V. 2 Issue 2 August, 2003
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Why Should I Model?
I'm often asked "Why should I model the contaminants at my site?" Consultants point out that they have tried establishing site-specific cleanup concentrations based on methods such as soil:water partitioning and soil leaching tests. Yet even after applying a groundwater dilution factor these site-specific concentrations are generally in the same ballpark as the baseline cleanup concentrations and in some cases even lower. They wonder if these methods cannot produce any substantial reduction in the extent of contamination why should modeling be any different? Furthermore, as the baseline regulatory concentrations were based on modeling wouldn't modeling simply produce the same results again?

The answer to all these questions is that site-specific modeling is often the only method that can produce significantly higher cleanup concentrations. Simple methods like soil:water partitioning, leaching tests, and groundwater dilution are designed to be extremely conservative. They cannot account for most site-specific conditions. In fact these methods are so conservative that they are not typically used to establish even the baseline values.

One of the reasons site-specific modeling works so well is that the baseline values were based on the worst case scenario or something very close to it. Application of the worst case results ensures adequate protection everywhere. However, this over kill approach can be quite costly. Modeling often provides the best method of establishing the extent of contamination.

Regulatory agencies used modeling because it produced the most accurate results, not because it produced the most conservative values. It would have been much easier to use soil:water partitioning and a dilution factor to develop the baseline values. However, this was not done as there would be less confidence in the results. It is the higher accuracy of modeling that makes it is possible to develop higher site-specific values. Application of site-specific values means that funds are not being spent foolishly cleaning up contamination that does not pose a threat.

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