Hydrogeology of the 100-N Area, Hanford Site, Washington

Abstract

Hydrogeologic units beneath the 100-N Area include the vadose zone (primarily Hanford formation). The unconfined aquifer (upper Ringold Formation), a series of confined aquifers in the Ringold Formation, and a series of confined aquifers in the basalts and interbeds. The uppermost aquifer is an unconfined sand and gravel unit in the Ringold Formation. It is 40 to 50 ft thick. The base of the aquifer is a series of fine-grained units in the Ringold Formation. Groundwater flows toward the Columbia River beneath most of the 100-N Area, except when river stage is high for extended periods of time. Groundwater chemistry has been affected by 100-N Area operations. Primary constituents of interest include: (1) {sup 90}Sr and tritium associated with the 1301-N and 1325-N sites, (2) sulfate and sodium associated with the 1324-N/NA site. and (3) petroleum products associated with leaks and spills between the N Reactor building and the river. Radionuclides are detectable in water flowing into the Columbia River from N-Springs. The most significant constituents in spring water are tritium-and {sup 90}Sr. Concentrations of these constituents have declined since 1987. These constituents have also been detected in river water immediately adjacent to the 100-N Area, but are rapidly dilutedmore » below detection limits.« less