The TS-CHEM team is pleased to announce the release of two new Microsoft Excel-based spreadsheet utilities – the SCL Plume Model, and the Plume Volume and Mass (PVM) Calculator. With straightforward inputs and intuitive numeric and graphic outputs, these tools allow environmental practitioners to quickly estimate the extent of plumes at specified points in time, and get a sense of key plume characteristics, including the volume of impacted groundwater within the contaminant plume, the mass contained within the plume, and/or the mass flux across a user-specified plume transect.
SCL Plume Model Spreadsheet
Since the mid-1980s, one of the most widely used analytical plume transport models has been what is generally referred to as the Domenico model. The Domenico model has been applied by regulatory agencies as the basis for a number of software tools (e.g., USEPA’s BIOSCREEN and BIOCHLOR; CA RWQCB spreadsheet; PADEP Quick Domenico spreadsheet), and has been widely applied and reported on in the professional and scientific literature. Beginning in approximately 2005, investigators began commenting on perceived inaccuracies in the approximate Domenico solution, and in 2007, an improved solution that maintains the efficiency of the Domenico solution, and reportedly improves on its performance was developed and published by Srinivasan et al. (2007). That efficient solution has been programmed into the SCL Plume Model spreadsheet, which can quickly generate calculated data outputs and model results charts that can assist practitioners in examining and better understanding plume behavior at their site of interest.
Input data for the SCL Plume Model include the common parameters required for an analytical plume transport model, including:
- source information (source dimensions and source concentration);
- aquifer parameters (hydraulic conductivity, horizontal hydraulic gradient, and effective porosity);
- contaminant transport parameters (dispersion, retardation rate, and degradation rate);
- time information (time at which source concentrations are to be calculated); and
- plot parameters (several inputs that control numeric and graphic model outputs).
Users can also specify a groundwater standard (which allows the user to examine where the plume concentration along the centerline drops below the specified concentration) as well as the distance to the nearest receptor (which allows the user to examine the model estimated constituent concentration at the receptor location).
The SCL Plume Model spreadsheet generates calculated data outputs (including concentrations along the plume centerline at a specified point in time) and model results charts (including a concentration vs. distance chart and plume contour chart).
Figure 1. SCL Plume Model spreadsheet interface, including model input tables, plume centerline chart, and plume contour chart
The slow dissolution of a chemical of concern (COC) from a subsurface waste zone or spill through soil into slowly seeping groundwater can form a sizeable area of downgradient contamination above some water quality standard (e.g. maximum contaminant level MCL), frequently referred to as a plume. It is often helpful in an environmental site investigation to develop certain metrics that describe properties of the groundwater plume to aid in forming a more quantitative conceptual site model. The Plume Volume and Mas (PVM) Calculator is designed as a Microsoft Excel spreadsheet-based tool that can assist site investigators with estimating key plume metrics, allowing them to easily input parameters describing the geometry of the plume as it has been mapped in the field, and then to calculate a variety of outputs, including:
- Areal extent and overall volume within the aquifer that is occupied by the plume;
- Volume of contaminated groundwater within the aquifer pore space;
- Mass of dissolved and sorbed chemical of concern in certain concentration contour zones of the aquifer;
- Overall mass of chemical in the plume; and,
- Mass flux across a user-specified transect.
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| Figure 2. Diagram of a typical groundwater contaminant plume (plan view) mapped from a horizontally spaced array of monitoring wells. |
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| Figure 3. Diagram of a typical groundwater contaminant plume (cross-section view) mapped from vertically spaced monitoring wells (e.g. shallow, intermediate, and deep intervals). |
The “field mapped” plan view and cross-sectional plume diagrams generated by the environmental investigator are used as the basis for measuring the ellipse dimensions (i.e., the length, width, and thickness for each isoconcentration contour) that form the required set of nested ellipsoid data to be input into the PVM Calculator.
Figure 4. Nested ellipsoids calculated by the PVM Calculator based on user-specified inputs.
In addition to entering estimated dimensions for each plume isoconcentration contour interval, the user can also specify parameters for the constituent of concern (including the name of the chemical and its associated density) and aquifer properties (including hydraulic conductivity, horizontal hydraulic gradient, and effective porosity). The user can also specify a location along the plume at which mass flux is calculated through a vertical plane (i.e., YZ plane) that is oriented perpendicular to the X direction of groundwater flow.
Based on the user-specified inputs provided, the PVM Calculator estimates the following for each isoconcentration contour interval:
- area
- volume
- dissolved and sorbed chemical mass
- chemical volume
These plume metrics are useful for a variety of conceptual site model development and remedy planning project steps.
The SCL Plume Model and PVM Calculator spreadsheet each include a detailed User Guide which provides a comprehensive overview of the tools, step-by-step instructions for all inputs, descriptions of the calculations that are performed, and references to literature on which the tools are based. And, the tools are available FREE of charge on the TS-CHEM website.
To learn more about the SCL Plume Model spreadsheet, or to download a copy, click HERE. To learn more about the PVM Calculator spreadsheet, or to download a copy, click HERE.
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