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Solidification/Stabilization Treatment Methods

John Poullain, P.E.


Course Outline

This two-hour online course provides basic info about Solidification/Stabilization (S/S) treatments widely used to remediate hazardous and toxic waste sites. Factors to consider for the selection of S/S treatment methods are discussed in this course. Required testing, sampling and optimization are also discussed. Remedial actions performed at a contaminated site must comply with federal, state and local regulations. S/S is used to remediate contaminated soils and sludge prior to final disposal and reduce the land needed for disposal as for traditional landfills.

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

Learning Objective

This course covers these topics:


Intended Audience

This course is intended for civil engineers and planners.


Benefit to Attendees

The student will become familiar with solidification and stabilization (S/S) methods used for treating contaminated liquids, soils and sludge at hazardous and toxic waste sites. The basic guidelines for the S/S treatment methods, the advantages and disadvantages and guidance in the selection of the most appropriate treatment method are discussed. The differences in the methods and benefits of their combined use and waste conditions not suitable for their use are explained. Understand proper sampling techniques and tests required for mix designs and optimization of mix ratios. Potential environmental risks caused by treatment, measures for minimizing risks and beneficial uses for a treatments' final products are also discussed.

Course Introduction

The student will become familiar with solidification and stabilization (S/S) methods used for treating contaminated liquids, soils and sludge at hazardous and toxic waste sites. The basic guidelines for the S/S treatment methods, the advantages and disadvantages and guidance in the selection of the most appropriate treatment method are discussed. The differences in the methods and benefits of their combined use and waste conditions not suitable for their use are explained. Understand proper sampling techniques and tests required for mix designs and optimization of mix ratios. Potential environmental risks caused by treatment, measures for minimizing risks and beneficial uses for a treatments’ final products are also discussed.

This course provides general technical guidelines and procedures for solidification and stabilization (S/S) methods of treatment at uncontrolled HTW 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 HTW material is within the feasible or economic limits of available technology. Landfills prohibit bulk or non-containerized liquid hazardous waste because liquid wastes and free liquids will leach into the groundwater over time without proper treatment and handling. To avoid groundwater contamination landfills may accept only containerized liquids, which do not have free liquids or are mixed with adsorbents or solidified to remove freestanding liquid. Lab packs and very small containers, ampules, may also be placed in a landfill. 

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. Disposal methods for radioactive waste are not discussed here since satisfactory disposal requires special landfills that are regulated by the Nuclear Regulatory Commission (NRC).

S/S treatments are relatively quick and low cost processes. Because of great variations in contaminants at waste sites, site specific design for the ratio of waste and additives is required. Treatment is accomplished by first mixing the waste with reagents using augers, excavators or backhoes and the pozzolonic agents to harden the waste and is then allowed to cure. Reagents commonly used are Portland cement, cement kiln dust (CKD), lime, lime kiln dust, fly ash, slag, gypsum and phosphate mixtures. Fly ash has a pozzolonic effect if mixed with Portland cement. CKD however does not have strong cementitious properties but is economical. Lime will adjust the pH and drive off water. A benefit from treating drilling fluids for instance is that after proper curing they may be reused or else left safely in place. The treatment and cure times will depend on the chemical types and amounts, extent of pollution and depth, subsurface conditions and whether mixed in place or removed for mixing. 
S/S are two different types of remediation methods which prevent or slow the release of harmful chemicals from contaminated soil, sludge and liquids. These methods targeted treating petroleum wastes such as oil field waste and wastewater, drilling mud, cuttings and oil based drilling fluids. The chemicals are not usually destroyed but are prevented from migrating into the environment. The solidification process essentially binds the contaminated waste and cements it into a solid form by mixing with reagents and then pozzolonic setting agents to harden the waste material which may be safely left in place or removed. Rain and ground water are prevented from dissolving or moving chemicals from the treated waste material. Reagents added to metal contaminated soil changes the metals to less soluble metal compounds and immobilize them.

Stabilization alters the chemicals to become less harmful or less mobile. Both methods are often used together as complementary treatments.
S/S techniques used to treat waste containing organic contaminants with traditional cements and pozzolonic materials have not always been successful and are then classified as hazardous. Organics have had adverse effects on cement hydration, structure formation and stabilization of contaminants. Safe disposal would then require a lined landfill with monitoring system or pretreated with thermal or biological processes. As mentioned in the text, organophillic clay modified with special additives holds some promise to chemically fix organic compounds. Organophillic clay can tolerate excessive hydration with out losing stability unlike the traditional cements and pozzolonic treatments. Br selective use of these clays and other compounds it is believed the reactive properties of the clay will chemically bind organic contaminants to a clay matrix. After mixing with the clays the waste can then be solidified with other reagents. Organic reagents such as asphalt, thermoplastics and urea-formaldehyde have also been attempted but they are prohibitively expensive compared to inorganic reagents. 

The advantages and limitations of S/S waste treatment methods are compared. The treatment methods present certain environmental risks and other concerns for consideration. Environmental risks include mismanagement of 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. The treated waste must be tested for proper sealing, strength and durability to provide a safe cleanup.

Course Content

This course is based primarily on the US EPA document, “TPR: Selecting and Using Solidification/Stabilization Treatment for Site Remediation”, EPA/600/R-09/148 (2009 Edition, 28 pages) PDF file.

The course also uses Chapter 4 of the US Army Corps of Engineers ETL, “Technical Guidelines for Hazardous and Toxic Waste Treatment and Cleanup Activities”, ETL 1110-1- 158 (1995 Edition, 18 pages) PDF file. The ETL included provide additional details for topics discussed in the above EPA document.

The link to the EPA document is "TPR: Selecting and Using Solidification/Stabilization Treatment for Site Remediation"
The link to the Engineers Manual is "Technical Guidelines for Hazardous and Toxic Waste Treatments and Cleanup Activities", Chapter 4, paragraph 4-21.

You need to open or download above documents to study this course.

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 HTW substances are heavy metals, including lead, cadmium and mercury and PCBs, dioxins, chlorine, sulfur, potassium and explosives. Solidification and stabilization methods are discussed and can be used to remediate contaminated soils and sludge prior to final disposal and reduce the land needed for disposal as for traditional landfills. 

Related Links

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

http://frtr.gov/matrix2/section4/4-8.html
A publication by the Fed Remed Technology Roundtable for treatment and disposal methods for waste treatment.

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.