The problem addressed by this proposal is the need to remediateheavy metals in groundwater and soils. The proposed method can immobilizemetals by chemically binding them into extremely stable phosphate phases(apatite minerals) in the soil, sediment, or in a permeable reactivebarrier. The stabilization is irreversible under most environmentalconditions for hundreds of millions of years, (e.g., pH 2 to 12 up to1000¡C, in the presence of aqueous and non-aqueous phase liquids, andunder disruptions such as earthquakes, ground subsidence or humanintrusion). Also, because of this extreme stability, the effects of soilheterogeneity, hydrology and other subsurface properties do not affectthe performance, and, themselves, and not affected by this treatment. Theobjective of Phase I is to demonstrate that the apatite treatment of leadzinc and cadmium-contaminated soil and groundwater from the Bunker HillMining Site (EPA Region 10) will permanently immobilize the metals in newstabile mineral phases. The specific work consists of a series of soilcolumn flow experiments using contaminated soils from the site which willbe mixed with four different types of apatite in each fashion as wouldoccur during either mixing (auguring) of soil in the field or emplacementof a permeable reactive groundwater barrier. Actual groundwater will beapplied to the top of the columns. Leachates will be collected every 24hrs. until "breakthrough". This will provide the loading capacity foreach type of apatite as demonstration of effectiveness of each type ofapatite. Together with batch tests, geochemical modeling and choice ofemplacement methods, these tests will determine the feasibility of thePhase II field work. Effectiveness and cost will determine the finalchoice of apatite for Phase II. The success of this work should haveimmediate benefit for almost all metal-contaminated sites.
