Investigation Report on the Major Secondary Environmental Incident Caused by the Leakage from the Tailings Pond of Gansu Longxing Antimony Industry Co., Ltd. on “11.23”

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Expert Analysis of the Investigation Report on the Severe Secondary Environmental Incident Caused by the Tailings Pond Leak at Gansu Longxing Antimony Industry Co., Ltd. on November 23 The Ministry of Environmental Protection released the findings of the investigation into this severe secondary environmental incident resulting from the tailings pond leak at Gansu Longxing Antimony Industry Co., Ltd. on November 23, and invited Professor He Xuwen from the School of Chemistry and Environment Engineering at China University of Mining and Technology to provide an analysis of these findings. 　　Question: What was the direct cause of this incident? Could you please provide a detailed explanation of the process used to determine the direct cause of this incident? 　　Answer: According to the findings of the investigation team, this incident was a major sudden environmental event resulting from an accident caused by a leakage at a corporate tailings pond. The direct cause of the incident was the damage and collapse of the arch slab in the drainage well of the Longxing Antimony Industry tailings pond, which led to the leakage of tailings and tailings water into the Taishi River. As a result, the antimony concentration in approximately 346 kilometers of the Taishi River, Xihan River, and Jialing River exceeded safe levels. 　　After the leakage incident occurred, the people’s government of Xihe County in Longnan City promptly organized relevant units and personnel to carry out emergency measures such as sealing off the source of the leakage and blocking pollutants. In accordance with the requirements of the People’s Government of Gansu Province, the Gansu Provincial Work Safety Supervision Bureau conducted an investigation into the circumstances and causes of the tailings leakage in December 2015, using methods such as on-site inspections, document reviews, evidence collection, and testing. On February 25, 2016, an investigation team from the Ministry of Environmental Protection brought together more than 10 well-known domestic experts to inspect the site of the tailings pond. They reviewed the investigation process carried out by the Gansu Provincial Work Safety Supervision Bureau and ruled out the possibility that human sabotage or natural disasters were responsible for the leakage. It was determined that the cause of the leakage was the damage and detachment of 8 arch plates located between two columns of the pump house at the 1st layer of the foundation of Pump Well No. 2 at the Longxing Antimony Industry tailings pond, at a depth of about 6 meters below the water surface and in a direction slightly northeast. This resulted in a gap measuring approximately 2.2 meters in height, 2.4 meters in width, and 5.28 square meters in area, which allowed around 25,000 cubic meters of tailings and tailings water to leak out from around the pump well and above the gap. There are two reasons for the damage and detachment of the arch slab in the drainage well, resulting in gaps. The first reason is that the arch slab was not installed in accordance with the design requirements, failing to achieve a ring-shaped compressed state; as a result, the slab suffered strength failure under the pressure of the tailings and broke away. The design documents require that the gap between the derrick and the arch slab during installation be filled with 50# cement mortar to form the well wall; however, on-site inspections revealed that wire was used to connect the arch slab and the columns, and larger gaps were partially filled with stones, without the use of cement for filling those gaps. Another reason is that the quality of the arch slab in the drainage well is far from meeting the design requirements. The design requires 6 Φ16 longitudinal bars and Φ8 stirrups to be placed inside the arch slab of the drainage well. However, on-site inspections revealed that the arch slab installed at the time of the accident was equipped with only 4 longitudinal bars of Φ8 diameter and Φ6 diameter stirrups; moreover, some of the rebar was exposed and severely corroded. The quantity and diameter of the rebar, as well as the strength of the concrete, did not meet the design requirements. 　　Question: In this incident, how was antimony determined to be the characteristic pollutant? 　　Answer: The types of heavy metal pollutants present in the wastewater from tailing ponds are related to the composition of the tailings. Following the incident, the on-site team conducted tests on the tailings remaining in the tailings pond, taking into account factors such as the composition of the ore produced by the enterprise. The test results showed that the tailings contained heavy metals such as antimony, copper, lead, zinc, cadmium, arsenic, and mercury. On November 24, monitoring results of heavy metal levels in relevant river basins in Gansu Province showed that lead, arsenic, and antimony exceeded the specified limits at some sampling points. After November 25, the concentrations of the other six heavy metals, with the exception of antimony, remained within the acceptable ranges. From November 29 to December 1, additional monitoring was conducted at 3 sampling sites in Gansu Province for 8 heavy metals, including beryllium, boron, nickel, molybdenum, cobalt, aluminum, barium, and thallium; the results showed that all 8 heavy metals were within the specified limits. After the incident, Shaanxi Province and Sichuan Province also monitored heavy metals such as antimony, copper, lead, zinc, and cadmium; the results showed that only antimony levels were above the standard. Based on the data monitoring from the three provinces, antimony was identified as the characteristic pollutant in this incident. 　　