Changes in source water quality following major wildfires, e.g., from ash inputs, erosion, and pH fluctuations, may affect the operation of water treatment plants. The 2013 Yosemite Rim Fire burned over 104,000 hc, including nearly half of the watershed for Don Pedro Reservoir. The Modesto Regional Water Treatment Plant treats water from Don Pedro Reservoir to provide approximately 50% of the domestic water supply of the City of Modesto. This study investigated the effect of fire-impacted organic matter on the pre-ozonation process of the Modesto Plant. Ozonation kinetics in both simulated storm runoff and storm water samples were studied using bench-scale ozonation experiments and a chemical kinetics model. Simulated storm runoff samples were created from mixtures of ash sampled from burned areas immediately after the Rim Fire. Storm water samples were collected from the Tuolumne River upstream of the Don Pedro Reservoir during large rain events following the Rim Fire. Recent storm water shows an increase in total organic carbon (TOC) by approximately 70 to 160% compared to averages from past storm water, indicating potential presence of fire-impacted organic matter. Bench-scale ozonation was performed by injecting an aliquot of concentrated aqueous ozone stock into a batch reactor equipped with a sampling pump. Samples were withdrawn at set time intervals and ozone and hydroxyl radical concentrations were measured. An ozonation kinetics model was used to derive rate constants for NOM with ozone by fitting to the batch ozonation results. The stormwater samples with elevated TOC levels had higher rate constants, suggesting that fire-derived organic matter is more reactive than background organic matter. The model allows comparison of ozonation pathways between fire-impacted and non-fire impacted source waters.

Effect of fire-impacted source water on ozonation kinetics in drinking water treatment

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.