Tata & Howard completed an Extended Period Simulation (EPS) hydraulic model of the water distribution system for the Town of Avon, Massachusetts. An EPS model was created to account for changes in the water distribution system over an extended period to include peak and minimum demands during both the summer and winter months. These changes included tank levels, pump controls, value operation, and demand variations.
The EPS model was used to estimate the water age in the water distribution system under winter and summer demand conditions. Water age is the time water takes to travel from a water supply source to a point within the distribution system. It is used as an indicator of water quality based on the assumption that the older the water is, the greater the likelihood that water quality has deteriorated. According to MassDEP Finished Water Storage Guidelines, a three to five-day complete water turnover is recommended in water storage tanks.
The EPS model was also utilized to evaluate the Town’s existing system operations. The model was used to determine the optimal tank operating range and the impact of the run times on the well pumps. Simulations were performed on both the Center Street and Page Street Tanks to evaluate operations under existing and projected average day demand (ADD), maximum day demand (MDD), and peak hour demands with a minimum pressure of 35 psi maintained throughout the distribution system.
In addition to analyzing the tank optimal operating levels, changes to the existing pump operations and the effect on tank levels and water age were evaluated. Two modified pump operations scenarios were evaluated. Both scenarios were run with the existing tank water level controls and allowing the Page Street Tank to drop four feet. A second modified pump operation scenario evaluated the Town’s lead/lag system. Results for the pump and tank level operations under these simulations were recorded for both summer and winter operations.
Based on the results from each operational modification, Tata & Howard made several recommendations for improvement to the water distribution system. These included allowing the water level in the Page Street and Central Street tanks to drop an additional six feet to improve water age during both the summer and winter demands.
In addition, to help improve the water age in the tanks to an optimal three to five-day complete water turnover as recommended by MassDEP Finished Water Storage Guidelines, Tata & Howard suggested installing mixing systems in each tank.