# Configuration of Non-Pumping Reactive Wells Considering Minimum Well Spacing
## 3 Results and Discussion
### Modeling Contaminant Transport through NPRWs  
#### 3.2.1 Prevention of Contaminant Spread by NPRW  
Contaminant transport through various PRB configurations was simulated numerically. Trench- and NPRWs were used to capture 3 m of contaminated plume in numerical simulations (Figure 4). The simulations tested different designs of multiple transect configurations considering the minimum well spacing. As a control, the conventional trench-type PRB was also modeled (Figure 4a), which could capture the contaminant plume completely. For groundwater contamination that occurs at a shallow depth where trenches can be  
Figure 4: Numerical modeling of contaminant transport through various PRB configurations: (**a**) trench-type PRB, (**b**) single transect, (**c**) double transect, (**d**) conventional triple transect, and (**e**) triple transect with sawtooth array of reactive wells. These configurations were constructed by assuming that well diameter, \(\mathrm{d}_{1}=0.25\) m and minimum well spacing, \(\mathrm{d}_{\mathrm{m}}=1.5\) m, and the hydraulic conductivity of the reactive media in the well was sufficiently higher than that of aquifer.  
installed, it is possible to completely capture the contamination. However, considering the limitations of deep aquifer remediation and the enormous amount of reactive media consumed to form a trench, the NPRWs, as shown in Figure 4b-e, can be used as an alternative PRB configuration.  
If the reactive wells were placed in a line and considered the field constraints, the single transect configuration could not prevent the contaminants from spreading downstream. Because each reaction well (d1 = 0.25 m) could capture contamination twice the width of the well diameter at most, the wells separated by 1.5 m intervals leaked contamination downstream (Figure 4b).  
The multiple transect configuration formed by adding wells downstream of the first transect could be an alternative configuration to complement the contaminant leakage (Figure 4c-e). The double transect increased the contaminant removal efficiency, because the second well transect located downgradient could capture the contaminant plume passing through the first transect (Figure 4c). Under the assumed well diameter and minimum well spacing, an additional transect was necessary for complete contaminant removal.  
When designing the configuration of a NPRW with three or more transects, various arrangements are possible, and the contaminant removal performance may vary substantially. The triple-transect configuration using a zigzag arrangement (Figure 3a) could not be constructed on site because the distance between the wells in the second transect and the adjacent wells was closer than the minimum separation distance. Figure 4d shows a conventional triple-transect configuration in which the third row of reaction wells is additionally constructed downstream of the first row in the double-transect configuration. This structure could not remove the contaminants that have leaked from the second transect but could remove contaminants that had not been completely removed by the first transect. The simulated contaminant plume through the sawtooth configuration shows complete prevention of contaminant spread (Figure 4e).