Evaluation the Efficacy of the Turf-Cutter Soil Decontamination Technology

Abstract

Abstract The testing begun in the framework of the CEC project ECP-4 “Decontamination technologies and strategies” have allowed to develop and to test new technology of the polluted soils decontamination by removal of the thin turf layer by the vibrating blade of the special machine (Turf-Cutter). The experiments were conducted at the radioactively contaminated soils of Ukraine and Belarus during 1992–2000. The machine “TURF HARVESTER” (USA) was used in the experiment. The first testing of the method was conducted on the well turfed radioecological polygon “Buryakovka”, 4 km from the Chernobyl NPP, with levels of contamination: 100 Ci/km2 by Cs-137, 80 Ci/km2 by Sr-90, 7 Ci/km2 by Pu-239. As the preliminary researches have shown, about 95% of the radionuclides were concentrated in the upper layer of the unploughed soil. In an outcome of tests on a selected plot the decontamination factor (Fd) 25–40 for different radionuclides was obtained. After removal of turf and opening the soil surface, the wind soil erosion and secondary resuspension the radionuclides was expect. It has not taken place, as special researches on an evaluation of the wind resuspension of radionuclides by the soil particles after the turf harvesting. This can be explained as follows. The vibrating blade does not decondence and decompose the soil layer remaining. At the same time, the thin turf and soil layer removal saves the vegetation regenerating organs and roots, which allows the grass restoration and surface fixation within one month after the experiment. The second test of a method was conducted on a polygon “Chistogalovka”, 3 km of the NPP. A high level of the radioactive contamination (150 Ci/km2 by Cs-137) and the weak turf cover of the rugged sand surface characterized the polygon. The turf removal at this polygon has allowed to receive Df = 10–15. Another testing was made at the Belorussian part of the Zone, which have demonstrated the possibility of the selected turf removal under the spotty radioactive contamination. The field gamma-spectrometer “Corad”, produced by the Kurchatov Institute (Russia), was used for the operative definition the highly contaminated spots. The selected removal of the mostly contaminated spots decreased the mass of the turf removed by 70%, obtaining the Df = 5–7. Next testing was conducted at the village Miliach (Rivne Province, Dubrovitsa district, Ukraine) at the pasture “Stav” with the contamination level by Cs-137 about 5 Ci/km2. This pasture was not influenced by any post-accident countermeasures. After the radioactive turf removal (Df = 15–20), the fodder grass was sow. The grass contamination was 15 times less, comparing to the control. The experimental fattening of 10 cows by a grass, skewed on the decontaminated plot, within 10 days, was carried on. A comparison the contamination of the milk from the experimental cows, which were fed by a grass of the turf-harvested plot, and the milk of the control cows, has shown the milk Df about 11 in 1993. The data obtained show high efficiency of the decontamination technology for the polluted soils based on the turf removal by the vibrating blade. Decontamination factor about 7–15 for the sandy and dusty-sandy soils with a weak turf layer up to 20–40 for the organic and wet silty soils with a strong turf layer was obtained. Important thing is, the best Dfs were obtained for the soils, which are critical on the intensity of the root uptake of the radionuclides. The high ecological and radioecological safety of the Turf-Cutter technology of the soil decontamination is also to be considered. The thin turf and soil layer removal does not deteriorate dramatically the migration situation and at the same time does not avoid the damaged ecosystem self-restoration. The volume of the matter harvested is comparatively low, because of the thin cutting. Being stored in the walls 2,5 m height, it occupies less 5% of the territory decontaminated, and the risk of migration the radionuclides outside the storage sites is comparative to those of the primary soil layouts. The field testing of the Turf-Cutter technology show correlation of its efficacy to the soil types, vegetation cover and the landscape conditions of the contaminated territory. It allowed, using some elements of the GIS-technologies and cartographic modeling, to prepare special evaluation and zonification the territories contaminated on the efficacy of the Turf-Cutter technology, and to identify the areas best for it’s mostly effective application. Following investigations confirm stable, long-term character of the improvements carried out. The sampling of 2000 at Miliach experimental plot shows the decontamination factor 10–11 for the grass and about 8 for milk. Moreover, as the Cs-137 still remains at the upper part of the soil profile, the Turf-Cutter technology is still actual for the territories of the post-Chernobyl radioactive contamination. Obviously, it can be suitable also for the removal of any other surface pollutant from the soil.