Environmental Modeling Community of Practice

EPA On-line Tools for Site Assessment Calculation

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Example One: Conducting a Site Investigation

"Full" site characterization is becoming increasingly important in evaluating potential impacts from a contaminant release, and in developing efficient remedial plans. Current trends toward risk-based decision-making and monitored natural attenuation also tend to require a greater degree of "up-front" site characterization to sufficiently demonstrate adequate protection of resources and potentially exposed populations. Despite differences in scope, field time and site conditions, there are constraints associated with every project, which encourage investigators to make efficient use of limited resources. Delays caused by mischaracterization during the investigative stage can be costly, resulting in budget overruns, regulatory penalties and damaged credibility with the public.

This example is from an investigation in which gasoline from a small retail station had impacted an adjacent residential area. Full plume delineation was needed, concurrent with interim remedial action, to mitigate localized impacts, evaluate the potential for future impacts and to assess the ultimate fate of the off-site ontaminants. Although a good portion of the case is beyond the scope of OnSite, we will work through some of the more important aspects using the outline below, and conclude by describing some of the future considerations.

Case Study Background
- Overview
- Site Background
- Project Directives
Investigative Techniques & Tools
- Initial Investigative Work
- Three Point Gradient Calculator
- Dissolved Component Delineation
- Effective Solubility
- Henry's Law Constant
- Seepage Velocity
- Plume Gradient
Fate & Transport Estimates
- Release Date
- Concentration, Arrival Date and Arrival at Receptor
Conclusions

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