Date of Award
Doctor of Philosophy (PhD)
Fernando L. Rosario-Ortiz
R. Scott Summers
The recent increase in wildfire activity has raised concerns among water utilities that rely on forested watersheds. Wildfires can alter the vegetation, soils, and hydrologic processes of watersheds serving as water supplies, which may negatively influence source water quality and treatment. An understanding of post-fire treatment challenges, and guidance on how water providers can prepare is needed.
To understand the impacts of wildfire on dissolved organic matter (DOM), disinfection byproduct (DBP) reactivity, and drinking water treatability, three approaches were taken: 1) a water intake below a burned watershed was monitored following a Colorado wildfire; 2) charred, riverbank sediment deposits were collected from the burn area and leached in the laboratory; and 3) surface soil and litter samples were heated in a furnace and leached. Turbidity, nutrients, optical properties, treatability, and DBP formation were addressed.
Following wildfire the source water DOM quantity and character were altered, suggesting lower molecular weight composition. After rainstorms in the fire-affected area, haloacetonitrile (HAN) and chloropicrin reactivity were elevated, indicating a potential link between wildfire, rainfall, and nitrogenous DBP (N-DBP) precursors. Post-fire source water required a higher coagulant dose to achieve DOM removal. Fire-affected sediments may leach DOM, creating challenges for meeting DBP maximum contaminant levels (MCLs) unless coagulant doses are increased or additional unit processes are added. Post-fire mobilization of burned sediments to source waters may enhance N-DBP precursors, which were not well removed by coagulation, however additional treatment, such as pre-ozonation/coagulation/biofiltration, reduced N-DBPs. Controlled heating of soil/litter showed the DOM of heated leachates had higher aromaticity, while the molecular weight was lower, resulting in a unique DOM composition. The change in DOM quality adversely affected coagulation treatment and finished water quality, including the exceedance of DBP MCLs.
Water providers should consider expanding water storage, exploring additional supplies, constructing pre-sedimentation basins, and increasing filtration and solids handling capacity. Treatment operations may need to be adjusted for higher coagulant demand from increased turbidity and DOM to meet regulatory requirements for turbidity, DOC removal, and DBP MCLs, specifically following precipitation events. Although N-DBPs are currently unregulated, attention should be given to post-fire HAN and chloropicrin formation.
Hohner, Amanda Kay, "Wildfire Disturbances to Water Quality: Implications for Drinking Water Treatment" (2016). Civil Engineering Graduate Theses & Dissertations. 422.