Tobyhanna Dam No. 2 Rehabilitation, PA
AEG, a SOCOTEC Company is supporting the Pennsylvania Department of Conservation and Natural Resources with geotechnical, geophysical, and environmental services for the complete replacement of Tobyhanna Dam No. 2 in Monroe County, Pennsylvania.
Key Information
Project: Tobyhanna Dam No. 2
Client: Pennsylvania Department of Conservation and Natural Resources (PA DCNR)
Location: Monroe County, PA
Services Provided: Geotechnical, Geophysical and Environmental
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The Challenge
Upgrading a High-Hazard Dam
Located in Tobyhanna State Park, Tobyhanna Dam No. 2 is an earthfill embankment structure originally built in the 1950s. The dam measures approximately 860 feet long and 18 feet high and includes a 62-foot spillway.
PA DCNR is undertaking a complete replacement to bring the structure in line with current safety requirements and enable it to withstand the Probable Maximum Flood (PMF).
The planned improvements include:
- raising the dam
- replacing the spillway
- upgrading related infrastructure.
Before design decisions could be advanced, the project team needed a clearer understanding of the existing embankment, subsurface materials, groundwater behavior, and surrounding environmental conditions.The site also presents an unusual historical constraint. Because the area was previously used as a military testing ground, the U.S. Army Corps of Engineers is expected to scan the lakebed for unexploded ordnance.
The Solution
A Multidisciplinary Site Investigation
AEG, a SOCOTEC Company, provided multidisciplinary investigation and engineering support to help DCNR evaluate existing conditions and inform the replacement of Tobyhanna Dam No. 2.
The scope of work included:
- Site Reconnaissance: AEG, a SOCOTEC Company prepared a Site Reconnaissance Report summarizing background research and field observations of the existing embankment and surrounding areas.
- Geotechnical Investigation: The team performed subsurface exploration, coordinated drilling operations, and conducted in-house laboratory testing to evaluate embankment stability and seepage risks. The findings were compiled in the Final Geotechnical Engineering Report (FGER), which included recommendations for armoring the dam breast and spillway channel walls.
- Geophysical Analysis: Electrical Resistivity Imaging (ERI) and Spontaneous Potential (SP) methods were used to assess material variability, saturation conditions, and potential seepage.
- Environmental Services: AEG, a SOCOTEC Company completed wetland identification and delineation, prepared a wetland investigation report, and supported environmental permitting efforts.
Together, these investigations provided DCNR with technical information on the dam’s existing conditions and potential risks to support the development of a safe, cost-effective, and environmentally responsible replacement strategy.
AEG, a SOCOTEC Company, provided multidisciplinary investigation and engineering support to help DCNR evaluate existing conditions and inform the replacement of Tobyhanna Dam No. 2.
The scope of work included:
- Site Reconnaissance: AEG, a SOCOTEC Company prepared a Site Reconnaissance Report summarizing background research and field observations of the existing embankment and surrounding areas.
- Geotechnical Investigation: The team performed subsurface exploration, coordinated drilling operations, and conducted in-house laboratory testing to evaluate embankment stability and seepage risks. The findings were compiled in the Final Geotechnical Engineering Report (FGER), which included recommendations for armoring the dam breast and spillway channel walls.
- Geophysical Analysis: Electrical Resistivity Imaging (ERI) and Spontaneous Potential (SP) methods were used to assess material variability, saturation conditions, and potential seepage.
- Environmental Services: AEG, a SOCOTEC Company completed wetland identification and delineation, prepared a wetland investigation report, and supported environmental permitting efforts.
Together, these investigations provided DCNR with technical information on the dam’s existing conditions and potential risks to support the development of a safe, cost-effective, and environmentally responsible replacement strategy.
The Results
Supporting Informed Dam Replacement Design
AEG’s work is providing PA DCNR and the wider project team with the technical information needed to advance the replacement of Tobyhanna Dam No. 2.
The investigation has helped establish a clearer picture of existing ground conditions, embankment materials, groundwater behavior, and environmental constraints, while also informing engineering recommendations for key elements of the new design.
This integrated approach supports the development of a replacement structure intended to meet modern safety standards, withstand the Probable Maximum Flood, and contribute to the long-term protection of downstream communities and recreational use within Tobyhanna State Park.
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