Targeted 3D Plume Analyses: Assessing Boundary Control on Large Complex Sites

Boundary control of dissolved-phase groundwater plumes can be assessed by examining the concentration changes in individual wells, but these trends can be difficult to interpret, especially for large sites, since their evolution in three-dimensions (3D) over time is complex. A more descriptive and comprehensive plume stability characterization method is designed to address this complex issue, by advancing the 2D moment analysis found in the Monitoring And Remediation Optimization System (MAROS) software (GSI, 2012). This new method examines changes over time in the overall mass, the migration of the center of mass, and the dispersion of mass in 3D. The new method leverages the 3D volumetric interpolation capabilities of Earth Volumetric Studio (C Tech, 2018) with Python automation to interpolate and calculate mass distributions of years of sample concentrations using thousands of wells. This method is used on subareas of a large Superfund site in California to assess the effectiveness of boundary control of migration of multiple analytes. The results of these subarea plume stability analyses are confirmed by separate mass flux analyses. The method has been approved by the EPA and provides an additional line of evidence to assess the adequacy of the boundary control system for meeting site objectives.