For presentation at the 46^th Annual Conference on Bioassay , Analytical, and Environmental Radiochemistry

November 12-17, 2000

Seattle, Washington

Investigation Of Factors Contributing To The Presence Of Unsupported Lead-212 In Acidic Drinking Water Supplies, Southern New Jersey

Bahman Parsa, William K. Nemeth, Reynaldo Obed, New Jersey Department of Health and Senior

Services, Box 361, Trenton, NJ 080625-0361: Zoltan Szabo, Vincent T. dePaul, U.S. Geological

Survey, 810 Bear Tavern Rd., W. Trenton, NJ 08628; and Nancy Stanley, New Jersey Department

of Environmental Protection, Bureau of Environmental Radiation, Box 415, Trenton, NJ 08625-0415

The U.S. Environmental Protection Agency is in the process of promulgating a final Maximum Contaminant Level (MCL) for gross alpha-particle activity of 15 picocuries per liter (pCi/L) and for radium-226 (Ra-226) plus radium-228 (Ra-228) of 5 pCi/L in community drinking-water supplies. Investigations regarding the development of compliance monitoring guidelines for gross alpha-particle activity have demonstrated the presence of unsupported short-lived radionuclides, such as radium-224 (Ra-224, half-life 3.66 days) and lead-212 (Pb-212, half-life 10.64 hours), both of which contribute to gross alpha-particle activity, especially in water from acidic aquifers. The concentration of

Pb-212 in ground water is mostly supported by Ra-224, but in some cases is unsupported (decaying at the rate of 10.64 hours with no ingrowth from parent) within some distribution systems. As part of its Drinking Water Initiative, the U.S. Geological Survey (USGS), in cooperation with the New Jersey Department of Health and Senior Services (NJDHSS) and the New Jersey Department of Environmental Protection (NJDEP), have investigated the factors contributing to the presence of unsupported Pb-212. A monitoring scheme was developed for acidic (pH less than 5) waters in areas with known high concentrations of radium in unconfined Coastal Plain aquifers requiring concurrent (within about an hour) samples from the well head, the point of entry, treatment effluent (if applicable). and the distribution system. Samples were analyzed in the laboratory for the concentrations of gross alpha-particle activity and unsupported Pb-212 (by gamma spectroscopy) within 8 hours of sample collection; concentrations of Ra-224, Ra-226, and Ra-228 were also determined. A field assessment using a portable alpha scintillometer was made of the presence of radon-220 (Rn-220, half-life 56 seconds), the immediate decay product of Ra-224.

Information pertaining to the drinking water supply system was gathered including well depth and age, aquifer characteristics, pH, pumping rate and duration, water treatment, age of distribution pipes, and distance of distribution pipes, and distance of distribution system samples from the well head and the water-treatment infrastructure (if present).

Initial results from 19 systems in the ongoing study indicate that the concentration of unsupported Pb-212 (maximum concentration 24 ± 2) was always greatest at the point-of-entry to, or in, the distribution system of the water supplies. Three potential factors may contribute to the presence of unsupported Pb-212 in the distribution system. These are:

The presence of Rn-220 in water, which generally corresponds to the presence of

Pb-212:

The water-treatment process where adsorption or ion exchange is utilized for

removal of radium or other cations from water. The inert gas Rn-220 appears to

be released into effluent from the bound Ra-224 and ultimately decays to unsupported Pb-212; and

The age and condition of water-distribution pipes; unsupported Pb-212 was not

noted where pipes were new. Scale build up through time likely contains adsorbed Ra-224 that can release Rn-220 into water in the distribution system, ultimately resulting in the presence of unsupported Pb-212.

Additional monitoring of the concentrations of short-lived radionuclides at the community water-supply systems with concentrations of unsupported Pb-212 of

5 pCi/L or high are needed to estimate the relative importance of each of the above three factors.