Wildfire can abruptly transform forests, char vegetation and soils, and may create an environment susceptible to post-fire erosion and runoff to nearby surface waters serving as potable water supplies. The rising trend in wildfire activity is increasing the risk to source waters, while post-wildfire implications on drinking water treatment are not well understood. To complement previous research, a laboratory based approach was used to address the effects of forest floor heating during wildfire on water quality. Surface soil and litter samples from three watersheds were heated in a furnace at 225°C and leached to evaluate changes to water-soluble compounds. Leachates were diluted to a dissolved organic carbon concentration of 5.0 ± 1.0 mgC/L. Heated and unheated (control) leachates were compared for dissolved organic matter (DOM) properties, treatability by alum coagulation, and disinfection byproduct (DBP) formation. Following heating, changes in optical properties and organic nitrogen suggest the DOM character shifted to lower molecular weight, nitrogen enriched, aromatic compounds. Carbonaceous DBP reactivity of the heated leachates was lower than control samples, however the differences were not significant. Chloropicrin reactivity was significantly elevated following heating (mean Δ = +1.3 μg/mgC), while haloacetonitrile reactivity showed minimal change. The heated leachates consistently exhibited an overall poor response to coagulation, even at increased coagulant doses (&gt;80 mg/L). DOC removal per mg alum was statistically lower for the heated leachates compared to the control samples (mean Δ= -0.06 mgC per mg-alum). The adverse effect of heating on the treatability of the leachates might be explained by a lower-molecular weight DOM composition. Following treatment all heated leachates exceeded DBP maximum contaminant levels (MCLs), whereas all control samples were below MCLs. Treated water nitrogenous DBP formation was also higher for the heated leachates, specifically chloropicrin. While findings suggest an altered DOM character, utilities may also experience an increase in influent DOC concentrations coupled with higher, or even extreme, sediment loads, resulting in compounding effects on water treatment.

Laboratory simulation of wildfire heating: Effects on DOM and water treatment

253rd National Meeting (2017)

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