Mahanoy Township Authority

Lofty Dam Rehabilitation

Mahanoy Township, PA

Background: The Lofty Dam is an earthen dam and serves as a DEP-permitted public water supply source. The dam is 1,100 feet long and had maximum height of about 28 feet and is classified as a C-2 dam by PADEP. The embankment was reportedly constructed with clay and gravel taken from the reservoir area. The upstream and downstream slopes are grassed. The primary spillway consists of a 29-foot wide concrete, ogee-section located near the left abutment.

Scope: The recommended improvements included raising the dam elevation to 6 feet. Benesch performed survey at the remote location, engineering analyses, developed contract drawings and technical specifications, prepared a design report, submitted permitting and provided bidding, contract administration and construction phase services. Services included survey, environmental clearances, hydraulic spillway review, structural design of parapet wall, PADEP permitting, and a wetlands/drainage system.

Unique Features: After the original bidding and NTP, cracks were found in the dam breast and modifications to the rehabilitation approach were required. After a geotechnical assessment, it was determined that the original dam material installed in 1896 included a weak fill zone and caused cracks. The additional improvements included removal of undesirable fill and reconstruction of the upstream slope using current design standards. Additional funds were acquired to complete these added modifications.

After more than 20 years, the dam is back at full capacity and serves as a critical resource for the Mahanoy Township Authority. The project was funded through a $3.8 million PennVEST Loan and a $1.7 million DCED CFA H2O Water/Sewer Grant.

Project highlights

  • Funding assistance with multiple sources
  • Discovery of a weak fill zone from original 1896 dam during construction required modifications to the scope
  • Raising dam elevation, replacement of undesirable fill and upstream slope reconstruction
  • Wetland mitigation