Evaluating Biochar as a Multi-Beneficial and Cost-Effective Soil Amendment Option for Maximal Stormwater Infiltration

Departments of Transportation (DOTs) are challenged to meet regulations for stormwater runoff in soils compacted during the construction process. Compacted soils exhibit limited root growth in vegetation, reduced infiltration and water storage, resulting in increased stormwater runoff. Biochar amended soils are a potential remedy to this issue. The addition of carbon enriched amendments such as biochar can enhance soil hydraulic properties including wet aggregate stability, water capture and hydraulic conductivity. As well as reduce the risk of environmental pollutants (organic and inorganic) from soils by forming complexes well as reduce the risk of environmental pollutants (organic and inorganic) from soils by forming complexes or through sorption. A recent field study conducted by Delaware DOT demonstrates biochar amendment’s ability to be used as a cost-effective stormwater best management practices (BMP). Stormwater runoff and peak flow rate in biochar amended sandy loam soil was decreased by roughly 50%, for a cost similar to an urban grass buffer. Biochar’s effect on soil varies by soil type, and there are limited studies on its impact to clay soils native to North Carolina. Additionally, the impact of biochar on a specific soil will also vary by biochar type, making it necessary to test against multiple biochar variations to identify an optimal mix. The overall goal of this research is to evaluate the cost-effective use of biochar for maximal stormwater infiltration and runoff quality in amended soils and assess its ability to provide social and ecological cobenefits resulting from healthy landscapes. In doing so, the effectiveness of a suite of biochars will be assessed over a range of application rates and clay soils native to North Carolina. Ultimately, this research will determine the optimal biochar amendment rate and type for soil improvement BMPs and quantify its multi-beneficial roles within urban watershed management. Specific objectives of this work include: (1) Create a NC geospatial webtool identifying NC biochar suppliers, detailing characterization and price for each selection. (2) Perform preliminary batch testing to assess biochar application rates on contaminant removal for a suite of biochar types. (3) Conduct bench-scale testing (column tests) of nutrient and metal losses in biochar amended soils. (4) Develop triple bottom line framework and model for assessing co-benefits of stormwater BMPs based on landscape improvements. (5) Development of recommended specifications for optimizing biochar amendment rates for soil improvement BMPs. Completion of this project will be a step towards the strategic implementation of biochar as a stormwater BMP with environmental and economic benefits to stormwater management. Anticipated research products include: (a) biochar vendor locator web-tool, (b) BMP embedded benefits modeling tool, (c) specifications for selection of biochar type based on the soil type and water quality benefits warranted, and (d) a design guide detailing best practices for adding biochar to NCDOT’s Stormwater BMP Toolbox.