Wildfire Threats to Groundwater Supplies: Implications for Pathogen and Particulate Contaminant Transport in Porous Media

Climate change-associated wildfires are increasing in frequency and severity, causing increasingly variable or deteriorated water quality, and challenging in-plant treatment processes beyond design and operational response capacities, to the point of service disruptions. Recent work has shown that the wildfire impacts on drinking water treatability can extend far downstream and be long-lasting. Notably, very little information regarding the impacts of severe wildfire on groundwater supplies is currently available.

Wildfire transforms fuels (i.e. biomass, soil organic matter). Pyrogenic carbonaceous material formed after wildfire includes particulate ash and biochar, which often contains toxic polyaromatic hydrocarbons, dioxins and furans, as well as some heavy metals. These mobile materials may be incorporated into soil profiles (change the soil properties, e.g., hydrophobicity, pH), redistributed, or removed from a burned site by wind and water erosion to source water. While surface water treatment technologies may have some capacity to remove these contaminants from surface water, the subsurface fate and mobility of these toxic particles has not been documented and is not understood. Moreover, the implications of potential changes in dissolved organic carbon on pathogen transport in these systems has not been documented. Because groundwater-based drinking water supplies do not typically require treatment beyond disinfection, it is possible that contaminated particles could enter drinking water wells after wildfire. Moreover, NOM-associated changes in water quality may increase the risk of pathogen transport through the subsurface.

Here, the impacts of wildfire on the transport E. coli and Cryptosporidium parvum oocysts in various porous media environments (e.g., particle properties, solution chemistry, organic matter character) were evaluated. Column tests were conducted using laboratory prepared wildfire ash-impacted water and wildfire impacted surface water collected after the 2017 Kenow Wildfire in Waterton, Alberta, Canada. These investigation demonstrate that under certain conditions potential post-fire shifts in water quality can substantially enhance particle/microbe transport in porous media, thereby underscoring the need to evaluate microbial risks to groundwater supplies after severe wildfire.