NHDOT: Pemigewasset Bridge

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Sanborn Head received a 2010 American Council of Engineering Companies (ACEC)-NH Engineering Excellence Award for our work on this project.

Replacement of the Route 175A bridge linking the towns of Holderness and Plymouth over the Pemigewasset River was a high priority for the New Hampshire Department of Transportation (NHDOT). The bridge was on the “Red List” of structurally deficient state bridges. Design and construction of a new bridge were complicated by gasoline contamination in soil and groundwater directly within the footprint of the new bridge abutment and riverbank improvements. 
 
Sanborn Head was awarded a 5-year contract by NHDOT for environmental engineering design and consulting associated with the bridge replacement project, including:
  • Preparation of a Remedial Action Plan to address the gasoline contamination, 
  • Preparation of design plans and specifications for the remediation aspects of the project, and 
  • Environmental engineering support and observation services during construction.
Complex challenges of the remediation project included preventing gasoline release to the river from soil and groundwater during riverbank excavation for channel widening and integrating the remediation system with the construction of the new bridge abutment on the same property. 
 
Bridge replacement was successful, and with the elimination of gasoline seepage from the riverbank, remediation has benefited the quality of the Pemigewasset River, an important economic, recreational, and environmental asset to the area.