PDH Online Course Description PDH Units/
Learning Units (Hours)
Solidification/Stabilization Treatment Methods

John Poullain, PE

This two-hour online course provides general guidelines for treating hazardous and toxic waste (HTW) at uncontrolled hazardous waste sites. The guidelines for the selection of solidification and stabilization (S/S) treatment methods for contaminated liquids, soils and sludge are discussed in this course. The differences in the two methods and benefits of their combined use and contaminated waste not suitable for their treatment are explained. Conducting treatability studies prior to S/S treatment, including the required testing, sampling and optimization to establish mix ratios are also discussed. Remedial actions performed at a contaminated site must comply with federal, state and local regulations.

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. 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 change 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.

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

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