## 4 Economic Feasibility Analysis
### LCC Analysis  
For LCC analysis, all the costs necessary for an appropriate life cycle based on one ton of the product, including the acquisition cost, dismantling cost, and sediment removal cost required for maintenance, were compared. In the design criteria for concrete structure durability, a compressive strength of 27 MPa or more suggests a useful life standard of 65 years or more and less than 100 years [28; 29; 30]. Because the eco-friendly rainwater detention system is a secondary concrete product and the compressive strength at 28 days of age is 29.0 MPa, its lifetime was set to 80 years. The lifetime of the existing system was set to 40 years because it uses PE materials and has low durability due to the surrounding earth pressure and creep. Tables 14 and 15 present the LCC analysis and sediment removal cost analysis results, respectively.  
The acquisition cost of the eco-friendly rainwater detention system is 58.3% lower than that of the existing system. In addition, the cost to remove sediments that are inevitably generated in rainwater detention facilities according to the \"standards on the types, structures, installation, and maintenance of rainwater runoff reduction facilities (2010, National Fire Agency)\" [31] is 23.7% lower than that of the existing system. This difference exists because the sediment removal process of the eco-friendly rainwater detention system is simpler than that of the existing system, reducing direct material and labor costs.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Category**} & \multicolumn{4}{c}{**Cost**} & \multirow{2}{*}{**Rotation Rate (\%)**} \\  & \multicolumn{2}{c}{**Eco-Friendly Rainwater**} & \multirow{2}{*}{**Existing System**} & \multirow{2}{*}{**(Eco-Friendly/Existing)**} & \multirow{2}{*}{**Remark**} \\  & \multicolumn{2}{c}{**Rainwater Detention System**} & & & & \\ \hline Lifetime & 80 years & 40 years & - & - & - \\ Acquisition cost & 1,040,552 & 2,500,976 & - & Based on 80 years \\ Dismantling cost & 14,947 & 29,894 & - & Based on 80 years \\ Total & 1,055,499 & 2,530,870 & \(-\)58.29\% & - \\ Sediment removal cost & 118,910 & 155,773 & \(-\)23.66\% & - \\ \hline \hline \end{tabular}
\end{table}
Table 14: LCC analysis.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Item**} & \multicolumn{4}{c}{**Existing System**} & \multicolumn{4}{c}{**Eco-Friendly Rainwater**} & \multirow{2}{*}{**Reduced Construction Cost**} \\  & \multicolumn{2}{c}{**Decision Water Quantity**} & \multicolumn{2}{c}{**Construction Cost (KRW)**} & \multirow{2}{*}{**Facility**} & \multirow{2}{*}{**Design Water Quantity**} & \multirow{2}{*}{**Construction Cost (KRW)**} & \multirow{2}{*}{**Construction Cost (KRW)**} & \multirow{2}{*}{**Reduction Rate**} \\  & D (W250) & 200 m & 7,095,140 & & & & \\  & D (W300) & 200 m & 7,911,940 & & & & \\  & E (W300) & 250 m & 10,733,625 & \(\mathrm{H}\) & & 37,807,760 & & \\ B* & E (W400) & 250 m & 13,142,375 & (W1000) & 43 m & (69.6\%) & 16,437,360 & 30\% \\ F (D800A) & 5 EA & 5,861,900 & & & & & \\  & G (W800A) & 5 EA & 7,138,040 & & & & \\  & Sub total & - & (100\%) & Sub total & - & 37,807,760 & & \\ C* & Utilization facility & 100 m\({}^{3}\) & 12,000,000 & Utilization facility & 100 m\({}^{3}\) & 12,000,000 & 0 & 0\% \\ Total & - & - & 94,991,020 & - & - & 78,553,660 & 17,011,920 & 18\% \\ \hline \hline \end{tabular}
\end{table}
Table 13: _Cont._Accordingly, the eco-friendly rainwater detention system has higher economic feasibility than the existing PE infiltration detention tank.