Dual Geophysical Data Set Interpretation For Landfill Plume Delineation

A contaminant plume containing high concentrations of Dense Non-Aqueous Phase Liquids (DNAPLs) and<br>inorganic contaminants emanates from the Bannock County Landfill, in Fort Hall Canyon, Idaho. These DNAPLs<br>and inorganics have been detected in nearby domestic and municipal water supply wells in an alluvial fan aquifer.<br>The alluvial fan aquifer is underlain by cemented, fluvial gravels. A surface electrical field survey was conducted<br>down gradient from the Bannock County Landfill to help delineate the extent of the plume. The field site is<br>relatively free of cultural interference that would adversely affect electrical-potential fields. Data collected during<br>the survey were correlated with seismic refraction data.<br>The mise-a-la-masse method for plume delineation was utilized for this investigation. The method is much easier to<br>use and data interpretation is less subjective than other electrical methods; however, it does not yield depth<br>information. The mise-a-la-masse method was used successfully to identify electrical-field anomalies near the<br>Bannock County Landfill. The seismic refraction method was used to determine depth to the subsurface structure.<br>The seismic refraction survey suggested that three buried channels exist beneath the site.<br>The electrical-field map correlates very well with the seismic data in those areas where the data sets coincide. Most<br>electrical-field highs are located above areas interpreted seismically as buried channels or basins. These features<br>may provide preferential flow paths for the contaminated groundwater and DNAPLs.