Soil-Water Partitioning Slider Calculator
The ESCI, LLC soil-water partitioning slider calculator is based on the USEPA Soil Screening Level Guidance soil-water partitioning equation. It is used to establish a residual soil contaminant concentration that will not exceed a specific groundwater concentration.
The soil-water slider can be found at the following link.
Using the Slider Calculator
Just click on a contaminant to calculate the soil-water partitioning result using default New Jersey Department of Environmental Protection parameters. Cleanup objectives for other regulatory agencies or for site-specific conditions can be calculated by varying the input parameters.
More than just a simple calculator, the sliders can be adjusted to determine the sensitivity of the soil-water partitioning equation to specific parameters. This has many uses. For instance, it can be used to determine what soil organic carbon content would be required to produce a value above a detected concentration. A determination could then be made as to the likelihood of identifying soil organic carbon at such levels.
The slider calculator is very versatile. For instance to view results for a Koc of greater than 1000 (L/kg), simply enter the desired Koc as the maximum value. Then move the Koc slider to the maximum value. Or to evaluate the influence of Koc over a wider range, simply enter a new maximum value and move the slider.
The slider calculator can be used to determine the sensitivity of the soil-water partitioning equation. For instance the default value for benzene is 0.069 µg/kg. Yet even with a soil organic carbon content of 0.1 kg/kg (10 percent) the result is just 1.225 µg/kg.
Are the soil-water partitioning equation results overly conservative? No, it does not appear so. 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 SESOIL leachate concentrations varied over several orders of magnitude depending on many factors including soil type and depth to groundwater.
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. These results are close to those produced by the soil-water partitioning equation that assumes an infinite soil source mass located below the water table. Their modeling indicates that the soil-water partitioning equation does in fact produce the worst-case scenario results.
Soil Leachate and Groundwater Concentrations
Both the soil-water partitioning equation and SESOIL produce soil leachate concentrations. The resulting groundwater concentration would be lower due to dilution. At a minimum a dilution-attenuation factor (DAF) equation should be applied to produce a groundwater concentration. The slider calculator will be expanded in the next newsletter to include the USEPA DAF equation. For now you will need to multiply the results by the default DAF value of 13.
The soil-water partitioning equation 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.