Hydraulic conductivity property is very important for groundwater flow modeling. It can be gathered through packer test and slug test. The high cost of the operational implementation of these tests lead to the limited availability of observational-based distribution of hydraulic conductivity data. Highly fractured rocks in Grasberg open pit mining and surrounding of PT Freeport Indonesia (PTFI) result in fractured-groundwater-flow media. It is related to the complex geological structure and

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... ological condition. Groundwater modeling needs 3D distribution data such hydraulic conductivity (K). On previous research, hydraulic conductivity is distributed homogenyneously at each layer model. In this paper, under limited observational hydraulic conductivity, isotropic hydraulic conductivity will be modeled based on the HC-System approach and will be three-dimensionally distributed using Artificial Neural Network (ANN). HC-System approach will be developed according to the packer test and slug test measurement using geotechnical data from drilling such as Rock Quality Designation (RQD), Lithology Permeability Index (LPI), Depth Index (DI), and Gouge Content Index. HC-System approach will be resulted in isotropic distribution of hydraulic conductivity. It is then checked at some points by the packer tests and slug tests observational data. It is further very beneficial for modeling of groundwater distribution flow with the heterogeny hydraulic conductivity.