Assessing potential wildfire ash organic carbon threats to drinking water: Key considerations

To evaluate the impact of wildfire on drinking water treatability, wildfire ash is often added to source water to reflect post-fire source water quality change. The use of varying experimental conditions has led to conflicting inferences across studies and inconsistent results, even between nominal replicates. Here, mixing time and ash concentration effects on wildfire ash-impacted water (WAIW) quality were investigated, and their impacts on leached water extractable organic matter (WEOM) from wildfire and prescribed fire ash were characterized at bench-scale. The effects of mixing time and ash-to-water ratios were investigated using both natural river water and ultrapure water. Notably, WEOM concentration and character varied considerably within the first 24 hours of mixing, and water type and ash mass concentration limit the leaching of WEOM into water. These results highlight the critical role of careful experimental design and well-justified approaches to support meaningful interpretation and comparability across studies.