Evaluation of Environmental Quality for Abandoned Coal Mine Based on Environmental Vulnerability Index

Peng Qi; Yu Shang

doi:10.32604/EE.2021.014203

1School of Law and Humanities, China University of Mining & Technology, Beijing, 100083, China
2School of Management, China University of Mining & Technology, Beijing, 100083, China
*Corresponding Authors: Peng Qi. Email: qp@cumtb.edu.cn; Yu Shang. Email: 108796@cumtb.edu.cn
Received: 10 September 2020; Accepted: 19 November 2020

Abstract: With the increasingly prominent environmental problems of abandoned coal mines, this paper discussed the significance of environmental vulnerability assessment of abandoned coal mines. Environmental vulnerability assessment is essentially an assessment of environmental quality. At present, the research object of environmental impact assessment method and program of mine is mostly single factor. However, the impact of abandoned coal mine on the environment is multifaceted, which was summarized into nine prominent common problems. Based on these nine factors, the environmental vulnerability assessment model of abandoned coal mine based on multi-factor evaluation was established by using the analytic hierarchy process (AHP) method, the ranking criteria of nine factor indexes was proposed, the evaluation process was established, and the evaluation index system of environmental vulnerability of abandoned coal mines was established. The environmental vulnerability assessment method of abandoned coal mines has universal applicability, which can provide the basis for the government and enterprises to carry out treatment and planning of abandoned coal mine and promote the optimization of governance effect.

Keywords: Abandoned coal mine; environmental vulnerability; analytic hierarchy process

Coal is one of the most important fundamental material energy resources for the development of economy. Chinese coal industry grew gradually from thin foundation. Especially in thirty years since reform and opening up, it has been increased rapidly with the fast development of China economy and it plays a strong supportive role. Meanwhile, the foundation of coal industry which statuses in the national economic construction has increasingly highlighted.

The number of coal mines in China is huge and exceeds the sum of other country’s coal mines. However, the amounts of abandoned coal mine are increasing due to some reasons, such as resource exhaustion after long-term exploration, political bankrupt, or being closed without license. The distribution of abandoned coal mines is in common with the production of coal mines in most provinces with different scale. It may hide a lot of risks and environmental problems which would endanger public safety and development of society.

Environmental vulnerability refers to the weak degree of environmental factors’ resistance to interference and their own recovery ability. In essence, environment vulnerability evaluation is evaluated on environmental quality. Based on the investigation, the evaluation can rank the environmental quality with certain principle, criterion and suitable mathematical method, which can expose the main environmental problems of abandoned coal mine with “poor” or “very poor” index. The purpose of evaluation is to provide references for government supervision, and also for post-treatment of abandoned mines. So environmental quality evaluation is very important and necessary. Only after ranking how environmental quality and evaluating how serious the environmental problem are, can government and companies make reasonable planning. Meanwhile, the limited fund can be put into the mines with the most serious environmental problems in order to achieve the best optimized effect.

EVI (environmental vulnerability index) evaluation is raised after the vulnerability index method for mine water-bursting prevention. It is used in environmental quality evaluation to provide a series of approaches. At present, the research object is regarded as an isolated individual in the mine environmental impact assessment methods and procedures in China. In terms of evaluation content and evaluation elements, single factor assessment such as environmental pollution, geological disasters, water and soil loss and noise pollution is paid more attention, and the environmental problems caused by multiple factors are less evaluated [1–6].

The impact of abandoned coal mines on the environment is multifaceted. Based on the investigation and analysis, the impact of abandoned coal mines on the environment is summarized into nine prominent common problems. The nine factors are taken as contributors in EVI evaluation method. With certain mathematical method, they are combined to identify the vulnerable degree in abandoned coal mine [5]. EVI evaluation method of abandoned coal mines has universal applicability and any abandoned coal mine environmental problems can be applied in the model.

1. Single factor evaluation. Single factor evaluation standard will be generated by analyzing each factor impact in environmental vulnerability.

2. Comprehensive evaluation. On the basis of analysis for single factor, the evaluation model could be built by evaluating the environmental vulnerability according to index weight with mathematical method.

This manuscript uses comprehensive evaluation method. To evaluate environmental quality of a coal mine, the multi-factor evaluation model must be built at first. Then, with some mathematics method, the index weight of each factor should be quantified and the value function should be defined. Finally, evaluation index will be confirmed by dividing evaluation value intervals. The specific work flow chart is as follows (Fig. 1) [7–10].

