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U.S. Department of Energy
Reactive Transport in 3-Dimensions

rtFlux Utility

Figure: Relative Mass Flow Through a Plane

Depiction of Mass Flow Through Grid Cells – The quantity of mass passing through a grid cell is a function of volumetric flow rate and concentration in that cell.

A flux plane software utility called rtFlux was developed as a Microsoft Excel-based pre- and post-processor for a RT3D simulation.  The rtFlux utility provides a method for the user to determine the mass flow of chemical species across one or more grid-orthogonal planes over time.  Mass flow results are presented as time series plots and as plots showing the spatial distribution of the relative mass flow terms for a given plane.

Flux planes of interest are defined as rectangular regions that are orthogonal to the model grid (i.e., the plane is aligned parallel to a row, column, or layer of the model grid).  The pre-processing step incorporates the flux plane definitions into the RT3D input files.  After running RT3D, the output files are processed by the utility to generate three graphs that describe the mass flux across the plane.  The first plot shows the time-varying mass flow rate (e.g., kg/day) of each chemical species passing through one of the defined planes.  The second plot depicts the cumulative mass that has passed through a plane over time.  The third plot generated from the rtFlux utility is a bubble plot depicting the relative volumetric flow rate, species concentration, or mass flow rate through a plane at each grid cell in the plane.  This bubble plot shows the location where the highest mass flux impacts occur, whether due to high volumetric flow rate or a high concentration (or combination of both).

Figure: Time-varying mass flow plot

Example Time-Varying Mass Flow Rate Plot – The user may select which species and which plane to view (including all at once) via drop-down selection lists.

Figure: Relative Mass Flow Through a Plane

Example Bubble Plot Showing the Relative Magnitude of Mass Flow Rate for a Specified Plane at a Particular Time Point in the Simulation (can also view Flow and Concentration)

The bubble plots are convenient for assessing the spatial distribution of volumetric flow, concentration, and mass flow within a plane.  The figure below shows an example of bubble plots for all three parameters.  Based on the plot of flow (top left), there is a confining unit at the top of the plane and there is a higher permeability unit at the bottom.  Concentration is coming through the center plane, with a relatively even distribution with depth.  Thus, the mass flux is highest at the bottom center where the high concentration and high flow rate intersect.

Example Plots for Volumetric Flow, Concentration, and Mass Flow Through a Plane – These plots help the user discern the spatial location of the highest mass flow and the importance of the flow field and concentration components.

The rtFlux utility can provide the information to compare two remediation scenarios.  For example, one could evaluate natural attenuation processes (no active remediation) versus installation of a pump-and-treat (P&T) system to intercept the bulk of the contaminant plume.  In this example, the P&T system is operated for 25.5 years, then the residual plume is allowed to naturally attenuate.  The plot of mass flow and cumulative mass across a plane of interest shows the impact of the P&T system in reducing the mass flow and the total mass of contaminant that must be dealt with via natural attenuation processes.

Figure:  Plot of Time-Varying Mass Flow for Two Remediation Scenarios

Mass Flow Rate and Cumulative Mass to Pass Through a Plane for Two Remediation Scenarios – In one case no action is taken (natural attenuation only) and in the other P&T is applied.  In both cases, the non-aqueous phase liquid source was removed.

The rtFlux software is available on the downloads page.  The rtFlux documentation discusses how to install and use the rtFlux software, the calculations that are performed, and gives some examples of the application of the rtFlux utility.  Note that while designed for use with RT3D, the rtFlux utility can also be used with MT3DMS simulations (with a simple change of select output file names).

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