Exploratory studies of the effect corrosion control strategies on radium accumulation in distribution system deposits and radon release into drinking water

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Project Period: 
1994
Project Investigator(s): 
RL Valentine, J Jackson, Department of Civil and Environmental Engineering, The University of Iowa
Abstract: 

Strategies used to control lead and copper corrosion often produce insoluble surface coatings on distribution system pipes. Changes in overall water chemistry resulting from treatment alterations could have a major impact on the nature of distribution system deposits. Increased incorporation of radium could occur resulting in an increase in radon in the distribution system. This study explored the incorporation of radium into and radon release from deposit material formed when several corrosion control strategies used in water distribution systems are implemented. Phosphate containing coatings and deposits are a concern because phosphate bearing minerals can accumulate large amounts of radium. Of particular interest is determining the radium content of deposits under experimentally difficult conditions where small amounts of deposits are formed and little radium is actually removed from the water, but where the amount of radium per unit mass of deposits could be very high. Experimental results conclude: 1) Radium activity of pure calcium carbonate was much lower than the solid produced when either iron or zinc phosphate was added. The removal mechanism appears to be surface adsorption; 2) Addition of zinc phosphate greatly reduced the quantity of solids produced in the presence of calcium; 3) Radium removed from water when iron was added with zinc phosphate was significantly greater than that obtained with iron only; 4) Presence of calcium reduced radium removal from solution in the presence of iron and greatly increased the mass of deposit formed when phosphate was no present; 5) Percentage of radium removed from solution using orthophosphate in the presence of iron was approximately the same as that obtained using zinc phosphate at comparable dosages as phosphate; 6) Contrary to what might be expected from a cation sorption mechanism, the radium activity per unit mass of solid actually decreased as the pH increased; and 7) Results indicate zinc phosphate in the presence of 160 mg Ca/L and phosphate significantly increased radium accumulation.

Publications: 

Field RW, Fisher EL, Valentine RL, Kross BC; Radium bearing pipe-scale deposits: implications for national waterborne radon sampling methods. American Journal of Public Health. 1995; 85(4):567-570

Fisher EL, Fuortes L, Valetine RL, Mehrroff M, Field RW; Dissolution of 225Radium from pipe-scale deposits in a public water supply. Environment International. 2000; 26(1-2):69-73