BioTrends

Calculating First-Order Degradation Rates

The EPA chlorinated solvents natural attenuation protocol (Wiedemeier et al., 1998) defines two methods that may be used to calculate first-order rates:

  1. The Conservative Tracer method, and
  2. The Buschek and Alcantar (1995) method.

Both these methods involve a number of calculation steps that can be cumbersome and time-consuming, particularly when you have to recheck your calculations or redo them entirely because you found a simple mistake. The data analysis tools included with BioTrends make it extremely simple to calculate first-order rates using either of these methods.

The Conservative Tracer Method

The tool for calculating first-order degradation rates using the Conservative Tracer method provides comprehensive features that result in significant time savings when performing this complex series of calculations.

You have the option of calculating the chemical degradation rate based on concentrations of the organic pollutant and conservative tracer measured at a pair of monitoring wells, or you can calculate the average rate based on a log-linear regression analysis of concentrations measured at wells along a primary flowpath.

All you have to do is specify the flowpath template, the chemical(s) and the conservative tracer, and the monitoring event(s) from which the analytical data is to be extracted from. You also specify the average groundwater velocity, and if retardation is to be included in the analysis, then you also specify soil parameters such as total porosity, bulk density, and the fraction of organic matter content (foc) in the soil. The program will automatically extract the Koc value from the chemical properties database (CHEMbase) and calculate the chemical retardation coefficients for you.

One of the most convenient features of this tool is the ability to calculate the organic-halogen content of all halogenated species measured during a specific monitoring event. For example, if you are using chloride as a conservative tracer at a site where PCE, TCE, DCE, and vinyl chloride are degrading, then calculating the total organic-chloride content and adding this to the measured inorganic chloride will result in a better mass balance for the conservative tracer. You can easily turn this calculation on or off depending on the specific needs associated with your site data.

The image below shows an example of the regression analysis used to calculate the average degradation rates for DCE along a primary flowpath at a site. You can easily change the selected flowpath template, chemical, or monitoring event - the appropriate analytical data will be extracted from the project database, the chart will be updated immediately, and a new set of degradation rates will be calculated based on the updated analytical data and regression analysis.

Buschek and Alcantar Rate Calcs

The tool for calculating first-order degradation rates using the Buschek and Alcantar method provides comprehensive features that result in significant time savings when performing this complex series of calculations.

You have the option of calculating the chemical degradation rate based on concentrations of the organic pollutant measured at a pair of monitoring wells, or you can calculate the average rate based on a log-linear regression analysis of concentrations measured at wells along a primary flowpath.

All you have to do is specify the flowpath template, the chemical(s), and the monitoring event(s) from which the analytical data is to be extracted. Specify the average groundwater velocity, the dispersivity, and if retardation is to be included in the analysis and soil parameters such as total porosity, bulk density, and the fraction of organic matter content (foc) in the soil. The program will automatically extract the Koc value from the chemical properties database (CHEMbase) and calculate the chemical retardation coefficients for you.

The image below shows an example of the regression analysis used to calculate the average degradation rates for DCE along a primary flowpath at a site. You can easily change the selected flowpath template, chemical, or monitoring event - the appropriate analytical data will be extracted from the project database, the chart will be updated immediately, and a new set of degradation rates will be calculated based on the updated analytical data and regression analysis.

The image below shows the Rates Page which presents a summary of the rates calculated along the specified flowpath for the chemical(s) you defined in the Series Page. The regression shown below included only one chemical (DCE), and the average half-life was calculated to be 4.2 years. If you change one or both of the input parameters shown on the form below (foc or dispersivity), the program will automatically recalculate the regression analysis and will then calculate new values for the average degradation rate and half-life along the flowpath.

Parent-Daughter Rate Calcs

When calculating first-order degradation rates using measured field data for a chemical species such as DCE, it's important to remember that the calculated rate is the total attenuation rate. The total rate includes the sum of the degradation rate and the production rate resulting from the degradation of the parent species such as TCE. So when it is required to determine the actual degradation rate, one must conduct a series of calculations to distinguish between the total rate and the degradation/production rates for a daughter product such as DCE.

BioTrends provides a simple tool for doing just that. The image below shows an example of the form that may be used to calculate the degradation rates for each chemical involved in a sequential transformation chain. All you have to do is select the parent chemical (e.g., TCE) and the daughter products (e.g., DCE and vinyl chloride). Then enter the total rate for each chemical. (The total rate is the rate that would be calculated by the Conservative Tracer or Buschek and Alcantar methods.)

Pressing the calculator button at the right of the form will cause the program to calculate the degradation and production rates for each daughter species. The molecular weights for the parent species and all daughter products are automatically extracted from the chemical properties database (CHEMbase). Note how the total rates for the daughter products are significantly lower than the total rate for the parent species (TCE), but the degradation rates for all three species are relatively similar. This shows how important it is to correct the total rates calculated from monitoring data when sequential transformations are occurring at a site.

NOTE - when running a sequential transformation model such as BioTracker, you must enter the degradation rates for each chemical. The production rates are calculated automatically during the model simulation.

References

Buschek, T.E. and C.M. Alcantar, 1995, Regression Techniques and Analytical Solutions to Demonstrate Intrinsic Bioremediation, in proceedings of the 1995 Battelle International Conference on In-Situ and On Site Bioreclamation, April 1995.

Newell, C.J., R.K. McLeod, and J.R. Gonzales, 1996, BIOSCREEN Natural Attenuation Decision Support System - User's Manual, United States Environmental Protection Agency, Report EPA/600/R-96/087, August 1996.

Wiedemeier, T.H., M.A. Swanson, D.E. Moutoux, E. Kinzie Gordon, J.T. Wilson, B.H. Wilson, D.H. Kampbell, P.E. Haas, R.N. Miller, J.E. Hansen, and F. Chapelle, 1998, Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Ground Water, United States Environmental Protection Agency, Report EPA/600/R-98/128, September 1998.

Documentation

BioTrends includes a comprehensive user's manual containing easy-to-follow instructions and step-by-step tutorials to guide you through the process of creating a project database and using the data analysis tools.

 Hardware Requirements

  • PC Pentium (100 MHz)
  • 32 Mb RAM
  • 25 Mb free disk space
  • SVGA display and mouse
  • Windows 95/98 or NT installed

Click Here To Go To The MoNA ToolKit Page

Click Here For Information On The Project DMS

Click Here For Information On SEQUENCE

Click Here For Information On BioTracker

Back to BioTrends Main Page

BioTrends Detailed Description