Environmental Fate of Radium in Ion-Exchange Backwash Waste Stream, and Septic-Tank Sludge and Liquids, Southern New Jersey.
Zoltan Szabo1, Eric Jacobsen1, Thomas F. Kraemer1, and Bahman Parsa2. (1) U.S.Geological Survey, 810 Bear Tavern Rd., Suite 206, West Trenton, NJ 08628, (2) New Jersey Department of Health and Senior Services, 361 Box, Trenton, NJ 08625
In 2000, the U.S. Environmental Protection Agency finalized a Maximum Contaminant Level (MCL) of 15 pCi/L (picocuries per liter) for gross alpha-particle activity and 5 pCi/L for combined radium (Ra) (sum of radium-226 (Ra-226) and radium-228 (Ra-228)). Ra-226, an alpha-particle emitter, and Ra-228, a beta-particle emitter, have sufficiently long half-lives (1,602 and 5.75 years, respectively) to accumulate on a time scale of years. Median values of naturally occurring Ra-226 and Ra-228 in about 140 water samples collected during 1997-2002 from the two major unconfined aquifer systems in southern New Jersey, the Kirkwood-Cohansey and the Potomac-Raritan-Magothy, were 1.4 and 1.9 pCi/L, respectively. Maximum values were 17.4 and 12.8 pCi/L, respectively. About 33 percent of the concentrations exceeded the MCL. These findings have led to the use of water softeners as widely available and convenient whole-house Ra treatment units for domestic well water because the units efficiently remove Ra along with constituents that cause water hardness. Maintenance includes regular backwashing of the ion-exchange media with brine. The brines commonly are flushed to septic systems. Because Ra is a known carcinogen, the fate of the Ra that is dispersed to the environment in effluent or applied to land in sludge as fertilizer is a matter of concern. Therefore, the U.S. Geological Survey, in cooperation with the New Jersey Department of Environmental Protection, is evaluating the environmental fate of the Ra that passes through residential water softeners. Water samples were collected at 15 domestic-well test sites during 2003-04 from five sampling points: the supply well (untreated ground water); kitchen (treated drinking water); the treatment system (backwash); the septic system (liquid septage); and a downgradient shallow observation well screened at the water table (effluent-bearing ground water). Solids (sludge) from the septic tank also were sampled, as were aquifer sands collected from drill cores obtained from multiple depths at adjoining locations where land application of sludge was not practiced. Results indicate that the ion-exchange treatment systems, when maintained, effectively removed Ra, lowering the gross alpha-particle activities to less than 3 pCi/L and the combined Ra concentrations to less than 1 pCi/L. These values represent at least a 10-fold reduction relative to the presence of these constituents in untreated ground water, which contained combined Ra at concentrations of less than 1 to 42 pCi/L. The Ra was re-concentrated into the backwash brine, which typically was enriched about 10- to 100-fold relative to the concentration in untreated ground water, with a maximum gross alpha-particle activity of 3,200 pCi/L and a maximum combined Ra concentration of 2,100 pCi/L. Combined Ra concentrations in the effluent in the septic tanks ranged from less than 1 to 7.0 pCi/L, about half the concentration typically found in the untreated ground water. Combined Ra concentrations in effluent-bearing water from the downgradient observation wells were similar to, or less than, those in the liquid in the septic tanks, except where sample pH was less than 5; in those cases, the combined Ra concentration was elevated (maximum, 27 pCi/L). These results indicate that Ra likely is mobilized from the aquifer matrix by effluent-bearing water in an acidic environment. The combined Ra concentration in sludge from the septic tanks ranged from less than 1 to about 10 pCi/g (picocuries per gram dry weight), about a 10-fold increase from the concentration in the sandy aquifer sediments, in which combined Ra concentrations ranged from 0.2 to 1.1 pCi/g. Analytical precision was poor for low-weight sludge samples (less than 20 grams), however. These results indicate that long-term land application of the sludge as fertilizer might result in an increase in Ra in the soils.