Section Two
SITE REMEDIATION
2    CRITICAL STATE OF THE ART REVIEW OF
VAPOR EXTRACTION
Sami A. Fam, President
Innovative Engineering Solutions, Inc.
Needham, Massachusetts 02192
Mindi F. Messmer, Senior Scientist
Deepak Nautiyal, Civil Engineer
Geraghty & Miller
Andover, Massachusetts 01810
Michael A. Hansen, Chemical Engineer
Geraghty & Miller
Indianapolis, Indiana 46204
INTRODUCTION
The vapor extraction technology induces airflow in the subsurface using an aboveground vacuum blower/pump system. Adequate air movement within the contaminated zones is of primary
importance to the success of the vapor extraction system (VES). The induced airflow brings
"clean" air in contact with the contaminated soil, nonaqueous phase liquid (NAPL), and soil
moisture. The contaminated soil gas is drawn off by the VES and the air in the soil matrix becomes recharged with new vapor phase contamination as the soil/pore water/soil gas/NAPL partitioning is re-established.
The objective of this paper is to review VES design procedures with particular emphasis on selecting the appropriate airflow rates in the subsurface and the utility of numerical modeling techniques in this selection process. In addition, the paper shall examine the effects of soil parameters on VES success with emphasis on the effects of soil moisture. The paper shall initially
introduce the VES design goals and vapor extraction theory.
VAPOR EXTRACTION THEORY
Figure 1 shows the basic components of a vapor extraction system; subsurface vapors are
withdrawn through an extraction well that may be vertically or laterally constructed. Recovered
vapors are routed to an aboveground vapor treatment unit, if required. The key to a successful
design is to place the wells and equipment so that when the system is in operation, an adequate
airflow pattern is created across the entire section of the unsaturated zone that is contaminated.
The distribution of contaminants within the four phases (pure contaminant/vapor phase/soil
moisture/adsorbed to soil) can potentially be represented by mathematical equations and the distribution can be simulated by computer models.1 The greatest difficulty in utilizing computer
simulations is the lack of complete understanding of nonequilibrium forces that govern vapor extraction efficiency towards the end of site remediation projects.
Contaminants that are released to the environment will be distributed in the subsurface in a
manner consistent with their physical properties. This subsurface distribution (in pore water,
vapor, adsorbed to soil or in pure NAPL) is termed partitioning. Partitioning is related to properties of the soil (type, moisture extent, etc.), as well as the contaminants (vapor pressure, solubility, etc.).
50th Purdue Industrial Waste Conference Proceedings, 1995, Ann Arbor Press, Inc., Chelsea, Michigan 48118.
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