BioTrends - evaluation of natural attenuation trends
BioTrends Category: natural attenuation
Evaluation of Natural Attenuation Trends
BioTrends provides an integrated suite of tools for conducting natural attenuation trend analyses, calculating first-order degradation rates, calculating the natural attenuation "score" for your site, and conducting groundwater modeling to predict pollutant plume attenuation. These tools are combined with a comprehensive data management system to provide a powerful and easy-to-use platform for evaluating Monitored Natural Attenuation.
BioTrends is especially useful when applied to quantify the efficacy of natural attenuation, and also to compile and analyze the long-term monitoring data that must be collected to ensure the reliability of this remedy once it has been implemented.
Once the required site data has been collected, the next step in a natural attenuation assessment is to evaluate the spatial and temporal trends for priority pollutants and geochemical indicators. Key questions that need to be answered include:
These questions are critical when evaluating whether natural attenuation is an effective remedy. That's why BioTrends was specifically designed to provide you with the tools you need to determine whether Monitored Natural Attenuation is a viable alternative for your site.
For example, you can take advantage of the dynamic link between the chart tools and the project database to quickly plot an x-y chart of concentration vs. distance along a primary flowpath downgradient from a source area. Just select the wells included in the flowpath, select the chemicals and monitoring events to be used for each data series, and the program will do everything else for you including extraction of the analytical data from the project database; automatic calculation of unit conversions (if necessary); and creation of the plots using "smart chart" tools specifically designed to work with chemical analytical data.
Or use another tool to plot an x-y chart of concentration vs. time by simply defining the chemicals, monitoring wells, and monitoring events you want to see on the chart. It's that easy! You can define any number of data series to view on the charts, and you can easily change the appearance of the lines and symbols for each data series.
"Non-detect" data is plotted using any of the chart tools included with BioTrends. You have the option of using a unique symbol shape and color to represent non-detect data in any of the chart data series. This allows you to instantly see data on the chart that represents a "non-detect" measurement which can be particularly useful when working with samples that were significantly diluted. For example, a pollutant method detection limit (MDL) for a contaminated groundwater sample may be as high as 10,000 ug/L. Using the special non-detect symbol makes it obvious when a chemical was not detected during an analysis - otherwise, the data shown on the chart makes it appear that the chemical was measured at a concentration of 10,000 ug/L at that location.
Often it becomes necessary to calculate first-order degradation rates for priority pollutants. These rates are used to determine how far down-gradient the contaminated groundwater may migrate before becoming stable in time. The EPA chlorinated solvents natural attenuation protocol (Wiedemeier et al., 1998) defines two methods that may be used to calculate first-order rates:
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 using slightly different data. The data analysis tools included with BioTrends make it extremely simple to calculate first-order rates using either of these methods. These tools allow you to calculate pollutant degradation rates between a pair of monitoring wells or average rates along a flowpath of wells using a log-linear regression analysis.
All you have to do is:
BioTrends will automatically go through all the calculation steps for you and will allow you to change any input parameters so you can assess the sensitivity of the final rate calculations to input parameters which may be uncertain. By integrating these calculation tools with the project database, the effort you have to expend is minimal, the potential for error when making these calculations is reduced significantly, and the time savings can be used to conduct a more thorough sensitivity analysis to determine a range of potential degradation rates given the uncertainty in your input data.
The EPA technical protocol for the natural attenuation of chlorinated solvents (Wiedemeier et al., 1998) presents a screening process that can be followed to provide a preliminary assessment of whether natural attenuation may be an effective remedy for a site. Although there are many factors which contribute to the overall performance of natural attenuation, it is sometimes helpful to perform a quick calculation of the natural attenuation "score" for a site. The higher the score, the more suitable natural attenuation is likely to be as a groundwater remedy.
The tool provided in BioTrends for calculating this natural attenuation score is also linked to the project database. So all you have to do is define the scope of the database search criteria (i.e., which monitoring stations and monitoring events to use for determining the min/max concentration values for specific chemicals) and specify how non-detect data should be handled. The program will then search the database and automatically calculate the natural attenuation "score" for your site by comparing measured chemical concentrations to the criteria defined by Wiedemeier et al., 1998. The only other step you have to do is specify whether various chlorinated solvents are present as daughter products at the site - the score will then be changed accordingly.
BioTrends comes with a simple screening tool that can be used for modeling three-dimensional advection-dispersion-degradation-sorption in groundwater using BIOSCREEN (Newell et al., 1996). BIOSCREEN is a simple spreadsheet analytical model that has been made available in the public domain. You can run this model simply by selecting the BIOSCREEN option from the BioTrends Menu.
If your modeling needs are more sophisticated than the representation provided with BIOSCREEN, you may want to consider using BioTracker, an innovative new screening model that provides unique visualization tools for evaluating and documenting natural attenuation modeling results. BioTracker is based on a numerical model (BioRedox) so it can be used to provide a more site-specific representation of the biodegradation reactions. For example, BioTracker can simulate sequential transformations for any number of chlorinated solvent or radio-nuclide parent-daughter species, and it can also simulate the accumulation of a halogen such as chloride with each reductive dechlorination reaction. Simulating halogen accumulation is an important feature when calibrating a sequential transformation model to observed field conditions.
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.
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.
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