Modeling TOC Threshold Exceedances for Meeting Disinfection By-Product Drinking Water Regulations Under the Impact of Climate Change.

Motivated by seasonal variability of source water total organic carbon (TOC), we developed monthly total organic carbon (TOC) thresholds, defined as the highest concentration of source water TOC such that a conventional surface water treatment plant will meet the DBP regulations at the maximum point in the distribution system. Three case studies were used: (i) a southeast US utility whose source water TOC significantly exceeds TOC thresholds every month of the year, (ii) a midwest US utility whose source water TOC exceeds TOC thresholds approximately half of the year, and (iii) a Rocky Mountain utility whose source water TOC significantly exceeds TOC thresholds for only three months of the year.

In our earlier work we have developed models that relate the climate variables precipitation and temperature to stream flow and then stream flow to water quality.  In this work, we have directly related climate variables to water quality, bypassing the need for stream flow. Specifically, the impact of climate change on TOC threshold exceedance for the three case studies was shown by developing statistical models relating TOC threshold exceedances with climate (precipitation, temperature etc.) and land surface variables such as vegetation index. These were found to have significant correlation with TOC from preliminary analysis. Statistical TOC-climate models projecting TOC exceedances for meeting DBP regulations will be developed using historic data and future climate projections.

For utilities that are currently able to meet the new regulations, the potential impact of climate change on source water TOC may increase future TOC threshold exceedances, and therefore provide the need for optimization and/ or advanced treatment. Projections of source water TOC concentrations can aid decision making and planning for treatment design and operation, specifically on advanced treatment options, as well as source water selection, for water utilities.