Visual Analysis Tool for Plume Behavior Assessments

Groundwater trend analysis for the purposes of demonstrating plume behavior has many facets. Wilcox has developed this radial trend tool (RaTT) using Microsoft Excel as a means to incorporate the analysis of the four common chlorinated volatile organic compounds (cVOCs) – tetrachloroethylene (PCE); trichloroethylene (TCE), cis-1,2-dichloroethylene (Cis), and vinyl chloride (VC) – into a single visual aid. An example of the RaTT is shown in Figure 1, and details of the RaTT construction are as follows.

  • Each cVOCis plotted within a dedicated quadrant of the graph.
  • Groundwater concentrations are normalized to the respective residential tap ground water screening levels (RTGWSLs).
  • The time-series data are plotted radially at regular intervals on a log scale. The innermost radial gridline corresponds to the RTGWSL for each constituent. Each progressive gridline moving outward represents an order-of-magnitude concentration increase relative to the RTGWSL.
  • The color coding of each plot corresponds to Mann-Kendall trend analysis results with red, yellow, and green corresponding to increasing, no trend, or decreasing trend results, respectively.
  • Residential and commercial vapor intrusion groundwater screening levels (VIGWSLs) for each constituent, normalized to their respective RTGWSL, are plotted as purple and blue dashed lines, respectively. Additional target concentrations can be incorporated as needed.

The RaTTdiagram quickly provides the following information for the four cVOCs:

  • Concentration changes in time.
  • Magnitude of concentrations relative to the RTGWSL.
  • Magnitude of concentrations relative to VIGWSLs or other target concentrations.
  • Mann-Kendall analysis results.

The plots can also be included on plume maps as part of a spatial variability analysis.