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Full report

• SSR106 - Groundwater seepage from the Ranger uranium mine tailings dam: Radioisotopes of radium, thorium and actinium (PDF 2.6 MB)

Separate sections

• Preliminary pages (PDF - 204 KB)
• Table of contents (PDF - 144 KB)
• Chapter 1 - Introduction (PDF - 221 KB)
• Chapter 2 - Examination of the existing borewater data (PDF - 310 KB)
• Chapter 3 - Radioisotope investigations (PDF - 277 KB)
• Chapter 4 - Results and discussion (PDF - 1,170 KB)
• Chapter 5 - Conclusions (PDF - 155 KB)
• Appendices and references (PDF - 504 KB)

Abstract

Monitoring of bores near the Ranger uranium mine tailings dam has revealed deterioration in water quality in several bores since 1983. In a group of bores to the north of the dam, increases have been observed of up to 500 times for sulphate concentrations and of up to 5 times for ²²⁶Ra concentrations. Results are presented here of measurements of members of the uranium, thorium and actinium decay series in borewater samples collected between 1985 and 1993. In particular, measurements of all four naturally-occurring radium isotopes have been used in an investigation of the mechanism of radium concentration changes.

For the most seepage-affected bores the major findings of the study include:

• ²²⁸Ra/²²⁶Ra, ²²³Ra/²²⁶Ra and ²²⁴Ra/²²⁸Ra ratios all increased over the course of the study;
• barium concentrations show high seasonal variability, being lower in November than May, but strontium concentrations show a steady increase with time. Calculations show that the groundwater is probably saturated with respect to barite but not with respect to celestite or anglesite;
• sulphide concentrations are low in comparison with sulphate, and are higher in November than in May; and
• ²²⁷Ac concentrations have increased with time, but do not account for the high ²²³Ra/²²⁶Ra ratios.

It is concluded on the basis of these observations that:

• increases in Ra isotope concentrations observed in a number of seepage-affected bores arise from increases in salinity leading to desorption of radium from adsorption sites in the vicinity of the bore rather by direct transport of radium from the tailings;
• increased salinity is also causing the observed increases in ²²⁷Ac and strontium concentrations; and
• formation of a barite solid phase is occurring in the groundwater and causing the removal of some radium from solution. This is the cause of the increasing radium isotope ratios noted above.