Dam Failure Research Articles

The Fundão dam failure: Iron ore tailing impact on marine benthic macrofauna

The Fundão dam failure, the worst environmental disaster in Brazilian history, launched 50 million m3 of iron ore tailings mud through the Doce River, reaching the Atlantic Ocean. Generally, mine tailings increase the sediment inflow, leading to mud burial of epibenthic macrofauna, and the raise of metal(oid)s concentration causing macrofauna long-term changes. After almost four years, tailings mud was still spreading on the Doce River Shelf, while impacts on marine macrofauna were still unknown. Herein, the IMS index (a tracer of Fundão dam tailings mud), sediment variables, organic pollutants, and metal(oid)s were integrated to uncover the drives of macrofauna structure from Costas da Algas to Abrolhos bank MPAs. Tailings mud was present only in Doce River Mouth and Degredo, organic pollutants and metal(oid)s above safety levels were concentrated in those same areas. Tailings mud (IMS index) drastically reduced species richness and diversity, favoring the abundance of opportunistic species. Mud, IMS index and Al, Ba, and V, metal(oid)s linked to dam failure, structured macrofauna composition in this impacted area, dominated by resistant groups as Nuculidae, Spionidae, and Magelonidae. Conversely, an opposite pattern was found for further and deeper sites with high CaCO3 content and total nitrogen that also showed large grain size, in areas known to harbour biogenic structures, sustaining a macrofauna composition distinct from the impacted areas, dominated by Syllidae and Crassatellidae, sensitives to impacts. Macrofauna composition was most structured by sediment variables, followed by the intersection between metal(oid)s-IMS and Mud, both gradients acting almost entirely on a broad spatial scale. Benthic macrofauna at the Doce River Shelf is still impacted by Fundão dam tailings mud, even after almost four years of the disaster, and may continue to, since the influx of tailings does not stop, and sediment resuspension is a recurrent source for those impacts.

Non-Stationary Hydrological Regimes Due to Climate Change: The Impact of Future Precipitation in the Spillway Design of a Reservoir, Case Study: Sube y Baja Dam, in Ecuador

Changes in flood loads and reservoir levels, produced by climate change (CC), represent an increasing concern for dam safety managers and downstream populations, highlighting the need to define adaptation strategies based on the dam failure risk management framework. Currently, thousands of dams worldwide, varying in use, age, and maintenance, may represent a threat to downstream cities in the case of structural failure. Several studies relate the failure of dams to several issues in the spillway, which may be even more vulnerable in CC conditions. This study provides a review of dam safety threats due to CC and approaches for the design/redesign of the spillway to cope with CC. A general four-stage methodology is proposed: data gathering and hydro-climatic, hydrological, and hydraulic analyses. Afterward, this methodology is applied to the spillway design for the Sube y Baja dam in Ecuador. The Probable Maximum Precipitation (PMP) increases around 20% considering CC under the Representative Concentration Pathway 8.5. Such an increment derived a 25% increase in the spillway maximum flow. These results show that the non-stationary hydrological regimes related to CC require a revision of engineering design criteria for hydraulic structures in general, and call for a consensus on design variables under CC.

Hydrodynamic Process of Partial and en Masse Dam Failure Induced Debris Flows

Because of landslides, seismic events, and/or unregulated human activities, a massive amount of loose solid materials are sometimes deposited at the confluence between the branch valley and stem stream, or blocked at the lateral channel contraction section in a river channel. Immersion of these granular materials in naturally-generated reservoirs tend to cause mass failure and even induce debris flow. However, the majority of previous studies primarily focused on post-event processes (i.e. flow hydraulics such as flood flow hydrographs, sediment transport or erosion, and river morphological changes) following dam failure. In this study, our attention is restricted to hydro-sediment dynamic processes that control unconsolidated dam failure as well as subsequent debris flow. This objective is achieved by conducting a series of experiments in a tilting flume and selecting the overtopping flows, vertical grading configurations, dam heights, and channel gradients as causative factors responsible for chain disaster in the form of dam failure and debris flow. We found that all experimental dams are either subject to partial failure through a gradual breach development or suddenly collapsed in en masse failure mode, debris flows induced by partial dam failures are likely to take place in the conditions of low overtopping flow and shallow channel slope. On the contrary, debris flows originated from en masse dam failures are shown to develop well in the opposite conditions. Also, the critical shear stresses for sediment entrainment under en masse dam failure cases are generally higher if compared with partial dam-failure equivalents. Moreover, the relative proportion of clear water to erodible solid materials is also related to dam failure mode, which will eventually determine debris-flow properties. These findings have strong implications for predicting and mitigating natural disasters of these kinds usually encountered in nature.

