TOC plus the disinfectants commonly used in drinking water treatment can combine to form potentially harmful DBPs. Water treatment systems face the problem and challenge of balancing the risks between microbial pathogens through the use of disinfection and the harmful DBPs that are formed.  Stage 1-DBPR is the first of a staged set of rules that reduces the allowable levels of disinfection byproducts in drinking water.  To accomplish this, the rule requires TOC be reduced to a required percentage.

The treatment technique uses TOC as a surrogate for natural organic matter, which is the precursor material of DBPs. TOC is used as a measurement of natural organic matter. A TOC concentration of greater than 2.0 mg/L in a system's raw water is the trigger for implementation of the treatment technique. If a water system is required to practice enhanced coagulation, the TOC must be reduced in the raw water by a specified percentage.

Subpart H water systems that use conventional filtration treatment are required to conduct TOC monitoring under the DBP precursor removal (enhanced coagulation or enhanced softening) requirements. Subpart H systems means public water systems using surface water or ground water under the direct influence of surface water as a source that are subject to the requirements of the Surface Water Treatment Rule.

The intent of the treatment technique is to establish TOC removal requirements based on enhanced coagulation/precipitative softening so that:

Adding additional amounts of coagulant or lime to coagulation or softening treatment trains, respectively, can increase the amount of TOC removed and thereby lower DBP levels in finished water.

ADDITIONAL INFORMATION:

1. EPA's manual titled "Enhanced Coagulation and Enhanced Precipitative Softening Guidance" (EPA-815-R-99-012, May 1999, PDF file) contains a two-step standard for TOC removal.  The 237-page manual covers TOC removal, Step 2 jar procedure, lab procedures and full-scale implementation. 
2. Refer to EPA's Web page for Stage 1 DBPR for key provisions of the rule, MCLs for DBPs, and required percentage removal of TOC.  The complete text of the Stage 1-DBPR federal register document from December 1998 is available from there.
3. Quick reference guide on Stage 1-DBPR in PDF.   
4. EPA manual for small systems titled "Small System Requirements for the Stage 1-DBPR: Small Entity Compliance Guide."  This 40-page manual contains step-by-step procedures for compliance with the Stage 1-DBPR (PDF).   
5. Additional manuals and quick reference guides for this topic are available from EPA's Web site titled "Microbial and disinfection byproducts rules: Implementation."  
6. Kentucky Administrative Regulations (KAR) for public water supply, Chapter 8:510 on disinfectant residuals, disinfection by-products, and disinfection by-product precursors; 401 KAR 8:510.