Numerical modelling of the groundwater inflow to an advancing open pit mine: Kolahdarvazeh pit, Central Iran

The groundwater inflow into a mine during its life and after ceasing operations is one of the most important concerns of the mining industry. This paper presents a hydrogeological assessment of the Irankuh Zn-Pb mine at 20 km south of Esfahan and 1 km northeast of Abnil in west-Central Iran. During mine excavation, the upper impervious bed of a confined aquifer was broken and water at high-pressure flowed into an open pit mine associated with the Kolahdarvazeh deposit. The inflow rates were 6.7 and 1.4 m3/s at the maximum and minimum quantities, respectively. Permeability, storage coefficient, thickness and initial head of the fully saturated confined aquifer were 3.5 x 10−4 m/s, 0.2, 30 m and 60 m, respectively. The hydraulic heads as a function of time were monitored at four observation wells in the vicinity of the pit over 19 weeks and at an observation well near a test well over 21 h. In addition, by measuring the rate of pumping out from the pit sump, at a constant head (usually equal to height of the pit floor), the real inflow rates to the pit were monitored. The main innovations of this work were to make comparison between numerical modelling using a finite element software called SEEP/W and actual data related to inflow and extend the applicability of the numerical model. This model was further used to estimate the hydraulic heads at the observation wells around the pit over 19 weeks during mining operations. Data from a pump-out test and observation wells were used for model calibration and verification. In order to evaluate the model efficiency, the modelling results of inflow quantity and hydraulic heads were compared to those from analytical solutions, as well as the field data. The mean percent error in relation to field data for the inflow quantity was 0.108. It varied between 1.16 and 1.46 for hydraulic head predictions, which are much lower values than the mean percent errors resulted from the analytical solutions (from 1.8 to 5.3 for inflow and from 2.16 to 3.5 for hydraulic head predictions). The analytical solutions underestimated the inflow compared to the numerical model for the time period of 2-19 weeks. The results presented in this paper can be used for developing an effective dewatering program

SIMULACIJA SANACIJE VODONOSNIKA SLABOPROPUSNIH LEĆA FENOMENOM POVRATNE DIFUZIJE

Fluid flow in a dual permeable medium (DPM) is essential in solute transport in mining and aquifer studies. In this paper, water flushing into a contaminated DPM containing fine-grained lenses with different geometries was investigated with the Lattice Boltzmann Method (LBM). The LBM model used in this study was D2Q9 with a relaxation time of 1, a cohesion value of 3 for a fluid density of 1 (mu.Lu-3). The saturated fluid in the DPM was a contaminant that usually stays in low permeable lenses and after flushing, it is leaked into the porous medium by a second fluid (water). This phenomenon is predominant when the displacing fluid has a lower concentration than the contaminated fluid. Diffusion and advection are the main mechanisms that control fluid flow in the porous medium. The results of the simulations showed: (1) advection controlled solute transport through the flushing phase, and back-diffusion occurred after the change in phase; (2) the lenses’ geometry influenced the fluid flow pattern and the remediation process. As a result, aquifer remediation strategies based on the lenses’ geometry and their permeability can help us select the appropriate environmental protection.Protjecanje fluida kroz medije s dvostrukom propusnošću bitno je kod proučavanja transporta otopljene tvari u rudarstvu ili kroz vodonosnik. U ovome radu, s pomoću metode Boltzmannove rešetke, istraženo je ispiranje vodom medija dvostruke propusnosti koji sadržava sitnozrnate leće različite geometrije. Metoda Boltzmannove rešetke u ovome istraživanju uključivala je korištenje modela D2Q9 s vremenom otpuštanja 1 te vrijednošću kohezije 3 za fluid gustoće 1 (mu. Lu-3). Medij dvostruke propusnosti zasićen je fluidom koji je ujedno predstavljao i zagađivač koji se obično zadržavao u slabopropusnim lećama iz kojih se širio nakon ispiranja poroznoga medija sekundarnim fluidom (vodom). Ova je pojava prevladavajuća u slučaju kada istiskujući fluid ima manju koncentraciju od kontaminiranoga fluida, a difuzija i advekcija dva su osnovna mehanizma koja kontroliraju tok fluida kroz šupljikavu sredinu. Rezultati simulacije pokazuju da: (1) advekcija kontrolira transport otopljene tvari tijekom faze ispiranja, dok se povratna difuzija odvija nakon promjene u fazi; (2) geometrija leća utječe na oblik toka i proces sanacije. Rezultat je strategija sanacije vodonosnika bazirana na geometriji i propusnosti leća koja može pomoći u zaštiti okoliša