Review of Investigations on Hazard Chains Triggered by River-Blocking Debris Flows and Dam-Break Floods

The Tibetan Plateau suffers from various types of geohazards (collapses, landslides, and debris flows.) due to abrupt changes in complex topography and weather conditions. Global warming and frequent high-intensity earthquakes in recent years have exacerbated the situation. Collapses and landslides provide vast amount of soil and debris which are conveyed downstream by runoff caused by extreme rainfalls to form large-scale debris flows; then, the debris flows block rivers and finally form dam-break floods, that is, a hazard chain triggered by debris flows. Along the evolution direction of the hazard chain, the affected areas are constantly amplified. This study first summarizes the related research studies on river blockage, debris-flow dam failure, and the hazard chain triggered by debris flows and then points out the drawbacks of existing research studies. Overall, the research (including mechanism, risk assessment, key prevention, and control technologies) on the hazard chain triggered by debris flows is still in its infancy and is disconnected among single hazard types in the hazard chain; meanwhile, the understanding of the mechanism of debris flow blocking the river is not enough; the established model and discriminant have minimal application scope, and there is no empirical model and dynamic model of debris-flow dam failure. Finally, several key scientific issues of this field were raised: 1) it is necessary to elaborate the coupling mechanism of debris-flow dam formation and construct the discriminant and numerical model of debris flow blocking the river with high precision and a wide application range. 2) It is necessary to further study the failure mechanism of a debris-flow dam, construct the numerical model of the failure process of a debris-flow dam, and accurately simulate the outburst flood hydrograph. 3) It is necessary to clarify the critical transformation conditions and dynamic evolution process of the hazard chain caused by debris flows, complete the accurate quantitative simulation of the whole disaster chain process, then establish a complete risk assessment system of the hazard chain, and finally develop some key prevention and control technologies suitable for the hazard chain.

Experimental study of the dam-break waves in triangular channels with a sloped wet bed

There has been little study on the impact of bottom slope on dam break wave propagating along a triangular wet channel. In this study, laboratory experiments are conducted in a large-scale triangular laboratory flume, covering a range of bed slope and rations of upstream over downstream water depth. Water surface and stage hydrograph wave height are collected using the non-intrusive measurement methods, which are used to obtain wave characteristics. Results show that for dry bed, the wavefront celerity increases with the increase of the slope; while for a wet bed, the wavefront celerity decreases as the slope increases and the decrease rate is significantly reduced. Moreover, the wavefront celerity decreases with the increase of water depth ratio. The maximum wave height at each measurement location decreases with the increase of water depth ratio. According to the arrival of the maximum wave height, the dam-break wave can be classified into two modes, namely Type A in which wave height gradually rises to the maximum when flow reaches and Type B in which the maximum wave height appears at the beginning of the dam failure. This study is useful for in-depth understanding of the dam-break wave evolution in sloping triangular wet rivers.

Precursory motion and deformation mechanism of the 2018 Xe Pian-Xe Namnoy dam Collapse, Laos: Insights from satellite radar interferometry

The sudden failure of hydraulic dams poses catastrophic hydrological risks to local communities and environments. The 2018 Xe Pian-Xe Namnoy Dam collapse in Southern Laos unleashed a flood wall that resulted in more than 70 deaths and left thousands homeless. While the causes of this event were clearly known as geological and engineering issues, the detailed process of dam degradation and potential hazards of other dams in the area remain unclear. In this study, we use radar satellites to investigate the precursory deformation of major dams in the Xe Pian-Xe Namnoy hydropower project. By combining independent component analysis and an Earth loading model to decompose the observed deformation into various time-dependent components, we study the possible deformation mechanism. We identify a precursory vertical deformation acceleration on the collapsed Saddle Dam D reaching up to 13 cm/yr two months before the failure. Two earth-fill saddle dams (E and F) also experienced accelerating subsidence of ∼ 9 cm/yr two months before the dam failure. The deformation pattern of these saddle dams resembles that of the collapsed Saddle Dam D, indicating a critical need for reinforcement interventions before being returned to service. In comparison, the rock-fill Xe Pian and Xe Namnoy Dams were relatively stable before the 2018 failure event. We show that water pressure, consolidation, thermal expansion, and precursory acceleration are the major mechanisms controlling dam deformation. Our results provide additional details for understanding the cause of the dam-break, and also to warn that other saddle dams associated with the project may also break if no further treatment is done. In addition, this study demonstrates the importance of space-borne radar interferometry and hybrid data analysis for early warning and hydrological safety management of small-to-medium-size dams, where in situ monitoring systems are often unavailable.

