Abstract
A scheduled, uncontrolled chemical monitoring program conducted by the Texas Rural Water Association during the spring of 2002 discovered perchlorate contamination in an elevated drinking water storage tank. The contaminated elevated storage tank (EST) was part of the Levelland, Texas municipal water distribution system. Subsequent investigations revealed that the most likely source of the perchlorate contamination was the impressed current corrosion protection system, which generated the perchlorate electrochemically in situ from the chlorinated drinking water stored in the tank. As a part of the authors' investigation into this phenomenon, batch scale laboratory experiments were designed and used to produce perchlorate ions in chlorinated tap water using an imposed electrical (direct current [DC]) current. This in situ generation process was found to follow an autocatalytic mechanism with respect to perchlorate ion concentration. Moreover, in parallel experiments, double-distilled water spiked with sodium chloride (NaCl) failed to produce perchlorate ion contamination over the same time period. The generation of perchlorate also appeared to be dependent on the type of metal used for the anode. Observations based on these experiments suggest that chlorinated water held in reserve in steel tanks and having an impressed current corrosion protection system will exhibit perchlorate ion contamination over time; that the proper choice of anode material used in an impressed current system can minimize perchlorate formation; and that perchlorate ion generation has autocatalytic characteristics and formation can be minimized by frequent dilution with fresh uncontaminated water.
