Nansemond Treatment Plant Advanced Nutrient Reduction Improvements Phase II

The Nansemond Treatment Plant upgrade is a major part of HRSD’s long-term plan to improve water quality and treatment capacity across Eastern Virginia. The project expands the facility from 30 MGD to 50 MGD to support regional growth, meet Chesapeake Bay nutrient reduction goals, and accommodate additional flow from the new Boat Harbor Pump Plant.

As the design-builder, Garney is partnering with Tetra Tech as lead engineer and MEB as a contract partner to modernize critical processes and construct new treatment, pumping, and electrical systems. The work includes a new influent distribution box, upgraded chemical feed systems, expanded effluent pumping supported by three 700-hp vertical turbine pumps, and a medium-voltage switchgear building with plant-wide duct banks to strengthen power reliability. New treatment facilities include a 95 ft primary clarifier, two 160 ft secondary clarifiers, two aeration tanks with fine-bubble diffusers, a 4 MG equalization basin, gravity thickeners with odor control, centrifuge dewatering, and a new RAS/WAS pump station. These upgrades enhance nutrient removal, improve storm resilience, and modernize core treatment processes.

This project plays a key role within HRSD’s Sustainable Water Initiative for Tomorrow (SWIFT), allowing the upgraded plant to supply treated water to the nearby SWIFT Facility for advanced purification and aquifer recharge being constructed. Together, these improvements strengthen regional infrastructure and support HRSD’s mission to protect water quality for future generations.

Solutions

Treatment & Capacity: A new 95 ft primary clarifier and two 160 ft secondary clarifiers increase treatment capacity to 50 MGD and improve effluent quality. Two aeration tanks with fine-bubble diffusers and a 4 MG equalization basin strengthen nutrient removal performance and provide additional storage during storm events.

Pumping & Power: A new RAS/WAS pump station with three 100-hp pumps, along with expanded effluent pumping supported by three 700-hp vertical turbine pumps rated at 26,000 GPM, improves hydraulic capacity. A medium-voltage switchgear building and plant-wide duct banks enhance power reliability and integrate new and existing systems.

Solids & Disinfection: Two 45 ft gravity thickeners with odor control, upgraded scum handling systems, and two centrifuges improve solids processing and dewatering. A new chlorine contact chamber strengthens final disinfection and supports permit compliance.

Nutrient removal: Upgrades to nutrient removal include a new influent distribution box, rerouted screened wastewater pipelines, renovated sludge loadout systems, upgraded methanol and sodium hypochlorite feed systems, and expanded effluent pumping capacity through three 700-hp vertical turbine pumps rated at 26,000 GPM.

Collaboration: Garney’s preconstruction, construction, and design teams led discipline-specific design workshops, evaluating alternatives and aligning decisions around cost and schedule impacts across all major scope areas.

Project Status  

Upgrades to the Nansemond Treatment Plant are scheduled for completion in 2026. Current progress includes installing conductors in new electrical buildings and motor control centers, continuing pump and piping work for the Primary Effluent Equalization Tanks and Aeration Tanks, and coating the Primary Gravity Thickener Tanks. Crews are also installing piping and equipment at Odor Control C and completing cover installations for the Influent Distribution Box, with Primary Clarifier 5 already finished.