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As a result
of the Chernobyl nuclear power plant (ChNPP) accident on April 26, 1986 huge
amounts of radioactive materials were ejected into the environment. The level of
radiocesium (Cs ) 137 and radiostrontium (Sr ) contamination at land surface in
the immediate vicinity of the Chernobyl site 90 reached dozens of mBq/m . The
most highly contaminated area is the 30 km Exclusion Zone 2 surrounding the
reactor (OECD, 1995). Within the Exclusion Zone, Sr is spatially well-correlated
90 with Cs contaminant concentrations. According to a hydrogeological study of
groundwater 137 contamination in the 30 km CEZ, Sr may contaminate drinking
water above acceptable limits for 100 90 years, or more (OECD, 1995).
By the summer
of 1987, the radioactive contamination products, including the short-lived Cs ,
144 Ru , and Cs from the ChNNP accident were detected in trace amounts in water
sampled from 106 134, shallow wells (Quaternary aquifers) and boreholes within
the Chernobyl Exclusion Zone. More recently, data generated by the
Radioecological Center, NAS of Ukraine show the presence of radionuclides, of
Chernobyl origin, within the principal aquifers that are being exploited for
potable water supplies in the Ukraine (Bublias, et al., 1999). Cs and Sr of
Chernobyl origin were found in 137 90 the confined aquifers both near the
Chernobyl site and in the Kiev city water intake that supplies potable water to
city and surrounding residents (Shestopalov, et al., 1999).
Prior to the
accident, it was generally accepted by the majority of then-Soviet Union
radioecologists, hydrologists, and hydrogeologists, that radionuclide subsurface
water pollution hazards were negligible for these aquifers because they were in
a highly protected water reserve. However, with new evidence of deeper
subsurface migration of Chernobyl-derived radionuclides, there is renewed
concern regarding the transport phenomena and associated impact on drinking
water quality and human health. The latest data from rock samples from the wells
within the contaminated area obtained at the end of 1998, indicate that the
total amount of radionuclide contamination in the upper 100 m of the subsurface,
the most soluble fraction, is between 20% to 30% of the total amount of
radionuclide accumulation in the soils during the active stage of the accident
(personal communication with Igor P. Onishchenko, Radioecological Center,
National Academy of Sciences of Ukraine). |
