Residual disinfectant, whether chlorine or chloramine, must remain in the distribution system of all customers to assure the continued ability to destroy microorganisms that could impact human health. Disinfectant concentrations decrease with increased time in the distribution system. This means customers further from the Wylie water treatment plant will experience concentrations lower than customers near the plant. NTMWD must assure every retail water recipient, such as Allen, is able to maintain the required minimum disinfectant concentrations, regardless of their distance from the water plant. The minimum concentration level for chlorine disinfectant is 0.2 parts per million; for chloramines it is 0.5 parts per million. This minimum is a point-in-time minimum, not a rolling annual average (RAA). Dropping below either minimum level means the system is unable to safeguard human health. This is a significant water quality violation and can cause the issuance of a boil water notice. NTMWD’s position is that producing either chloramine or chlorine-only water at the plant in the 3.8 to 4.0 ppm range is necessary to assure adequate residual disinfectant levels throughout the entire regional water distribution system.
The other means to reduce Disinfection By Product (DBP) production in the distribution system is by reducing the organics, termed Total Organic Carbon (TOC), coming out of the water plant. The organics are the contaminants that interact with the disinfectant to create DBPs. In 2020, NTMWD will complete construction of Biologically Active Filters (BAF). These filters contain live beneficial microorganisms that consume TOC and reduce the levels of contaminants available to form DBPs in treated water.