## 4 Results and Discussion
### Simulations of Advective Transport
Table 3 lists the detailed information for the results of particle tracking simulation for a specified release point in Case II. Note that the particle release point is the highest velocity based on the flow simulations obtained from the HD and ECPM models. Previous investigations had shown that the highest velocity was usually obtained along the intersections between the DH and fractures. In Case II, we had assigned a relatively large fracture aperture of 0.1 m. The large fracture aperture could reduce the number of  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{1}{c}{**Parameters**} & \multicolumn{1}{c}{**ECPM**} & \multicolumn{2}{c}{**HD**} & \multicolumn{1}{c}{**DFN**} & \multicolumn{1}{c}{**HD**} \\  & & & **(Fractures and Matrix)** & & **(Fractures Only)** \\ \hline \multirow{6}{*}{Trace length} & Mean (m) & 5.61 & 6.38 & 5.51 & 5.38 \\  & STD (m) & 0.35 & 1.01 & 0.63 & 0.37 \\  & CV & 0.062 & 0.158 & 0.114 & 0.069 \\  & Min. (m) & 5.07 & 5.12 & 5.11 & 5.10 \\  & Max. (m) & 6.39 & 10.48 & 9.04 & 7.77 \\ \hline \multirow{6}{*}{Travel time} & Mean (s) & 4.0 \(\,\times\,10^{8}\) & 2.1 \(\,\times\,10^{8}\) & 3.2 \(\,\times\,10^{6}\) & 3.9 \(\,\times\,10^{6}\) \\  & STD (s) & 2.3 \(\,\times\,10^{8}\) & 6.4 \(\,\times\,10^{7}\) & 4.7 \(\,\times\,10^{6  
cells for the ECPM model to capture the flow and transport influenced by the fracture geometries. However, this large fracture aperture might create differences in the highest velocities obtained from the ECPM and HD models. The location of a cell center in the ECPM model might not be consistent with the virtual fracture assigned on the element face. In most practical problems, the highest velocity is the critical parameter for safety assessment in the near field of a disposal facility. The velocity is one of the parameters for calculating the buffer erosion and canister corrosion rate inside the deposition hole. The highest velocity location is also the point for releasing the containment in most practical problems [5]. Therefore, the value and location of the highest velocity are essential for the corresponding safety assessment of the disposal facility. The highest velocity location in the ECPM model is (2.4375 m, 3.6875 m, 7.0625 m) in Figure 10a,b, while the highest velocity location in the HD model is (3.390 m, 3.573 m, 5.000 m) in Figure 10c,d. In addition, \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **ECPM Model** & **HD Model** \\ \hline Start location (x, y, z) (m) & 2.4375, 3.6875, 7.0625 & 3.390, 3.573, 5.000 \\ End location (x, y, z) (m) & 4.830, 4.147, 0.125 & 4.995, 4.114, 0.000 \\ Velocity at the start location (m/s) & 1.31 \(\times\) 10\({}^{-10}\) & 6.25 \(\times\) 10\({}^{-9}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The results of the particle tracking simulation for Cases II. Figure 10: The particle release location and the particle trace for the ECPM and HD models in Case II. (**a,b**) The start location and particle trace for the ECPM model; (**c,d**) The start location and particle traces for the HD model. The statistics for the advection transport are summarized in Table 4. In general, the particle travel times obtained from the HD model are relatively small, leading to a relatively high transport velocity (Table 4). The mean velocity of the HD model could be two times higher than that in the ECPM model. Table 4 also shows that the HD model obtains relatively low STD values for the trace lengths and travel times but obtains high variation in transport velocity. Note that the HD model has considered virtual fractures in the simulation procedures. The particle release locations are precisely defined in the HD model. The fractures in the HD model act as a high-velocity pathway for groundwater flow. The particle migrations could be in fractures or rock matrices, depending on the local flow dynamics. For most practical problems, capturing the complex flow dynamics near DHs and fractures is essential for accurate evaluations of the large-scale and long-term transport processes.