Mechanisms for surface contamination of soils and bottom sediments in the Shagan River zone within former Semipalatinsk Nuclear Test Site

•Concentrations of artificial radionuclides have been determined in the Shagan River bottom sediments.•Concentrations of artificial radionuclides have been determined in the soils of the Shagan River Valley.•Concentrations of artificial radionuclides have been determined in the shoreline soils of the Shagan River.•Sources and mechanisms of radioactive contamination of the soils, bottom sediments and shoreline soils have been determined.

The Shagan River is the only surface watercourse within the former Semipalatinsk Test Site (STS). Research in the valley of the Shagan River was carried out to study the possible migration of artificial radionuclides with surface waters over considerable distances, with the possibility these radionuclides may have entered the Irtysh River. The investigations revealed that radioactive contamination of soil was primarily caused by the first underground nuclear test with soil outburst conducted at the “Balapan” site in Borehole 1004. The surface nuclear tests carried out at the “Experimental Field” site and global fallout made insignificant contributions to contamination. The most polluted is the area in the immediate vicinity of the “Atomic” Lake crater. Contamination at the site is spatial. The total area of contamination is limited to 10–12 km from the crater piles. The ratio of plutonium isotopes was useful to determine the source of soil contamination. There was virtual absence of artificial radionuclide migration with surface waters, and possible cross-border transfer of radionuclides with the waters of Shagan and Irtysh rivers was not confirmed.