# Configuration of Non-Pumping Reactive Wells Considering Minimum Well Spacing
## 4 Conclusions  
The NPRW is proposed as a passive treatment method for contaminated groundwater in deep subsurface environments. Various well configurations have been developed to effectively prevent the spread of groundwater contaminants. In sites where multiple wells are constructed adjacent to each other, sufficient distance between wells is recommended to ensure ground stability and well structure safety. Therefore, the minimum separation distance between wells must be considered as an important limiting condition for efficient NPRW design. Under these constraints, a well array with a single transect requires wells with a diameter as large as the minimum well spacing to block groundwater contamination. However, when the size of the well is large, well construction becomes difficult and the cost increases rapidly. The contaminant leaks that occur between small diameter wells spaced apart can be compensated by configurations with multiple transects that install additional wells downstream; however, the number of wells doubles or triples, increasing cost. Therefore, a practical design of well configurations that uses an appropriate well size and optimizes the arrangement is required. In this research, we proposed a novel triple transect configuration considering the removal efficiency as well as the constraints in the well construction field (well diameter and minimum well spacing). The novel NPRW has a triple or quadruple transect configuration of reactive wells arranged in a sawtooth shape. The number of wells has been optimized for sufficient contaminant removal. The contaminant removal performance of the NPRWs with multiple transect configurations could be estimated using the performance curve developed from the relationship of contaminant removal efficiency with well spacing and well diameter. This performance curve allows the selection of practical configurations of NPRWs considering the field conditions, the construction constraints (minimum well spacing and well diameter), and the target removal efficiency of contaminants. The sawtooth configuration and performance curve proposed in this study are expected to be used for the practical design of configurations of NPRWs with respect to well diameter and well spacing under field conditions. It should be noted that since this study focused on designing the feasible construction of NPRWs, it was assumed that the reactive material filled in the wells immediately removes contaminants. For a more practical design of NPRWs with sawtooth array, the diameter of well can be increased or the well spacing can be decreased depending on the performance of the reactive material, and if necessary, a conservative design can be made by applying a safety factor to the performance curve. For this, follow-up studies are required.  
[PERSON]-Y.G. performed writing--original draft and visualization. [PERSON]-H.K. performed conceptualization and validation. [PERSON] performed supervision and funding acquisition. S.L. performed writing-review and editing; project administration. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Korea Environmental Industry & Technology Institute (KEITI) through the underground environmental pollution risk management technology development business program, funded by the Korea Ministry of Environment (MOE) [grant number 2018002470002, ARQ202101728001]; and the National Research Foundation of Korea (NRF) grant funded by the Korea Ministry of Science and ICT [grant number NRF-2017R1C1B3009500].  
Data Availability Statement: Data sharing not applicable.  
This work was supported by the Korea Environmental Industry & Technology Institute (KEITI) and the National Research Foundation of Korea (NRF).  
The authors declare no conflict of interest.