Comprehensive Geophysical Investigation over a Former Radioactive Waste Site, Hanford, Washington

Several geophysical methods were combined to characterize a technetium-99 (Tc-99) plume beneath a former radioactive waste site, including a magnetic gradiometry survey, a broadband multi-frequency electromagnetic survey and a high resolution resistivity (HRR) survey. The 50 acre site was previously used for the disposal of fission products formed during uranium processing, where high volumes of liquid mixed waste were discharged to unlined trenches over a two year period from 1956 to 1958. The magnetic and electromagnetic surveys identified buried infrastructure used during the construction of the disposal site. The HRR survey, which consisted of electrical resistivity measurements along transects parallel and perpendicular to a trench in the southern portion of the site, identified an electrically conductive plume coincident with Tc-99 data obtained from a nearby borehole. The data were used to confirm assumptions used in an unsaturated flow model, including recharge and hydraulic properties.