Date of this Version
Nebraska Transportation Center, Report SPR-P1(12) M315
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.