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The Accumulation Of Radium And Other Radionuclides In Drinking Water Distribution Systems
Citation:
Morris, E. A. AND D. A. LYTLE. The Accumulation Of Radium And Other Radionuclides In Drinking Water Distribution Systems. Presented at AWWA WQTC, Charlotte, NC, November 04 - 08, 2007.
Impact/Purpose:
To inform the public
Description:
The tendency for iron solid surfaces to adsorb trace contaminants such as arsenic is well known and has become the basis for several drinking water treatment approaches. It is reasonable to assume that iron-based solids, such as corrosion deposits present in drinking water distribution systems, have similar adsorptive properties and could, therefore, concentrate trace contaminants. The concern would be that the potential to re-release the contaminants back into the distribution system would exist. Furthermore contaminants such as radium could precipitate or coprecipitate in the distribution as well. Changes in water chemistry or flow could cause the release of the contaminants back to the water resulting in the potential for elevated contaminant levels at the consumer’s tap. Naturally occurring radionuclides are an issue for water utilities in many regions of the United States. Elevated or even trace levels of radium, uranium and thorium can enter and accumulate in the distribution system with time. Past researchers have reported that the radioactive decay of radium that had accumulated in the distribution system even led to elevated radon levels. The objective of this work was to determine the composition of distribution system solids collected form water systems in the Midwest that reported measurable levels of radium in their finished waters. Specifically fire hydrant flushed samples were collected, and the solids concentrated, separated and analyzed. The solids were analyzed for total radium, uranium, and thorium isotopes, gross alpha and beta activity, and a number of common elements including Fe, Mn, Ca, Mg, Ba, P, and others. At the time of abstract preparation, 18 solid samples collected from 7 different water systems located in Wisconsin (3) and Minnesota (4) had been analyzed. The sites have historically had concerns with radium in their source waters. Total radium (226,228) values in the fire hydrant flushed solids ranged from 37 to 592 pCi/g. Radium-226 values ranged from 23 to 241 pCi/g and radium-228 values ranged from 16 to 351 pCi/g. Total thorium (228, 230, 232 isotopes) ranged from 16.1 to 100.4 pCi/g. And total uranium (233, 234, 235, 236, 238 isotopes) ranged from 3.3 to 11.5 pCi/g solid. Gross alpha and beta activity ranged from 13 to 698 pCi/g, and 22 to 637 pCi/g, respectively. The major components of the solids included iron (average of 19% by weight), calcium (9.6%), phosphorous (6.2%) and magnesium (0.7%). The reported composition values will be compared to values reported in drinking water residuals and other waste streams for comparison. Finally, correlations between elemental components of the solids will be reported and discussed.