In an urban waterway cleanup setting, it is essential to understand and quantify the potential impacts of continued inputs (such as combined sewer overflows, stormwater, or direct process discharges) from the waterway drainage basin to identify contaminant sources and mitigate any potential for recontamination of the planned remedy. Sediment investigation, remediation and cost allocation is a very complex and lengthy process. Distinguishing in-water, waterfront and upland sources and attributing remediation costs for those sources is a task which has taken decades to accomplish. Although land uses may vary greatly, major transportation (roadways, bridges, dedicated outfalls and supporting maintenance facilities) is a commonality amongst urban waterway drainage basins.

This presentation discusses a multi-step modeling approach to characterizing transportation-related stormwater and quantifying its potential impacts to surface and subsurface sediment. This approach utilizes TIGSED, a tool based on the SEDCAM model, which is uniquely adaptable and can be modified to account for multiple source areas, operating periods, release mechanisms, and discharge points. The model ultimately can be used to answer two key questions: (1) will transportation runoff result in some degree of contamination exceeding site thresholds, and (2) what are the cost impacts of these discharges? Specifically, the presentation elaborates on various features of the model, each of which work together to provide a quantitative basis which a transportation entity can utilize in a private allocation setting or other regulatory context (e.g., EPA, state regulatory agencies). We discuss the various transportation-related environmental data inputs, key assumptions, and complexities of this multi-step approach and how they may be used to assess the impacts of transportation-related runoff in a river setting.