally constructed for flood control, the Corps began investigating the possibility of using the reservoir for water supply storage. As part of that investigation, the USACE Philadelphia District retained GEI to conduct a comprehensive evaluation of the dam’s condition and safety under current operating criteria. Work involved review of design, construction, and performance records; site inspections and field investigations to develop additional data; installation of instrumentation; seismic deformation analyses; and static stability and liquefaction potential evaluations.

Of particular concern were artesian pressures in the dam foundation soils that had been detected in previous site investigations. Field investigations conducted by GEI, including a geophysical resistivity survey, were focused on searching for highly permeable zones reported to be located in the foundation soils.

Among GEI’s remedial recommendations were:

• Installation of a series of relief wells across the downstream toe of the dam to protect against artesian pressures
• The potential for high uplift pressures in the foundation soils
• GEI also provided field observation services during installation and development of the relief well system.