STAR (In Situ) Pilot Test to Treat Coal Tar Impacting Two Hydrogeologic Units

Former Industrial Site in New Jersey

STAR was evaluated as an alternative to excavation and disposal and Low Temperature Thermal Desorption (LTTD) at a 37-acre former manufacturing facility in New Jersey impacted with coal tar. A Pre-Design Evaluation (PDE) was conducted within two hydrogeologic units (i.e., surficial fill and underlying sand units) to evaluate key design parameters such as: 1) contaminant mass destruction rates; 2) STAR well radius of influence (ROI); and, 3) vapor emissions levels, in preparation for the design of a full-scale remedy for the site.

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Image 1: Vapor collection barrier and equipment used in the deep sand unit test.

Pre-Design Evaluation (PDE)

The PDE within the surficial fill unit demonstrated sustained destruction rates in excess of 800 kg/day resulting and the destruction of more than 4,500 kg of coal tar. This treatment was supported solely through air injection at a single well following a 90-minute ignition period. Deep sand unit testing (twenty-five feet below the water table) resulted in the treatment of a targeted six-foot layer of impacted fine sands to a radial distance of approximately twelve feet. Analysis of collected vapors showed that approximately 1% of the total remediated mass was volatilized (and collected for subsequent treatment); whereas approximately 99% of the coal tar was destroyed via smoldering combustion. Post-pilot sampling for both units demonstrated a substantial reduction in coal tar volume within the target treatment zones, with volatile and semi-volatile organic compound concentrations reduced (on average) by greater than 99% in zones where combustion was observed or detected. These results (and additional parameters) were used to develop a full-scale STAR design for the site.

Temperatures Achieved

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Image 2a: Maximum temperatures achieved after 11 days of operation during the deep sand unit test. Note that no physical barrier to groundwater flow was installed or used within the deep sand unit during this test.
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Image 2b: Cross-section showing the attainment of combustion temperatures within the six-foot thick target treatment zone. Note that the water table is located at approximately three feet below ground surface.

Soil Cores Before and After Pilot Test

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Image 3a: Pre-PDE soil core showing the coal tar-impacted soils within the deep sand unit (approximately 25 feet bgs).
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Image 3b: Post-PDE soil core showing the extent of remediation within the deep sand unit (approximately 25 feet bgs).

Selection of STAR for Full-scale Application

The PDE results were used to develop a full-scale STAR design consisting of approximately 1500 surficial fill ignition points and 500 deep sand ignition points and two treatment systems (air distribution and vapor collection/treatment system).

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Image 4: Carbon footprint of STAR versus alternative technologies

Conclusions

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

The PDE:

  • Resulted in the destruction of more than 4,500 kilograms of coal tar within the surficial fill unit and more than 800 kilograms of coal tar within the deep sand unit.
    Showed radii of influence from a single point of ignition up to 30 feet in the shallow fill unit and up to 12 feet in the deep sand unit.
  • The full-scale design incorporated key design parameters evaluated during field testing and integrated a detailed Conceptual Site Model (CSM)
  • Full scale remediation began in early 2014 and is anticipated to continue through 2016.

More Information

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