MODELING TOC AND UV-254 ABSORBANCE FOR RESERVOIR PLANNING AND OPERATION

Using data from the Wachusett Reservoir, which is the downstream reservoir of the multiple-source water-supply system for eastern Massachusetts, a simple mass-balance model for TOC was developed, and TOC concentrations were correlated to absorbance of UV light at a wavelength of 254 nm (UV-254) so that the input and output of the decision support system developed for adaptive management of the reservoir system on a weekly time scale could be presented in familiar units. A quasi-mechanistic TOC model that combined the simulation of advection, diffusion, settling, and autochthonous production was combined with simple observational inputs. The performance of the model was assessed in the context of its ability to predict UV-254 levels accurately so that the treatment-plant operators can plan adequately for 7-d periods with minimum information while keeping required chlorination rates optimally low. The mass-balance formulation is provided. The model was calibrated against TOC measurements covering the period from June 1999 through December 2000. The model performed well. Inserted into the decision support system, the model predicted TOC concentrations and corresponding UV-254 absorbance levels based on optimized flow schedules for each 7-d planning period.