Characterizing Fire Impacted Dissolved Organic Matter (DOM) Before And After Coagulation Treatment
Meyer, John 1 ; Hohner, Amanda K 2 ; Cawley, Kaelin 3 ; Rosario-Ortiz, Fernando L 4
1 University of Colorado at Boulder
2 University of Colorado at Boulder
3 University of Colorado at Boulder
4 University of Colorado at Boulder
The Hewlett Gulch wildfire that burned from May 14to May 22, 2012 and the High Park wildfire that burned from June 9to June 30, 2012 affected a combined total area of 381 km2 of the Cache la Poudre watershed. The Cache la Poudre River serves as one of the main sources of drinking water for the Front Range cities of Ft. Collins and Greeley in northern Colorado. Motivation for this project comes from the fact that wildfire frequency and intensity has increased in recent decades and often burn forested watersheds which serve as municipal water sources.
Previous research has shown that wildfires can alter watershed sediment transport and affect water quality parameters such as dissolved organic carbon (DOC). DOC can react with hypochlorous acid during disinfection to form disinfection byproducts (DBPs). Currently the Environmental Protection Agency regulates total trihalomethanes (TTHMs), and five haloacetic acids (HAA5) at maximum contaminant levels (MCLs) of 80 μg L-1 and 60 μg L-1 respectively. In addition to increased sediment transport, wildfires can change the character and physical properties of the DOM which can have implications for treatment and DBP formation. DOC levels can be reduced with alum coagulation, however the use of alum to treat fire-impacted waters is not well understood. The objective of this research is to determine the character of organic matter in fire impacted waters compared to that of control samples, and the changes that occur upon treatment with alum coagulation
Samples were collected from the City of Fort Collins Drinking Water Intake (PNF), representing a fire impacted site, and also from a control location (PBR) upstream and outside of the burned area. Samples were treated with alum coagulation at the bench scale at varying alum doses to optimize DOC removal. Fluorescence analysis was performed on both the control samples as well as the fire impacted samples to determine certain characteristics of the DOM such as the source (terrestrial or aquatically derived). In addition, size exclusion chromatography (SEC) analysis was performed to better understand the DOM size distribution of the samples before and after coagulation at varying doses. Preliminary results show that coagulation preferentially removed terrestrially derived organic matter compared to microbial/aquatically derived organic matter. Furthermore, size distribution varied with spring snowmelt and some samples showed slight differences between the fire impacted and control samples. Lastly, SEC results generally showed the removal of high molecular weight compounds during coagulation.