AWWA ACE99353

The amount and nature of dissolved organic carbon (DOC) has become increasingly important to the water treatment process. Chlorination of DOC in water during microbial disinfection for drinking water creates disinfection byproducts (DBPs). Levels of two classes of DBPs, trihalomethanes (THMs) and haloacetic acids (HAAs), face tightening USEPA restrictions. This paper addresses the following questions: given the extreme variability in hydrologic regime that is typical of arid climates, how much variation in reservoir DOC production is likely to occur? what factors drive the production and consumption of DOC in reservoirs?; what is the relationship between DOC and DBP precursors (THMs and HAAs) in arid regions?; and, is the observation of net DOC production one that can be generalized to other reservoir systems in the region? Water budgets were developed using data from the US Geological Survey and the Salt River Project. Continuous flow records (daily average) were used to compute river inflow and outflow. Daily records of volume and evaporation were provided and water budget components were computed on a daily time step over the course of the study. Samples were collected on an approximate monthly basis. DOC mass balances were computed by two methods: in the simple method, loading within each time interval was computed from the total flow within the time interval multiplied by the concentration at the midpoint of the interval; total loading was computed as the sum of loading for all time intervals.