MODEL DEVELOPMENT OF ACID MINE DRAINAGE USING CATCHMENT AREA APPROACH IN OPEN PIT COAL MINE

• Main Author: Sonny Abfertiawan, Muhammad
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/55163
• Institution: Institut Teknologi Bandung

Open pit coal mine which includes excavation and dumping of overburden material has potential impact on the changing of topografi and land covers. As a further impact, this changes will directly influence hydrology condition which is characterized by increasing the discharge at downstream of disturbed catchment area. In addition, the presence of sulfide minerals contained in overburden can potentially degrade the water quality of both surface water and ground water due to the generation of acid mine drainage (AMD). The change of quantity as well as quality will continually and dynamically occur in line with mining sequence and reclamation of disposal area until the periods of mine closure. Therefore, study related to modelling of quantity and quality is important to be conducted in order to prevent and manage the risk of AMD generation. This research aims to develop integrated models that can be used to predict the quantity and quality of stream water by using catchment area approach. The modeling was conducted by taking a case study of Ukud River that located at Lati Mine Operation, East Kalimantan to validate the result of simulation. Hydrological modeling was conducted by using topographically based semi-distributed hydrological model (TOPMODEL) to simulate the discharge fluctuation at downstream of river. TOPMODEL was chosen since its ability to simulate rainfall-runoff in various type of catchment area. Moreover, in the process of simulation, this model considering the physical characteristics that can accommodate the changes of catchment areas in open pit coal mines. These method had been successfully performed to simulate the discharge fluctuation of Ukud River. From simulation results, maximum discharge was obtained for 54,343 m3/hour and an average discharge of 3,287 m3/hour. To evaluate the simulation, Nash Sutcliffe Efficiency (NSE) was used and obtained at 0.54. This value has met the criteria so that the results are relatively similar to the observed data and acceptable. Furthermore, the discharge simulation data was used in generation and transport model of AMD. AMD generation and transport model was conducted by using geochemical reaction approach in disturbed catchment area. It was performed using PHREEQC, a computer program for simulating chemical reactions and transport processes in natural or polluted water. Simulation using data on January 2013 showed that in subDAS A1 which is an active mining area, there were 40 moles of sulfide minerals that react to 52.7 m3 of water so that the pH value drops to 4.3. This result realtively closed the observed data during the same period which ranges from pH 3.8 to 4.4. The simulation results indicate that load of pollutant from disturbed subcatchment area influence the fluctuation of pH changes in the mainiv river stream. Furthermore, the simulation of water quality at downstream was carried out using dilution factor approach. The system was assumed to be completely mixed system. The simulation results on January 2013 showed a significantly decrease in quality at the point P1. The pH value decreased from 7 to 5.08. The pH value has a decline trend till it reaches 4.12 at point P6 which is the downstream of river. Sulfate and metals concentration were also simulated on point P1 to P6. This simulation results showed increased concentrations of sulfate up to 27 mg/L at point P6. Fe concentration also increased from 0.178 mg/L to 2.94 mg / L at the point P1. However, this concentration decreased from 2.94 to 1.57 mg/L at point P6 since dilution factor and precipitation occurred along the stream. Concentration of Al and Mn also increased reach to 0.48 mg/L and 2.48 mg/L at point P6. Evaluation of the simulation results was conducted by comparing it with observed data. This result relatively similar to observed data. The pH value of observations at the sampe period recorded at 4.19. In general, the simulation results is quite close to the observed data so that this method is valid and can be used. Integrated modeling in this study can be used to estimate the chemical characteristics of the river from catchment areas that distrubed by mining activities. This approach seems promising to be integrated into the surface coal mine planning process. Catchment area characteristics should become an important considerations when analyzing the mine area layout and particularly in determination of out pit overburden disposal area to minimize risk of AMD generation.