The environmental vulnerability index method introduces primary model of EVI (Formula 1). According to the value range of vulnerability index, the amount of ranks is obtained. Finally, the ranks of environmental vulnerability are calculated based on grades of evaluation.

EVI is environmental vulnerability index; Wi is weight of the i factor, and ∑i=1nWi=1 ; fixy is geographic coordinates; n is the number of factors.

The factors which affect the environmental vulnerability are complicated. They are varied to some degree in different region and varied according to how the environment is spoiled and how serious it is. So it is necessary to use proper mathematical approach to define the contribution rate of each factor to EVI.

The Analytic Hierarchy Process (AHP) is a qualitative and quantitative combination of multiple criteria decision theory. It is a simple, flexible and practical multi-criteria decision method, which was put forward by American operation research professor T. L. Saaty in the 1970s. It is also one of effective ways to transform semi-qualitative and semi-quantitative questions into quantitative problems.

The AHP method can reflect the thought of system analysis and system synthesis more thoroughly. It can use little quantitative information to make the decision mathematically, and then provide convenient decision way for multi-criteria, multi-objective or non-structural properties of complex decision problems, which is based on the exploration of the essence, influencing factor and internal relations of the complex problem. This method is particularly suitable to solve the problem that the decision result is difficult to be directly and accurately obtained. The AHP method divides complex problems into objects, criterion, scheme (factor) and other number of levels. Elements in each level of the layer will be compared according to certain criterion, which constitutes the judgment matrix. By calculating the largest eigenvalue and its corresponding orthogonal eigenvectors of the judgment matrix, the factor weight would be obtained. On this basis, the proportion of the factor in each layer could come out. At last, the solution (weight) will be obtained [11,12].

According to the analysis of nine factors affecting the environmental quality of abandoned coal mines, the research objects were divided into three levels. Environmental vulnerability assessment of abandoned coal mines is the ultimate aim of the problem and should be used as the target layer (level A) of the model. The environmental vulnerability of abandoned mines is determined by the problem of “three wastes,” geological disasters, ecological and resources destruction in coal mines, but the influence mode must be reflected by relevant factors. This is the intermediate link of solving the problem. Namely, the criterion layer (level B) of the model. Solid wastes such as coal gangue, mine waste-water, mine exhaust, ground subsidence and cracks, slope failure, land resource destruction, soil and water loss and pollution, landscape destruction, water environment and water resources destruction, etc. The nine factors constitute the decision layer (level C) of this model, and through decision making on this level, the required solution can be finally achieved, and the environmental vulnerability of abandoned coal mines can be classified [4] (Fig. 2).

Figure 2: Hierarchical model of environmental vulnerability assessment of abandoned coal mine

Comparing the influence of n factors X={x1,x2,x3,...,xn} on a particular factor Z . Take two factors xi and xj at a time, the ratio aij represents the impact of xi and xj on Z , and the results of the comparison A=(aij)n×n are expressed in a matrix, corresponding to the feature vector w of the maximum feature value of λ max [13–15].

A=[w1/w1w1/w2w1/w3⋯w1/wnw2/w1w2/w2w2/w3⋯w2/wnw3/w1w3/w2w3/w3⋯w3/wn⋯⋯⋯⋯⋯wn/w1wn/w2wn/w3⋯wn/wn]

For different individual abandoned coal mines, after establishing an environmental vulnerability assessment hierarchy model, a judgment matrix is established according to the actual environmental conditions of the target mine. The contribution value of various factors to the vulnerability of mine environment is obtained by calculation and analysis [5]. The paper adopts the following indicators as the basis for environmental quality evaluation of abandoned coal mines based on national or industrial standards and combined with the actual conditions of abandoned coal mines.

For setting rank criteria of solid waste in abandoned coal mines, the paper mainly considers the land pressure effect of solid waste, the spontaneous combustion effect of coal gangue, the radon stability of solid waste accumulation area, dust lifting and filtration pollution [6]. According to the relevant national standards, the environmental rank criteria of solid waste like coal gangue index shall be formulated (Tab. 1).

The rule making of environmental rank criteria of mining wastewater index is mainly from two aspects: underground wastewater and surface wastewater. The rank of underground wastewater evaluation index mainly considers the pollution of various metal objects and chemical elements in waste water. The rank of surface wastewater evaluation index mainly takes into account factors such as the discharge water quality index and the area of stagnant water by mining subsidence or extracting well water and waste water for coal dressing.

