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Home My WebLink AboutNC0003425_History_20160101I. History / Background Roxboro Steam Generating Station Duke Energy's Roxboro Steam Generating Station is a four -unit coal fired steam electric generating facility located along Hyco Reservoir in Person County. The facility has been in operation since 1966 and has a capacity of 2558 megawatts. Roxboro Steam Generating Station is permitted to discharge wastewater under NPDES Permit No. NC0003425 to Hyco Reservoir. The Roxboro Steam Generating Station operates an active ash basin, constructed in 1973 and a partially active ash basin constructed in 1966. The active ash basin receives wastewater flow from the ash removal system, yard drain sumps, low volume wastes, effluent from a 15,000 GPD domestic wastewater treatment system, blowdown from Unit 4 cooling tower, ash landfill leachate and runoff, emergency overflow from FGD system as well as stormwater. The ash basin discharges via internal outfall 002 to the heated discharge canal (Outfall 003). § 130A-309.210 of the Coal Ash Management Act of 2014 requires owners of coal combustion residuals surface impoundments to identify and assess all discharges from the impoundments and to implement corrective action to prevent unpermitted discharges from the impoundments to the surface waters of the State. Identification of discharges includes engineered channels designed or improved for the purpose of collecting water from the toe of the impoundment (toe drains), as well as non -engineered seeps and weeps. One method of proposed corrective action allowed under the Act is to make application for a National Pollutant Discharge Elimination System (NPDES) permit amendment to bring the unpermitted discharge under permit regulations. A Discharge Assessment Plan for the unpermitted discharges at the Roxboro Steam Generating Station was submitted by Duke Energy to the department on April 29, 2016. Duke Energy identified 16 unpermitted seeps at the Roxboro Steam Generating Station; 11 seeps from the ash settling basin, 4 from the ash landfill and one from the gypsum pile. The seeps from the ash basin flow to the discharge canal. The seeps from the landfill and the gypsum pile flow to the intake canal. A summary of the proposed changes to the NPDES permit can be found on the Fact Sheet for NPDES Permit Development in Attachment B. The facility operates the following outfalls: Outfall 003 — Heated Discharge Canal to Hyco Reservoir. The discharge canal combines all internal outfalls (002, 005, 008, 009, 010) before discharging to Hyco Reservoir. In addition, once -through cooling water from condensers for units 1,2, and 3, once -through cooling water from heat exchangers, seepage from ash pond, and stormwater runoff from plant drainage areas are discharged to the discharge canal. • Outfall 006 — Coal Pile Runoff discharges directly to Hyco Reservoir. Coal pile runoff wastewaters include runoff from the coal pile, limestone pile and gypsum pile, truck wheel wash area and coal handling areas. Treatment is accomplished by neutralization, sedimentation and equalization. • Internal Outfall 002 — Ash Pond discharging to the discharge canal. The ash pond receives wastewater from the following source: ■ Bottom ash transport waters ■ Silo wash water ■ Ash landfill leachate and runoff (this landfill receives CCR from Mayo and Roxboro plants) ■ Dry -ash handling system wash water ■ Blowdown from Unit 4 cooling tower ■ Coal mill rejects and pyrites ■ Sewage treatment plant effluent ■ Low volume waste consisting of boiler blowdown, equipment maintenance cleaning wastewaters, RO reject wastewater and floor drains. Low volume wastes are treated by neutralization. ■ Emergency overflow from FGD system blowdown. • Internal Outfall 005 —Cooling tower blowdown from Unit 4. • Internal Outfall 008 — Treated domestic wastewater. The treatment system consists of a screen, communitor, surge tank, aeration tank, clarifier, chlorine contact chamber and sludge holding tank. A new package plant will be installed to replace the existing plant. • Internal Outfall 009 - Chemical metal cleaning waste. Wastewaters from cleaning of the boilers is generated every five to eight years. Every three to five years wastewaters are generated from cleaning the heat exchangers. The wastewaters generated can be treated by evaporation or by neutralization and precipitation. • Internal Outfall 010 — Flue Gas Desulfurization (FGD) treatment system discharging to the discharge canal. The scrubber system removes SOx by mixing flue gas with a limestone slurry. The blowdown from the scrubber is discharged to a gypsum settling pond system then to a bioreactor which utilizes microorganisms to reduce soluble contaminants to insoluble forms (under anaerobic conditions) that then precipitate from solution. Wastewater is discharged to the ash pond effluent channel. An emergency overflow from the FGD system blowdown discharges to the ash pond. The following proposed outfalls are included in the permit: Outfall 001(Seeps) - The facility identified 16 unpermitted seeps. Seven seeps are engineered drains from the ash basin flowing to the discharge canal. Four non -engineered seeps also flow to the discharge canal. Four seeps from the ash landfill and one from the gypsum pile flow to the intake canal through a common outfall. This outfall was previously designated as outfall 001 in the permit and will be reinstated to monitor the seeps. • Internal Outfall 012 - Low volume waste and other wastewaters. A new dual basin treatment system will be constructed to treat wastewaters than now go to the ash basin.