Initial Distribution and Interannual Decrease of Suspended Sediment in a Two‐Basin Lake Following a Massive Mine Tailings Spill: Quesnel Lake, BC, Canada

AbstractOn 4 August 2014, a tailings dam failure at Mount Polley Mine in central British Columbia led to the largest short‐term release of mine waste into a lake ever recorded. Once released by the breach, slurry entered the smaller of Quesnel Lake’s two basins, called the West Basin, from which the lake drains northwest into the Quesnel River. An estimated 38,000 ± 11,000 tonnes of fine solids remained suspended in the West Basin on 10 September 2014, 37 days postspill. This decreased to within background levels (<300 tonnes) by June 2015, by which time ∼4,000 tonnes of sediment had flowed from the West Basin into the Quesnel River, and ∼31,000 tonnes had been transported east into the main basin, the direction opposed to the mean hydraulic gradient. Here, we evaluate sediment transport in Quesnel Lake following the Mount Polley tailings dam spill. We apply conservation of mass in two ways: using data collected between 12 August 2014 and 15 October 2020 to estimate suspended sediment mass and mass flows into and out of the West Basin; and using one‐ and two‐basin completely mixed models. Suspended sediment concentrations were highly elevated through the first three seasons postspill, then fluctuated within a gradually decreasing, seasonal cycle. The observed mass trend and an analytical mass balance model of a simplified, two‐basin system suggest that suspended sediment mass will fall to below the median prespill mass by 7 ± 5 years postspill.

Large Scale Laboratory Experiment: The Impact of the Hydraulic Characteristics of Flood Waves Caused by Gradual Levee Failure on Inundation Areas

As a levee failure and the consequent flooding cause significant financial losses and sometimes human casualties, they have led to considerable concern among city officials. Therefore, researchers have devoted considerable effort to investigating the hydraulic characteristics of sudden transient flow in the form of propagated waves to inundation areas during a levee and/or dam failure. A large number of studies, however, have mostly focused on simple one-dimensional cases investigated numerically and/or experimentally, and thus, important hydraulic characteristics, particularly near the failure zone, have not been adequately captured because of three-dimensional complexities. Taking these complexities into consideration, this study conducts a large-scale experiment to examine the characteristics of wave propagation in an open area caused by a gradual levee failure. From the experimental observations, this study provides the propagation speed of a wave front and suggests a formula for the maximum flood depth corresponding to the peak flood wave in the inundation area. We expect the findings to provide hydraulic engineers and scientists with fundamental insights into transient flow during a gradual levee failure. By contributing to our theoretical understanding, the measurements can also be used as validation tools for future numerical simulation and are likely to contribute to the establishment of emergency action plans that can help city officials cope with flood inundation.

Modelling the long-term geomorphic response to check dam failures in an alpine channel with CAESAR-Lisflood

Globally, between 1950 and 2011 nearly 80,000 debris flow fatalities occurred in densely populated regions in mountainous terrain. Mitigation of these hazards includes the construction of check dams, which limit coarse sediment transport and in the European Alps number in the 100,000s. Check dam functionality depends on periodic, costly maintenance, but maintenance is not always possible and check dams often fail. As such, there is a need to quantify the long-term (10–100 years) geomorphic response of rivers to check dam failures. Here, for the first time, a landscape evolution model (CAESAR-Lisflood) driven by a weather generator is used to replicate check dam failures due to the lack of maintenance, check dam age, and flood occurrence. The model is applied to the Guerbe River, Switzerland, a pre-Alpine catchment containing 73 check dams that undergo simulated failure. Also presented is a novel method to calibrate CAESAR-Lisflood's hydrological component on this ungauged catchment. Using 100-year scenarios of check dam failure, the model indicates that check dam failures can produce 8 m of channel erosion and a 322% increase in sediment yield. The model suggests that after check dam failure, channel erosion is the remobilization of deposits accumulated behind check dams, and, after a single check dam failure channel equilibrium occurs in five years, but after many check dam failures channel equilibrium may not occur until 15 years. Overall, these findings support the continued maintenance of check dams.

