Highway monitoring station USGS 415157072291301 along State Route 74 near Vernon, Connecticut.
Quality of Stormwater Runoff Discharged from Connecticut Highways
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By New England Water Science Center
March 6, 2023
Existing highway-runoff data do not adequately address the informational needs of stormwater professionals in Connecticut because there have been relatively few studies of highway runoff in the Northeastern United States. Consequently, the U.S. Geological Survey, New England Water Science Center, in cooperation with Connecticut Department of Transportation (CTDOT), is conducting a 4-year project to characterize highway runoff and constituent concentrations discharged from nine highways throughout the State.
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The CTDOT operates and maintains an extensive road network comprising 10,000 miles of roadways, and most of this road network is susceptible to stormwater issues. Stormwater discharge from highways can adversely affect the quality of the water body into which it drains, called a receiving water. If the stormwater discharge degrades the water quality, it could fail to meet Connecticut surface-water-quality standards. Environmental mitigation based on inadequate evaluations of stormwater impacts can be costly, ineffective, and counter-productive. Therefore, this study will provide stormwater professionals in CTDOT with scientifically-defensible highway-runoff data collected from Connecticut highways to accurately assess the possibility of runoff adversely affecting receiving water bodies and the potential benefits of implementing stormwater control measures, such as structural best management practices to mitigate those risks.
Understanding the quality of highway runoff from Connecticut highways will identify how certain variables, including traffic volume and land cover, affect the concentrations of selected constituents. Additionally, this project will inform runoff-quality modeling efforts that will minimize the expense of water-quality monitoring by estimating the potential effects of runoff on receiving waters. Furthermore, data collected in this study will expand the current knowledge-base of highway-runoff concentrations of selected constituents, and provide new data that can be used to identify possible environmental effects of highway runoff on receiving waters in the Northeast and other regions of the United States. Most of the existing highway-runoff data from 1975 to 1985 was not collected in New England or in areas representative of the region. Also, automobile technology, fuel additives, construction materials, and highway maintenance practices have changed in the past 40 years, so the existing dataset is no longer representative of current highway-runoff quality.
Many studies have shown that stormwater runoff can be a source of suspended solids, nutrients, metals, and polycyclic aromatic hydrocarbons, which can result in exceeding aquatic life criteria and secondary drinking water guidelines in receiving streams and lakes. Highway runoff is a complex mix of inorganic and organic constituents from multiple sources including atmospheric deposition, local soils, automobiles, road residuals, winter-maintenance materials, and other sources. The natural or developed land cover next to roadways can affect concentrations and loads of various water-quality constituents that are discharged to receiving waters. For example, highways located within cities with high impervious area often have higher particulate deposition rates compared to highways surrounded by forest with low impervious area. Traffic volume, climatic regions, storm characteristics, length of dry antecedent period, highway maintenance practices, and other factors also change highway-runoff quality. As a result, highway-runoff concentration data taken from the same location can vary by orders of magnitude within a storm and between storms.
To characterize the quality of highway runoff from Connecticut highways, nine water-quality monitoring stations were installed in parts of northeastern, central, and southeastern Connecticut representing different traffic volumes, local climatic conditions and precipitation chemistry, roadway material and maintenance practices, surficial soils, and land covers. These monitoring stations are operated for about two years at each location. Automated monitoring methods at each station are used to characterize the quantity and quality of runoff at each site. Each monitoring station is equipped to continuously measure discharge, specific conductivity, air temperature, and precipitation, and to automatically collect composite samples of highway runoff for up to 18 selected runoff events. Composite samples of highway runoff are analyzed for concentrations of total phosphorus, total nitrogen, dissolved major ions (including deicing elements), suspended sediment, total-recoverable metals, and polycyclic aromatic hydrocarbons.
Highway monitoring station
Highway monitoring station USGS 415157072291301 along State Route 74 near Vernon, Connecticut.
Existing highway-runoff data do not adequately address the informational needs of stormwater professionals in Connecticut because there have been relatively few studies of highway runoff in the Northeastern United States. Consequently, the U.S. Geological Survey, New England Water Science Center, in cooperation with Connecticut Department of Transportation (CTDOT), is conducting a 4-year project to characterize highway runoff and constituent concentrations discharged from nine highways throughout the State.
Sources/Usage: Public Domain. View Media Details
The CTDOT operates and maintains an extensive road network comprising 10,000 miles of roadways, and most of this road network is susceptible to stormwater issues. Stormwater discharge from highways can adversely affect the quality of the water body into which it drains, called a receiving water. If the stormwater discharge degrades the water quality, it could fail to meet Connecticut surface-water-quality standards. Environmental mitigation based on inadequate evaluations of stormwater impacts can be costly, ineffective, and counter-productive. Therefore, this study will provide stormwater professionals in CTDOT with scientifically-defensible highway-runoff data collected from Connecticut highways to accurately assess the possibility of runoff adversely affecting receiving water bodies and the potential benefits of implementing stormwater control measures, such as structural best management practices to mitigate those risks.
Understanding the quality of highway runoff from Connecticut highways will identify how certain variables, including traffic volume and land cover, affect the concentrations of selected constituents. Additionally, this project will inform runoff-quality modeling efforts that will minimize the expense of water-quality monitoring by estimating the potential effects of runoff on receiving waters. Furthermore, data collected in this study will expand the current knowledge-base of highway-runoff concentrations of selected constituents, and provide new data that can be used to identify possible environmental effects of highway runoff on receiving waters in the Northeast and other regions of the United States. Most of the existing highway-runoff data from 1975 to 1985 was not collected in New England or in areas representative of the region. Also, automobile technology, fuel additives, construction materials, and highway maintenance practices have changed in the past 40 years, so the existing dataset is no longer representative of current highway-runoff quality.
Many studies have shown that stormwater runoff can be a source of suspended solids, nutrients, metals, and polycyclic aromatic hydrocarbons, which can result in exceeding aquatic life criteria and secondary drinking water guidelines in receiving streams and lakes. Highway runoff is a complex mix of inorganic and organic constituents from multiple sources including atmospheric deposition, local soils, automobiles, road residuals, winter-maintenance materials, and other sources. The natural or developed land cover next to roadways can affect concentrations and loads of various water-quality constituents that are discharged to receiving waters. For example, highways located within cities with high impervious area often have higher particulate deposition rates compared to highways surrounded by forest with low impervious area. Traffic volume, climatic regions, storm characteristics, length of dry antecedent period, highway maintenance practices, and other factors also change highway-runoff quality. As a result, highway-runoff concentration data taken from the same location can vary by orders of magnitude within a storm and between storms.
To characterize the quality of highway runoff from Connecticut highways, nine water-quality monitoring stations were installed in parts of northeastern, central, and southeastern Connecticut representing different traffic volumes, local climatic conditions and precipitation chemistry, roadway material and maintenance practices, surficial soils, and land covers. These monitoring stations are operated for about two years at each location. Automated monitoring methods at each station are used to characterize the quantity and quality of runoff at each site. Each monitoring station is equipped to continuously measure discharge, specific conductivity, air temperature, and precipitation, and to automatically collect composite samples of highway runoff for up to 18 selected runoff events. Composite samples of highway runoff are analyzed for concentrations of total phosphorus, total nitrogen, dissolved major ions (including deicing elements), suspended sediment, total-recoverable metals, and polycyclic aromatic hydrocarbons.
Highway monitoring station
Highway monitoring station USGS 415157072291301 along State Route 74 near Vernon, Connecticut.
Highway monitoring station USGS 415157072291301 along State Route 74 near Vernon, Connecticut.