## 4 Summary and Conclusions  
This work investigates the hydraulic conductivity of CO\({}_{2}\)-carbonated olivine-admixed marine clay for potential use as a liner material in engineered landfills. The AR technique was used to optimize the olivine particle size during the grinding process to get olivine particles in a defined particle size class before treating the marine clay, while RSM was used in designing the experiments, evaluating the results, and optimizing the variables responsible for reducing the hydraulic conductivity of the carbonated olivine-admixed clay. The effects of various factors, including olivine content, carbonation time, and carbonation pressure on the hydraulic conductivity, were studied by ANOVA. The major findings from the study are summarized as follows:  
* With increasing olivine content, carbonation time, and pressure, the hydraulic conductivity of the treated-clay decreased. The decrease in the hydraulic conductivity is due to the hydration reaction that resulted in the formation of M-S-H and M-A-H phases. Further hydraulic conductivity reduction is attributed to the formation of more carbonates, including mesquehonite, hydromagnesite, and dybignite. * The quadratic model was considered the best fitted and non-aliased model between the control factors and response. ANOVA analyses revealed that the main and quadratic effects of olivine content, carbonation time, and carbonation pressure significantly affected the hydraulic conductivity. * It was found that the predicted values from the model are in strong agreement with their experimental counterparts. Within the set of conditions applied in the current study, the model can be used for prediction. * Based on the optimization study, the optimum value of the hydraulic conductivity was suggested as 2.0 \(\times\) 10\({}^{-11}\) m/s and was attained under the following operating conditions: 24.7% olivine content, 20.1 h carbonation time, and 161 kPa carbonation pressure, with a designated maximum desirability function (D = 1.0). * Comparative analyses of the hydraulic conductivity reduction of the carbonated samples and cured specimens demonstrate that CO\({}_{2}\)-carbonated olivine-admixed soils have a great capacity to sequestrate CO\({}_{2}\) and minimize CO\({}_{2}\) emissions while rapidly decreasing the hydraulic conductivity of soils significantly relative to cured specimens. In summary, CO\({}_{2}\)-carbonation and olivine blend have proven to be a sustainable technique to reduce the hydraulic conductivity of marine clay, while employing the AR \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Solution Number**} & **Optimized Model Values** & **Experimental Run Values** & **Percentage Error** \\ \cline{2-4}  & **Hydraulic Conductivity** & **Hydraulic Conductivity** & \\  & **m/s** & **m/s** & **(\%)** \\ \hline
1 & 3.79 \(\times\) 10\({}^{-11}\) & 3.72 \(\times\) 10\({}^{-11}\) & 1.88 \\
2 & 5.16 \(\times\) 10\({}^{-11}\) & 5.09 \(\times\) 10\({}^{-11}\) & 1.38 \\
3 & 2.99 \(\times\) 10\({}^{-11}\) & 2.93 \(\times\) 10\({}^{-11}\) & 2.05 \\
4 & 6.12 \(\times\) 10\({}^{-11}\) & 6.00 \(\times\) 10\({}^{-11}\) & 2.0 \\
5 & 6.22 \(\times\) 10\({}^{-11}\) & 6.08 \(\times\) 10\({}^{-11}\) & 2.30 \\
6 & 6.09 \(\times\) 10\({}^{-11}\) & 5.93 \(\times\) 10\({}^{-11}\) & 2.70 \\
7 & 4.95 \(\times\) 10\({}^{-11}\) & 4.87 \(\times\) 10\({}^{-11}\) & 1.64 \\
8 & 5.78 \(\times\) 10\({}^{-11}\) & 5.68 \(\times\) 10\({}^{-11}\) & 1.76 \\
9 & 5.47 \(\times\) 10\({}^{-11}\) & 5.34 \(\times\) 10\({}^{-11}\) & 2.43 \\
10 & 6.19 \(\times\) 10\({}^{-11}\) & 6.10 \(\times\) 10\({}^{-11}\) & 1.48 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Validation of optimized model response by experimental runs indicating percentage error. technique to optimize the olivine particle size and RSM to design the experiment and obtain optimum operating conditions in achieving maximum hydraulic conductivity reduction.