A Modified Mise‐A'‐La‐Masse Method for Contaminant Plume Delineation

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Abstract
Ground‐water monitoring to delineate contaminant plumes in complex hydrogeologic settings often is uncertain. This uncertainty is manifested by the fact that ground‐water contaminants often migrate along preferred pathways formed by lateral and vertical heterogeneity within definable stratigraphic units. A somewhat obscure surface, electrical geophysical method first suggested in 1920 holds great promise as a tool to help delineate conductive contaminant plumes in suitable hydrogeologic environments. This tool known as the mise‐a'‐la‐masse method has been used with success by other investigators to map conductive orebodies.A modified mise‐a'‐la‐masse method was used with great success in this investigation during a controlled field experiment. The method was used to track the evolution of a conductive tracer plume migrating through fluvial sands and gravels under a forced hydraulic gradient. Voltage differences between 171 stationary, surface electrodes and a reference electrode were monitored over time to map an evolving tracer plume. For this particular experiment, the method proved to be sensitive to changes in the specific electrical conductance of the ground water of less than 10% above the baseline values. Data derived by the modified mise‐a'‐la‐masse method show close agreement to specific electrical conductance measurements of ground‐water samples collected from wells during the tracer experiment. However, uncertainty in the significance of the variable specific electrical conductance data, especially at early times during the experiment, is reduced greatly by comparison with the plume maps generated by the modified mise‐a'‐la‐masse method.