Section Three
SITE REMEDIATION
C. GROUNDWATER REMEDIATION
15    VAPOR EXTRACTION/VACUUM-ENHANCED
GROUNDWATER RECOVERY: A HIGH-VACUUM
APPROACH
Michael A. Hansen, Staff Engineer
Geraghty & Miller, Inc.
Indianapolis, Indiana 46204
Mark D. Flavin, Project Scientist/Hydrogeologist
Geraghty & Miller, Inc.
Indianapolis, Indiana 46204
Sami A. Fam, Technical Director
Remedial Engineering
Geraghty & Miller, Inc.
Andover, Massachusetts 01810
INTRODUCTION
Releases of organic solvents/petroleum products are a common cause of groundwater unsaturated
soil contamination. When these constituents are released to the subsurface, they can partition into
four distinct yet interrelated phases; non-aqueous phase liquids (NAPLs) adsorbed to saturated or
unsaturated soil particles, free-phase NAPLs, soluble constituents dissolved in the groundwater, and
volatile constituents in the soil pore space of the vadose zone. The four phases of contamination are
intimately related by equilibrium partitioning. Dynamic equilibrium of contaminant partitioning and
mass balance approaches to contaminant quantification and treatment should be the cornerstone of
remedial investigations and site remediation processes. The optimal plan for remediation will consist
of an integrated strategy that addresses all four phases of contamination. The selected site remediation must not only address each constituent phase, but address each in the most efficient manner with
respect to the rate of mass removal.
The combination of vapor extraction and groundwater pump-and-treat remediation has been successfully practiced as a remedial technique in medium and high permeability geologic formations. The
success of this technique can be severely restricted in low permeability formations due to the diminished air and groundwater flows that can be achieved by standard remedial recovery/equipment. An
example of these formation types are the silty-clay till formations of central Indiana, which will not
allow air or groundwater flow at rates acceptable for rapid site restoration and can further hinder
mass removal of constituents due to the presence of highly adsorptive silts and clays.
In order to overcome the air and groundwater flow restrictions of these low permeability formations, high vacuums created by liquid-ring pumps can be utilized. The application of these high
vacuums (up to 25 inches of mercury as opposed to 3 to 6 inches of mercury for conventional vacuum
blowers) creates a much greater driving force for air flow in the vadose zone and will also increase the
rate of groundwater recovery. This increased air and groundwater flow will allow for greater constituent mass removal rates thus allowing for more rapid site closure.
MASS BALANCE APPROACH TO SITE REMEDIATION
Site remediation is a chemical treatment process (just as the treatment of domestic and industrial
wastewater), and remedial technology selection must emphasize the scientific principles of dynamic
partitioning and mass balance.1 In order to allow for restoration of an entire site, each of the four
49th Purdue Industrial Waste Conference Proceedings, 1994 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
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