Aqualink -- Computer-Assisted Evaluation of DBP Control Alternatives

The fection cant Rule upcoming treatment is expected By-products Disinfectant-Disinchallenges to trigger (D-DBP) for signifiutilfection By-products (D-DBP) Rule is expected to trigger significant t atment challenges for utilities throughout the United States. These challenges focus around the apparent conflict between the D-DBP Rule and other regulations already in effect, such as the Surface Water Treatment Rule (SWTR) and the Total Coliform Rule (TCR). The SWTR requires that disinfectant dosages and residual concentrations be maintained to achieve required levels of primary disinfection (pathogen inactivation) and secondary disinfection (distribution system disinfection). Because the TCR limits the presence of coliforms in the distribution system, the TCR also effectively requires that minimum disinfectant residuals be maintained in the distribution system. At the same time, the D-DBP Rule may seek to limit both the concentration of disinfectants and disinfection by-products (DBPs) in the distribution system. The challenge to water utilities is not limited to striking a balance between DDBP control and microbiological control. For example, compliance with the Lead and Copper Rule (LCR) also has implications with regard to a utility's ability to comply with the D-DBP Rule. Two possible methods for controlling lead dissolution are (1) the maintenance of pH 8 or higher in the distribution system and (2) the use of corrosion inhibitors at lower pH values. One one hand, many utilities favor the second alternative because it is likely to be associated with lower trihalomethane (THM) concentrations. On the other hand, many of these utilities may be unaware that this alternative is likely to be associated with higher haloacetic acid (HAA) concentrations. Therefore, utilities must be prepared to balance the formation of different DBPs, while addressing the requirements of the SWTR, TCR, and LCR.