Image

Credit: Photos: Jim Strickland/Black Star

Chuck Hill, Bryan Blake, Glen Whisler, and Kevin Eberle (from left) watch the BNR system in action.
Image

Credit: Photos: Jim Strickland/Black Star

The plant's administration building is the only LEED-certified wastewater-related building in the nation. Inside are educational panels that explain the treatment process to visitors.

Durham County's Triangle Wastewater Treatment Plant in North Carolina has set a new standard in public works. Redesigned and constructed over six years, the plant was completed on time and $3 million under estimated construction costs. The facility also has the nation's only LEED-certified (Leadership in Energy and Environmental Design) waste-water administration building.

Since the early 1960s, the plant has been a chief component of Research Triangle Park, one of the largest research parks in the world. The park employs 37,500 people and has connections with surrounding universities, including Duke University and the University of North Carolina at Chapel Hill. The Triangle Waste-water Treatment Plant covers an 18,200-acre area and serves 8000 customers. After decades of service, the facility had a host of issues.

A study in 1997 revealed that the plant's treatment units, influent pumping station, tertiary filters, and effluent flow meter occasionally flooded. In addition, the plant's discharge had trihalomethane levels exceeding limits set by the National Pollutant Discharge Elimination System permit program. With sewage flows to the plant expected to double by 2023, the facility needed improvement.

The Durham County public works department selected McKim & Creed of Wilmington, N.C., to engineer and construct the project. Durham County and McKim & Creed delineated four main priorities: replace the 6 mgd tertiary treatment facility with a 12 mgd biological nutrient removal (BNR) process, promote job-creating growth within Research Triangle Park, fit the needs of a growing population, and meet current nutrient removal requirements.

The team also wanted to improve the water quality of Jordan Lake, a recreation area downstream from the plant. “In addition to all the typical water quality parameters, the two that are a particular concern in the Jordan Lake area are nitrogen and phosphorus,” said Durham county engineer Glen Whisler. The new BNR system has improved the effluent discharged to Northeast Creek, one of Jordan Lake's tributaries. Jordan Lake is now a source of drinking water.

McKim & Creed divided the project into two phases. The first phase constructed new headworks and an ultraviolet and post-aeration structure. The second phase added the BNR system, clarifiers, tertiary filtration system, and the administration building.

One impressive feature of the Triangle Wastewater Treatment Plant is the LEED-certified administration facility. The facility qualified for LEED certification by using low-energy, recycled, and regionally manufactured materials in construction.Wastewater from the building also is treated and rerouted to the HVAC system and low-flow toilets. Using reclaimed water has reduced potable water use by 32%.

The first two phases were constructed for $28.3 million. When the new plant was completed in April 2005, it began treating a portion of the wastewater while the old plant was still operating. “The very delicate part of that is transitioning the flow from the existing facility to the new facility,” said McKim & Creed project manager Bryan Blake. This required coordination among the designers, the building contractors, and the operators of the existing facility. The old plant was taken off line in May 2005.

During the design phase, the team encountered an unusual opportunity: The neighboring town of Cary asked if it would be possible for Durham County's new plant to treat part of their waste-water. “They knew they were getting a little tight on capacity,” said Chuck Hill, utility division manager for Durham County.

With Cary in mind, McKim & Creed designed a 12 mgd facility composed of four 3 mgd treatment modules. Durham County agreed that the Triangle Wastewater Treatment Plant would treat 5 mgd of Cary's wastewater through 2010.