New Charlotte Water Facility Meets Stringent Standards

The Stowe RWRRF will serve western Mecklenburg County and municipalities across the river in eastern Gaston County. This interlocal partnership will transform the way the region’s water resources are managed, creating a more sustainable future. (CLTWate)

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According to Nicole Bartlett, Charlotte Water (CLTWater) engineering division manager, new federal environmental requirements to meet more-stringent nutrient levels required upgrades to the existing wastewater treatment plants in Charlotte’s neighboring cities of Mount Holly and Belmont in eastern Gaston County. Planning studies found it would be more cost-effective, efficient and environmentally friendly to build a regional wastewater treatment facility that could replace the municipal wastewater treatment plants and provide the additional capacity needed in western Mecklenburg County.

As a result, CLTWater broke ground for the Stowe Regional Water Resource Recovery Facility (Stowe RWRRF) in June 2023. The entire project, which Bartlett also manages, will cost more than $600 million and is funded via CLTWater’s revenue bonds. It’s expected to be operational in the first quarter of 2027 and require 10 full-time employees to staff it 24/7.

It’s named for the late Joseph Stowe, who in 1982 became the director of the Charlotte-Mecklenburg Utility Department, now known as Charlotte Water or CLTWater. The award-winning Stowe had been lauded for his impact on the community and utility staff as well as his knowledge of global water and wastewater issues.

Addressing top concerns about CLTWater’s water resources and systems regarding flow, capacity and storage, Ron Hargrove, CLTWater deputy utilities director for operations, notes “access to quality water sources is paramount. Much like others in the industry, modeling water use for a large community such as the Charlotte region is a challenge with ever-changing climate, regulatory environments and economic landscapes.”

 

Belmont and Mount Holly have aging wastewater treatment plants, each located on the opposite side of the Catawba River from Charlotte. “If the existing Belmont and Mount Holly wastewater treatment plants were to remain in use, each facility would need to undergo extensive and expensive upgrades to increase capacity and meet stringent environmental regulations,” says Bartlett.

Wastewater Treatment Details

According to Will Shull, HDR project manager, the Stowe RWRRF includes one primary clarifier (100 feet in diameter) and two biological nutrient removal basins of five-stage fermentation consisting of various anaerobic, anoxic, deoxygenation, post anoxic and aerobic zones.

There will be two 160-foot-diameter secondary clarifiers, multiple flow distribution structures, multiple chemical buildings, one tertiary filtration building with deep-bed filters, one UV disinfection facility, one post-aeration structure, an outfall, two sludge and scum pump stations, RAS/WAS pump station, and a biosolids transfer pump station.

 

The City of Belmont’s wastewater treatment plant (Top) will be replaced by a pump station that will convey wastewater through force mains deep in the bedrock beneath the floor of the Catawba River to Charlotte Water’s system. The Mount Holly Pump Station (bottom) will replace the aging municipal wastewater treatment plant to send wastewater flows under the Catawba River to Charlotte Water’s system. ( CLTWate)

 

The Stowe RWRRF will not have onsite solids treatment; solids cleaned from the water at Stowe RWRRF will be treated at another CLTWater facility. The project will encompass the Stowe headworks and influent pump station with mechanical bar screens, vortex grit removal basin and Parshall flumes for flow monitoring.

“There are multiple first-stage and second-stage pumps that serve to send flow into the front of the remainder of the treatment facility,” says Shull. “The headworks facility also has day tanks and storm-equalization basins.”

Flow will travel from Mount Holly into the Stowe headworks via one of two force mains installed via Horizontal Directional Drilling (HDD). “The major benefit of the HDD process is that it allowed for the installation of the force main without disrupting the Catawba River like other methods would, such as open cutting the river,” says Shull. “This method also reduces environmental impacts to the Catawba River.”

The HDD process involves drilling a pilot hole and subsequent reaming passes to make the hole larger through the underground bedrock to form a pathway that the force mains conveying the wastewater from Gaston County to Mecklenburg County can be pulled through.

Each force main is a 26-inch OD HDPE line fused together with no joints for leaks to occur; they’re 3,100 liner feet and located roughly 75 feet under the bottom of the Catawba River and Long Creek. 

 

 

The Stowe Headworks and Influent Pump Station (Top) will perform the first two stages of the wastewater treatment process to remove large debris and grit. The wastewater then is pumped to the Stowe RWRRF through force mains deep below Long Creek. The existing Long Creek Pump Station (bottom) is being upgraded to feed into the new Stowe Headworks and Influent Pump Station for the first two treatment processes prior to being pumped under Long Creek to the Stowe RWRRF. (CLTWate)

 

“A key aspect of Stowe RWRRF will be its implementation of the latest technologies and cutting-edge treatment techniques to more effectively clean and purify wastewater,” says Shull. “It will achieve this goal through embracing a modern densified activated sludge (DAS) biological nutrient removal (BNR) process to decrease nutrient discharges—primarily nitrogen and phosphorus—into the Catawba River.”

According to Shull, DAS intensifies or optimizes the BNR process by accelerating the settling and compaction of activated sludge.

“Research indicates that the improved settling observed in DAS is linked to the greater proportion of large particles called granules vs. smaller particles known as flocs compared to conventional activated sludge systems,” he says.

