## 3 Data Collection and Its Characteristics  
As stated above, CBIII-250, D245S, and DML drills were used at the mine for drilling boreholes, with the diameter of boreholes in the range of 200 mm to 250 mm. For data collection, the drilling diameter/diameter of boreholes (\(d\)), the penetration rate of the drill (\(P\)), the moisture content (\(W_{ln}\)), the silt content (\(S\)), the density of rock mass (\(\rho\)), the compressive strength (\(\sigma_{c}\)), and the rebound hardness number (\(R\)) were used as independent variables to predict PM\({}_{10}\) concentration. Figure 3: The distance from the mine to the residential area. Figure 2: Simplified geological conditions of the Coc Sau open-pit coal mine. As mentioned, CEIII-250, D245S, and DML were the component drills used in the mine with \(d\) in the range of 200 to 250 mm. With an average depth in the range of 12 to 15 m, the drills can penetrate the rock with \(P\) in the range of 0.16 to 0.41 m/min. For humidity moisture (\(W_{tn}\)), the core drilling rock samples were carefully preserved and brought to the laboratory. Each drilling hole was collected as a sample by combining representative rock in the drilling core. In the laboratory, a total of 245 samples were used to determine the natural water content of rock (\(W_{tn}\)). The method was conducted by Vietnam's standard of TCVN 10321:2014 [63]. The equation (1) for calculating the natural water content of the rock is as follows:  
\[W_{tn}\ =\ \frac{g_{1}-g_{2}}{g_{2}-g_{0}}\cdot 100 \tag{1}\]  
where \(g_{0},g_{1},g_{2}\) are the weights of the sample box without a rock sample, of the sample box and the natural rock sample, and of the sample box and the dried rock sample, respectively. For silt content (\(S\)), the fine particles present in the drill cutting was determined (in %). For determining the properties of rock mass (\(\rho\), \(\sigma_{c}\)), indirect experiments in combination with Protodiakonov's strength index were used. To determine \(R\), a rebound hardness tester was used, i.e., a Schmidt hammer. For measuring PM\({}_{10}\) concentration, KANOMAX digital dust monitor model 3442 was used in this study (the manual of KANOMAX can be found at the following link [[https://kanomax.biz/asia/products/dust_monitors/model_3442_3443.html](https://kanomax.biz/asia/products/dust_monitors/model_3442_3443.html)]([https://kanomax.biz/asia/products/dust_monitors/model_3442_3443.html](https://kanomax.biz/asia/products/dust_monitors/model_3442_3443.html))). This instrument (model 3442) is a light scattering portable dust monitor using a semiconductor laser radiation light source [64]. The principle of this method is that when the dust is irradiated, the scattered light intensity from the dust is proportional to the mass concentration. Two monitoring stations with this instrument were installed: One in the upstream and the other in the downstream. To ensure the accuracy of the predictive models, the datasets from independent drilling locations were collected to eliminate the maximum of PM\({}_{10}\) concentration from other mining operations. In other words, there were no other activities (e.g., loading/unloading, transporting, blasting) on the same work sites of the drilling operation. Furthermore, the dust monitor was set around the drill with the distance being in the range of 5 to 10 m to ensure a maximum of PM\({}_{10}\) concentration from the drilling operation was obtained (Figure 3). With 245 drilling operations, PM\({}_{10}\) concentration was measured in the range of 0.148 to 1.306 gm/s. Figure 4 illustrates the data collection process for this study, and the data used is summarized in Table 2. Also, Figure 5 shows the relationship between input and output variables used in this study.