Use of GIS and Detailed Geomorphic Mapping to Evaluate Contaminants Dispersed by Fluvial Processes

Detailed geomorphic investigations are conducted in canyons of the Pajarito Plateau at Los Alamos National Laboratory (LANL) as part of Resource Conservation and Recovery Act facility investigations. Contaminants that include radionuclides such as plutonium-239 were discharged into the canyons in liquid effluent from radiochemistry facilities beginning in 1943, initially associated with efforts to build the first atomic bombs in World War II. These contaminants have been carried downstream by flash floods and redeposited in channels and on floodplains.

The detailed geomorphic history of flooding during the last 60 years strongly affects the distribution and potential environmental risk from these contaminants. In the field investigations, geomorphic units deposited since the initiation of LANL operations (post-1942) are delineated and mapped at a high resolution to establish a depositional history that guides sample selection. The different geomorphic units indicate differences in sediment age, sediment thickness, and contaminant concentrations. Field maps are digitized onto topographic basemaps with a contour interval of two feet, typically at a scale of 1:200. The digitized polygons are used to calculate area sums for each geomorphic unit and estimate contaminant inventories. The contaminant inventory helps guide focused risk assessments, evaluate remediation alternatives, and develop models for potential impacts of future contaminant transport.