SIMULACIJA ZAGAĐENJA PODZEMNIH VODA S MJESTA ODLAGANJA RUDARSKOGA OTPADA

Mining wastes are a great source of pollutants. Open-pit backfill materials can be found as waste rock and as tailings. The aim of the current study was the investigation of the contaminant transportation pathways by groundwater flow from these waste materials through heterogeneous porous media. Numerical Lattice Boltzmann Method (LBM) was used for examining the effects of different factors on pollutant transportation through groundwater beneath the waste materials. Grain size, vertical and horizontal fracturing, and hydraulic pressure gradient were factors considered here. The results showed that contaminant transportation by the groundwater flow from the waste materials through porous media depends on primary and secondary matrix porosity of the open-pit material, heterogeneity in permeability of aquifer rock, and hydraulic head of groundwater.Rudarski otpad velik je izvor onečišćenja. Kao materijali za zatrpavanje otvorenih jama mogu se koristiti otpadne stijene i jalovina. Cilj ove studije bio je istražiti putove transporta onečišćenja podzemnim vodama iz ovih otpadnih materijala kroz heterogene porozne medije. Boltzmannova metoda numeričke rešetke (LBM) korištena je za određivanje učinaka različitih čimbenika na transport onečišćujućih tvari kroz podzemne vode ispod otpadnih materijala. Čimbenici koji su uzeti u obzir bili su veličina zrna, okomite i vodoravne pukotine te hidraulički gradijent tlaka. Rezultati su pokazali da prijenos onečišćenja protokom podzemnih voda iz otpadnih materijala kroz porozne medije ovisi o poroznosti primarne i sekundarne matrice otkopanih materijala, heterogenosti propusnosti stijene vodonosnika i hidrauličkom tlaku podzemne vode

Numerical modeling of gas flow in coal pores for methane drainage

The sudden explosion of methane during underground coal mining is a major dilemma. To mitigate its occurrence and reduce the extent of methane diffusion, gas drainage operations are carried out before mining. This paper investigates methane gas flow in a coal block in order to calculate the pressure of gas and its molecule velocity for methane gas drainage operation. A coal piece surrounded by cleats was used for geometrical modeling and numerical simulation. Movements of fluid and gas molecules in a porous medium were successfully simulated. The numerical solution is based on COMSOL Multiphysics software. The validity of the numerical simulation was assessed using an analytical model with satisfactory results

The management of water resources between traditions and sustainability: the qanats of Shahrood Province (North-eastern Iran)

Qanats, Iran, multidisciplinary study, water supply

Probabilistic risk assessment of acid mine drainage generation resulted from chalcopyrite oxidation process within Sarcheshmeh copper mine tailings

A probabilistic predictive method for estimating the risk of acid mine drainage generation within the copper tailings dump of the Sarcheshmeh copper mine, Iran, has been presented in this paper. For this purpose, the input and output parameters were determined after gathering historical data and building an appropriate database. Some of the critical parameters, including depth, and concentrations of bicarbonate, chloride, nitrate, and nitric, were considered input data, while the output parameters were chalcopyrite, pH. The best distribution functions on each input parameter were found by Chi Sq. criteria. Subsequently, the best linear statistical relationships between the input and output data were determined. Then, the best probability distribution functions of output parameters were defined by inserting the input parameters in the obtained linear statistical relationship. The results showed that the remaining chalcopyrite fraction values were between 0.1094 % and 0.2159% at a 90% probability level. In contrast, the pH values would be expected between 3.13 and 8.04 at this probability level

Application of Computational Fluid Dynamics (CFD) for Simulation of Acid Mine Drainage Generation and Subsequent Pollutants Transportation through Groundwater Flow Systems and Rivers

Many environmental problems associated with the mining industry involve the understanding and analysis of fluid or gas flow. Typical examples include groundwater flow, transport of contaminants, heat transfer, explosions, fire development and dust movements. Both experimental work and numerical models can provide the necessary information for solution of any particular problem. The long-term pyrite oxidation, acid mine drainage generation and transportation of the oxidation products are noted to be the most important problems that can be modelled in order to predict the transport of thecontaminants through groundwater and rivers flow systems, to interpret the geochemistry and achieve a better understanding of the processes involved

Application of a geographic information system (GIS) for selecting the location of a coal wastes dump - a case study

The Gheshlagh mining region, which includes more than ten active and several abandoned coal mines, is one of the most significant regions for coal mining in northern Iran. Due to the lack of more suitable ecological and environmental strategies for coal wastes management from these mines, a large amount of wastes has been dumped in the vicinity of the mines. The primary purpose of this research is to propose a new methodology for selecting a site for coal waste piles applying GIS in the Gheshlagh region. For this, the coal waste piles have been firstly detected by field observations and based on environmental aspects. All the required maps, including farmlands, surface streams such as seasonal rivers, forests, and residential areas have been run in the ArcView software package. Finally, the best location of the site for dumping the coal wastes with an area of 27 hectares has been detected and suggested in the Gheshlagh coal region using the IDRISI software package considering environmental and economic aspects. These studies are beneficial for mine planners to reduce the environmental issues nearby the mining operations

