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  The Impact of Ground Water/Surface Water Interactions on Contaminant Transport With Application to an Arsenic-Contaminated Site (22 pp, 2.58 MB) (EPA/600/S-05/002) January 2005

This document provides an overview of the dynamics of the chemical processes that govern contaminant transport and speciation during water exchange across the ground water/surface water (GW/SW) transition zone. It presents results from a field study examining the fate of arsenic during ground water discharge into a shallow lake at a contaminated site.

A conceptual model of the GW/SW transition zone is defined. This provided a starting point for prioritizing tasks carried out during site characterization, which was done to define contaminant mass flux across the GW/SW transition zone. This information is critical for establishing site-specific risks and alternatives for remedial intervention to reduce or eliminate these risks.

Developing a knowledge base for delineating the biogeochemical processes controlling subsurface transport of the contaminant is one component of the investigative effort to define human or ecological risk. The discussion that follows necessarily ignores specific risk receptors. Because risk is dependent on the degree of current and future contaminant exposure to the receptor, it is important to define contaminant mass distribution (aqueous, solid, and gas) and the dynamics of mass redistribution within the regulatory boundaries established for the site. However, receptor response to contaminant exposure may not vary proportionally to contaminant mass or media-specific concentration. Therefore, the overall risk characterization effort must be guided by knowledge of both contaminant and receptor distribution within the investigative boundary.


Robert Ford

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