Drinking water treatment response following a Colorado wildfire.
Wildfires can greatly alter the vegetation, soils, and hydrologic processes of watersheds serving as drinking water supplies, which may negatively influence source water quality and treatment. To address wildfire impacts on treatment, a drinking water intake below a burned watershed and an upstream, unburned reference site were monitored following the High Park wildfire (2012) in the Cache la Poudre watershed of northern Colorado, USA. Turbidity, nutrients, dissolved organic matter (DOM) character, coagulation treatability, and disinfection byproduct formation were evaluated and compared to pre-fire data. Post-fire paired spatial differences between the treatment plant intake and reference site for turbidity, nitrogen, and phosphorus increased by an order of magnitude compared to pre-fire differences. Fluorescence index (FI) values were significantly higher at the intake compared to the reference site (Δ = 0.04), and higher than pre-fire years, suggesting the wildfire altered the DOM character of the river. Total trihalomethane (TTHM) and haloacetonitrile (HAN4) formation at the intake were 10.1 μg L-1and 0.91 μg L-1higher than the reference site. Post-fire water was amenable to conventional treatment at a 10 mg L-1higher average alum dose than reference samples. The intake was also monitored following rainstorms. Post-rainstorm samples showed the maximum observed FI values (1.52), HAN4 (3.4 μg mgC-1) and chloropicrin formation yields (3.6 μg mgC-1), whereas TTHM and haloacetic acid yields were not elevated. Several post-rainstorm samples presented treatment challenges, and even at high alum doses (65 mg L-1), showed minimal dissolved organic carbon removal (<10%). The degraded water quality of the post-rainstorm samples is likely attributed to the combined effects of runoff from precipitation and greater erosion following wildfire. Wildfire impacts cannot be separated from rainfall effects due to the lack of post-rainstorm samples from the reference site. Results suggest for this study region, wildfire may have consequences for influent water quality, coagulant dosing, and DBP speciation.
Department of Civil, Environmental and Architectural Engineering, University of Colorado, Boulder, CO 80309, USA.
Amanda K
AK
Hohner
Department of Civil, Environmental and Architectural Engineering, University of Colorado, Boulder, CO 80309, USA.
Kaelin
K
Cawley
City of Fort Collins Utilities, Fort Collins, CO 80521, USA.
Jill
J
Oropeza
Department of Civil, Environmental and Architectural Engineering, University of Colorado, Boulder, CO 80309, USA.
R Scott
RS
Summers
Department of Civil, Environmental and Architectural Engineering, University of Colorado, Boulder, CO 80309, USA. Electronic address: Fernando.rosario@colorado.edu.
Fernando L
FL
Rosario-Ortiz
D003120:Colorado; D060766:Drinking Water; D022882:Trihalomethanes; D018508:Water Purification; D060753:Water Quality; D014881:Water Supply
D060766:Drinking Water; D022882:Trihalomethanes
Coagulation; Disinfection byproducts; Dissolved organic matter; Fluorescence; Nitrogenous DBPs; Wildfire