The practice of mitigating roadway runoff through infiltration has increased in recent years because of its ability to reduce stormwater volume, increase groundwater recharge, and reduce peak flows and pollutant transport. Some state DOTs are required to use infiltration Best Management Practices (BMPs) for their roadway projects unless infiltration is proven infeasible. Research to date has focused on the ability to capture stormwater discharge and pollutants using infiltration. However, little attention has been given to the other potential environmental and infrastructure effects of using infiltration BMPs. These potential effects may include issues of water balance (e.g., groundwater mounding) and the introduction or mobilization of contaminants into groundwater.While infiltration has quickly become the BMP of choice, there is growing concern that requiring infiltration BMPs may inadvertently lead to other consequences to the natural and built environment. For instance, research has shown that heavy metals and hydrocarbons are generally captured by the upper layers of soil, but breakthrough of these contaminants can occur. Research is needed to better understand the capabilities of infiltration BMPs in different environmental settings and to identify the potential limitations and overall environmental effects of infiltration BMPs.
The objective of this research is to develop guidance for state DOTs to determine appropriate siting of stormwater infiltration BMPs based on the limitations, risks, and benefits in the context of the built and natural environments (e.g., surface water and groundwater, soils, existing infrastructure). The guidance should address a broad range of issues and needs associated with choosing and siting infiltration BMPs for mitigating roadway stormwater that may include but not be limited to the following:
- Limitations (e.g., cost, maintenance, regulatory, receiving waters, geotechnical)
- Effects of climate, soils, topography, geology, vegetation, and land use
- Effects of pollutants of concern on surface water and groundwater quality
- Effects on surface water and groundwater quantity (e.g., recharge, baseflow augmentation, groundwater mounding)
- Identification of gaps in the body of knowledge
- Options for improving the effectiveness and reducing risks
The guidance should outline decision-making processes and criteria that would assist agencies in identifying flexible solutions.
A kick-off teleconference of the research team and NCHRP shall be scheduled within 1 month of the contract’s execution. The research plan proposed must be divided into tasks, with each task described in detail. The tasks must be divided into two phases. Phase I will consist of information gathering and planning tasks, culminating in the submittal of an interim report. The interim report will describe the work completed in the Phase I tasks and provide an updated research plan for the Phase II tasks and an outline of the guidance. The updated Phase II research plan should address the manner in which the proposer intends to use the information obtained in Phase I to satisfy the project objective. A face-to-face interim meeting with NCHRP will be scheduled to discuss the interim report. Work on Phase II tasks shall not begin until the updated research plan is approved by NCHRP. The project schedule shall include 1 month for NCHRP review and approval of the interim report. The final deliverables will include the guidance plus a final report that documents the entire research effort and other deliverables as described in the research plan. Deliverables should also include an executive summary and Microsoft PowerPoint presentation describing the background, objectives, research method, and findings that can be used to present key issues and conclusions critical to stakeholders. Proposers may recommend additional deliverables to support the project objective.