In AP&T, soil flushing with dilute phosphoric acid was combined with iron coprecipitation, to reduce the size of an arsenic plume 80 – 90% in about eighteen months of treatment. A residual plume remains stable at about 10 – 20% of its historical maximum since the cessation of treatment, i.e., about 15 years. The project resulted in two patents: US Patent No. 6,210,078 B1 and corollary Canadian Patent No. 2,307,961.
In ISCF, a chemical reagent is added to the porous media to immobilize the contaminant in place, that is, to reduce leaching to groundwater. ISCF is useful where other technologies are not feasible, for example, under structures or in congested areas. Iron compounds are preferred for arsenic, due to their high adsorptive capacities, low cost, and ease of handling and implacement. Delivery may be through injection, infiltration, or other methods. Laboratory studies demonstrated that ferrous sulfate and ferrous sulfate plus lanthanum chloride can reduce arsenic leachability up to 88% and 96%, respectively, in some soils. Column experiments, which simulated more than 240 years of rainfall, demonstrated that the technology is permanent. Field studies indicated an inverse correlation between iron-treated areas and groundwater contamination, for example, an arsenic plume is diminished in iron-treated areas. ISCF is very cost-competitive with other technologies such as excavation and disposal, and solidification / stabilization. ISCF is the subject of a pending patent application, US 2010/0098494 A1.
AP&T and ISCF can be combined in a treatment train at a contaminated site, for example, use AP&T until the point of diminishing returns, followed by ISCF to treat the residual contaminant.
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