Determination of Changes in Water Quality, Streambed Sediment, and Benthic Macroinvertebrates as a Result of Stormwater Runoff from Selected Bridges in South Carolina
Science Center Objects
Past stormwater monitoring has indicated that bridge deck runoff has relatively high concentrations of a variety of constituents such as nutrients, solids, pesticides, trace metals, and polycyclic aromatic hydrocarbons (PAHs). The objective of this investigation is to quantify the downstream changes in receiving water-quality conditions during periods of observable stormwater runoff from selected bridge decks in South Carolina.
The results of the stream water-quality sampling, streambed-sediment sampling, and benthic macroinvertebrate community structure at upstream and downstream locations will be used to characterize the effects of bridge deck runoff on receiving waters in South Carolina.
Project Chiefs: Celeste Journey, Kevin Conlon, Andral Caldwell
Period of Project: June 1, 2013 to March 30, 2018
Cooperator: South Carolina Department of Transportation
Past stormwater monitoring has indicated that bridge deck runoff has relatively high concentrations of a variety of constituents such as nutrients, solids, pesticides, trace metals, and polycyclic aromatic hydrocarbons (PAHs) (Pitt and Maestre, 2005; Driscoll and others, 1988; Dupuis, 2002; Malina and others, 2005; Marsalek and others, 1997; McKenzie and Irwin, 1983; Wagner and others, 2011). The recent USGS investigation in North Carolina characterized the quality of stormwater runoff from over 15 bridge decks with existing collection systems (Wagner and others, 2011); however, most bridges in South Carolina do not have stormwater collection systems. The South Carolina Department of Transportation (SCDOT) and the U.S. Geological Survey (USGS) South Atlantic Water Science Center are working cooperatively to conduct a comprehensive study on the effects of stormwater runoff from bridge decks on receiving water-quality, sediment-quality, and biological conditions in South Carolina.
The bridge decks to be considered in South Carolina currently utilize open chutes, scuppers, and downspouts to drain stormwater directly into the receiving water at evenly spaced intervals rather than into collection basins or other structural systems. Additionally, the requested focus of this investigation is to provide the SCDOT with data needed to adequately assess the effect of bridge runoff on receiving water quality, but not to directly sample, analyze, and characterize the quality of stormwater from six bridge decks in South Carolina. Therefore, this investigation will adopt similar approaches employed by the recent research in North Carolina, where possible, to allow a more regional scope to the problem; however, deviations from the North Carolina research will be required to address the specific needs of the SCDOT.
The objective of this investigation is to quantify the downstream changes in receiving water-quality conditions during periods of observable stormwater runoff from selected bridge decks in South Carolina. The information collected might help to estimate or predict changes in water quality at bridge crossings with similar characteristics. Additionally, comparison of sediment-quality conditions and benthic macroinvertebrate community structure at upstream and downstream locations from selected bridge decks will assess cumulative impact of bridge deck runoff effects on receiving water. However, the approach and methods utilized in this investigation will not produce data that can be used to determine event mean concentrations or to assess National Pollutant Discharge Elimination System (NPDES) permit requirements, but these data will provide valuable information in helping understand the changes to receiving water quality and aquatic ecosystems as a result of bridge deck runoff.
The existence of stormwater collection systems at bridge decks allows automated instrumentation to directly measure water-quantity and water-quality conditions of bridge deck runoff. However, the evenly distributed release of stormwater runoff from open chutes, scuppers, and downspouts on bridge decks to receiving waters in South Carolina limits that ability to directly measure those same conditions of bridge deck runoff. Instead, the approach to quantify the effects of bridge deck runoff on receiving waters when no collection systems are present will be to measure water-quality conditions at upstream (not affected by bridge deck runoff) and downstream (affected by bridge deck runoff) locations at selected bridge sites. Quantity of bridge deck runoff will be estimated using existing bridge deck runoff equations, based on rainfall amount and intensity (Jens, 1979; Morgali and Linsley, 1965). At large rivers or poorly mixed sites, the lack of representativeness of a single point sample (collected using automated samplers) relative to a depth-integrated, equal-width-increment sample will preclude instrumentation of automated sampling equipment. Therefore, this investigation will evaluate mixing conditions prior to sampling at selected bridge sites to determine if automated instrumentation is possible. If automation is not possible, manual sampling techniques will be adopted. If continuous streamflow gaging stations are present, stream water-quality sampling to determine loadings of selected constituents will be conducted at a subset of the 6 bridge deck sites.
