The characteristics of groundwater flow and pollutants transport around the Samkwang mine and the Kimpo landfill site were analyzed with MODFLOW, TRAFRAP, MT3D models. The methods for the contamination reduction were also studied. New mathematical model was developed to predict the flow velocity of groundwater using the analysis results of tritium concentrations in rainfall and groundwater. Hydraulic conductivity, hydrodynamic dispersion coefficient, distribution coefficient, and biodegradation coefficient were measured through the field and the laboratory test. The tritium concentration in rainfall and groundwater sampled at a tunnel in the study area were analyzed for this study.
First of all, the analysis results of groundwater flow system for the study area were as follows. Through the field hydraulic test, the hydraulic conductivity in the gneiss of the study area was $1.7×10^{-5}×z^{-1.3}m/sec$(z : depth from the surface, (m)) and the flow times of flow paths of the rainwater infiltrated from the water system boundary were between 15 and 263 years. The total volumetric flow rate of groundwater in study area was 307 m3/day. The groudwater flow system was analyzed by TRAFRAP model with consideration of fracture zone, and the results revealed that the flow paths of groundwater were formed about 100m lower than those without fracture zone. To verify above results, the flow rate of groundwater at the east outlet of the study area was measured by a current meter. The difference between the groundwater flow rate measured by a current meter and that calculated by MODFLOW was about 10%.
As a device to verify the flow time of groundwater analyzed by a numerical model, a mathematical model was developed to calculate the flow time of groundwater using tritium. The difference of the new model from Cleary's existing model is that tritium concentration along the depth is calculated at once with integral equation instead of superposition technique. The developed model was applied to a tunnel in the Samkwang mine, and the flow time of groundwater around the tunnel was analyzed. Using the new model and tritium concentration in rainfall and groundwater sampled at the study area, the flow times of groundwater from the surface to the study points in the tunnel located at 44, 92, 102, and 205 m below the surface were calculated to be 2.0, 4.0, 4.5, and 9.0 years, respectively. The flow velocity of groundwater in the ground medium of the study area were also calculated to be 22 m/year.
Using MODFLOW and MT3D models, the characteristics of pollutants transport around the Kimpo landfill site were analyzed. The results showed that the leachate water level near the center of landfill site on the present state was EL.(+)8 - EL.(+)15 m. The 65% of the infiltrated leachate is dewatered through the drainage facilities, and the remaining 35% flow out to the surroundings. The maximum discharge concentrations of chloride, phenol, and COD to the seashore area were 1584, 0.23, and 0.0 mg/ℓ, respectivly. When 5 sets of RCWL(Radial Collector Well Lateral) were established as a device for contamination prevention, the percentage of leachate dewatered through drainage facilities and RCWLs was 70%, and the maximum discharge concentrations of chloride, phenol, and COD to the surroundings were 1157, 0.17, and 0.0 mg/ℓ, respectively. When the wells dewatering the condensed water were used to dewater leachate, the percentage of leachate dewatered is 71%, and the maximum concentrations of chloride, phenol, and COD are 1109, 0.16, and 0.0 mg/ℓ, respectively. When the interception well was established up to 2 or 3 layers, the percentage of leachate dewatered through drainage facilities and RCWLs was increased to up 92% in case of 2 layer interception and, 97% in case of 3 layer interception. The discharge concentrations of chloride, phenol, and COD to the surroundings became very low. Therefore, the method of interception well establishment was most suitable of all methods.
