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SEQUENCE - for visualizing and evaluating natural attenuation
SEQUENCE Categories: visualization, natural attenuation
SEQUENCE Description
SEQUENCE for Visualizing and Evaluating
Natural Attenuation
Introduction to SEQUENCE
SEQUENCE (U.S. Patent Pending) is a revolutionary new software package that provides an innovative
approach for visualizing the effects of natural attenuation based on a modified radial diagram method. Given the
simplicity and effectiveness of this visualization approach, SEQUENCE visual aids are ideally suited for preparing presentations of natural attenuation to both technical and nontechnical audiences.
Specifically, SEQUENCE visual aids may be used to simultaneously show spatial and temporal trends for multiple
organic pollutants on one site map. For some sites, this one radial diagram map may provide the primary line of
evidence necessary to support natural attenuation as a site remedy. In addition, the unique functionality and flexibility of SEQUENCE allows for the preparation of SEQUENCE-Redox Maps which are now being used to
identify trends in geochemical indicators (including electron acceptors and metabolic by-products). These trends which are clearly identified from SEQUENCE-Redox Maps provide an important secondary line of evidence
supporting the occurrence of natural attenuation in groundwater.
Click here for background information on natural attenuation processes.
Here's How SEQUENCE Works...
SEQUENCE is based on a modified radial diagram method and may be used to plot radial diagrams representing
measured concentrations or calculated molarity values for one or more chemicals. Each radial diagram represents
chemical data corresponding to one monitoring well location and consists of multiple axes (one for each chemical)
extending radially around a uniform origin (see above figure). Each axis can plot multiple measured values thus allowing you to easily compare sampling data from multiple sampling events and/or compare downgradient
contaminant levels vs. background concentrations.
Identifying Trends in Geochemical Indicators Using SEQUENCE-Redox Diagrams
The following figure is an example of a SEQUENCE-Redox radial diagram. This diagram depicts the
concentrations of typical electron acceptors (oxygen, nitrate, sulfate) and metabolic by-products (manganese,
iron, methane) measured in groundwater. The outer data series represents background concentrations of these
redox indicators that may be measured in an aerobic aquifer. The inner data series represents the concentrations
of these redox indicators that may be measured at a monitoring well situated in a portion of the aquifer where extensive biodegradation reactions have occurred.
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The axes of a SEQUENCE-Redox diagram are aligned in the same 'sequence' that these geochemical indicators
are influenced during the biodegradation of organic compounds. For example, oxygen is the most preferred of the
available electron acceptors in groundwater because it provides the greatest amount of energy for microbial metabolism. When the oxygen has been depleted, the next electron acceptor in the sequence to be used in
biodegradation reactions is nitrate. Once the dissolved nitrate has been depleted, microorganisms in the soil will
preferentially reduce the solid manganese and iron coatings on soil particles resulting in the dissolution of manganese and iron into groundwater. As the manganese and iron in the soil become depleted, the
microorganisms will preferentially reduce sulfate during the biodegradation of the organic compounds. The most
reducing conditions during biodegradation will occur when the supply of all of these electron acceptors has been
depleted and the microorganisms begin reducing carbon dioxide in groundwater to produce methane (this process is referred to as methanogenesis).
In summary, the concentrations of the dissolved electron acceptors (oxygen, nitrate, sulfate) will decrease during
biodegradation, and the concentrations of the dissolved metabolic by-products (manganese, iron, methane) will
increase. SEQUENCE has been specifically designed with the unique graphical capabilities required to prepare these specialized SEQUENCE-Redox diagrams for analyzing the natural attenuation trends by:
- Orienting the axes of the radial diagram in the same sequence that these indicators are influenced during biodegradation.
- Specifying scale and directions for each axis (i.e., concentrations increase radially away from or towards
the origin), based on whether the indicator is an electron acceptor or a metabolic by-product.
- Plotting both the background concentrations and measured well concentrations on the same radial diagram
for a simple and quick comparison of biodegradation effects on each of these indicators.
Evaluating Degradation of Multiple Organic Contaminants
The following figure is an example of a SEQUENCE BTEX-CAH radial diagram map. This diagram depicts the
concentrations of the primary contaminants measured in the groundwater (BTEX, TCE, DCE, VC and Cl). The
outer data series (indicated by the purple line) represents the concentration levels for each of these contaminants
as they are measured at the source of contamination. The inner data series (indicated by the red line) represents
the concentrations of these contaminants measured at the monitoring wells located downgradient from the contaminant source.
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These diagrams, when plotted on a site map, clearly demonstrate decreasing concentrations of BTEX, TCE and
DCE downgradient of the contaminant source. This trend of decreasing contaminant levels provides a defensible
primary line of evidence that natural attenuation processes are actively degrading the contaminant levels in the
groundwater. In addition, the increased concentrations of degradation by-products such as VC and Cl in Wells B, C and D provide further evidence of intrinsic biodegradation breaking down the BTEX, TCE and DCE in the
groundwater. The formation of degradation by-products provides a secondary line of evidence to support the
occurrence of TCE natural attenuation at the site. The decreasing concentrations of vinyl chloride at Station F, as
shown on the above BTEX-CAH radial diagram map, suggests that this potentially harmful daughter product is also being attenuated farther downgradient from the source area. SEQUENCE can also be used to evaluate and
illustrate temporal trends at selected sampling locations for multiple sampling events. This type of analysis can be
used to clearly illustrate decreasing (or increasing) concentrations of multiple contaminants at multiple locations
over time. Compare this analysis method with typical analysis methods requiring multiple contour maps for each
contaminant of concern and you will immediately see the advantages of using SEQUENCE to prepare a clear and concise presentation of the relevant data.
The SEQUENCE Data Management System
 SEQUENCE comes with a built-in data management system for storing
and maintaining water quality sampling data obtained during the field sampling events. The SEQUENCE data management system utilizes modern database technology for conveniently handling data for multiple
sampling rounds and for many different projects. In addition, the SEQUENCE data management system has many value-added features including:
- A flexible data import utility for bringing in data from existing database files or spreadsheets
- Station templates that allow you to display data only from a selected group of stations/sampling locations
- Flexible concentration units and built-in conversion routines that allow you to use different concentration units for each chemical species
- Maximum concentration levels (MCLs) for each chemical species can be used to graphically identify samples which exceed regulatory limits
- Transparent handling of non-detect analysis values
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The input data required by the SEQUENCE data management system
includes the following:
Although radial diagrams have been used for many years to plot the
relationships between multiple chemical species at different locations, the specialized graphical flexibility required to plot SEQUENCE radial diagrams is not available in any other commercial plotting software.
