Evaluation of the environmental impact of bridge deck runoff.
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2012-12-01
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Abstract:Bridges are located in very close proximity to receiving waters, and regulatory agencies often require specific stormwater
control measures for bridge deck runoff. While there is some information available on roadway runoff, few studies have
focused on bridge deck runoff. Currently, there is no information available regarding the impacts of bridge deck runoff on
receiving waters in Nebraska. Due to the cost, maintenance, and design issues associated with implementing structural
controls for bridge deck runoff, it is important to develop a better understanding of the relationship between bridge deck
runoff and potential impacts to receiving streams. The objectives of this research were to evaluate the quality of bridge
deck runoff; to determine the effects of bridge deck runoff on surface water bodies in Nebraska by evaluating water and
sediment chemistry; and to evaluate the effects of bridge deck runoff on aquatic life. The goal was to identify the potential
environmental impacts of bridge deck runoff on receiving streams, and to determine design criteria that could be used by
NDOR or regulatory agencies to identify when structural controls for bridge deck runoff may be necessary to protect instream
water quality and aquatic life. Throughout the course of the project, we conducted in-stream dry weather sampling,
sediment sampling, wet weather bridge runoff sampling, and preliminary toxicity testing. Statistical analysis of upstream
and downstream in-stream samples showed that bridges did not impact the quality of the water body. Sediment sampling
did not show an increase in streambed sediment concentrations from downstream to upstream. The concentrations of
bridge runoff samples were higher than literature event mean concentration (EMC) values. This was mainly due to the fact
that the summer of 2012 had only two rain events of significant size and there was a large antecedent dry period (ADP)
between storms, making the samples much more concentrated. Two runoff events were also used in a 48-hour 5 dilution
series toxicity test with fat head minnows, and no negative effects were found. These preliminary results show that there
were no apparent effects of bridges on water quality and aquatic life.
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