Large-scale landslide dam breach experiments: Overtopping and “overtopping and seepage” failures

Landslide dams form when landslide materials reach rivers causing complete or partial blockage. It is known that overtopping water flows and seepage flows are two crucial processes that induce dam failure. In several instances, the landslide dams collapse is caused by the coupled influence of seepage flows and overtopping water. This study aims to evaluate the contribution of seepage flows to the overtopping failure of landslide dams in terms of dam stability, breach duration, and flow discharge. We conducted two field experiment tests to simulate landslide dam failure modes: overtopping failure and overtopping-seepage coupling. Results show that the internal erosion due to seepage induces the loss of fine particles, resulting in a fourfold increase in dam deformation relative to when seepage is minimal. In the case overtopping and seepage failure, the outburst duration is shortened by two-thirds, but the peak outburst discharge is increased by nearly two times compared with the pure overtopping failure. Sediments accumulate at the downstream channel for overtopping failure, but erosion is observed before accumulation when the “overtopping and seepage” failure occurs. Fine grain sizes are limited to the downstream bed for both failure modes, which indicates the equal mobility of sediments involved in the outburst flood from a landslide dam breach.

Numerical simulation of overtopping breach processes caused by failure of landslide dams

Numerical simulation of overtopping breach processes caused by failure of landslide dams

Lectio praecursoria

In this lectio praecursoria, which I presented as part of my doctoral defense at the University of Eastern Finland on 5 November 2021, I delve deep into the Brazilian anti-mining movement to understand the context in which activism take place, their main strategies and course of actions, and their ability to influence the overall mining debate in Brazil in the 2010s. It sheds light on the key challenges faced by groups fighting for more environmental and social justice in mining conflictual situations. More specific, the research covers the 2013–2017 time frame, when discussions on the mining framework and a severe tailings dam failure happened. These two cases are analyzed and their effects on anti-mining activism are explored through a twofold focus on social movements and environmental justice studies. The study contributes to scientific discussions on mining and society by seeking conceptual bridges across political-ecologically oriented studies on social movements against mineral extraction. It also expands, significantly, analyses of social movements in Brazil by contributing to the international comparative literature on the social and environmental impacts of mining, Brazilian and Latin American studies, studies on mining history, sociology of mining, and mining policy.

Reuse of iron ore tailings for production of metakaolin-based geopolymers

Mining tailings are becoming more and more abundant and consequently it has been shown to be a material of great concern, especially after the dam failures in Brazil, Bento Rodrigues, 2015 and Brumadinho, 2019. In this work, iron ore tailings (IOT) were used as an aggregate in the production of geopolymers based on metakaolin used as a precursor and activated in alkaline solution. The alkaline solution was produced from a commercial solution of sodium silicate Na2SiO3 (SS) and a 10 M solution of sodium hydroxide NaOH (SH) prepared from solid flakes (3:1 mass ratio of SS:SH). Two syntheses were carried out, one by mixing metakaolin (MK) with the activator solution (AS) (1:1 mass ratio of MK:AS), called matrix, and another with the addition of aggregate (AG) to the matrix (1:1:2 mass ratio of MK:AS:AG), called geopolymer. XRD, FTIR, Mössbauer and SEM were used to analyze the inputs and materials produced, in addition to the analysis of compressive strength. The matrix reached a strength of 45.88 MPa with 7 days of curing, while the addition of IOT generated an increase in strength to the material, reaching values between 59.59 and 64.90 MPa also with 7 days of curing.

