Soil Mixing in Contaminated Soils

Speaker: Nathan Coughenour, Geo-Solutions


Soil mixing, first developed in the 1950s, features techniques that mechanically mix soils with or without additives. More often the term refers to any process in which reagents are injected and mixed into the soil.

Processes vary and include:

  • In Situ vs. Ex Situ
  • Dry vs. Wet Reagent Addition
  • Single Auger vs. Multi Auger
  • Auger vs. Bucket vs. Rotary Drum

The purpose of soil mixing is to create an efficient soil-reagent composite with improved properties relative to the in situ soils.

The most popular applications for soil mixing are geo-environmental, which include in situ stabilization / solidification (ISS); in situ treatment (which is experiencing growing acceptance and use); and containment walls. Geo-technical applications are also useful and include ground improvement; excavation support; liquefaction control; near surface soil property improvement; and cutoff walls

Soil mixing has become a widely accepted means for cost-effective site remediation, with solidification and treatment offering varying approaches. In solidification, contaminants are not purposefully changed to less harmful forms, but exhibit improved physical characteristics or improved handling properties. Through stabilization, contaminants are transformed into less harmful or less mobile forms.

Similarly, the differences between in situ solidification (ISS) and in situ treatment (IST) are negligible. But ISS is generally cheaper than IST, has a lower reagent cost and there are less concerns about safety concerns about handling materials.

While ISS and IST are both acceptable remediation strategies, IST is often viewed as a more robust solution.

Other strategies employed in soil mixing include auger mixing, large diameter auger sequencing, multi-auger, DSM sequencing, DSM augers, and jet grouting.

A few case studies from Geo-Solutions:

Cleanup of glassware manufacturing facility in East Rutherford, NJ

Problem: Site contaminated by TCE and related byproducts.

Solution: Treatment included combination of potassium permanganate with cement. A number of obstructions were removed, including deep foundations, and 242 9-foot diameter columns were installed. Post-construction monitoring showed a 99 percent reduction in TCE concentration.

Cleanup of chemical manufacturing company in Robbinville, NJ

Problem: Site contaminated by xylene and pesticides.

Solution: Reagents hydrated lime and sodium persulfate were applied, and 91-foot diameter columns installed. Process controls used to ensure proper amounts of reagents were added to and mixed with soil.