A Civil Action - The Woburn Toxic Trial > Learning Modules > Movement of Contaminants

# Movement of Contaminants

### Woburn Resources across the site

Overarching Questions:
Key Issues:
Resource Collections:

## Module Goals:

- Understand how the compounds of interest, TCE and daughter compounds, which are derived from chlorinated solvents, migrate through the shallow subsurface.
- Review how the experts illustrated the movement of the contaminates.
- Understand why the fate and transport assesments are critical to groundwater investigations.

### Student Assignment

## Overview

Movement of contaminates through the subsurface is often complex and difficult to predict. Different types of contaminates react differently in subsurface, and one of the challenges for hydrogeologists is to collect meaningful data that can eliminate some of the uncertainty.

## How does Contamination move from surface to subsurface?

Most contaminants are introduced to the subsurface through soils. the interaction between soils and a contaminant are key in projecting the "fate and transport". Contaminants that are highly soluble, such as salts moved readily from surface soils into the saturated subsurface with every rainfall event. Those contaminants which are not highly soluble have considerably longer residence times in the near surface soils. Liquids spilled to surface soils can continue to migrate downward (assuming that pore saturation by the liquid contaminant is maintained in the soils) or those liquids readily evaporate, thus limiting their potential for reaching the saturated subsurface. For additional discussions regarding the fate and transport of contaminants refer to Contaminate movement through soils, an overview provided by the the US Department of Agriculture. The US geologic survey also has a helpful summary regarding the interaction between surface soils, streams and groundwater. See the USGS Primer for additional information.

## Advective groundwater movement.

the most common mode of contaminant migration in the subsurface occurs as advective flow with groundwater. Advective flow is best described as a fluid's ability to flow through a porous media. Darcy's Law provides the fundamental explanation for water flow through subsurface porous media. Based on the flow principles described in Darcy's Law, dissolved contaminants will move at the same rate as the solvent. learn more

## Looking at a specific example.

Since each type of containment presents its own challenges and physical uniqueness in the aquifer, sometimes it is best to focus on a particular type of contaminant to understand the basics of the transport. Since the main contaminant at Woburn is TCE, let's look at the characteristics of TCE moving through subsurface. The migration of TCE is further described in this link.

## Student Assignment

## More Information

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