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EPA On-line Tools for Site Assessment Calculation

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Example One Summary

The development of a site conceptual model, which is updated and revised, as new information is obtained, is a useful concept in performing a typical site investigation. In our example we used the technique to help us visualize the movement of contaminants and to identify potential exposure pathways. A flexible work plan which, incorporates real time data analysis and decision making is an integral component in successfully completing an efficient, thorough investigation.

The calculators helped to guide our investigation along by assisting us in deciding how to proceed, and in identifying a major deficiency in the conceptual model. If we had not discovered that the plume was diving, we would have misjudged the length of the MTBE plume by 2,750 feet. The difference in plume length (450 ft vs. 3,200 ft) might have allowed us to wrongly conclude that plume control measures taken within the first 400 feet of the site were adequate to prevent further off-site impacts. This would have allowed MTBE above 50 ug/L to reach the surface water canal without evaluating the effects. Although impact to the surface water in this case was not an emergency issue, the receptor could just as easily been a series of domestic wells, a public wellfield or a reservoir.

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