Chernobyl groundwater contamination

The

Other sources of groundwater contamination included: radioactive waste dumps on the territory of “exclusion zone”; cooling water reservoirs connected with aquifer; initial radioactive fallout which took place in first hours after the accident; and forest fires that led to accelerated spread of contaminated particles on soils of the surrounding area^[4] On the whole, the researchers recorded the probability of accumulation of nearly 30% of the overall surface contamination in the underground rock medium.^[2] This discovery demonstrates hazardous scales of radionuclides underground migration on the one hand, but the important function of igneous rock as protective shield against further spread of contaminants.

Recent revelations of facts concealed by the Soviets show that the problem of groundwater

After the disaster, the Soviet Government aimed took delayed and inefficient measures at neutralization of consequences of the accident. The issue of groundwater contamination was improperly addressed the first several months after the disaster, leading to colossal financial expenses with negligible result. At the same time, proper monitoring of the situation was mostly absent^[3] The primary attempts of disaster relief workers were directed to prevention of surface waters contamination. Large-scale radionuclide content in the underground water was monitored and detected only in April–May 1987, almost a year after the disaster^[5]

Migration pathways of contamination

Unfortunately, hydrological and geological conditions in

As to Cesium-137, this nuclide demonstrates lower migration potential in Chernobyl soils and aquifers. Its mobility is hampered by such factors as: clay minerals which fixate radionuclides in rock, absorption and neutralization of isotopes through ion-exchange with other chemical components of water; partial neutralization by vegetation metabolic cycles; overall radioactive decay.^[4] Heavy isotopes of Plutonium and Americium have even lower transportation capacity both in and outside the exclusion zone. However, their hazardous potential should not be discarded considering extremely long half-life and unpredictable geo-chemical behavior^[5]

Agricultural damage

Groundwater transportation of

Health risks

The health impacts of groundwater contamination for population of Ukraine, Belarus and bordering states are usually perceived as extremely negative. The Ukrainian government initially implemented a costly and sophisticated remediation program. However, in view of limited financial resources and other more urgent health problems caused by the disaster, these plans were abandoned^[10] Not least, such a decision owed to the research results of domestic scholars showing that groundwater contamination does not contribute to the overall health risks substantially in regard to other active pathways of radioactive exposure in the “exclusion zone”,^[2][4] In particular, radioactive contamination of unconfined aquifer, which is usually considered a serious threat, has fewer economical and health impact in Chernobyl because subsurface water in “exclusion zone” is not used for household and drinking needs. The probability of using this water by local residents is excluded by a special status of Chernobyl area and relevant administrative prohibitions. The only group directly and inevitably exposed to health threats are emergency workers engaged in water drainage practices related to Chernobyl Nuclear Power Plant reactors deactivation and waste disposal operations.^[7]

As to contamination of confined aquifer, which is a source of technical and household water supply for

