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Application of the radon rule.

In 1991, the EPA proposed a 300-pCi/L (11 Bq/L) maximum contaminant level (MCL) for radon-222 in community water supplies and all nontransient, noncommunity public water systems. This means that all groundwater distribution systems will require analyses of one sample at each entry point quarterly the first year after adoption of the regulation and annually after compliance is established. There is scientific consensus that regulating radon's maximum contaminant level at the point of entry into the distribution system will ensure a waterborne radon-222 concentration lower than 11 Bq/L at the point of use. This article reports a case study that refutes this. Delta, Iowa, has a population of about 400. Delta's water distribution system serves 170 residences and has been operating since 1957. The system consists of nearly 1400 ft of 4-in. water main and more than 500 ft of 1-in. pipes serving each home. Average water usage has been relatively stable over the past 30 years at 34,000 gpd. Between 1957 and 1989, Delta obtained water from eight different alluvial wells drilled into Pleistocene sand and gravel with depths ranging from 275 to 518 ft near the Skunk River. Historical well-water analyses showed soluble iron concentrations as high as 2.2 mg/L and radium-226 concentrations averaging 93 mBq/L. Use of the eight wells was terminated in 1989. Since October 1989, Delta has obtained its water supply from What Cheer, Iowa, via a 1.5-mi water main. The University of Iowa's Hygienic Laboratory's survey of 153 Iowa municipal water supplies performed during August 1992 detected raw and finished waterborne radon-222 concentrations of 12 Bq/L and 15 Bq/L, respectively, for What Cheer. That for Delta was found to be (point-of-use) 54 Bq/L. To verify that the residential water-borne radon-222 concentrations used by Delta citizens were greater than the concentration entering the Delta water distribution system, a survey was undertaken on samples from 25 Delta homes on October 7, 1993. Eighty-nine percent of the homes surveyed were more than 20 years old, and 30 percent exceeded 75 years of age. The age of plumbing systems ranged up to 56 years, with an estimated median age of 19 years. The Delta analyses were repeated in five homes to examine temporal radon-222 variation. Point-of-use household water samples were collected from either the kitchen or bathroom faucets. Collection and analyses of water samples for radon-222 analyses followed water sampling procedures and analyses protocols recommended by the EPA. Point-of-use concentrations in the 25 homes sampled ranged from 3 to 99 Bq/L (mean [+ or -] SD = 41 [+ or -] 24 Bq/L)and were significantly higher than the concentration in the concurrently sampled finished water entering the Delta water system from What Cheer (mean [+ or -] SD = 16 [+ or -] 2 Bq/L). Twenty-two of the 25 communities sampled in Delta exceeded the finished waterborne concentrations of water entering the Delta water system from What Cheer. To ascertain the source of the elevated radon concentrations, pipe-scale fragments obtained from various Delta homes were studied. Previous investigations by the University of Iowa had shown that distribution system deposits in the form of pipe scale increase waterborne radon-222 concentrations. Electron probe elemental analyses detected a preponderance of iron (83 percent) and traces of silicon and calcium. Iron oxides, which ordinarily occur in water systems, selectively scavenge other elements primarily by adsorption or co-precipitation and may bind radium. In addition, radium can adsorb and/or coprecipitate to various substances, including iron and manganese oxides. Subsequent investigation identified several members of the uranium-238 decay chain, including 10 Bq/[g.sup.-1] of radium-226 and 5 Bq/[g.sup.-1] of radon-222 progeny. This supports the authors' assertion that the distribution system scaling deposits generated an increase in waterborne radon-222 concentrations. The authors call this source of enhanced radon occurrence the "Delta Factor". It was concluded that to establish the validity of samples that represent the waterborne radon-222 exposure to consumers, sampling must be done both at the point of entry and the point of use. Also, it is recommended that all future sampling procedures include a specific sampling time at a uniform flow.

"Radium-bearing Pipe Scale Deposits: Implications for National Waterborne Radon Sampling Methods." By R. William Field, Eileen L. Fisher, and Burton C. Kross, College of Medicine, Department of Preventive Medicine and Environmental Health, and Richard L. Valentine, Department of Civil and Environmental Engineering, University of Iowa. American Journal of Public Health, April 1995.
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Author:Billings, Clayton H.
Publication:Public Works
Date:Jul 1, 1995
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