## 5 Conclusions and Discussion  
The region of Okcheon in South Korea needs a stable water management system that can provide high-quality drinking water and water for agricultural use; this system should be based on sources other than surface water. To provide a sufficient amount of water, it is very important to predict the locations of uncontaminated usable groundwater with accuracy. Therefore, this study estimated the groundwater of the un-surveyed area by analyzing the relationship between the well locations and the surrounding environment including the topographic factors using three models. For the models applied in this study, half of well location data (43 well locations) were used as training data and the other half were used as validation data. Total 18 topography, soil, and land cover variables were used as independent variables. Finally, the estimated potential groundwater maps were provided by using three models of LR, RF and BRT. From the results of the LR, RF and BRT models, the following relationships between wells data and the examined factors could be established. GPP is higher in gentle slopes, hydraulic slopes, lower relative slope positions, and shorter slope lengths because rainfall running off from the upper regions accumulates in the lower regions. This in turn positively influences the aquifer. In addition, the TRI is an index representing the altitude difference between two adjacent areas in open terrain. The GPP is higher where the altitude difference is not significant. On the other hand, distance from fault, lineament, and channel network showed a negative correlation with GPP. Groundwater in aquifers hydrologically flows from high to low gradients like surface water. As a result, most of the groundwater charged in areas of low altitude and some are eventually discharged back to the river, the lowest zone. In the end, most areas with large amounts of groundwater are close to the river, which are clearly reflected in this study. These results indicate that closeness to rivers increases the GPP of an area, as is known from the hydrogeological point of view. In case of \"distance from the fault\" factor, [PERSON], et al. (2018) mentioned that the deformation along faults in the shallow crust (<1 km) introduces permeability heterogeneity and anisotropy, which has an important impact on processes such as groundwater. While the results in this paper show that voids between defects have a positive effect on groundwater recharge, direct assessment of the impact between defects and groundwater recharge remains a difficult discussion. We considered that needs to be further discussed through various experiments. In conclusion, the three proposed models were able to estimate the location of groundwater wells with an average GPP probability of over 80%. These results validate the usefulness of the three models for groundwater resource development. The final GPP map proposed in this paper used 86 limited wells data, so there is a limit to reflect the real world. However, if we collect more wells data for this region in the future and perform a GPP analysis, you can expect better results. Also, it is showed from the results that the accuracy is higher when GPP is predicted using T values rather than SPC  
Figure 5: ROC curves for the GPP maps with T/SPC values produced by (**a**) LR model, (**b**) BRT model and (**c**) RF model. values. Despite the limitations, these GPP mapping methods can be efficiently applied in the future for national groundwater development and utilization planning in Korea. [PERSON] and [PERSON] conceived and designed the experiments; [PERSON] performed the experiments; All the authors analyzed the results, [PERSON] wrote the paper. This research received no external funding.