V. 4 Issue 4 July, 2008
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Soil-Water Partitioning & Dilution-Attenuation Factor Slider Calculator
The ESCI, LLC soil-water partitioning slider calculator has been expanded to include the dilution-attenuation factor (DAF) equation. Making it a comprehensive tool used to develop site-specific soil cleanup concentrations protective of groundwater quality.

The slider calculator is based on the USEPA Soil Screening Level equations. It is used to establish a residual soil contaminant concentration that does not exceed the groundwater quality standards. The New Jersey Department of Environmental Protection (NJDEP) calls this the impact to groundwater soil remediation standard (IGWSRS). The equation is divided in to two parts. The first presents results for the soil-water partitioning equation. The second presents results for the DAF.

The slider calculator can be found at the following link.

Using the Slider Calculator
Just click on a contaminant to calculate a soil cleanup objective using default NJDEP parameters. Cleanup objectives for other regulatory agencies or for site-specific conditions can be calculated by varying the input parameters.

The slider calculator is very versatile. For instance to expand the Koc range simply enter a new maximum value. Then move the Koc slider to the desired value.

Sensitivity Analysis
More than just a simple calculator, the sliders let you quickly determine the sensitivity of the equations to variations in input parameters. This has many uses. You could for instance crank up the soil organic carbon content until the result exceeds your detected soil concentration. A determination could then be made as to the likelihood of identifying soil organic carbon at such levels at your site.

Take a few minutes to play with the input parameters. Itís fun to see how the results vary. I spent some time looking at the DAF parameters and found that using potential site-specific input values actually lowered the DAF.

For instance the default NJDEP DAF is 13 with a hydraulic conductivity of about 1.0E-2 cm/sec. Setting the hydraulic conductivity to 1.0E-3 cm/sec lowers the DAF to 2.268. Reduce the hydraulic conductivity to 1.0E-4 cm/sec and the DAF drops to 1.131. Select hydraulic conductivity values below 1.0E-4 cm/sec and the DAF is essentially 1.

As the DAF is reduced so does the soil cleanup concentration. The default value for benzene is 0.81 parts per billion (ppb). Reducing the DAF to 2.268 lowers the soil cleanup concentration to 0.135 ppb. A DAF of 1.131 lowers the cleanup value to 0.067 ppb.

Too Conservative?
Are the soil-water partitioning and DAF equations overly conservative? No. Soil cleanup objectives based on the soil-water partitioning and DAF equations were designed to be safely used everywhere.

Some regulatory agencies such as the Wisconsin Department of Natural Resources and the Ohio Environmental Protection Agency used the SESOIL vadose zone model to establish their baseline soil cleanup objectives protective of groundwater quality. They found that the SESOIL leachate concentrations varied over many orders of magnitude depending on numerous factors including climate, soil type, and depth to groundwater.

Model such as SESOIL and AT123D produce a far more accurate result and thus can produce significantly higher soil cleanup concentrations. However, to ensure protection of groundwater quality throughout a state their baseline soil cleanup objectives were essentially based on the worst-case scenario results. Not surprisingly this consisted of a massive SESOIL source located directly above the water table. SESOIL leachate concentrations for the worst-case scenario are similar to those produced by the soil-water partitioning equation. Their modeling indicates that the soil-water partitioning equation does essentially produce the worst-case scenario results.

Time to Move On
Although the combined soil-water partitioning and DAF equations looks rather complex they were designed to produce extremely conservative results. In fact, results for many contaminants are so small that concentrations are below the practical quantitation limits.

The soil-water partitioning equation and DAF results are not the end of the road. Rather they represent a simple first cut. Future issues of this newsletter will look at alternative methods including the synthetic precipitate leaching procedure (SPLP) and transport and fate modeling.

Learn More
The slider calculator is fun to play with and learn from. If you want to learn more about the development of cleanup objectives then attend the ESCI training seminar on September 25 and 26 in New Brunswick, New Jersey.

Nothing like the ESCI slider calculator exists anywhere else. Please pass this newsletter on to those you believe would benefit from use of the slider calculator.

Soil-Water Partitioning & Dilution-Attenuation Factor Slider Calculator
Using the Slider Calculator
Too Conservative?
Time To Move On
Learn More
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