Geology of the Separation Areas, Hanford site, South-Central Washington

Abstract

The major geologic units beneath the Separation Areas are: basement rocks of undetermined origin, the Columbia River Basalt Group with intercalated sediments of the Ellensburg Formation, the Ringold Formation, and the glaciofluvial sediments (Hanford Formation). A loess deposit (early Palouse soil) occurs between the Ringold and Hanford formations in parts of 200 West Area. The surface of the Separation Areas is veneered with loess and sand dunes of varying thickness. The sediments of the Hanford Formation are the most significant geologic unit in the transport and sorption of radionuclides from surface and near surface waste storage facilities. The Hanford sediments in the Separation Areas effectively isolate and sorb most radiocontaminants (half life greater than one year) discharged to or stored in the ground due to a thick sequence of unsaturated sediments with an adequate sorption capacity. The general horizontal bedding of the Hanford sediments promotes lateral spreading of moisture and retards downward transport of radionuclides.