8    PERMEABLE BARRIERS: A NEW ALTERNATIVE FOR
TREATMENT OF CONTAMINATED GROUNDWATER
Bruce M. Thomson
Stephen P. Shelton
Department of Civil Engineering
University of New Mexico
Albuquerque, NM 87131
Edward Smith
U.S. Army Construction Engineering Research Laboratory
Urbana,IL 61820
INTRODUCTION
Restoration of aquifier systems which have become contaminated with toxic or hazardous compounds is one of the most challenging problems currently facing environmental engineers and scientists. Conventional aquifer restoration alternatives can be broken into four categories:
1. Contaminant of the aquifier contaminants.
2. Removal of mobile pollutants, followed by surface treatment of contaminated water or
recovery of free product, and subsequent disposal or reuse of treated water.
3. Removal of contaminated soil, followed by treatment and/or disposal.
4. In situ stabilization of aquifer contaminants.
Frequently a combination of these methods is used to maximize the performance of the treatment
process. These alternatives are briefly described below.
Contaminant of groundwater pollutants is the most immediate concern following determination of
a contamination problem. It can be achieved either through the use of a physical barrier such as a
grout curtain, slurry cutoff wall or sheet piles, or by creation of a hydraulic barrier resulting from a
combination of pumping and injection wells. Containment technology is reviewed by Spooner, et al.1,
and Kelly.2
Removal of mobile contaminants from the aquifer system is achieved by directing pollutant migration toward wells or trenches from which it can be recovered or removed. Variations of this process
include free product recovery of petroleum products floating on a water table, vacuum extraction of
volatile organic compounds, and pump-and-treat processes for soluble constituents. These processes
are limited to volatile, liquid, or soluble pollutants; insoluble compounds remain attached to soil
particles in the aquifer or vadose zone. Bouwer, et al. , Wagner, et al.4, and Guswa et al.5 have
prepared reviews ot processes for management and treatment of groundwater contamination problems involving mobile contaminants.
In situ stabilization of hazardous wastes is a relatively new treatment process which shows considerable promise as an alternative to conventional pump and treat methods. Its principal application to
date has been in groundwater systems which are contaminated with biodegradable organic materials.
In situ treatment is accomplished by stimulating the growth of naturally occurring soil microorganisms by introducing essential nutrients (e.g. nitrogen and phosphorous) and appropriate electron
acceptors (e.g. oxygen or hydrogen perioxide) required for the organism's growth. Lee, et al.6,
Wilson, et al.7, Borden, et al.8, and Amdurer, et al.9 have prepared reports and reviews of in situ
biological waste stabilization technology, while Sims, et al. discussed in place remediation of contaminated soils. In situ technology is limited to applications in which the contaminants are
degradable.
Although conventional groundwater restoration problems, when properly designed and implemented, are generally effective, they have numerous problems associated which include:
45th Purdue Industrial Waste Conference Proceedings, © 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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