The 6 bridge deck sites for stormwater runoff sampling will be distributed across South Carolina. The 6 sites will be selected based on
(1) location relative to three physiographic regions (Piedmont, Upper Coastal Plain, and Lower Coastal Plain) in the state,
(2) a range of bridge characteristics, including AADT, bridge type, bridge deck area, and bridge deck material,
(3) SCDHEC 303(d)-listed impairment in the receiving water,
(4) existing continuously recording streamflow gaging station, and
(5) accessibility. The sites selected for 2014 are Lynches River at Effingham, SC (USGS gaging station 02132000) and North Fork Edisto River at Orangeburg, SC (USGS station 02173500). The sites selected for 2015 are Turkey Creek above Huger, SC (USGS gaging station 02172035) and South Fork Edisto River near Denmark, SC (USGS station 02173000). The USGS will sample 2 new sites in 2016.
Water-quality samples will be analyzed for a wide range of constituents, including fecal indicator bacteria, suspended sediment, nutrients, major and trace metals, and semivolatile organic compounds (SVOCs), which include PAHs. Both dissolved and total recoverable concentrations of trace metals will be measured. Bed-sediment quality will be measured once during low-flow conditions at the 6 bridge sites. Benthic invertebrate community structure will be measured once during July to August timeframe at the 6 bridge sites. Samples at each bridge will be collected once a year at a location upstream from the bridge and at a second location downstream from the bridge. Bed sediment will be analyzed for nutrients, major and trace metals, and SVOCs.
Benthic macroinvertebrate community surveys will be conducted using Hester-Dendy Multiplate artificial substrate sampler deployed at upstream and downstream locations during the targeted July to August timeframe. Hester-Dendy Multiplate are artificial substrates that permit standardized sampling when direct sampling of natural substrates is prohibitive and eliminate subjectivity in sample collection technique (Davis and others, 1996; Barbour and others, 1999).
Fine-grained sediments will be analyzed for trace metals, total and organic carbon, and semivolatile organic compounds including PAHs and pthalates. Total-digestion concentrations of inorganic elements will be measured and reflect the underlying mineralogy of the sediment. Sediment-quality guidelines are variously based on total-digestion or total-recoverable concentrations. Samples will be analyzed by the USGS National Water Quality Laboratory and the USGS Kentucky Sediment Laboratory.
The aforementioned sampling methods will be conducted at all 6 selected bridge deck sites. The results of the stream water-quality sampling, streambed-sediment sampling, and benthic macroinvertebrate community structure at upstream and downstream locations will be used to characterize the effects of bridge deck runoff on receiving waters in South Carolina.
The benefits of this investigation to the SCDOT and others include: (1) an understanding of the relative contribution of bridge deck runoff to total instream constituent concentrations and loads at selected sites, and (2) an understanding of the effect of bridge deck runoff on streambed runoff on streambed sediment quality and benthic macroinvertebrate community structure at bridges. In support of the USGS Water Resources Mission (https://water.usgs.gov/mission.html), this investigation will provide data and information to “protect and enhance water resources for human health, aquatic health, and environmental quality.”
It is anticipated that the findings of this investigation will provide the data needed to assess the effects of stormwater runoff from bridge decks on receiving water quality, sediment quality, and biological conditions in South Carolina. The findings will be documented in a USGS Scientific Investigations Report, which describes the data collection and approach used to characterize the bridge deck runoff and determine the impact of bridge deck runoff on receiving waters of the state.
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