Assessment of Surface Water and Sediment Impacts to Mountain Island Lake from Riverbend Steam Station Coal Ash Basin Discharges
No Thumbnail Available
Date
2017-12-03
Authors
Advisors
Journal Title
Series/Report No.
Journal ISSN
Volume Title
Publisher
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.