Wildfires cause substantial changes to surface water quality including increased concentrations of natural organic matter (NOM) and changes to NOM characteristics. NOM, partly consisting of dissolved organic carbon (DOC), acts as primary precursor to the disinfection byproducts (DBPs) that include trihalomethanes (THMs). Treatment of fire-affected waters is further complicated by sudden shifts of DOC concentrations caused by precipitation events that facilitate transport of burned organic matter. Water providers affected by wildfires require characterization of fire-altered DOC, evaluation of treatment alternatives, and forecasts of post-fire recovery duration. The objective of this talk is to present a case study effort to characterize the physico-chemical properties of DOC over time in a fire-affected watershed and to evaluate treatment alternatives for reduction of DBPs. Surface waters, organic matter, and ash from areas impacted by two wildfires in Santa Barbara County, California, were evaluated along with DOM derived from a nearby non-impacted watershed. The DOC size distribution was characterized by ultrafiltration (UF). DOC type and polarity were characterized by excitation-emission matrix (EEM) fluorescence and the Polarity Rapid Assessment Method (PRAM), respectively. The removal of DOC and THM formation potential on the wildfire-impacted waters were evaluated on pilot-scale by pre-ozonation, powdered activated carbon, ferric chloride and ferric sulfate in a flocculation-sedimentation-filtration system. Precipitation after wildfires was found to have a significant impact on the leachatability of DOC. First flush precipitation event removed 72% of leachable DOC content, while the second event removed additional 19% of the total post-fire leaching potential. Pre-ozonation with ferric sulfate was found to be most effective in reducing the THM formation potential of the fire-altered water. The characteristics of fire-impacted and unaffected DOC show substantial differences in size, polarity and fluorescence characteristics. Change in these characteristics can be used to optimize water treatment processes and forecast the return of water quality to pre-fire conditions.

Wildfires: Burning questions regarding drinking water supplies and treatment

253rd National Meeting (2017)

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