RADIONUCLIDES IN GROUNDWATER IN NOVA SCOTIA - PRELIMINARY RESULTS FROM A PROVINCE-WIDE TESTING PROGRAM

The weathering of naturally-occurring radionuclides in soil and rock can produce elevated levels of radionuclides in ground and surface waters used for drinking water supplies. The Guidelines for Canadian Drinking Water Quality have Maximum Acceptable Concentrations (MAC) for 14 naturally-occurring radionuclides, most of which are daughter products of the uranium and thorium decay series.

The presence of elevated concentrations of naturally-occurring uranium in groundwater in Nova Scotia was first identified in 1978. In response to this discovery, the Provincial Uranium Task Force was formed to investigate the occurrence of uranium in drinking water supplies. The investigation included testing of more than 700 water wells for uranium and two of its daughter products, radium-226 and radon-222. The results indicated that uranium commonly occurs in drilled wells at concentrations exceeding 0.02 mg/L, which is the current MAC for uranium. The occurrence of uranium was found to depend on bedrock type, with two bedrock types in Nova Scotia being identified as most likely to have groundwater with elevated uranium levels: 1) granite batholiths, and 2) sandstone and shale of the upper Carboniferous sedimentary basin.

In 2002, an environmental assessment of a school in Hubley, Nova Scotia identified lead-210 above the MAC in the school’s water well. Lead-210 is a daughter product of the uranium series which was not previously tested for in groundwater in Nova Scotia. As a result, an inter-governmental Special Well-Water Advisory Group was formed and a Province-wide groundwater testing program was initiated. The program involved sampling well water at 178 schools across the Province. The samples were analysed for total uranium, lead-210 and radium-226.

The preliminary results of the 2002 testing program identified 17 of 178 wells exceeding radionuclide guidelines. Of the 17 exceedances, 16 exceeded for lead-210, three exceeded for total uranium and lead-210, and one exceeded for total activity. The range of lead-210 concentrations for the 16 samples exceeding the MAC was 0.12 to 0.65 Bq/L, compared to the MAC of 0.1 Bq/L. These results indicate that lead-210 can occur above the MAC in well water in Nova Scotia and that lead-210 can be a concern even if uranium concentrations are below guidelines.