Groundwater residence time downgradient of Trench No. 22 at the Chernobyl Pilot Site: Constraints on hydrogeological aquifer functioning (original) (raw)
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Applied Geochemistry, 2012
This article discusses and analyzes data for geochemical monitoring of groundwater, collected in 1998-2008 at the international experimental radioecological study site (Chernobyl Pilot Site) located in the Red Forest radioactive waste dump site in the Chernobyl exclusion zone. Groundwater in the zone of influence of the studied waste trench no. 22T was characterized by a specific geochemistry. Along with a high content of 90 Sr (of an order of n  1000-n  10,000 Bq/L) groundwater showed elevated concentrations of Ca, K, NO À 3 , SO 2À 4 and of some trace elements (in particular stable Sr), and had more acidic pH values compared to ''background'' aquifer conditions. The observed water quality changes are apparently related to degradation of organic matter (pine forest remnants, litter, humus containing topsoil layer) buried inside trench no. 22T, which have lead to acidification of groundwater and leaching of cations adsorbed on the exchange complex of soils buried inside the trench. Regime monitoring data for the project period of 1998-2008 shows a progressive decrease of concentrations of the leached ions accompanied by an increase of pH in the chemical plume emerging from the trench. This can be explained by a combined effect of a gradual decrease of the inventory, humification of the original organic matter inside the trench, and of nutrient element uptake by roots of the newly planted pine forest on top of the trench. The identified trends of evolution of geochemical regime favor attenuation of subsurface migration of 90 Sr from Red Forest waste dumps due to an increase of the 90 Sr distribution coefficients, and stabilization of plumes of contaminated groundwater.
Journal of Geochemical Exploration, 2008
A study of the 137 Cs distribution and mobility in alluvial soil profiles was performed in the basin of the Iput river (Bryansk region) to reveal peculiarities of the flood plain contamination after the accident at the Chernobyl NPP. Four study plots have been located on the medium and low-level riverside flood plain of the rivers Iput and its right tributary Buldynka. Soil profiles were sampled manually and continuously in the increasing increments of 2 to 5 cm down to 50 cm below the soil surface. Soil profiles have been analysed for the 137 Cs specific activity, organic matter content, granulometric composition, absorbed bases, exchangeable potassium and 137 Cs, mobile iron and manganese and mineral composition of the clay fraction (b 0.001 mm).
Radiation Protection Dosimetry
After the Chernobyl accident, a designated area of ~1000 m2 within the University farm of Aristotle University of Thessaloniki in Northern Greece was utilized as a test ground for radioecological measurements. The profile of 137Cs in the soil was monitored from 1987 to 2023, with soil samples collected in 5-cm-thick slices (layers) down to a depth of 30 cm. The mean total deposition of 137Cs in the area, backdated to the time of the Chernobyl accident, was determined to be 18.6 ± 1.8 kBq m−2 based on four follow-up profile measurements of 137Cs in the soil for the years 2022 and 2023. It is noteworthy that this value is similar the total deposition at the site, which was independently measured to be about 20 kBq m−2 during the first year after the Chernobyl accident. The fractional contribution of each soil layer (e.g., 0–5 cm, 5–10 cm, 10–15 cm, etc.) to the total deposition of 137Cs (0–30 cm) is presented and analyzed. A compartment model was utilized to forecast the temporal evol...
High 36Cl/Cl ratios in Chernobyl groundwater
After the explosion of the Chernobyl Nuclear Power Plant in April 1986, contaminated material was buried in shallow trenches within the exclusion zone. A 90Sr plume was evidenced downgradient of one of these trenches, trench T22. Due to its conservative properties, 36Cl is investigated here as a potential tracer to determine the maximal extent of the contamination plume from the trench in groundwater. 36Cl/Cl ratios measured in groundwater, trench soil water and leaf leachates are 1-5 orders of magnitude higher than the theoretical natural 36Cl/Cl ratio. This contamination occurred after the Chernobyl explosion and currently persists. Trench T22 acts as an obvious modern point source of 36Cl, however other sources have to be involved to explain such contamination. 36Cl contamination of groundwater can be explained by dilution of trench soil water by uncontaminated water (rainwater or deep groundwater). With a plume extending further than that of 90Sr, radionuclide which is impacted by retention and decay processes, 36Cl can be considered as a suitable tracer of contamination from the trench in groundwater provided that modern release processes of 36Cl from trench soil are better characterized.
