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Overview of RBCA Tier 2
Analyzer
The RBCA Tier 2 Analyzer utilizes an innovative
analytical flow solution for fast and easy modeling of
complex groundwater flow systems it provides a rigorous
treatment of the many complex reactions and processes
involved with the biodegradation of contaminated
groundwater. These two features make it the ideal
software package for applications including:
- Simulating natural attenuation of contaminated
groundwater,
- Evaluating groundwater pump-and-treat remediation
systems, and
- Predicting downstream impacts for risk assessment
studies
Expert System Advantages
It is a
well-known fact that the two biggest challenges of
modeling natural attenuation processes are:
- Finding reliable references for the many different
input parameters required by the model, and
- Waiting for the simulation to finish calculating.
The RBCA Tier 2 Analyzer addresses both of these
problems by providing an on-line expert system with
published parameter values and references for many
different soil conditions and common chemicals of
concern. In addition, the RBCA Tier 2 Analyzer uses a
powerful and innovative solution method that allows you
to solve complex models involving biodegradation of
multiple chemical species in a matter of minutes! Try
that with RT3D and you could be waiting for hours.
Imagine the time you could save on just your first
project alone!!
The Flow Model
The analytical flow model
allows the user to account for complex boundary
conditions representing pumping wells and injection
wells, flow boundaries, rivers and lakes with complex
geometries, and regional hydraulic gradients. The
analytical flow model is based on the super-position of
the Dupuit-Forchheimer solution for flow to one or more
wells with the effects of a regional hydraulic gradient
(Bear, J. 1979. Hydraulics of Groundwater. New York:
McGraw-Hill). This analytical solution is capable of
simulating complex model boundaries and 'leaky' boundary
conditions by using an iterative solution that
dynamically links the hydraulic impacts of the wells
and/or water body(s) on the aquifer. Modeling results
include heads, velocities and pathlines for determining
well capture zones and groundwater travel times.
The Plume Generator
The initial condition
plume generator provides the user with the capability of
generating physically realistic distributions of
contaminant plumes and electron acceptors using real
field measurements. The automatic plume generation
program utilizes the super-position of multiple Gaussian
plumes along a user-specified centerline. This
interpolation technique is ideally suited for sparse,
highly-variable data such as groundwater contamination
measurements, and it ensures a concentration
distribution consistent with observed groundwater flow
patterns. Initial concentration distributions can also
be imported from Surfer Grid (.grd) files.
The Transport Model
The RBCA Tier 2
Analyzer solves for advective-dispersive contaminant
transport with equilibrium/non-equilibrium sorption and
complex decay reactions. Five different contaminant
transport scenarios are provided:
- Single constituent
- Sequential decay of PCE due to reductive
dechlorination
- BTEX biodegradation (instantaneous decay with a
single electron acceptor)
- BTEX biodegradation (instantaneous decay with
multiple electron acceptors)
- BTEX biodegradation (kinetic-limited decay with
multiple electron acceptors)
The RBCA Tier 2 Analyzer is also the first
commercially-available model to incorporate the physics
of multi-site, rate-limited partitioning of chemical
mass between soil and groundwater. Rate-limited
desorption (RLD) of organic contaminants is the most
significant limitation of pump-and-treat groundwater
remediation systems. The effects of RLD are seen in the
extended periods of low mass removal rates which were
not predicted by models using local equilibrium
sorption/desorption assumptions. Now, for the first
time, you have a modeling software package that allows
you to account for and predict the effects of RLD
desorption on groundwater extraction systems.
The RBCA Tier 2 Analyzer uses the Eulerian-Lagrangian
solution technique to solve the governing equation of
solute transport. This technique utilizes the Method of
Characteristics (MOC) for solving the advective part of
the equation, and it uses the Alternating Direction
Implicit (ADI) method for solving the dispersive part of
the equation. This combination of solution techniques
ensures the best results in the shortest time by
avoiding the numerical dispersion and small time steps
often encountered by other numerical approaches.
Output Graphics
The RBCA Tier 2 Analyzer
includes an impressive selection of graphical
capabilities for visualizing and interpreting the
modeling results. Output graphics include:
- Contouring and color shading of head and
concentration values
- Flow pathlines and velocity vectors
- Concentration time-series graphs for any location
in the model domain
Full color, high-resolution graphics of all modeling
results can be directed to any printer or plotter
supported by Windows 95/98/NT.
The images below are thumbnail images of modeling
results. | 
