By Chelsea Mitchell, PhD candidate, Washington State University, Washington Stormwater Center*

Figure 1. Bioretention systems are designed to drain and filter stormwater runoff. Credit Carly Thompson, WSU Puyallup.
Stormwater runoff has become one of the greatest environmental challenges we face in western Washington, a region with heavy rainfall and widespread urbanization. In parts of the landscape dominated by impervious surfaces, such as roads, buildings, and parking lots, rainfall is not able to infiltrate the ground (Figure 1). Instead, the resulting runoff picks up pollutants, causes flooding and changes our waterways. These issues are expected to become more severe with population growth and climate change.
There is a bright spot on the horizon, though. A charcoal-like product known as biochar has potential to address these issues when used in stormwater management. Biochar is formed when biomass is heated under low or no oxygen conditions in a process called pyrolysis. By limiting the oxygen level, you limit combustion and the release of carbon dioxide during biochar production. The resulting material has a stable, carbon-rich structure which resists being degraded for hundreds to thousands of years, keeping the carbon locked in place. Continue reading