| Summary: | Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 1995 Much of the nuclear activity of the former Soviet Union took place within or adjacent to the confines of the Ob River drainage basin. These activities include weapons production and reprocessing at Chelyabinsk-65 (also called Chelyabinsk-40 and Mayak) and the Siberian Radiochemical Plant of Tomsk-7, nuclear weapons testing at Semipalatinsk and uranium mining and milling on the Ishym River. These sites have been the locations of accidental and planned releases of major amounts of radioactive materials since the dawn of the nuclear era. More important, these sites contain vast amounts radioactive waste, in storage, released to the environment, and injected into geologic formations at relatively shallow depth. In total there is thought to be on the order of 2.5 billion curies of radioactive materials presently located within the Ob River basin. Since the Ob is one of the largest rivers flowing into the Arctic, there has been considerable concern over past delivery of radioactive contaminants to the Arctic and the potential for much larger future releases. This project was initiated as part of the Arctic Nuclear Waste Program (ANWAP), administered through the Office of Naval Research, to attempt to characterize the time history of radioactive contaminant transport in the Ob River and to identify the sources of those contaminants. The project has focused on the use of sediment cores to define the distributions of the particle reactive isotopes Cs-137, Pu-239,240, and Pu-238 with depth in sediments. To preserve a temporal record, the sediments need to be deposited more or less continuously and to not be subject to mixing. Meeting these criteria led to a focus on sampling in the shallow "sor" and oxbow lakes that are abundant in the flood plain of the Ob delta as sources of undisturbed sediment. To gain access to the lakes on the ...
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