United States
Environmental Protection
Agency
Office of
Research and
Development
Office of Solid Waste
and Emergency
Response
EPA/540/S-92/017
January 1993
& EPA Summary Paper
In-Situ Bioremediation
of Ground Water
Introduction
The Robert S. Kerr Environmental Research Laboratory (RSKERL) has developed a number of Issue Papers and Briefing
Documents which are designed to exchange up-to-date information related to the remediation of contaminated soil and ground
water at hazardous waste sites. In an attempt to make the content of these documents available to a wider audience, RSKERL
is developing a series of Summary Papers which are condensed versions of the original documents.
There are a number of techniques that may potentially be used for dealing with problems resulting from the contamination of
ground water with organic compounds. These include physical containment using slurry walls or grout curtains, or hydraulic
controls using pumping wells or interceptor systems to manipulate the hydraulic gradient; free product recovery techniques; or
the extraction of contaminated ground water followed by treatment at the surface. Also, ground water can sometimes be
treated in place using chemical or biological processes. In-silu chemical treatment, for example, may involve the
neutralization, precipitation, oxidization, or reduction of contaminants by injecting reactive materials into the subsurface.
Bioremediation Concepts
An emerging technology for the in-silu remediation of ground water is the use of microorganisms to degrade contaminants
which are present in aquifer materials. Although in-silu. bioremediation has been used for a number of years in the restoration
of ground water contaminated with petroleum hydrocarbons, its application to other classes of contaminants is relatively
recent.
Most biological in-silu treatment systems are carried out by stimulating indigenous microorganisms to degrade those organic
contaminants dissolved in ground water and attached to aquifer solids. The process, which is an adaptation of earlier attempts
to remediate gasoline-contaminated aquifers, involves the circulation of oxygen and nutrients through a contaminated aquifer
using extraction and injection wells. The placement of the wells depends on the size and configuration of the affected area, and
the hydraulic conductivity of the ground-water formation.
Research is under way to test the use of nitrate instead of oxygen during in-silu treatment systems to promote the anaerobic
degradation of organic contaminants. Investigations into additional methods to enhance in-situ bioremediation include the
addition of a readily degradable substrate to aid in the degradation of more recalcitrant molecules, and the addition of a non-
toxic substitute for a specific contaminant in order to induce degradative enzyme activity that will affect both the substitute and
the specific contaminant.
In addition to the stimulation of indigenous microbial populations to degrade organic compounds in a contaminated aquifer,
another technique, which has not been fully demonstrated, is the addition of microorganisms with specific metabolic
capabilities. These microbial populations have been altered to degrade specific compounds by enrichment culturing or genetic
manipulation. Enrichment culturing involves exposure of microorganisms to increasing concentrations of a contaminant.
Genetic manipulation is accomplished by exposure of organisms to a mutagen, followed by enrichment culturing, or by the
Superf und Technology Support
Center for Ground Water
Robert S. Kerr Environmental
Research Laboratory
Ada, Oklahoma
Technology Innovation Office
Office of Solid Waste and Emergency
Response, US EPA, Washington, D.C.
Walter W. Kovalick, Jr., Ph.D.
Director
Printed on Recycled Paper
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use of DNA recombinant technology to change the genetic structure of the microorganism. It is important to note that the inoculation of
specialized microbial populations into the subsurface may not result in degradation for a number of reasons including the concentration of the
contaminant, geochemistry of the formation, or other organisms that are toxic or inhibitory to the inoculated organisms.
There are a number of advantages to the use of in-silu bioremediation. Unlike other aquifer remediation techniques, it can often be used to treat
contaminants that are sorbed to aquifer material or trapped in pore spaces. The time required using in-situ bioremediation can often be faster
than extraction and treatment processes. For example, a gasoline spill was remediated in 18 months using in-situ bioremediation, while pump-
and-treat techniques were estimated to require 100 years. In-situ bioremediation often costs less than other remediation options.
There are also disadvantages to in-silu bioremediation. Many organic compounds are resistant to degradation as are heavy metals. In addition,
organic compounds that otherwise might be subject to degradation may be toxic or inhibit the growth of microorganisms at concentrations often
found at contaminated sites. Injection wells may also become clogged from profuse microbial growth resulting from the addition of nutrients
and oxygen.
In-silu bioremediation is difficult to implement in low permeability aquifers that do not permit the transport of adequate supplies of nutrients
and electron acceptors to active microbial populations. Aquifers with hydraulic conductivities of 10"4 cm/sec (100 ft/yr) or more are usually
considered good candidates for in-silu bioremediation.
This Summary Paper has been developed from the Ground-Water Issue Paper titled "In-Silu Bioremediation of Contaminated Ground Water."
EPA/540/S-92/003, February 1992.
For further information about the Technology Support Center at RSKERL, contact:
Mr. Don Draper, Director
Technology Support Center
U.S. Environmental Protection Agency
Robert S. Kerr Environmental Research Laboratory
P.O. Box 1198
Ada, OK 74820
(405) 436-8603
United States I K RATF
Environmental Protection Agency DI-ICTA cccc DAIH
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EPA/540/S-92/017
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