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Rehoboth Beach Ocean Outfall

Rehoboth Beach, DE

Project At-a-Glance

  • 3,800-ft HDD installation of 24-inch diameter HDPE
  • Challenging onshore and marine conditions
  • Complex geology along HDD alignment


  • Project of Year, Honorable Mention”- North American Society of Trenchless Technology 2018

Project Narrative

Under a consent order issued by Delaware Department of Natural Resources, the City of Rehoboth Beach was required to eliminate the discharge of treated effluent from the Rehoboth Beach Wastewater Treatment Plant into the Lewes-Rehoboth Canal. After detailed studies and the evaluation of options the City proposed an ocean outfall as a compliance remedy. Trenchless pipe installation via Horizontal Directional Drilling (HDD) beneath Rehoboth Beach, an important environmental resource and a popular tourist destination was the selected means to install the new outfall that connected into a new submarine diffuser array. Brierley Associates served as HDD specialist by the City’s prime design professional to assist with HDD planning, geotechnical characterization, design and construction oversight.

Following a detailed pipe materials analysis, and completion of subsurface investigations, Brierley developed the HDD design for two outfall options. The design deliverables included plan and profile geometries, pipe stress calculations, and frac-out analyses. Both HDD options were bid, and a revised alignment length of 3,800-ft utilizing 24-inch diameter DR-11 HDPE was developed with the selected Contractor.

Brierley provided on-site monitoring of the Contractor’s activities during critical stages of the work, including pilot hole drilling, and product pipe pullback.

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