Development of Model for TTHMs Prediction: Application to Rural Water Distribution Systems in Eastern Kentucky

Several years after the institution of disinfection requirements in 1974, it was determined that chlorine can interact with organic compounds in the water supply to create disinfection by-products (DBPs). Many DBPs are carcinogenic, neurotoxic, genotoxic, mutagenic, and teratogenic. The EPA limits TTHM values in the water distribution system to be less than 80 ug/L. Several water distribution systems in Kentucky have had problems maintaining this balance between adequate disinfection and formation of TTHMs.
Studies have shown that DBPs can form both at the water treatment plant and in the distribution system. In this study, a commercial software for modeling water distribution hydraulics (i.e., KYPIPE) was modified for both the modeling and prediction of chlorine and TTHMs in a water distribution system. This was accomplished by linking KYPIPE with EPANET, another software package developed by EPA for modeling water age and the transport of constituents (such as chlorine) through the distribution system. EPANET requires bulk and pipe wall decay coefficients for each pipe in the water distribution system although each coefficient is typically assumed to be the same for all pipes in the system. These coefficients were first taken from literature and adjusted to meet the results from field sampling. Prediction of TTHMs formation was accomplished through the correlation models developed to relate DBP formation to either water age or chlorine demand.
The developed model was validated against a system with known chlorine and DBPs measurements. The same procedure was further used to predict the chlorine and DBP values for two distribution systems in eastern Kentucky. Each model were first calibrated against measured chlorine and DBP values obtained from field sampling. Once calibrated, the models were then validated against another independent data set. In each case, the model was able to predict chlorine and DBP values within an acceptable tolerance.