United States
Environmental Protection
Agency
Office of
Research and
Development
Office of Solid Waste
and Emergency
Response
EPA/540/S-93/502
May 1993
«EPA Summary Paper
In Situ Bioremediation of
Contaminated Vadose
Zone Soil _
r-^1 n-faction ARency
U.S. Environmerv.. ,tect
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.
In situ bioremediation of subsurface soils contaminated with organic chemicals is an alternative treatment technology that, in
certain cases, can meet the goal of achieving a permanent cleanup at hazardous waste sites. Consideration of such
alternatives is encouraged by the EPA for implementing its requirements at Superfund sites. In many cases, in situ
bioremediation techniques can be used in conjunction with chemical and physical treatment processes (i.e., "treatment
trains") as effective means for comprehensive site-specific remediation.
Bioremediation has been shown to be effective in reducing overall mass of a variety of organic contaminants. Full scale
systems have been utilized to remediate soil contaminated with both crude and refined petroleum hydrocarbons (i.e., diesel
fuel, gasoline, etc.) and wood treating chemicals (i.e., creosote and pentachlorophenol). To date, bioremediation has not
been shown to effect significant removal of highly structured and insoluble organic compounds such as polychlorinated
biphenyls and dioxins.
In Situ Systems
Effective in situ bioremediation often requires implementation of biodegradation enhancement methods. Appropriate
methods of enhancing in situ bioremediation efforts for a particular site depends on the phase(s) in which contaminants
occur, i.e., solid, aqueous, gaseous, or non-aqueous phase liquid (NAPL); heterogeneity of subsurface matrix; and types of
recovery/delivery systems being utilized. Bioremediation enhancement at a specific site may be achieved by: increasing
bioavailability of contaminants of concern; reducing toxicity to microorganisms; delivering adequate supplies of moisture,
nutrients, and electron acceptors (i.e.,oxygen); and/or by introducing specific substrates that stimulate appropriate indigenous
microbial degradative activity.
A variety of strategies may be implemented to maximize biodegradation activity in contaminated subsurface soils; however,
success of the in situ bioremediation effort for any given site is often determined by effectiveness of the recovery/delivery
systems employed to remove major sources of contaminants and to transport appropriate amendments (i.e., nutrients,
electron acceptors.etc.) to the location of the remaining contaminants. Overcoming effectiveness limitations to
biodegradation is the primary goal of a delivery system, and development of adequate delivery technologies continues to be
the major challenge associated with effective implementation of in situ bioremediation for contaminated subsurface soils.
Superfund 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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At the present time, systems utilized to deliver required amendments to the subsurface can be divided into two categories: 1) gravity/forced
hydraulic delivery, and 2) extraction/injection air delivery methods. Both systems are impacted in effectiveness by the soil type. Gravity
delivery methods include flooding, ponding, ditches, and sprinkler systems which deliver water and amendments to the contaminated
subsurface by applying solutions to the soil directly over the contaminated area. Gravity systems also may be installed in the subsurface just
above the contaminated soil zone. Subsurface-installed gravity methods include infiltration galleries (or trenches) and infiltration beds.
Forced hydraulic delivery systems are used to deliver fluids under pressure into a contaminated area through well points. Air delivery
systems are associated with bioventing, an in situ bioremediation technology which utilizes oxygen contained in the air phase to enhance
biodegradation of subsurface organic contaminants. Air can be delivered either via extraction or injection methods. Extraction systems
incorporate soil vacuum extraction techniques, where a low flow of fresh air is continually pulled through the contaminated zone. Injection
systems deliver fresh air under pressure through well points to the contaminated subsurface zone, and the air is allowed to permeate out
through the contaminated zone and back to the surface. An injection system can be installed with one or several companion extraction wells
to achieve more extended horizontal flow. Soil bioventing has been demonstrated in several field applications for fuel hydrocarbon
contaminants; however, the technology has not yet been demonstrated at field scale for other types of organic contaminants(i.e., polycyclic
aromatic hydrocarbons, pesticides, etc.). The bioremediation of contaminants in soil is often greater than that in ground water because more
oxygen is contained in air than can be dissolved in water. In comparison to bioventing, other problems encountered in saturated media are the
hydraulic limitations to providing oxygen and nutrients to the zone of biological activity, and a tendency for anaerobic conditions to develop in
saturated versus unsaturated materials.
This Summary Paper has been developed from the Engineering Issue Paper (EPA/540/S-93/501) titled "In situ Bioremediation of
Contaminated Unsaturated Subsurface Soils" by Sims, et al. For further information concerning this document, contact: John Matthews (405)
436-8600.
For information on the availability of RSKERL publications,
contact:
For information on the Technology Support Center itself,
contact:
Publications
RSKERL
P.O.Box 1198
Ada, Ok 74820
(405)436-8651
Mr. Don Draper
RSKERL
P.O.Box 1198
Ada, Ok 74820
(405)436-8603
'U.S. Government Printing Office: 1993 — 750-071/80031
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
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EPA/540/S-93/502
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PERMIT No. G-35
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