Lower Dorchester Wastewater Treatment Plant Expansion

Garney is leading Dorchester County’s largest infrastructure project and its first-ever CMAR, expanding the Lower Dorchester Wastewater Treatment Plant to support the region’s rapid growth. Designed by Hazen & Sawyer, the project included a 15‑month preconstruction phase. Construction is now underway on the full expansion to 16 MGD in partnership with Atlantic Electric, Harper General Contractors, BRW Construction, and CITI.

To meet immediate needs, Garney first delivered an interim re-rate that temporarily increased the plant’s permitted capacity to 10 MGD. This approach ensured the facility could meet current regulatory requirements while laying out the groundwork for long-term improvements.

Originally designed for 8 MGD, the plant was not expected to need additional capacity until 2050, the plant’s timeline was accelerated by continued growth across the region. The expansion goes beyond added capacity, it modernizes a facility originally built in the 1980s. Work includes new headworks, aeration basins, two secondary clarifiers, sludge handling facilities, blower building, UV disinfection, RAS pump station, maintenance building, yard piping, and electrical distribution, along with rehabilitation of existing structures.

Solutions 

Maintaining Power and Operations: To prevent service interruptions, the team rerouted the plant’s electrical feed away from active treatment areas. Early coordination with electrical contractors and engineers enabled a solution using complex directional drilling beneath existing utilities, and future structures, eliminating extended outages and reducing operational risk.  

Budget and Schedule Certainty: Through value engineering, the project team identified nearly $23 million in potential savings by optimizing materials, equipment, and sequencing. Multiple GMPs supported risk management and cost control. Phased delivery allowed early procurement of long-lead process equipment and electrical gear, advancing critical work ahead of the full expansion. As a result, the Re-Rate portion of the project, which increased the interim plant capacity from 8 MGD to 10 MGD, was delivered one year earlier than it would have been via a standalone project.

BIM Coordination and Constructability: Detailed BIM modeling and construction sequencing supported work within a constrained, active facility. The team coordinated the installation of thousands of feet of new piping and duct banks, avoiding clashes with existing systems and underground utilities while improving constructability and jobsite safety. 

Project Status 

Construction is ongoing with the new treatment facilities scheduled to come online in 2026. Following startup, work will shift to rehabilitating existing structures before the full 16 MGD capacity is reached in late 2027.