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Treatment Technologies for Contaminated Soils

John Poullain, P.E.


Course Outline

This three-hour online course serves as general guide for the treatment of contaminated soils. The course documents are intended to aid in the selection of remedial actions and treatment of hazardous waste contaminants by various biological, chemical, physical or thermal methods or combinations of them. Treatment of contaminated soils by biological treatment, thermal desorption, solidification/stabilization, composting, and slurry bioreactor methods are discussed. Treatment methods for liquid wastes are briefly discussed. Several methods such as, biological and stabilization/solidification may be applicable for treating contaminated liquid wastes. Remedial actions performed at a contaminated site must comply with federal and state regulations. The text provides web links and references for additional information.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

Topics covered by the course:

Intended Audience

This course is intended for civil engineers, project managers, and planners.

Benefit to Attendees

The student will become familiar with several methods used for treating contaminated soils at hazardous and toxic waste sites. The basic guidelines for O&M of a treatment method, their advantages and disadvantages and guidance in the selection of the most appropriate method for treatment are discussed. Potential environmental risks caused by treatment, measures for minimizing risks and beneficial uses for a treatments' final products are also discussed.

The methods and basics of incineration and thermal desorption methods for disposing of contaminated material in waste landfills are also discussed.

Course Introduction

This course provides general technical guidelines and elements for methods of treatment at uncontrolled hazardous and toxic waste disposal sites. Remedial action at an uncontrolled hazardous waste site consists of on site control, on site treatment, on site storage or off site disposal or combinations of these. On site and off site landfill disposal is a viable option when the volume of material is within the feasible or economic limits of available technology. Disposal methods for radioactive waste are not discussed here since satisfactory disposal requires special landfills that are regulated by the Nuclear Regulatory Commission (NRC).

Biological Treatment Methods (In Situ) Biological methods are relatively slow compared to other treatment processes. However many in situ applications provide adequate remediation to permit on site use of the treated soils instead of expensive offsite disposal as hazardous waste. Oily sludge has been treated with biodegradation but chlorinated solvents such as perchloroethylene (PCE) and trichoroethylene (TCE) present problems for dechlorination of residual contaminant.

An anaerobic process being field-tested called anaerobic reductive dechlorination (ARD) speeds the in situ bioremediation of PCE and TCE by injections of electron carbon sources into the subsurface. Sites being treated by air sparge/soil vapor extraction (AS/SVE) methods showed diminishing returns from the site treatments with about a 85 – 90% reduction of VOCs in the groundwater. Some were converted over to anaerobic systems such as ARD, which continued additional reductions in the chlorinated solvent levels after AS/SVE treatments had plateaued.
Also being studied is injection of soluble and insoluble substrates. Solubles such as methanol or sodium lactate penetrate further into the subsurface to enable the anaerobic environment for ARD to be established. Insolubles such as vegetable oil emulsion are a slow-release electron donor and serve to maintain the anaerobic condition.

It was concluded the total time for remediation of soils and sludge containing PCE and TCE were reduced with ARD anaerobic treatment and took less time than if only one method had been applied to the sites. Contaminated sites in New Jersey for instance had promising VOC reductions to closure levels of safety with the anaerobic method, which served as a polishing step for the remediation. Field data in 2003-2004 for sites in New Jersey did indicate after two years perimeters and down gradient areas required additional injection points for completion. Overall success for ARD was on a site by site basis and is being further evaluated.  

Biological Treatment Methods (Ex situ) Biological treatment methods include Bioslurry Reactors (BSR), composing, biopiles and landfarming. BSRs have advantages over other ex situ methods in mixing techniques, which provides more certainty in the uniformity of treatment. Since BSRs operate in a controlled environment they can better homogenize, screen and continuously mix the contaminated material. The treatment time is shorter because the oxygen transfer and microbe populations are improved. Oxygen transfer is especially easier to maintain than with in situ methods.

BSRs can operate in both aerobic and anaerobic modes. In the aerobic mode it is continuously supplied with oxygen which is being depleted by the treatment process. Degradation of contaminants is possible in the anaerobic mode by using an alternative electron acceptor or oxidizer such as nitrate, sulfate or carbon dioxide.

