Abstract: In systems and methods for treatment of underground contamination, a reducing compound is provided as a substantially insoluble material in an underground formation. The reducing compound accordingly remains substantially in place, even over long periods of time, and is not washed out by underground water movement or diffusion. Accordingly, the reducing compound acts continuously to chemically reduce and remove contamination. When used for treatment of chromium ore processing residue contamination, the reducing compound may be formed and remain in the pores of the residue. As hexavalent chromium diffuses from the residue, it is reduced by the reducing compound. The reducing compound may be injected as a liquid into the underground formation, and then change to a more solid form. Chlorinated solvent contamination may also be treated.

Abstract: In systems and methods for treatment of underground contamination, ferrous sulfide is provided as a substantially insoluble material in an underground formation. The ferrous sulfide accordingly may remain substantially in place, even over long periods of time, regardless of underground water movement or diffusion. As a result, the ferrous sulfide may act continuously to chemically reduce and remove contamination. When used for treatment of chromium ore processing residue contamination, the ferrous sulfide may remain in the pores of the soil or residue. As hexavalent chromium diffuses from the soil or residue, it is reduced by the ferrous sulfide. The ferrous sulfide may be injected as a liquid into the underground formation, and then change to a more solid form. Chlorinated solvent contamination, dissolved chromium from other than COPR contamination, and other dissolved metals may also be treated.