STAR (In Situ) Pilot Test to Treat Coal Tar-Impacted Soils in a Former River Meander

Former Coke Plant in Belgium

The AMS Site in Belgium used to produce coke for steel making. Investigations have shown that the backfill of a former meander of a nearby river is nearly saturated with coal tar below the water level (from 7 to 9 meters below ground surface [bgs]). Its excavation and treatment would be very expensive and create numerous nuisances for the neighborhood. Therefore, the agency in charge of its cleanup (SPAQuE) is looking for a cost-effective in-situ treatment technology.

Treatability Testing

The STAR treatability study was conducted for soils collected from three locations at the Site. Each test sample demonstrated strong self-sustaining smoldering behavior; that is, elevated and steady (or rising) reaction temperatures were maintained throughout the test interval following ignition, with smoldering front propagation velocities ranging from 2.9 metres per day to 6.9 metres per day. Analysis of pre- and post-STAR test soils showed reductions of F1 and BTEX, F2-F4, and SVOCs concentrations, generally to levels below detection limits.

The following images show consine treatability study results for: Magnetite formation was noted during the test for the TR17-30 samples indicating mineralogical changes as a result of the smoldering process.

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Image 1a: Before and after: P507
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Image 1b: Before and after: TR17-30 shallow
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Image 1c: Before and after: TR17-30 deep

System Description

STARx development has focused primarily on the treatment of waste oils and sludges associated with the oil and gas and chemical manufacturing industries and stock-piles of excavated contaminated soils. The STARx system is capable of destroying greater than 99.9% of contaminant / waste mass and an extensive prototype testing program has been underway since 2012. This prototype testing program has been designed to evaluate the ignition system, operational robustness, reactor material robustness, range of operation conditions (temperature and pressure as a function of time and space), the factors affecting burn rates and volatile emissions, treatment efficiency / remediation performance.

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Image 2: Vapor collection barrier and equipment used in the in situ pilot test.
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Image 3: Extent of treatment within the deep and shallow test intervals.

Alternating lenses of fine grained and coarse grained materials encouraged lateral air flow but prevented vertical combustion front propagation from high permeability units at depth vertically upwards into low permeability units above. However, combustion initiated within the shallow low permeability units successfully propagated both vertically and laterally.

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Image 4a: Pre-pilot soil core showing the coal tar-impacted soils at ignition point IP-3.
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Image 4b: Post-pilot soil core showing the extent of remediation within the “burn zone” of the deep target treatment interval.

Conclusions

The STAR technology is a rapid, safe, and low cost remedial alternative for source areas.

In situ pilot testing at the AMS Site demonstrated:

  • self-sustaining smoldering combustion (i.e., no energy input into the system following ignition)
  • limitations with respect to treatment efficiency and vertical propagation as a result of significant heterogeneity and the presence of low permeability clay horizons.

More Information

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