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IRON TUBERCULATION: PHYSIO-CHEMICAL CHARACTERIZATION OF A SINGLE PIPE FROM A DRINKING WATER DISTRIBUTION SYSTEM
Citation:
GERKE, T. L., D. A. LYTLE, M. R. SCHOCK, M. K. DE SANTIS, AND B. J. MAYNARD. IRON TUBERCULATION: PHYSIO-CHEMICAL CHARACTERIZATION OF A SINGLE PIPE FROM A DRINKING WATER DISTRIBUTION SYSTEM. Presented at 2007 AWWA Annual Conference, TORONTO, ON, CANADA, June 24 - 28, 2007.
Impact/Purpose:
To inform the public
Description:
The nature of iron tubercles inside unlined iron pipes of drinking water distribution systems are influenced by water quality and therefore susceptible to changes in water chemistry. The underlying assumption is that tubercles in a system have similar physio-chemical properties. However, this assumption has not been validated. The purpose of this research was to evaluate the physio-chemical variability of iron tubercles from a single distribution system. Three iron tubercles removed from a 0.11m long unlined cast iron pipe were examined. Each tubercle had three distinct regions: a core overlain by a shell and surface layer and morphologically formed two groups. One group of tubercles had a core region composed of iron oxy-hydroxides and magnetite–rich, vein-like features, and a second group was composed of magnetite with pockets of iron oxy-hydroxides. The shell-like layer for both groups was dominated by magnetite. Chemically, of ten metals analyzed in the scale, only lead, copper, and chromium concentrations substantially differed within or between tubercles. Based on the dominant core region mineral phases, distinct water qualities must have existed within each tubercle. The extent of variability observed reflects the complex nature of iron corrosion and tuberculation and local differences in water quality under which tubercles form. Thus, extrapolations and predictions for system-wide characteristics or responses to water treatment/quality changes based on the examination of a single tubercle or pipe section are likely highly uncertain and possibly unreliable.