In face of persistent disintegration of radioactive materials and highly unfavorable radiation background in “exclusion zone”, permanent monitoring was and remains crucial both for deescalation of environmental degradation and preventing humanitarian catastrophes among neighboring communities. Monitoring also allows to reduce parameter uncertainties and improve models of assessment, thus actually leading to more realistic vision of the problem and its scales.^[7] Until the late 1990s, methods of data collection for groundwater quality monitoring were of low efficiency and reliability. During installation of monitoring boreholes, the wells were contaminated with “hot fuel” particles from the surface ground, what made initial data inaccurate. Decontamination of boreholes from extraneous polluters could take 1,5–2 years. Another problem was insufficient purging of monitoring wells before sampling. This procedure, necessary for replacement of stale water inside boreholes with new water from aquifer, was introduced by monitoring personnel only in 1992. The importance of purging was immediately proved by substantial growth of Strontium-90 indexes in samples^[3] The quality of data was additionally worsened by corrosion of steel components of monitoring wells. Corrosive particles substantially altered radioactive background of aquifer. In particular, excessive content of iron compounds in water got into compensatory reactions with Strontium thus leading to deceptively lower Strontium-90 indexes in samples. In some cases, irrelevant design of well cages also impeded monitoring accuracy. The well constructions implemented by Chernobyl Nuclear Power Plant personnel in early 1990s had 12 meters long screening sections allowing only vertically arranged sampling. Such samples are hard to interpret as an aquifer usually has unequal vertical distribution of contaminants^[3]) Since 1994, the quality of groundwater observation in Chernobyl zone sufficiently improved. New monitoring wells are constructed with poli-vinylcloride materials instead of steel, with shortened screening sections, 1–2 m^[3] Additionally, in 1999-2012 there was created an experimental monitoring site in proximity to radioactive waste dumps area westward Chernobyl Nuclear Power Plant, called “Chernobyl Red Forest”. The elements of the new monitoring system include laboratory module, station for unsaturated zone monitoring, network of monitoring boreholes and meteorological station^[4] Its primary objectives include monitoring of such processes as: radionuclides extraction from “hot fuel particles” (HFP) dispersed in surface layer; their subsequent transition through the unsaturated aquifer, and condition of phreatic (saturation) zone. HFP are particles which emerged from burnt wood and concrete during initial explosion and subsequent fire in the “exclusion zone”. Unsaturated aquifer is provided with water and soil sampler, water containment sensors and tensiometers. Work of an experimental site allows to make real-time surveillance of Strontium-90 migration and condition in aquifer, yet simultaneously raises new questions. The monitoring staff noticed that fluctuations of water levels directly influence the release of radionuclides from sediments, while accumulation of organic matter in sediment correlates with geochemical parameters of aquifer. Additionally, for the first time the researchers detected Plutonium in deep-laying groundwater, which means that this contaminant also has a capacity to migrate in confined aquifer. However, specific means of this migration still remain unknown.^[11]

The researchers forecast that in case of inviolated protection of nuclear waste dumps in exclusion zone, the concentration of Strontium-90 up to 2020 will be much lower in subsurface water than admissible maximum indexes. Also, contamination of the Pripyat River as the most vulnerable surface water route by underground tributaries is unlikely in the next 50 years^[2] At the same time, the number of monitoring wells is still insufficient and needs expansion and modification. Also, the boreholes are distributed within the exclusion zone unevenly, without consideration of hydrological and radioactive specifics of the area (Kovar&Herbert, 1998^[3]

Lessons learned

Chernobyl accident revealed complete unpreparedness of the local authorities to the resolution of environment-related issues of a nuclear disaster. Groundwater management is no exception. Without accurate real-time data and adjusted emergency management plans, the government spent enormous funds for groundwater remediation, which later proved to be needless. At the same time, really crucial top-priority measures, such as reliable isolation of the damaged 4th reactor, were performed on a poor-quality level. If the “Shelter” had been constructed without deficiencies as completely hermetic and isolating the 4th reactor from contact with external aerial, soil and groundwater mediums, it would make much greater contribution to prevent entering nuclides in and their migration throughout groundwater network^[5] Taking these failures into account, the following are lessons learned from Chernobyl tragedy for groundwater management:

• The necessity of consistent and technologically reliable monitoring system capable to produce high-quality real-time data;
• Exact monitoring data as a primary basis for any remedial practices and melioration policies;
• Criteria and purposes of groundwater management activities, be it remediation, construction works or agricultural restrictions, are to be identified at the stage of analysis and prior to any practical realization;
• Problems of groundwater contamination must be regarded in the wider perspective, with close correlation to other pathways and forms of contamination, because they all are interconnected and mutually influenced;
• It is always highly advisable to engage international experts and leading scholars to peer-reviewing of designed action plans;
• Groundwater management in areas of radioactive contamination must be based on integrated ecosystem approach, i.e. considering its influence on local and global ecosystems, well-being of local communities and long-lasting environmental impacts.^[4]

References