1a. Objectives (from AD-416):
Evaluate the benefit of FGD-gypsum in revegetation and reduction of Hg vapor emissions from CA mercury mine waste contaminated serpentine soil materials. These soils are estimated to cause at least 50% as much Hg emission as all U.S. coal-fired power plants. Prevention of Hg emission from the mine wastes could be an important environmental benefit (in addition to cessation of waterway contamination) which might be traded for reduced emission goals from power plants.
1b. Approach (from AD-416):
Conduct greenhouse trial of mixtures of FGD-Gypsum and other locally (mid-CA) available soil amendments (composts, biosolids, manures) which might be useful in establishing persistent vegetative cover on Hg mine wastes and geochemically Hg rich soils from CA. Because these soils are extremely deficient in Ca, addition of gypsum is expected to strongly aid vegetation establishment and persistence. Effective cover would prevent sunlight from hitting the soil (which causes photo-reduction of Hg2+ in soil which allows the Hg vapor release from the mine waste. Climate-adapted vegetation would be used in the test. Hg vapor emissions of the surface amended and control soils will be measured and compared to controls. Evaluation of the nutrition of plants from several treatments will help characterize how well the amendment mixtures should support persistent revegetation of these mine wastes.
3. Progress Report:
Light-induced reduction and emission of mercury (Hg) vapor from mercury contaminated soil materials is now believed to cause mercury emissions equal to one-third to one-half of the amounts emitted by coal-fired power plants in the U.S. Very few Hg contaminated soils have been remediated except where water erosion contaminated streams could cause risk through fish consumption. Many of the mercury contaminated areas in the western U.S. are on serpentine soil areas where calcium is deficient for plants and the extreme infertility of the disturbed mercury mine and smelter wastes remain barren which promotes mercury emissions. An ARS researcher visited sites at the New Idria Superfund Site, and at a Bureau of Land Management (BLM) site in CA and collected samples. Samples from the New Idria site contain mercury at 10,000 times higher than background U.S. soils and require remediation to limit emissions of Hg vapor. Soils from the New Idria site are not so severely low in calcium as the BLM site. Greenhouse tests have been planned and started to test the ability of compost and FGD-Gypsum to aid in establishing appropriate local vegetation for the semi-arid site. Some of the mine waste soils were rich in sulfides (pyrite) and have become extremely acidic and phytotoxic (pH <4.5), while others remain calcareous. During the FY, a site visit was made to Hg contaminated sites in CA, and regular email contact with the EPRI project manager was maintained.