The one-way factor standard in the scale of mine wastewater index (Tab. 2) implements the Surface Water Environmental Quality Standard (GB3838-2002) and Quality standard for ground water (GB/T14848-93). The main indexes include water temperature, pH value, dissolved oxygen, chemical oxygen demand (COD), five-day BOD (BOD5) and ammonia nitrogen (NH3-N), total phosphorus (P), total nitrogen (N) (including major metallic elements and harmful elements).

The unidirectional factor index in mine waste air emission index grade standard (Tab. 3) is mainly implemented by reference to the comprehensive emission standard for atmospheric pollutants (16297-1996). Each factor index value is approved and evaluated according to this standard.

4.4.4 Rank Criteria of Geological Hazard Index for Ground Surface Subsidence, Crack and Slope Instability

The environmental grade standard of abandoned coal mine geological hazard index is mainly based on rank criteria of geological hazard and damage degree index (Tab. 4).

The rank criteria of ground surface subsidence and ground crack index are as follows (Tab. 5).

Table 5: Rank criteria of geological hazard scale index (Ground surface subsidence, Ground crack)

The rank criteria of land resource damage degree index of abandoned coal mine mainly includes damaged land, land desertification index (Tab. 6) and occupied and damaged land index (Tab. 7).

The standards for classification of soil erosion and pollution indexes in abandoned coal mines (Tab. 8) are mainly drawn up from four aspects: Soil erosion, soil pollution levels, comprehensive soil pollution index and pollution level. The specific individual indicators are carried out with reference to the soil environmental quality standard (GB 15618-1995).

The rank criteria of failure of landscape index based on the actual environment of the abandoned coal mine, and Tab. 9 is formulated.

4.4.8 Rank Criteria of Water Resource and Water Environment Impact and Damage Index

Rank criteria of water resource and water environment impact and damage index (Tab. 10) mainly considers the influence of coal mining on aquifer water quantity, water ecology, people’s production and living, industrial and agricultural production and other factors on water resources and water environment.

Table 10: Rank criteria of water resource and water environment impact and damage index

Take a certain abandoned coal mine as example. After the weight of each factor has been quantified, the influence value should be obtained. China Geological Survey issued the standard of China geological survey “Principle of Survey in Regional Environmental Geology (try out) (DD2004-02)” in October, 2004. With the degree of regional environmental geology, the evaluation region can be divided by the index value of geological environmental quality. The classification is good, better, worse and bad. By analogy with this principle, the index factor of environmental vulnerability in abandoned coal mine can be classified as I, II, III and IV.

The standard score of each assignment: I=0.3 , II=0.5 , III=0.7 and IV=0.9 . The standard of assignment of each factor and the comprehensive evaluation are defined by weighted score (Tab. 11).

Table 11: Value-determined standard rank and weighted score corresponding standard of different factors

After the weight of each factor is obtained and quantified, the environmental vulnerability should be classified. Quantitative value is between 0.3 and 0.9 with Wi∈[0,1]and∑i=19Wi=1 . The index of EVI is between 0.3 and 0.9 according to the formula of environmental vulnerability in abandoned coal mine, Formula 2.

In this paper, the degree of environmental vulnerability evaluation can be classified as weak, relatively weak, moderately weak and strong weak. They are as follows (Fig. 3):

Once the environmental vulnerability method is chosen to evaluate the vulnerable degree of abandoned coal mine, the EVI can be used according to the above classification.

The method of environmental vulnerability evaluation is a new type of evaluation on multi-factor. When dealing with the problems of abandoned coal mine, it has the following advantages and characteristics.

First, according to the complexity and diversity of the influencing factors, it overall considers the influence and overcomes the one-sidedness of single factor, which combines the universality and particularity of environmental problems and achieves harmony and unification.

Second, the integrity and system of environmental vulnerability index method is strong. Through the discussion of EVI model, it is obviously that both of the application of mathematic theory and the definition of quantitative value are indispensable with strong system.

At last, the EVI evaluation method is universal in abandoned coal mine. This method comprehensively considers several problems of abandoned coal mine. Each problem is regarded as a factor, which can make the environmental problems applied in the model by the contribution of weight.

In a word, with the resources of some coal mines exhausted and small-scale coal mines shut down or integrated, the environmental evaluation is of great necessity and significance. It is required to strengthen the research of environmental evaluation method in abandoned coal mine, which are the important premise and the only way to achieve the scientific treatment on environmental problems with broad development space and bright future.

Funding Statement: Research Funds for Yue Qi Young Scholars (No. 2018QN11); the Fundamental Research Funds for the Central Universities (2009QG09).

Conflicts of Interest: The authors declare that they have no conflicts of interest to report regarding the present study.

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