Hydrogeological investigations of backfilled surface coal mine sites

Australia is one of the major coal producing countries in the world. Coal mine abandonment, groundwater rebound due to cessation of dewatering and associated pollution problems are a cause of serious concern throughout the world, and in particular, in Australia. Coal mining often leads to major environmental pollution problems when pyritic mineral is associated with the coal. The oxidation of pyrite usually generates acid mine drainage (AMD). The generation of AMD containing Fe++, Fe+++, SO4-- and H+ is a source of great concern and can contaminate water resources. Prediction of groundwater inflow into a mining excavation is important for the design an effective dewatering system during the feasibility stage of a surface mining operation. A two-dimensional numerical finite element model called SEEPAV has been used for predicting the inflow of water into a surface mine working. The SEEPAV is a 32-bit graphical software that operates on the PC under Microsoft Windows 95, 98, Me, NT, 2000, and XP operating systems. This model has a capability to simulate saturated/unsaturated flow conditions and to calculate the height of the seepage faces the mining excavation taking into account the hydraulic conductivities and the water content as a function of pore water pressure. The SEEPAV model with some modifications has also been used to predict the groundwater rebound within backfilled open cut mines. This model has the ability to simulate groundwater flow problems in partially saturated porous media. Flexibility in the model is achieved by assigning different boundary conditions to the model. The results of the model of groundwater rebound are presented and compared with those obtained from analytical solutions, using the existing numerical model as well as with the field monitored data observed in the UK . This model calculates realistic results that can be used by mine operators and environmental engineers to control the quality of mine drainage in a backfilled open cut mine operation. A two-dimensional numerical finite volume model using PHOENICS as a computational fluid dynamic (CFD) package has been developed to simulate the transport of oxygen and long-term oxidation of pyrite as well as transport of oxidation products from a backfilled open cut coal mine. Gaseous diffusion was considered to be the principal mechanism for the transport of oxygen through the spoil. It was assumed that both oxygen and ferric iron produced by bacterially mediated oxidation of ferrous iron participate in the oxidation of pyrite. The pyrite oxidation reaction is based on shrinking-core model. The model takes into account the effects of both surface reaction kinetics and the rate of oxidant diffusion into the particle. The model also assumes the particles have spherical shape and considers the rate of pyrite oxidation to be first with respect to oxidant concentration and pyrite surface area. Complexation of ferric iron is assumed to take place within the spoil solution. The model can take into account the role of sulphate reduction bacteria governed by Monod type kinetics. The model also incorporates acid neutralisation reactions, linear and equilibrium-controlled ion exchange reactions as well as the effects of precipitation of ferric iron. In this present model, chemical and bacterial oxidation of Fe2+, pyrite oxidation by oxygen and ferric iron, oxygen diffusion and bacterial sulphate reduction are relatively slow and assumed to be kinetically controlled but ion exchange and complexation reactions as well as precipitation reactions are fast and these are assumed to be equilibrium controlled reactions. Comparisons were made with published numerical modelling results and close agreement was achieved. It was found that for the development of inflow and post-mining rebound models, a study of the hydrogeological characteristics of spoil is important. A comprehensive model of pyrite oxidation in the backfilled site of an open cut mine should not ignore the role of iron-oxidising bacteria. In the absence of bacteria, oxygen is the only important oxidiser of pyrite and the oxidation rate is highly dependent on the effective diffusion coefficient. Although the oxidation of pyrite in the presence of air and bacteria is unavoidable, the numerical model developed here provides useful tool for assessing the effectiveness of a rehabilitation strategy to reduce pollutant production within oxidising pyritic material

Application of artificial neural network coupled with genetic algorithm and simulated annealing to solve groundwater inflow problem to an advancing open pit mine

In this study, hybrid models are designed to predict groundwater inflow to an advancing open pit mine and the hydraulic head (HH) in observation wells at different distances from the centre of the pit during its advance. Hybrid methods coupling artificial neural network (ANN) with genetic algorithm (GA) methods (ANN-GA), and simulated annealing (SA) methods (ANN-SA), were utilised. Ratios of depth of pit penetration in aquifer to aquifer thickness, pit bottom radius to its top radius, inverse of pit advance time and the HH in the observation wells to the distance of observation wells from the centre of the pit were used as inputs to the networks. To achieve the objective two hybrid models consisting of ANN-GA and ANN-SA with 4-5-3-1 arrangement were designed. In addition, by switching the last argument of the input layer with the argument of the output layer of two earlier models, two new models were developed to predict the HH in the observation wells for the period of the mining process. The accuracy and reliability of models are verified by field data, results of a numerical finite element model using SEEP/W, outputs of simple ANNs and some well-known analytical solutions. Predicted results obtained by the hybrid methods are closer to the field data compared to the outputs of analytical and simple ANN models. Results show that despite the use of fewer and simpler parameters by the hybrid models, the ANN-GA and to some extent the ANN-SA have the ability to compete with the numerical models