ROBERT A. EVANGELISTA

FRENCH DRAIN INTERCEPTOR TRENCH, SOIL VAPOR EXTRACTION (SVE), LOW TEMPERATURE THERMAL TREATMENT (LT3), and STEAM/HOT AIR INJECTION WITH ACTIVE SOIL MIXING

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Chemical Commodities, Inc., which purchased off-specification and surplus chemicals for resale, was located in a residential neighborhood of Oletha, KS, where children played close to the facility’s fence. Inside, soil and groundwater containing toxic volatile organic compounds (VOCs), predominantly trichloroethene (TCE), lay in wait.

 

French Drain Interceptor Trench

Initial soil borings, sampling, and analyses found contaminated groundwater migrating away from the site. To contain and capture the renegade groundwater before it reached an adjacent rail line, an initial objective was to design and implement a French drain interceptor trench. A deep but narrow ditch was excavated through soil and cut into the underlying harder shale. Upon completion, groundwater and toxicants fell into the cut and were pumped to the surface for storage and disposal. Viva la France!

 

Soil Vapor Extraction (SVE)

As project engineer, I explored the feasibility of three technologies to remove the poisonous VOCs from soil: soil vapor extraction (SVE), low temperature thermal treatment (LT3), and steam/hot air injection with active soil mixing. These technologies mobilize VOCs from the soil phase to the vapor phase, where the VOCs are destroyed or captured. The major challenge for all the technologies was the highly plastic clayey soil, which looked like a Tootsie RollTM. In this difficult soil, organic contaminants formed concentrated pockets of dense nonaqueous phase liquids (DNAPLs).

Soil vapor extraction (SVE) used a vacuum to mobilize VOCs from the soil to the vapor phase, where the VOCs can be captured and destroyed. Contaminated soil from the site was placed in a bench-scale SVE chamber. Eighty-three percent of the VOCs were “sucked” from the soil into a canister of activated carbon, even though the clayey soil had low pneumatic permeability.

 

Low Temperature Thermal Treatment (LT3)

Low temperature treatment (LT3) used oven-like temperatures to heat and evaporate soil-bound VOCs to the vapor phase, where VOCs can be incinerated in an afterchamber. Soil was placed into a bench-scale LT3 and pushed through a heated chamber by a screw auger. After the LT3, ninety-one percent of the VOCs were forced from the treated soil.

 

Steam/Hot Air Injection with Active Soil Mixing

Steam/hot air injection with active soil mixing employed injected steam (which heats the soil) and hot air (which pushes VOC vapors to the surface). During steam/hot air injection soil was actively mixed in place (in situ) by a blade auger. The toxic VOC vapors were captured at the surface and condensed into a pure liquid, while the steam and air was reheated and reinjected. I reviewed and evaluated a full-scale system “steam cleaning” VOCs from soil in the Port of Los Angeles. The advantages of this technology were the avoidance of harmful volatile chemicals that can evaporate into the air during soil excavation, the recovery of the contaminants into a pure liquid that could be used as a liquid fuel, and active soil mixing to minimize pockets of DNAPLs remaining in treated soil.

 

More Information

R. Evangelista, Extent of Contamination Determination, Building Decontamination Guidelines, and Bench-Scale Remedial Test for Chemical Commodities, Inc., Oletha, KS. Prepared for the U.S. Environmental Protection Agency, 1989. PDF 8.1 MB

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