- Project involved HDD installation of about 25,000-ft of new force main
- Interbedded coastal plain deposits consisting of silt, clay and sand
- Environmentally sensitive corridor with residences
- 4,100-ft HDD crossing beneath South River limited to October 1 through December 15
- Consent Decree driven schedule
The Mayo Water Reclamation Facility operated by Anne Arundel County receives septic tank effluent via a pump station system from Mayo peninsula residents. Once pump station capacity was reached, the County imposed a moratorium on future residential development.
The approved selected alternative involved construction of approximately 25,000-ft of new force main to convey wastewater from the Mayo area northward to the existing Annapolis Water Reclamation Facility (WRF). Upon placing the new force main in service, the Mayo WRF was converted into a regional sewer pumping station.
The County’s design consultant retained Brierley Associates to serve as a trenchless specialist to assist with concept development, lead design for Horizontal Directional Drilling (HDD), and provide on-site field engineering during construction. One of the design challenges posed to the team was the subsurface conditions consisting of deep, very soft soils.
Due to the length of this project, construction was divided into five separate contracts to install twelve HDD segments. The first of these contracts was the 4,100-ft alignment beneath the South River.
To mitigate the potential of inadvertent drill fluid losses, a bore depth of over 100-ft deep below the river bottom was chosen. Through our design analysis, we selected a 24-in diameter, DR-7 HDPE that was capable of withstanding the installation forces
Given the sensitive ecosystem and regulatory requirements, the window for construction beneath the South River was limited to October 1 through December 15. Lastly, permitting timeframes posed challenges to taking a conventional Design-Bid-Build approach. This was overcome by Anne Arundel County executing a pre-purchase of 4,580-ft of 24-in diameter DR-7 pipe and 5,820-ft of 20-in diameter DR-11 pipe and expedited construction bid process that ultimately led to successful installation within the limited window of opportunity imposed by Maryland DNR.