Question: What impact has this incident had on the environment? 　　Answer: After the emergency response to the incident was completed, Longnan City in Gansu Province, Hanzhong City in Shaanxi Province, and Guangyuan City in Sichuan Province commissioned technical assessment agencies to carry out environmental damage assessments in accordance with relevant documents such as the \"Recommended Methods for Environmental Damage Assessment\" issued by the Ministry of Environmental Protection. This work is divided into two phases: the emergency response phase and the medium- to long-term environmental impact assessment. According to the damage assessment conducted during the emergency response phase, this incident resulted in the leakage of 25,000 cubic meters of tailings and tailing water, with direct economic losses amounting to 61.2079 million yuan. It also caused the antimony concentration in 346 kilometers of rivers in Xihe County, Gansu Province, to exceed safe levels, as well as in areas within Guangyuan City, Sichuan Province. This incident affected the water supply for 108,000 people in the three provinces of Gansu, Shaanxi, and Sichuan, and led to elevated antimony levels in groundwater wells in some areas of Gansu. Approximately 257 mu of farmland along the Taishi River in Xihe County, Gansu Province, was contaminated to a certain extent as it was directly flooded by polluted water; the proportion of farmland soil with levels exceeding the standard in the 0–40 cm depth layer was 20%. 　　Question: How can similar secondary environmental incidents resulting from tailings pond leaks be prevented and avoided? 　　Answer: To prevent such incidents from occurring, the key is to urge enterprises to strictly fulfill their responsibilities regarding safety and environmental protection. Enterprises should, in accordance with the law, carry out tasks such as risk assessment of tailing ponds, identification and rectification of potential hazards, as well as the preparation and filing of emergency plans. They should also organize regular emergency training and drills to understand the characteristic pollutants present in tailing ponds and the appropriate emergency response measures, thereby enhancing their ability to prevent risks and handle incidents promptly. In this process, the degree of implementation at each stage is crucial for ensuring that risks can be effectively controlled, potential hazards can be identified and eliminated in a timely manner, and that appropriate actions can be taken in case of any issues – practical results must be achieved. 　　For **and relevant departments, it is necessary to strictly control the admission of enterprises that operate tailing ponds. They should conduct scientific assessments and impose strict limits on the distance between such ponds and sensitive locations such as densely populated areas and drinking water sources, in order to prevent the occurrence of \"ponds above residents\" – those located at a very short distance downstream from residential areas or important facilities, with high dams and significant potential energy – as well as \"ponds along rivers, lakes, or coasts\" – those situated near rivers, lakes, or coastlines, or upstream of residential drinking water sources. This approach helps to reduce the risk of environmental pollution caused by accidents involving tailing ponds. At the same time, it is necessary to fully leverage **inter-departmental cooperation in order to create a coordinated effort for the supervision of tailing ponds, and to comprehensively improve the daily supervision capabilities as well as the accident response skills of all relevant departments. Local environmental protection departments should have a comprehensive understanding of information regarding environmental risks such as characteristic pollutants in tailing ponds within their administrative areas, as well as sensitive environmental sites in the surrounding area, particularly drinking water sources. They should urge enterprises to carry out environmental risk assessments for tailing ponds, identify and address potential environmental safety hazards, and file environmental emergency response plans in accordance with relevant requirements. 　　In the event of accidents such as dam failures or leaks in tailing ponds, companies should take effective measures to seal them up immediately. Local authorities must coordinate all relevant departments to carry out emergency response actions; the safety supervision and management departments should actively organize emergency rescue efforts, while the environmental protection departments should submit reports and provide updates in accordance with relevant regulations, as well as conduct environmental emergency monitoring.