Final Scope

Bioretention stormwater control measures are increasingly being used by state departments of transportation (DOTs) to meet stormwater permit requirements. Stormwater bioretention includes a range of measures aimed at removal of contaminants and pollutants using materials such as soils, plants, and other filtering media.

The objective of this synthesis is to document current state DOT practices for the implementation and use of bioretention stormwater control measures (BSCM).

Information to be gathered includes (but is not limited to):
• Extent of DOT implementation and use of BSCM;
• Decision criteria for selecting and locating BSCM;
• Considerations for selecting the types of BSCM used;
• Siting considerations constraints (e.g., nearby contaminated soil, groundwater, or wetlands; high sediment loads; steep terrain, erodible soils);
• Limitations and barriers to the use of using BSCM (e.g., cost, regulatory, availability of materials);
• Requirements for physical and chemical characteristics of bioretention soil mix (e.g., content, gradation, nutrients, micronutrients, or sourcematerial);
• Allowances for bioretention soil mix variations or substitutions (e.g., biochar amendments);
• Quality control requirements (e.g., project-specific material acceptance criteria prior to placement);
• Underdrain usage (e.g., when to use an underdrain), underdrain matrix material (e.g., specifications for crushed rock or permeable base), and underdrain pipe material, elevation, and slope;
• Written DOT guidance on the use of impermeable liners;
• Compaction methods used (e.g., ASTM methods, determined by contractor);
• Type of outlet control, if any (e.g., weir, stand pipe, orifice);
• Plant types used (e.g., annuals, perennials, trees, shrubs, grass);
• Use of temporary or permanent irrigation;
• Maintenance considerations;
• Performance monitoring and inspection frequency;
• Mechanism for tracking BSCM assets;
• Bioretention-related terms and definitions from the literature (e.g., raingardens, bioretention, bioswales, planting soil, bioretention mix, filter media).

Information will be gathered through a literature review, a survey of state DOTs, and follow-up interviews with selected agencies for the development of case examples. Information gaps and suggestions for research to address these gaps will be identified

Status

Completed report can be found at NCHRP Synthesis Report 599.