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DISTRIBUTION SYSTEMS AS RESERVOIRS AND REACTORS FOR INORGANIC CONTAMINANTS
Citation:
SCHOCK, M. R. DISTRIBUTION SYSTEMS AS RESERVOIRS AND REACTORS FOR INORGANIC CONTAMINANTS. Chapter 6, M. J. MacPhee (ed.), Distribution System Water Quality Challenges in the 21st Century - A Strategic Guide. AWWA Research Foundation, Denver, CO, , 105-140, (2005).
Description:
This paper provides a review of numerous drinking water and geochemical investigations and recent studies of pipe deposits and water treatment materials. This analysis shows that there is growing evidence from analogous natural water systems and some analytical studies that many regulated drinking water constituents, along with other potential contaminants, are not conservative in the distribution system. Examples include (but are not restricted to): arsenic, aluminum, bismuth, radium, radon, lead, antimony, tin, copper, manganese, uranium, and nitrite. Distribution system materials may concentrate metals and become a reversible reservoir. When water chemistry changes, excessive concentrations of noxious contaminants can be generated or mobilized, exposing the public without detection. When water sources are changed to ones free of contaminants, a residual of the contaminant may persist in the system for months to years, continuing to expose consumers. Higher levels of contaminants may be seen in buildings and schools than at distribution system entry points, because of the accumulation in the scales over time. This may occur even when the influent concentration to the distribution system is safely below regulatory levels. Monitoring programs based on evaluations at the entry points to the distribution system are incapable of detecting important occurrence and chemical reactions causing mobility of many metals, radionuclides, and other inorganic species (e.g. NO2-) at concentrations of potential public health concern. Therefore, much more research is needed to develop more protective monitoring schemes, and to understand the treatment impacts on the stability of distribution system scales and the potential for them to sorb, desorb, coprecipitate, or conversely, dissolve or release contaminants.