A new look at the statistics of tailings dam failures

Tailings dams are commonly built incrementally to increase the storage capacity of the Tailings Storage Facility (TSF), usually without interrupting the mining activities. Dam management practices, lack of knowledge on tailings behaviour and the poor performance of monitoring and management processes have resulted in disastrous tailings dam failures with human and economic losses, as well as huge environmental consequences to ecosystems and local communities. In the literature, correlation analyses have been carried out considering different variables: stored volume, released volume, runout distance, dam height, peak discharge. Several databases of tailings dam failure are available online, each with different levels of detail. This paper computes the statistics of tailings dam failures using an up-to-date database on failures and a catalogue of existing TSF. The existing correlations between stored and released volumes have been verified using a larger database. The new proposed regression analysis considers the functional relationship between released volume and characteristics of the dam such as height and stored volume (i.e., dam factor). The effect of construction type, fill material and failure mode on the released volume has also been evaluated as well as the frequency of tailings dam failure as function of the construction method. Tailing dams built using the upstream construction method turn out to be more prone to failure, and more susceptible to static and dynamic liquefaction. The new correlation provides more reliable estimates of the expected released volume as a function of dam height and stored volume and should prove useful for runout analyses and risk assessment of tailings dam failure. Finally, the analyses carried out show that there is no correlation between the water pond extension and the released volume.

Numerical simulation of dam-breach flood waves

Dam breach due to the earthquake, Land sliding inside the dam reservoir, dam overtopping as a result of intense precipitation in a watershed are examples of dangerous risks which flood caused by any of them should be predicted by suitable hydraulic or numerical models in the framework of a risk management plan. In the present research, 2DHec-Ras model has been applied in order to flood modeling of Sattarkhan dam. This dam is in the North West of Iran, located 15 km from the west of Ahar city, in the East Azerbaijan province, Iran. The downstream part of the dam to Ahar city has been studied considering the population and infrastructures in this district according to two different scenarios of dam failure. The first scenario includes piping of flow and dam failure profile with steep side walls while the second scenario consists of inclined sidewalls in the dam breach profile and overtopping of flow as the main cause of breaching. The population centers have been selected in the downstream area of dam according to the field facts. The maximum flood depth reaches up to 9.1 m for the first scenario and 7.1 m for the second scenario at the Islamic Azad University and Tabriz-Ahar road, respectively. The results show the notable risk for some of the population centers in the downstream of the dam. Furthermore, the arrival time of flood, recession time, and maximum velocities in the targeted areas for preparing emergency action plans has been calculated.

Temporal evolution of backward erosion piping in small-scale experiments

Backward erosion piping (BEP) is a form of internal erosion which can lead to failure of levees and dams. Most research focused on the critical head difference at which piping failure occurs. Two aspects have received less attention, namely (1) the temporal evolution of piping and (2) the local hydraulic conditions in the pipe and at the pipe tip. We present small-scale experiments with local pressure measurements in the pipe during equilibrium and pipe progression for different sands and degrees of hydraulic loading. The experiments confirm a positive relation between progression rate and grain size as well as the degree of hydraulic overloading. Furthermore, the analysis of local hydraulic conditions shows that the rate of BEP progression can be better explained by the bed shear stress and sediment transport in the pipe than by the seepage velocity at the pipe tip. The experiments show how different processes contribute to the piping process and these insights provide a first empirical basis for modeling pipe development using coupled seepage-sediment transport equations.

Propagation network of tailings dam failure risk and the identification of key hazards

The tailings dam system is complex, and the dam structure changes continuously over time, which can make it difficult to identify key hazards of failure and characterize the accident formation process. To solve the above problems, based on complex network theory, the paper uses the identified hazards and the relationship between hazards to construct the propagation network of tailings dam failure risk (PNTDFR). The traditional analysis methods of network centrality usually focus on one aspect of the information of the network, while it cannot take into account to absorb the advantages of different methods, resulting in the difference between identified key nodes and real key hazards. To find the key hazards of tailing dam failure, based on the characteristics of multi-stage propagation of failure risk, the paper proposes a multi-stage collaborative hazard remediation method (MCHRM) to determine the importance of hazard nodes by absorbing the advantages of different centrality methods under different hazard remediation (deletion) ratios. The paper applies the above methods to Feijão Dam I. It can be found that when the priority remediation range is increased to 45%, the key hazards obtained by the MCHRM will cover all the causes of accidents proposed by the Dam I failure investigation expert group. Besides, the paper compares the monitoring data, daily inspection results and safety evaluation information of key hazards with the ‘Grading standards of hazard indicators’, and obtains the formation process of the Dam I failure and 30 key hazards in trigger state.

