# Assessment Framework for the Maintainability of Sewer Pipeline Systems
## 5 Study Findings
### Ranking Defects via the Risk Index  
The risk index was used as the final step to highlight the defects' ranks based on the results obtained from the previous two steps. This step was completed to ensure the defect rankings were accurate, as shown in Table 7. Taking both probability and impact into account, the defects that ranked the highest were D10 (the dumping of fat, oil, and grease (FOG)), followed closely by D7 (hydraulic overflow) and then D8 (sediment accumulation), as reported in Table 7. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Failure**} & \multirow{2}{*}{\begin{tabular}{c} **Defect** \\ **Category** \\ \end{tabular} } & \multirow{2}{*}{**Defect**} & \multicolumn{4}{c}{**Probability**} \\ \cline{5-8}  & & & **Code** & \(\sum W\) & **A** & **N** & **RII** & **Weighted Mean \%** \\ \cline{5-8}  & & & D1 & 54 & 5 & 18 & 0.6 & 5.96 \\ \cline{5-8}  & & & D2 & 51 & 5 & 18 & 0.567 & 5.629 \\ \cline{5-8} Pipe collapse & & & D3 & 60 & 5 & 18 & 0.667 & 6.623 \\ \cline{5-8}  & & & D4 & 61 & 5 & 18 & 0.678 & 6.733 \\ \cline{5-8}  & & & D5 & 54 & 5 & 18 & 0.6 & 5.96 \\ \cline{5-8}  & & & D6 & 66 & 5 & 18 & 0.733 & 7.285 \\ \hline \multirow{5}{*}{\
\begin{tabular}{c} Sewer system \\ overflow (SSO) \\ \end{tabular} } & & & D7 & 67 & 5 & 18 & 0.744 & 7.395 \\ \cline{5-8}  & & & D8 & 68 & 5 & 18 & 0.756 & 7.506 \\ \cline{5-8}  & & & D9 & 52 & 5 & 18 & 0.578 & 5.74 \\ \cline{5-8}  & & & D10 & 68 & 5 & 18 & 0.756 & 7.506 \\ \cline{5-8}  & & & D11 & 65 & 5 & 18 & 0.722 & 7.174 \\ \cline{5-8}  & & & D12 & 64 & 5 & 18 & 0.711 & 7.064 \\ \cline{5-8}  & & & D13 & 61 & 5 & 18 & 0.678 & 6.733 \\ \cline{5-8}  & & & D14 & 56 & 5 & 18 & 0.622 & 6.181 \\ \hline \multicolumn{2}{c}{Odor and ground water contamination} & \multirow{2}{*}{
\begin{tabular}{c} Quality \\ defects \\ \end{tabular} } & & & D15 & 59 & 5 & 18 & 0.656 & 6.512 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The probability of occurrence of defects. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Failure** & **Defect Category** & **Defect** & \multicolumn{4}{c}{**Parameters**} \\ \hline \hline \multirow{8}{*}{D1} & \multirow{8}{*}{**Code**} & \multirow{8}{*}{**Code**} & \multicolumn{4}{c}{**Impact**} & \multirow{8}{*}{**Impact**} \\ \cline{3-4}  & & & & **Within the Defect** & & \\ \cline{3-4}  & & & **RII** & **Weighted Mean \%** & **Rank** & **RII** & **Weighted Mean \%** \\ \cline{3-4}  & & P1 & 0.7 & 26.033 & 2 & \\ \cline{3-4}  & & P2 & 0.778 & 28.926 & 1 & \\ \cline{3-4}  & & P3 & 0.667 & 24.793 & 3 & \\ \cline{3-4}  & & P4 & 0.544 & 20.248 & 4 & \\ \cline{3-4}  & & P1 & 0.744 & 30.594 & 1 & \\ \cline{3-4}  & & P2 & 0.6 & 24.658 & 2 & \\ \cline{3-4}  & & P3 & 0.567 & 23.288 & 3 & \\ \cline{3-4}  & & P4 & 0.522 & 21.461 & 4 & \\ \cline{3-4}  & & P1 & 0.8 & 28.916 & 2 & \\ \cline{3-4}  & & P2 & 0.811 & 29.317 & 1 & \\ \cline{3-4}  & & P3 & 0.789 & 28.514 & 3 & \\ \cline{3-4}  & & P4 & 0.367 & 13.253 & 4 & \\ \cline{3-4}  & & P1 & 0.722 & 26.104 & 3 & \\ \cline{3-4}  & & P2 & 0.789 & 28.514 & 1 & \\ \cline{3-4}  & & P3 & 0.778 & 28.112 & 2 & \\ \cline{3-4}  & & P4 & 0.478 & 17.269 & 4 & \\ \hline \multirow{8}{*}{D5} & \multirow{8}{*}{D6} & \multirow{8}{*}{D7} & \multirow{8}{*}{D7} & \multirow{8}{*}{D7} & \multirow{8}{*}{0.686} & \multirow{8}{*}{6.752} \\ \cline{3-4}  & & P1 & 0.733 & 27.615 & 1 & \\ \cline{3-4}  & & P2 & 0.722 & 27.197 & 2 & \\ \cline{3-4}  & & P3 & 0.589 & 22.176 & 4 & \\ \cline{3-4}  & & P4 & 0.611 & 23.013 & 3 & \\ \cline{3-4}  & & P1 & 0.767 & 27.935 & 2 & \\ \cline{3-4}  & & P2 & 0.778 & 28.34 & 1 & \\ \cline{3-4}  & & P3 & 0.622 & 22.672 & 3 & \\ \cline{3-4}  & & P4 & 0.578 & 21.053 & 4 & \\ \hline \multirow{8}{*}{D7} & \multirow{8}{*}{D7} & \multirow{8}{*}{D8} & \multirow{8}{*}{D7} & \multirow{8}{*}{0.778} & \multirow{8}{*}{6.971} \\ \cline{3-4}  & & P1 & 0.811 & 28.627 & 2 & \\ \cline{3-4}  & & P2 & 0.856 & 30.196 & 1 & \\ \cline{3-4}  & & P3 & 0.778 & 27.451 & 3 & \\ \cline{3-4}  & & P4 & 0.389 & 13.725 & 4 & \\ \cline{3-4}  & &