## 4 Economic Feasibility Analysis
### Design and Construction Costs  
The construction cost was calculated by applying the material cost, labor cost, and expenses, based on the design water quantity. When the material cost was calculated based on the main structure (infiltration facilities) of each system, the labor costs required for installation and the expenses were compared. The construction costs were found to be KRW 54,245,120 and KRW 37,807,760 for the existing and eco-friendly rainwater detention systems, respectively. When the eco-friendly rainwater detention system was applied, the total construction cost decreased by approximately 30% owing to reduction in the material and construction costs by approximately 45% and 15%, respectively. This decrease occurred because of the reduction in production cost caused by the mass-production possibility of red clay water-permeable blocks, which constitute the primary structure of the eco-friendly rainwater detention system, and the simple construction through the assembly of the red clay blocks. Table 13 presents the details of the construction cost.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Item**} & \multicolumn{3}{c}{**Existing System**} & \multicolumn{3}{c}{**Eco-Friendly Rainwater**} & \multicolumn{3}{c}{**Reduced Construction Cost**} \\ \cline{2-9}  & \multirow{2}{*}{**Facility**} & \multirow{2}{*}{**Design Water**} & \multirow{2}{*}{**Construction**} & \multirow{2}{*}{**Cost (KRW)**} & \multirow{2}{*}{**Facility**} & \multirow{2}{*}{**Design Water**} & \multirow{2}{*}{**Construction**} & \multirow{2}{*}{**Construction**} & \multirow{2}{*}{**Reduction**} \\  & & & & & & & & \\ \hline \multirow{4}{*}{A *} & A (T0.24) & 300 m\({}^{2}\) & 11,663,100 & A (T0.24) & 300 m\({}^{2}\) & 11,663,100 & 0 & \\  & A (T0.25) & 400 m\({}^{2}\) & 17,082,800 & A (T0.25) & 400 m\({}^{2}\) & 17,082,800 & 0 & 0\% \\ \cline{1-1}  & Sub total & 700 m\({}^{2}\) & 28,745,900 & Sub total & 700 m\({}^{2}\) & 28,745,900 & 0 & \\ \hline \hline \end{tabular}
\end{table}
Table 13: Details of the construction cost.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Category**} & \multirow{2}{*}{**Facility Name**} & \multicolumn{2}{c}{**Specific**} & \multirow{2}{*}{**Unit Design**} & \multirow{2}{*}{**Design Water**} & \multirow{2}{*}{**Design Quantity (2)**} & \multirow{2}{*}{**Quantity (m3/h)**} & \multirow{2}{*}{**Total**} \\  & & & **Infiltration** & & & & \\ \multirow{4}{*}{Pavement} & Permeable pavement & & & & & & \\  & & (T0.24) & & & & & \\  & Permeable pavement & & & & & & \\  & & & (T0.25) & & & & & \\  & & & & & & & \\  & Infiltration gutter & & & & & & \\  & & W250 & & & & & \\  & & Infiltration gutter & & & & & \\  & & W300 & & & & & \\ A * & C * & Infiltration & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & Dry well & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & Rainwater & & & & & & & \\ utilization & & & & & & & \\ \hline \multirow{4}{*}{B *} & \multirow{4}{*}{Pavement} & Permeable pavement & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\ \multirow{4}{*}{B *} & \multirow{4}{*}{Rainwater detention tank} & Permeability pavement & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 12: Design water quantity of the existing system and eco-friendly rainwater detention system.