Citation:

Triantafyllidou, S., D. Lytle, A. Chen, L. Wang, C. Muhlen, AND T. Sorg. Patterns of Arsenic Release in Drinking Water Distribution Systems. AWWA Water Science. John Wiley & Sons, Inc., Hoboken, NJ, 1(4):e1149, (2019). https://doi.org/10.1002/aws2.1149

Impact/Purpose:

The first reported case of arsenic release from the distribution system co-occurred with high iron, lead, and copper during red water complaints in a small midwestern water utility. This and other notable case studies of inorganic and radionuclide contaminant release prompted research on the subject in the last two decades. But except for studies specific to lead and copper contamination, or extensive investigations after visible water quality disturbances and consumer complaints, they have rarely been combined with tap water sampling, which is a direct measure of contaminant release at the point of water consumption. The goal of this analysis was to analyze field data from 20 drinking water distribution systems of the USEPA's Arsenic Demonstration Project (i.e., Arsenic Demo), to primarily answer the following research question: How did the temporal pattern of arsenic release at sampled building taps compare to the arsenic content of treated well water? In other words, did arsenic behave as a conservative contaminant in a given distribution system (i.e., IN=OUT), or as a non-conservative contaminant (i.e., IN≠OUT) during the Arsenic Demo? Three arsenic release patterns at consumer taps were identified, ranging from mostly conservative behavior in “simpler” systems (Pattern A with low iron/manganese in source well water and plastic pipe materials in the distribution system) to non-conservative release in more “complex” systems (Pattern B and Pattern C with high iron/manganese in source well water, iron pipe materials, and occasional arsenic treatment complications). These temporal trends (three distinct patterns of arsenic release during several months to more than a year depending on system) and spatial trends (three patterns of arsenic release between 20 distribution systems, and differences between 3 sampled buildings within each one), as supplemented with other inorganic data (Fe and Mn) and some general information on pipe materials, indicate a range of underlying arsenic release mechanisms from distribution pipes back into the water based on field observations.

Description:

Retrospective analysis of 20 small water systems from the USEPA’s Arsenic Demonstration Project revealed three patterns of arsenic release at the tap, after arsenic treatment of the source well water. Following an initial destabilization period, Pattern A (6/20 systems) reflected arsenic concentrations that did not change as water travelled through pipes. This conservative contaminant behavior was observed in systems with low iron/manganese in source water and plastic piping. Pattern B (8/20 systems) reflected continual release of arsenic at the tap, beyond the arsenic content of the incoming treated water, for months to more than a year after arsenic treatment (non-conservative behavior). Pattern C systems (6/20) experienced multiple arsenic spikes at the tap, reflecting non-conservative arsenic behavior which was more unpredictable than Pattern B. Pattern B and C systems had high iron/manganese in source well water and iron piping, whereas Pattern C systems additionally experienced occasional arsenic treatment complications.

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