Vertical profiles of 137 Cs and 239,240 Pu were measured in soils collected from two sites in southern Sweden and three sites in southern Poland and were modeled using both a solute transport model and a bioturbation model to better understand their downward migration. A time series of measured 137 Cs profiles indicates that 137 Cs from Chernobyl was found at the soil surface in 1986 but it has migrated progressively downward into the soil 4.5-25.5 cm since. However, because of dispersion during the migration and mixing following Chernobyl deposition and the much higher activities of 137 Cs from Chernobyl, stratospheric fallout of 137 Cs from the 1960s cannot be identified as a second 137 Cs activity maximum lower in the soil column at any of the sites. Conversely, the 240 Pu/ 239 Pu ratio indicates that no Chernobyl-derived Pu is present in any of the cores with the exception of one sample in Sweden. This difference may be attributed to the nature of the release from Chernobyl. Cesium volatilized at the reactor temperature during the accident, and was released as a vapor whereas Pu was not volatile and was only released in the form of minute fuel particles that traveled regionally. Both the solute diffusion and the bioturbation models accurately simulate the downward migration of the radionuclides at some sites but poorly describe the distributions at other sites. The distribution coefficients required by the solute transport model are about 100 times lower than reported values from the literature indicating that even though the solute transport model can simulate the profile shapes, transport as a solute is not the primary mechanism governing the downward migration of either Cs or Pu. The bioturbation model uses reported values from the literature of the distribution coefficients and can simulate the downward migration because that model buries the fallout by placing soil from depth on top and mixing it slightly throughout the mixing zone (0.6-2% per year of mixing). However, mixing in that model predicts concentrations in the top parts of the soil profiles which are too high in many cases. Future progress at understanding the downward migration of radionuclides and other tracers will require a more comprehensive approach, combining solute transport with bioturbation and including other important soil processes.
Geography and Natural Resources, 2016
We examine the use of two alternative techniques for assessing the redistribution volumes of sorbed 137 Cs within the upper components of the fluvial network, based on the concept of catchment as a lithodynamical system. In terms of one of them, we made a substantive analysis of changes in reserves on accumulative positions where the 137 Cs distribution curves showed a significant increase in radionuclide content levels. We carried out a typization o the accumulation surfaces in order to extrapolate data, obtained for a group of soil profiles, to the territory of the entire catchment and to make a direct assessment of the increases in accumulation. An alternative technique was used to assess the volumes of accumulated sediment loads on accumulative positions by analyzing the 137 Cs distribution curves, and to correlate with denudation zones in the drainage area under consideration. Values of the wash-out rates for the period 1986-2012 have been obtained, which are necessary for the formation of the accumulative layer observed. We calculated the volume of 137 Cs swept away during 26 years after the Chernobyl accident, based on information regarding the volumes of initial reserves in the denudation zones and a correlation between the erosion rate and a specific reduction in reserves. It is established that the technique on the basis of analyzing the wash-out zones featuring high economical efficiency can be used in assessing 137 Cs migration for larger territories with relatively low labor-consuming effort.
Behaviour of long-lived Chernobyl radionuclides in a soil?water system
The Analyst, 1992
Field and laboratory experiments have been used to study the behaviour of long-lived radionuclides in the zone affected by the Chernobyl accident. Speciation of soSr sni 137f,s in soils and bottom sediments was determined. The principal distinction of the Chernobyl fallout was that it contained a relatively small proportion of exchangeable forms because a considerable fraction of the radionuclides was incorporated as part of the insoluble fuel particles. Disintegration of fuel particles in soils and bottom sediments results in transition of non-exchangeable forms into exchangeable forms. Radionuclide species have different pathways and rates of migration in soils and bottom sediments: Migration of each chemical form was described by a convective-dispersive equation taking into account transformation processes of radionuclide species in soils or bottom Sediments. Adsorption of goSr and 137Cs in the environment is controlled by the cation-exchange capacity and the selectivity of the solid phase (i.e., soil, bottom sediments and suspended matter) and the cationic composition of the liquid phase (l.e., soil solution, surface run-off and r.iver or lake water). The corresponding parameters for the processes were obtained.
Long-Term Monitoring of Radionuclides in Soils and Groundwater: Lessons Learned from Chernobyl
The Chernobyl region has a humid climate with mild, short winters and a warm summer. Average annual precipitation ranges from 550 to 750 mm/yr. The relief consists of slightly undulating plains and ridges, and irregularly located bogs. The relatively dense network of Pripyat and Dnieper River tributaries forms boggy valleys of moderate relief. Approximately 50% of the land in the exclusion zone is covered by forest, 30% by arable farmland, and the remaining 20% by urban areas, forest, marshlands, and water bodies (Shestopalov 1996, p. 22). The soils are relatively homogeneous, with mostly podsols and peaty podsols serving as the topsoil layer within the Exclusion Zone.