Predicting the Influence of Seasonal Thermally Induced Cracking on a Reinforced Concrete Arch Dam

Many of the world's concrete dams are approaching the end of their expected service life and many of these dams are cracked due to environmental effects. It is thus desirable to be able to extend the service life of many of these dams. It is therefore important to develop reliable methods of analysis to assess the current status of these dams and to determine the safety of these, partly damaged structures. A slender reinforced concrete arch dam is used as a case study with the aim of predicting the structural response, the cracks found in-situ and of assessing the safety of the dam. This dam has cracked extensively along the downstream face primarily due to seasonal temperature variations. A detailed finite element model has been developed to simulate the history of the dam with the variations in ambient conditions that have occurred over its lifetime. The results show good agreement regarding both the crack pattern and displacement of the dam. A procedure to simulate a progressive dam failure, starting from the current state, is utilized to assess the current level of safety. The results show that the cracking has a limited effect on the safety factor of the dam.

Study on Deformation and Fracture Evolution of Underground Reservoir Coal Pillar Dam under Different Mining Conditions

Coal mine underground reservoir water storage technology is an effective technical way to achieve high efficiency of coal mining and protection of water resources. The stability of coal pillar dam plays a decisive role in the safe and stable operation of underground reservoirs. Mining of adjacent working faces and long-term water erosion are the main influencing factors of stability of coal pillar dam. In this paper, a fluid-solid coupling calculation model for the deformation and evolution of coal pillar dam was established by FLAC3D numerical simulation software and the underground brine reservoir of Lingxin Coal Mine of Shenning group as an engineering background. The paper studied systematically the deformation, failure, and stress evolution of the dam with coal pillars soaked in water for a long time under different working face inclining length, coal pillar width, mining height, and water pressure. The simulation results showed that the degree of deformation and failure of the coal pillar dam continued to increase with the continuous advancement of the working face. The plastic zone of the coal pillar dam was increased by approximately 23.53%, the maximum vertical stress was increased by approximately 95.78%, and the maximum vertical deformation was increased by approximately 68.18%. The influence of each factor on the deformation and failure of overburden strata is quite different. The development range of plastic zone, the maximum vertical stress, and the maximum vertical deformation were increasing with the increased of working face inclined length and mining height. The increasing width of coal pillar would lead to the decrease of maximum vertical stress. The increase of water pressure would lead to the decrease of maximum vertical deformation. It can be seen that the inclined length of the working face is the main factor affecting the deformation and failure of the coal pillar dam. Coal pillar width and mining height are the main factors affecting the development of plastic zone. This study reveals the law of deformation and fracture evolution of coal pillar dam under different mining conditions, which can provide a reference for the design of coal pillar dam of coal mine underground reservoir.

Ecotoxicological impacts of the Fundão dam failure in freshwater fish community: Metal bioaccumulation, biochemical, genetic and histopathological effects

This study investigates the ecotoxicological impacts of the Fundão dam rupture, one of the major environmental disaster that occurred in Brazil and in the world mining industry history, through multi-biomarkers responses and metals bioaccumulation in the fish community of different trophic levels. Specimens of the fishes (omnivorous/herbivorous and carnivorous) were collected along the Doce River channel and its affluent Guandú River, and in different lakes and coastal lagoons adjacent to the river channel, in the Espirito Santo State, Southeast of Brazil. Four sampling collections were carried out over two years (2018 to 2020, during dry and rainy seasons). For both trophic groups the biomarkers responses indicated physiological alterations related to metals exposure and showed strong seasonal variations. The principal component analysis and integrated biomarker response index showed that DNA damage and lipid peroxidation were more associated with dry season 2 (Sep/Oct 2019) and the oxidative damage in proteins, metallothioneins concentration and the activity of superoxide dismutase in the gills showed a greater association with rainy season 2 (Jan/Feb 2020). On the other hand, the enzymes of energy metabolism, catalase and histological damage in the liver and the gills, were more associated with the dry and rainy campaigns of the first year of monitoring. The multivariate approach also suggested a temporal intensification in the bioaccumulation of metals and biological effects in the lacustrine environments. Thus, these results demonstrate that the release of mineral residues from the rupture of the Fundão mine dam affects the health status of the fish from the Doce River basin, provoking metals bioaccumulation, hepatic and branchial damage in the fish besides inducing of enzyme activity related to metal contamination, even four years after the rupture.