Wildfire effects on source-water quality--Lessons from Fourmile Canyon fire, Colorado, and implications for drinking-water treatment

Abstract

Study Rationale and ApproachThe degree to which wildfire degrades water quality and supply depends on wildfire extent and intensity, postwildfire precipitation, watershed topography, and local ecology.Potential effects of wildfire on municipal water supplies and downstream aquatic ecosystems include the following:• Changes in the magnitude and timing of snowmelt runoff, which influence filling of water-supply reservoirs,• Increased loading of streams by nutrients, dissolved organic carbon, major ions, and metals,• Postfire erosion and transport of sediment and debris to downstream water-treatment plants, water-supply reservoirs, and aquatic ecosystems, and• Changes in source-water chemistry that can alter drinkingwater treatment.The Fourmile Canyon fire in Boulder County, Colorado (September 6-10, 2010) burned 23 percent of the Fourmile Creek Watershed (10 square miles or 2,600 hectares), destroyed more than 160 homes, and was one of the costliest wildfires in Colorado history (figs. 1 and 2).The wildfire left the area at risk of substantial erosion (Ruddy and others, 2010), potentially degrading the water supply of the communities of Pinebrook Hills and Lafayette, which draw water from Fourmile Creek and Boulder Creek downstream of the burned area (fig.2).Mine tailings and waste rock from historical placer and lode mining U.S. Department of the Interior U.S. Geological