Permeable Treatment Bed Method This treatment method uses a shallow aquifer to remediate contaminants. It's basically an underground reactor made of materials like limestone, activated carbon or green sand. The reactor may lose capacity rapidly depending on the amount of contaminants carried by groundwater and the amount of reactor material used by becoming plugged. The treatment bed is therefore no longer permeable and will allow groundwater to diver the reactor or to channel through the bed.

Stabilization/ Solidification Treatment Methods Sorbents like fly ash, kiln dust or pumice chemically react with water in contaminated material to form a cementious matrix for safer and improved handling of the material. Sorbents function by raising the pH, which helps to precipitate and immobilize some metal contaminants to their least mobile form. Metals that are toxic to microorganisms are immobilized at higher pH. Elevating the pH can protect the microorganism from toxic poisoning and thus maintain their decontamination. However the solidified material may be porous at that stage and must be sealed or placed in an approved landfill to total immobilize the contaminants. The solidified and concentrated contaminants can be leached out by groundwater and contaminate the groundwater and aquifers at the site.

Remedial actions must comply with the regulatory guidelines of the Department of Defense Environmental Restoration Program (DERP), the Formerly Used Defense Sites (FUDS) Program, Resources Conservation and Recovery Act (RCRA), the US Environmental Protection Agency (EPA) and the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA or commonly called "superfund"). Waste sites must be investigated for a wide range of conditions, including ground water levels, surface drainage and subsurface ground conditions.

The advantages and disadvantages of various hazardous waste treatment methods are compared. The treatment methods present certain environmental risks and other concerns for consideration. Considerations for a treatment method include energy use and O&M costs, experience of personnel, requirements for soil dewatering and excavation, odors and adequate treatment performance. Environmental risks include mismanagement of condensation drainage, inadequate treatment levels and air pollution control. Leachate, migration of contaminants, runoff and wind erosion can contaminate the subsoil, groundwater and nearby surface water.

If treatment of materials is required before disposal, incineration or thermal desorption and other methods discussed here are employed for decontamination. These systems also serve to reduce the land required for disposal. Incineration and thermal desorption methods are similar but differ primarily in their operating temperatures. Thermal desorption has high enough heat that vaporizes or turns the contaminant into gas (max. temperature about 1000° F) but does not combust the contaminated material. This method is effective for low boiling contaminants and uses less energy. Thermal desorption alone does not destroy organics. Incineration is a combustion process that oxidizes the contaminants by thermal destruction at temperatures ranging from about 1300° F to 3000° F.

Course Content

This course is based primarily on the EPA document, “In Situ Treatment Technologies for Contaminated Soil”, EPA 542/F-06/013 (2006 Edition, 35 pages). It is also based on Section 3.2 on the EPA document, “Biodegradation Technologies for Remediation of Contaminated Sites”, EPA/625-06/015 (2006 Edition, 11 pages).

In Situ Treatment Technologies for Contaminated Soil

Biodegradation Technologies for Remediation of Contaminated Sites

Terms

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Course Summary

State and federal regulations have to be complied with at hazardous and toxic waste sites in order to remove any threat to human health, welfare or to the environment. Hazardous and toxic waste includes materials defined as hazardous waste, hazardous substance and pollutants. Among the substances are heavy metals, including lead, cadmium and mercury and PCBs, dioxins, chlorine, sulfur, potassium and explosives. Bioslurry Reactors, Solidification/stabilization, and other methods discussed can be used to remediate contaminated soils prior to final disposal and to also reduce the land needed for disposal.

References

For additional technical information related to this subject, please refer to:

http://www.epa.gov/epaoswer/osw/hazwaste.htm
US EPA comprehensive information about hazardous waste, landfills, definitions and RCRA requirements.
http://www.epa.gov/garbage/landfill/sw_combst.htm
US EPA information on combustion and pollution control, energy production from waste incineration.


Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

Take a Quiz

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.