Assessment of Surface Water and Sediment Impacts to Mountain Island Lake from Riverbend Steam Station Coal Ash Basin Discharges

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Title: Assessment of Surface Water and Sediment Impacts to Mountain Island Lake from Riverbend Steam Station Coal Ash Basin Discharges
Author: Street, Andrew
Abstract: Abstract A preliminary assessment of constituents of potential concern associated with coal combustion residuals (CCRs) in Mountain Island Lake (MIL) near the Riverbend Steam Station (RBSS) was conducted from March 2015 through August 2017. Sediment samples from the upper three-inches of the lake bottom were collected from the cove where the coal ash basin outfall for the RBSS discharges into MIL (hereinafter referred to as “the discharge cove”) in addition to samples from upstream and downstream reference coves. Total/whole surface water samples were also collected from the discharge cove in addition to samples from upstream and downstream locations. Copper (Cu), chromium (Cr), nickel (Ni) and polychlorinated biphenyls (PCBs) were detected in discharge cove sediment samples above Threshold Effect Concentrations (TECs) during one or more sampling events. Arsenic (As) was detected in discharge cove sediments above TECs, Probable Effects Concentrations (PECs) and North Carolina Residential Preliminary Soil Remediation Goals (Residential PSRGs). Concentrations of the above constituents in sediment indicated a gradient effect with maximum concentrations observed at the coal ash basin outfall decreasing with distance from the source. Aluminum (Al), As, cadmium (Cd), Cu, iron (Fe), manganese (Mn), zinc (Zn) and turbidity were detected in surface water samples at concentrations exceeding 15A North Carolina Administrative Code (NCAC) 02B .0211 and .0216 Surface Water Standards for Class WS-IV Waters (2B Standards) and/or United States Environmental Protection Agency (USEPA, aka EPA) Nationally Recommended Water Quality Criteria for Aquatic Life and Human Health (EPA Standards) during one or more sampling events. Al, Cu, Fe, and Mn were detected above 2B Standards and/or EPA Standards at upstream reference locations indicating that these metals may be naturally occurring. Of the remaining metals detections above 2B Standards and/or EPA Standards, As appeared to be correlated to the coal ash basin discharge. The results of this preliminary assessment suggest that although permitted coal ash basin discharges at the RBSS rarely exceed surface water quality standards, CCR related contaminants have accumulated in sediment at levels of concern. Given that localized exceedances of surface water standards are often permitted in a mixing zone, the potential for enrichment of hydrophobic and bioaccumulative contaminants with an affinity for organic matter in mixing zone sediment is high. Although the U. S. Environmental Protection Agency (USEPA) made several significant improvements to the National Pollutant Discharge Elimination System (NPDES) Program in 2015 for the steam power generating industry by significantly decreasing the volume of coal ash wastewater and the pollutant 5 loading associated with wet disposal practices, discharge monitoring programs at coal ash settling basins may not adequately detect and address all constituents of concern associated with coal ash basin effluent. Regulatory processes associated with issuing, renewing and closing NPDES permits at coal-fired power plants should be adequately protective not only of surface water but also sediment quality. NPDES permitting agencies should give consideration to specifying collection of sediment samples in close proximity to ash basin outfalls and to adding PAHs and PCBs to the target analyte list for sediment and fish tissue sampling programs that are often performed during the 5-year permit renewal process.
Date: 2017-12-03
URI: http://www.lib.ncsu.edu/resolver/1840.20/34906


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