Duke Energy Marshall Steam Station

Client: Duke-Energy Corporation

Location: Marshall Steam Station , NC

Summary: Cardno ENTRIX is an integral part of the Duke-Energy Team designing and constructing treatment wetlands to remove selenium and mercury from blowdown generated by the FGD scrubber being installed at the Marshall Steam Station in Terrell (NC). As part of the Marshall team, Cardno ENTRIX was responsible for the conceptual design, preparing wetland construction engineering plans and specifications, permitting of the facility including erosion control measures, providing construction oversight for the wetland, installing plants in the wetland cells and monitoring their health and development, and operation and maintenance of the system during the first year of operation. Treatment wetlands can be constructed in transmission line right-of-ways and waste areas, have the support of the regulatory community, offer a ?green? technology, provide effective treatment for multiple constituents, have reasonable construction costs, and very low operating costs.

• Pilot studies, conducted in partnership with Clemson University, to determine design specifications and removal efficiencies for selenium and mercury using inflow concentrations up to 7 mg/L and x mg/L, respectively.
• Dual equalization/cooling basins followed by three parallel trains of wetland cells and effluent monitoring prior to discharge to the Plant?s existing ash basin.
• Constructed wetland treatment system that occupies approximately 30-acres of the site, with 12.5-acres of active wetlands system and treats up to 1.25 MGD FGD wastewater.
• Construction on land that was believed to be unusable (one cove of the ash basin and under existing power transmission lines).
• A FGD treatment system that does not require plant harvesting, constant chemical addition, or continuous sludge removal. The system uses gravity flow from the equalization basin through the discharge and does not have any electrical requirements.
• The construction and planting were completed in the summer of 2005. Wastewater will be added in the fall of 2007.
• Construction cost of the wetland system at Marshall Steam Station was 6.25 million dollars and the CTW system will have an annual operating budget of less than $150,000 or $ 0.35/1000 gallons including laboratory testing.

• Cardno ENTRIX produced the Conceptual Design Report for Regulatory review and performed final design and construction oversight, planting and operations and maintenance of the wetland system.
• Constructed Wetland Treatment System was built on land that was believed to be unusable.
• The 12.5-acre wetland system will cost 6.25 million dollars to construct and less than $150,000 annually (less than $0.35/1000 gallons) to operate.
• Constructed wetlands provide low cost, effective treatment for multiple constituents and has the support of the regulatory community.