Investigation of a groundwater flow system becomes important for safety assessment of underground facility, and for development of water resources. A new analysis method treating groundwater chemistry data is required along with the development of a sampling technique for the water in deep crystalline rocks. In this study, new method is developed, which estimates groundwater mixing condition using multivariate analysis and principal component analysis to the water chemistry. Computer program coded for this analysis was tested for practical use. The results were as follows;
1. Using test data, the discriminability of the mixing model was checked. The correspondence of the compositions of end-members and the mixing ratios between the pre-assumed values and the model output was satisfactory.
2. The method was applied to field data of groundwater sampled from boreholes. The result of the analysis reveals the mixing condition of groundwater and that agree with geotomography data.