Development of Biochar Specification Criteria as Soil Amendment for Slopes, Conveyances and Stormwater Treatment Systems, Phase 1.

Project summary:

Stormwater runoff from roadways is a major contributor of nonpoint source pollution of aquatic bodies and carries contaminants such as heavy metals, pathogens, nutrients (e.g., phosphate, nitrate), and organic contaminants (e.g., polycyclic aromatic hydrocarbons, PAHs; chemicals from vehicle fluid and tire rubber). Roadway swales and basins, when constructed with high permeability materials, act as low impact bioretention systems (BRSs). In addition to high-permeable materials, swales may be constructed with fillers composed of organic materials (e.g., compost) and local soils. Although current BRS designs have demonstrated adequate performance in many aspects, the design has room for improvement in a) increasing the lifespan of the BRSs, b) decreasing the costs of BRS construction, c) reducing peak flow rates during rain events, and d) improving contaminant removal performance.

The objective of this project is to develop knowledge, tools, and protocols to inform best practice standards for effective implementation of biochar in BRSs for treating roadway runoff. This project will be performed in two phases, with the first phase focusing on biochar production, characterization, and contaminant sorption (adsorption plus absorption) performance. Results from the first phase will inform decisions for the second phase, which will look at vegetation growth studies and soil hydrology evaluations. Researchers anticipate the primary project output (following completion of Phase 2) to be a tool or protocol (e.g., a decision-making matrix) to provide standardized guidance for best practices regarding the practical implementation of biochar in BRSs treating roadway runoff. The work plan for Phase 1 is presented herein, which will result in following outputs:

1) Recommendations for locally available (Minnesota-based), suitable biomass feedstocks and feedstock-specific pyrolysis conditions which can be reproduced at scale.

2) Biochar physical property specification criteria associated with contaminant-removal targets which can be assessed at reasonable costs.

3) Protocols for screening-level contaminant-removal performance tests based on broadly accessible materials and methods.

4) Plans for further evaluations to verify treatment performance and evaluate hydraulic and soil health effects, to be proposed as a part of Phase 2 investigations.