Improved sludge settleability allows operation at increased mixed-liquor suspended solids concentrations and secondary clarifier solids loading rates, reducing required aeration basin volume and infrastructure costs. This is expected to reduce future expansion costs by more than $20 million.

DAS is accomplished at the Stowe facility by providing biological and physical selective pressures. “Biological selection for well-settling solids is achieved through multi-zone anaerobic and anoxic zones, which provide for a high food/mass gradient and allow for rapid uptake of readily biodegradable carbon under ‘feast conditions,’” adds Shull.

 

 

“Physical selection is provided through surface wasting and subsurface wasting using telescoping valves under quiescent conditions such as density wasting.”

Beyond implementing DAS, Stowe RWRRF also will include flexible BNR basins to allow operation in multiple process configurations with baseline operation as part of a five-stage BNR process.

The Stowe RWRRF design also will allow for advanced process controls, including ammonia-based aeration control, nitrate-based NRCY and supplemental carbon feed control, orthophosphate-based chemical phosphorus removal, and real-time solids-retention time monitoring to calculate optimal wasting rate.

“These advanced controls will reduce energy and chemical usage while meeting strict effluent nutrient requirements,” says Shull. “For example, high-speed, gearless turbo blowers using magnetic bearings will provide processed air to the BNR basins. Turbo blower technologies offer best-in-class efficiency while minimizing maintenance. Variable pressure-based blower control, utilizing most open-valve control, furthermore will reduce the energy associated with blower operation.”

The Stowe facility’s construction will decrease the number of places where wastewater is discharged into the Catawba River. It will use enhanced environmental-quality benchmarks to ensure treated water discharged into the Catawba River meets heightened water-quality and nutrient-removal standards.

Shull believes the project will have a beneficial impact on the area’s growing ecotourism industry, including boating, rafting and kayaking, enabling the public to benefit from scenic natural surroundings while pursuing water sports.

“The regional collaboration between Charlotte Water, Belmont and Mount Holly not only provides more cost-effective and environmentally conscious wastewater management services, but also fosters a more-resilient and sustainable region,” he adds. “It allows Charlotte Water to optimize the use of its water resources, particularly the pristine Catawba River that borders its communities.” 

The facility will treat wastewater closer to where it’s generated, reducing the 27-mile route it previously took to pump wastewater from North Charlotte to Pineville, cutting down on energy consumption and reducing potential wastewater spills.

The project also includes a 230-foot-long three-lane bridge across Long Creek with two travel lanes and one lane serving as a utility pipe corridor and a multi-use path via an elevated walking/biking surface above the pipe corridor. A one-mile-long access road with two vehicular lanes and a separate paved 10-foot-wide multi-use path parallel to the driveway is part of the project, including the installation of a culvert for a tributary creek. The site also includes backup generators in a building with space to add an additional generator as needed.

“Some of the land surrounding Stowe is also intended to be a location for future solar-energy collection,” says Bartlett. “The Stowe RWRRF Administration Building is being designed to be LEED certified. Stowe RWRRF will include multiple electric vehicle chargers both on the public and private parking sides of the facility.”

Project Setbacks

Bartlett notes that as a project manager, the most challenging aspect was the impact of COVID-19, which began shortly after detailed design had started, necessitating that portion of the project be moved to a virtual platform.

The project team included design staff, Owner’s Advisor staff, Charlotte Water staff (e.g., operations, maintenance, system protection, security, engineering, safety, IT, public communication and others) as well as staff from the contractor.

“It was a management challenge to keep that large group of people with varying demands of their job outside of Stowe design apprised of all the workshop topics and decision timelines,” Bartlett notes.

“The project management team was able to mitigate this challenge by holding multiple types of meetings and workshops with different stakeholders, utilizing different virtual platforms to encourage participation, planning agendas up to 30 days out and sharing meeting minutes afterwards.”

Post-COVID economic inflation impacted projects nationwide, including the Stowe project.

CLTWater continues to assess cost impacts and supply chain challenges from post-COVID inflation to successfully deliver the project, explains Bartlett. CLTWater worked with its Owner’s Advisor and project design team to implement value-engineering modifications to address cost inflation.

The project included field surveys along the alignments, including threatened and endangered species, as well as bathymetric river surveys.

Designed for the Future

An ongoing challenge will be the impact of climate change, including dramatic temperature swings and the intensity and frequency of severe storms to which facility operations must adapt.

“Stowe RWRRF is designed with a state-of-the-art instrumentation, controls and operation system to help operating staff adapt as quickly as possible to environmental concerns,” adds Bartlett. “Severe storms can cause increased flow rates, power loss and potentially impact deliveries like chemicals, which the facility needs to properly operate.”

Stowe RWRRF has flow flexibility both in equalization tanks and the ability to send flow to other treatment facilities.

“Stowe’s power feed was designed to run off transmission, which has more reliability than a distribution line, as well as onsite generators,” says Bartlett. “Chemical storage has been designed such that even in storm events, sufficient onsite storage is available.”

For other municipal entities embarking on similar projects, Bartlett notes it’s important to be transparent about the costs and schedule through routine check-ins. “Complete independent cost estimates to support the project costs being provided by the contractors,” she adds.

Frequent communication is key to convey to stakeholders the return on investment. “We have a project website for the public that communicates FAQs, project cost, project schedule, project information,” she says. “We post to various social media accounts. We give tours to both internal and external stakeholders.”