Historic Water Quality Data as a Forensic Tool to Understand the Connections Between Environmental Watershed Perturbations and Disinfection Byproduct Formation in Drinking Water

Abstract:

Watershed health is crucial to maintain water quality for downstream communities. Forested ecosystems are experiencing temperature and moisture shifts, resulting in biogeochemical cycling changes that could have unexpected consequences downstream during municipal water treatment. Disinfection byproducts (DBPs) for example, are constituents of concern that form when dissolved organics react with chlorine during water treatment. Alarmingly, past work has shown increased DBP formation in surface waters sourced from watersheds impacted by large-scale bark beetle infestation. Here we present an analysis of publicly available water quality and climate data in the state of Colorado used to conduct a historic analysis across surface water-sourced municipalities. This analysis revealed a subset of Colorado water treatment facilities that harbored increasing trends of two major DBPs, haloacetic acids and trihalomethanes, over the past 10-20 years. The observed trends varied across watershed and location, but with commonalities in declining forest health associated with climate related impacts of increasing air temperatures, decreasing soil moisture, and endemic bark beetle infestation. One area of interest from these trends is the Coal Creek Watershed which serves as the drinking water supply for the town of Crested Butte, Colorado. This location was selected for further site-based studies to benchmark DBP forming conditions associated with changes in seasonal flows. Interestingly, there was a decoupling in peak dissolved organic carbon and UV absorbance as a DBP formation precursor suggesting that downstream structural changes in dissolved organics rather than total quantity could be the driver of temporal changes and resulting increased DBP concentrations during treatment. Ongoing work is focused on identifying sources and reactive components to enable predictive tools and management strategies for mountain communities that rely on surface waters from watersheds with possible declining forest health.