Total organic carbon (TOC) is the total amount of organic matter in the water, and is used to evaluate water quality. TOC concentrations are regulated by the Safe Drinking Water Act through the Long-Term 2 Enhanced Surface Water Treatment Rule and the Stage 2 Disinfectant Byproduct Rule. Both Rules identify removal requirements based on source water characteristics such as alkalinity and source water TOC levels. Generally, TOC is removed through the addition of coagulants during the floculation and sedimentation processes and through the filtration process.
Dissolved organic carbon (DOC) measures the total amount of organic matter that can pass through a filter no larger than 0.45 µm. Since high levels of DOC may interfere with disinfection efficiency, DOC concentrations are monitored for removal before the disinfection stage of the water treatment process.
Both TOC and DOC are related to the formation of disinfection byproducts (DBPs). When left over organic matter reacts with residual chlorine, DBPs may form (please see "Disinfection Byproduct Data" for more information).