The EPA has published the final Stage 2 Disinfection By-Product Rule (DBPR2) and the Long-Term 2 Enhanced Surface Water Treatment Rule (LT2). These rules will affect all but the smallest water systems. This two-part series will focus on the DBPR2 and measures that drinking water utilities can take to successfully comply followed by the LT2 next month.

Disinfection by-products are compounds formed as a result of chemical reactions between disinfection chemicals and carbon compounds. These reactions can occur in the treatment plant as well as in the distribution system. The two DBP’s targeted by the regulation are tri-halomethanes and haloacetic acids. Both of these are known to cause cancer and may pose reproductive and development risks. Any community water system or nontransient noncommunity water system that uses a disinfection method other than ultraviolet light will be subject to DBPR2.

DBPR2 sets the Maximum Contaminant Levels for Total Tri-halomethanes (TTHM) and Haloacetic Acid 5 (HAA5) at 80 mg/L and 60 mg/L respectively and must be calculated based on a Locational Running Annual Average (LRAA). This is a change from the prior rule that allowed for a Running Annual Average (RAA) across the entire system. An LRAA is a running average of samples collected at a designated sampling point within the distribution system. Multiple sampling points must be chosen through a process called the Initial Distribution System Evaluation (IDSE).

A utility has four options for completing the IDSE:

• Follow the Standard Monitoring Plan that determines the number of sampling locations based on system size and source of water.

• Perform a System Specific Study based on hydraulic modeling and historical sampling data.

• Apply for a waiver by certifying to the primacy agency that the last 8 consecutive quarters of TTHM and HAA5 monitoring have results of less than 40 ug/L TTHM and 30 ug/L HAA5.

• Obtain an automatic waiver for very small systems serving less than 500 people.

Another major component of the new DBPR2 rule requires each utility to determine if they risk violating the MCL by examining each quarter’s results and performing some simple calculations. If certain triggers are exceeded, a written report must be submitted within 90 days. That report must address aspects of treatment and distribution system operation that can be improved to reduce DBPs.