The mass balance paradigm is an important new approach to evaluating Monitored Natural Attenuation (MNA) at chlorinated solvent sites. By using the mass balance approach, site managers can demonstrate that the assimilative capacity of a particular system is either capable (or incapable) of managing the mass flux of chlorinated solvents emitted from a source zone. In addition, a detailed mass balance at a site can provide valuable insight on:
However, the mass balance approach can be difficult to apply at sites with current solute transport models, particularly numerical models.
Most numerical models do not:
The BIOBALANCE Toolkit was developed to address these shortcomings. Other notable developments incorporated in BIOBALANCE include:
The toolkit comprises of the following modules:
Source Module: The source module uses simple mass balance models to provide estimates of the reduction in Remediation Time Frame (RTF) for a given amount of source depletion. The module has the capacity to address the impact of different remediation strategies on the source mass and the mass flux from the source (e.g. reducing flux via a permeable reactive barrier, or reducing source mass from a source depletion technology). Both vadose zone and submerged sources can be modeled.
Competition Module: This module calculates how mass flux of competing electron acceptors such as dissolved oxygen, nitrate, and sulfate into the source zone translates into lost electron donor capacity. The impact of ferric iron reduction and methane generation is also included in the mass balance.
Donor Module: Users can estimate the sustainability of a source zone based on either NAPL composition data or dissolved constituent data. In this module, stoichiometric relationships are used to calculate the ratio of electron donor to the chlorinated solvent present in the source zone.
Plume Module: This module helps predict the benefit of remediation strategies on plume length and mass flux. Plume length vs. time and mass flux vs. distance curves are generated using an analytical groundwater model. The relative contribution of natural attenuation processes such as dispersion, sorption, degradation, and source decay to mass flux are calculated and presented in a graphical format.
Final Mass Balance: Key mass balances on solvents, donors, and competing electron acceptors over the lifetime of the source are integrated and presented. The spreadsheet tool uses hydrogeologic, geochemical, and contaminant data that are typically generated from MNA projects at chlorinated solvent sites to simulate the long-term behavior of sources at these sites.
Limited technical support is available from David Adamson.
The Biobalance Toolkit model requires a computer system capable of running Microsoft® Excel (2000/XP) for Windows (2000/XP) and Microsoft Word for Windows (2000/XP), and reading Adobe Acrobat pdf documents. Operation requires an IBM-compatible PC equipped with a Pentium or later processor running at a minimum of 450 MHz. A minimum of 256 MB of system memory (RAM) is strongly recommended. Computers not meeting these recommendations will experience slow running times and/or problems with memory.
The BioBalance Toolkit is not compatible with Excel 2007.
Unzip all the files to the same folder. The zipped files contain the BioBalance Toolkit spreadsheet, associated word and pdf files, the help file, and the User’s Manual.
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