AWWA JAW71678

A two-phase study investigated the source of high arsenic at consumers' taps in a small water system and the effectiveness of treatment to resolve the problem. The community used the common practice of chlorination and polyphosphate addition to control iron. A relatively low water velocity within the system may have allowed arsenic-bound iron particles to settle, only to be mobilized by the opening of a faucet and subsequent rapid change in water velocity. Replacing polyphosphate treatment with an oxidation/filtration unit and adsorption unit installed in series reduced arsenic concentrations to < 1 µg/L. Arsenic (and potentially other contaminants) can accumulate in the distribution system, and their release back into the water may result in elevated levels at consumers' taps. The water industry should be aware that changes in such processes as treatment, operation, and system maintenance can affect the release of any contaminants present in the distribution system. Includes 22 references, tables, figures.