LDA

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How it Works

FECC’s Chlorinated Source Contamination Removal Technology uses Large Diameter Auger (LDA) Soil Mixing to combine thermal treatment followed by injection of ZVI iron powder to remove the volatile, absorbed, soluble and DNAPL contaminant mass. The concept behind the technology is to use the thermal soil mixing treatment to quickly remove the majority of VOCs (> 80 %) followed by injection and mixing of iron into the heated soil and groundwater. The ZVI continues to remove the remaining chlorinated VOCs long after the drilling equipment has been removed. The thermal treatment applies a mixture of high-pressure steam and hot air to remove contamination. The LDA mixing increases the contact of the absorbed, dissolved and DNAPL VOCs with the steam/hot-air mixture to increase the rate of contaminant removal by heating and vaporization.

The cutter bits are moved vertically to selectively treat areas of greater contamination as detected by a continuous measurement using an in-line off-gas analysis flame ionization detector (FID). The effectiveness of the heating varies among the chemicals, principally according to their boiling point. The injected air acts as the medium to transport the volatilized contaminant and air mixture to the surface, where it is captured in a shroud under an applied vacuum and transferred to a thermal destruction system or carbon absorption beds. The thermal removal process is highly effective in the initial stage, but this quickly slows and reaches the point of diminishing returns. The ZVI slurry is injected into the thermally-treated cell to continue the removal after the mixing equipment is removed, with the goal of obtaining > 99 % removal. The cost of the iron and its injection is significantly less than the cost of the additional thermal treatment. The result is significantly improved overall removal at a much lower and more affordable cost.

Experience

The LDA thermal treatment uses conventional soil mixing technology that was first demonstrated in 1988 ( USEPA 1991) and since then has been applied at many sites. The combination of in-situ soil mixing hot air steam injection and iron powder as a polishing agent for the remediation of chlorinated VOCs was first implemented as a proof of concept project at Argonne National Laboratory (ANL 1998) on approximately 8,000 cubic yards of clay soil. The study demonstrated the removal of over 90 percent chlorinated VOC. A full-scale pilot test of this combined innovative technology was completed in January 2003 Cape Canaveral AFS (CCAFS), to verify its efficacy in saturated sands. The addition of ZVI to thirty-two test cells from a depth of 20 to 55 feet bgs. indicated greater than 95 percent removal of chlorinated VOC (BEM 2003). In 2004/2005 FECC performed the follow-on full scale remediation and treated approximately 48,000 cubic yards using the combined thermal ZVI process (La Mori, et. al. 2006 & BEM 2006).

Performance and Cost

The process has been applied at the former Space Launch Complex 15 (SLC15) at CCAFS for full scale commercial remediation. The contamination consisted of a variety of chlorinated VOC, most notably trichloroethylene (TCE) and 1,1,2-trichloro-1,2,2-trifluoroethane (Freon 113) but also vinyl chloride, cis 1,2, DCE and PCE located 20’ – 55’ bgs in 2 separate areas known as the Launch Stand and Deluge Basin areas. The summary results of the successful remediation of ~ 48,000 cubic yards of saturated sandy soil are presented in the Table. The cost of the projects was $7.16 million. This included mobilization, demobilization, site preparation,pre and post-treatment chemical analysis sampling, engineering oversight, drilling subcontractor expenses and all materials and maintenance. The cost was $149.24 per cubic yards.

The Process

Key Features of FECC Thermal ZVI

  • Below ground mixing provides active remediation and assures that treatment agents contact contamination.
  • A Data Acquisition System, including FID and GC for process monitoring, feedback and control, allows operational decisions to be made in real time.
  • Immediate removal and capture and destruction of off-gas contamination.
  • Provides the capability to combine several treatment processes in a single operation to achieve faster closure.
  • Operates equally well in vadose and saturated zones to 80’-100’ bgs.