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Occurrence of Radium-224, Radium-226, and Radium-228 in Water of the Unconfined Kirkwood-Cohansey Aquifer System, Southern New Jersey

By Zoltan Szabo, Vincent T. dePaul, Thomas F. Kraemer, and Bahman Parsa

U.S. Geological Survey Scientific Investigations Report 2004-5224

The body of the report is available in PDF Format ( 4,814 KB)

Abstract

Water in the unconfined Kirkwood-Cohansey aquifer system in the New Jersey Coastal Plain contains elevated concentrations (above 3 pCi/L (picocuries per liter)) of the alpha-particle-emitting radionuclide radium-224. Previously, water from the aquifer system had been found to contain radium-226 and radium-228. This observation is of concern because the previously undetected presence of radium-224 may pose an additional, quantifiable health risk that currently is not accounted for by the Maximum Contaminant Level (MCL) of 5 pCi/L for combined radium (the sum of radium-226 plus radium-228 is termed "combined radium") in drinking water.

Water samples were collected from a regional network of 88 wells for determination of concentrations of radium-224, radium-226, and radium-228; gross alpha-particle activity; and concentrations of major ions and selected trace elements. Both gamma and alpha spectroscopic techniques were used to determine concentrations of radium-224, which ranged from <0.5 to 16.8 pCi/L (median 2.1 pCi/L, interquartile range 1.2-3.7 pCi/L). Concentrations of radium-226 and radium-228 in the same samples ranged from <0.5 to 17.4 pCi/L (median 1.7 pCi/L, interquartile range 0.9-2.9 pCi/L) and <0.5 to 12.8 pCi/L (median 1.6 pCi/L, interquartile range, 0.9-2.6 pCi/L), respectively. Concentrations of radium-224 typically were greater than those of the other two radium radionuclides, as evidenced by the highest median, third quartile, and maximum concentrations, as well as the highest concentration among the three radium radioisotopes in 52 (59 percent) of the 88 samples.

Concentrations of 5.0 to 5.5 pCi/L of radium-224 result in a gross alpha-particle activity of about 15 pCi/L (the MCL) 36 to 48 hours, respectively, after sample collection when ingrowth of radium-224 progeny radionuclides is considered, even with the unlikely assumption that no other alpha-particle-emitting radionuclide is present in the water. Concentrations of 3.4 to 3.7 pCi/L radium-224 result in a gross alpha-particle activity of 10 pCi/L 36 to 48 hours, respectively, after sample collection when ingrowth of Ra-224 progeny radionuclides is considered. In this latter case, it is possible that the summed alpha-particle activity from radium-226 present at a concentration less than or equal to 5 pCi/L (the MCL for combined radium) and from radium-224 present at a concentration about 3.4 pCi/L or greater may exceed the 15-pCi/L MCL for gross alpha-particle activity. In this study, gross alpha-particle activities were measured within 48 hours after sample collection and were found to exceed the MCL of 15 pCi/L in nearly half (43) of the 88 samples collected. The concentration of radium-224 exceeded that of radium-226 in 55 (62.5 percent) of the 88 samples.

Concentrations of radium-224 correlate strongly with those of both radium-226 and radium-228 (Spearman correlation coefficients r=0.74 and 0.91, respectively). Concentrations of radium-224, radium-226, and radium-228 were greatest in the most acidic ground water. Concentrations of radium-224 and combined radium-226 and radium-228 in samples of ground water with pH less than 4.7 exceeded 5 pCi/L in 33 and 67 percent of the samples, respectively. Concentrations of radium-224, radium-226, and radium-228 (measured separately) were greatest in water from the southern part of the aquifer outcrop area. In water from the northern part of the aquifer system outcrop area, radium-224 concentrations were as high as 3.6 pCi/L, and concentrations of combined radium and gross alpha-particle activity in some samples exceeded their respective MCLs.

The presence of gross alpha-particle activities greater than 15 pCi/L and combined radium-226 and radium-228 concentrations greater than 5 pCi/L in the southwestern part of the aquifer system outcrop area is common and had been documented before 1997. Results of this study confirm these earlier findings. In northeastern and southeastern parts of the aquifer outcrop area, gross alpha-particle activities exceeded 15 pCi/L only in isolated areas (primarily central Ocean County and southeastern Atlantic County) but with greater frequency in this study (when the 48-hour holding time for gross alpha-particle activity analysis was used) than in previous investigations (before 1997), indicating that radium-224 contributes considerable gross alpha-particle activity to drinking water produced from the aquifer system.

Table of Contents

Abstract

Introduction

Purpose and Scope

Study Area

Hydrogeologic Setting

Land Use

Previous Investigations of Radionuclide Occurrence in the Aquifer System

Methods

Design of Sampling Network and Sampling Procedures

Quality-Assurance Program

Analytical Methods

Radium-224

Radium-226, Radium-228, and Ancillary Constituents

Reporting of Radionuclide Concentrations

Land-Use Classification and Statistical Analysis

Occurrence of Radium-224, Other Radionuclides, and Gross Alpha-Particle Activity

Radium-224

Radium-226 and Radium-228

Gross Alpha-Particle Activity

Quality-Assurance Results

Factors Affecting Distribution of Radium-224

Other Radioactive Constituents

pH

Geography

Nitrate

Land Use

Effects of Improvements in Analytical Protocols on Measured Distributions of Radioactive Constituents

Contribution of Recently Detected Radium-224 to Gross Alpha-Particle Activity

Summary

Acknowledgments

References Cited

Appendixes

  1. Selected well-record information for wells used to measure radioactive constituents in water from the Kirkwood-Cohansey aquifer system, southern New Jersey, 1997-99
  2. Results of analyses for radionuclides, major ions, and selected trace elements in quality-assurance blank samples from the Kirkwood-Cohansey aquifer system, 1997-99
  3. Concentrations of radionuclides in water samples from the Kirkwood-Cohansey aquifer system, southern New Jersey, 1997-99
  4. Concentrations of inorganic constituents in, and physical properties of, water samples from the Kirkwood-Cohansey aquifer system, southern New Jersey, 1997-99

Glossary


 

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Richard Kropp, Director

U.S. Geological Survey

New Jersey Water Science Center

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