## 3 Materials and Methods
### The Solidification/Stabilization Process of Pollutant Soil in the Field  
Solidification/stabilization requires the immobilization of the polluted soil constituents through a process of chemical modification into insoluble substances or by encapsulating the solid. Mixing the polluted soil with cement results in this process. The treated soil in the site underwent a solidification/stabilization process at the Khurmala oil field treatment area. The soil was mixed with CEM II (1 ton cement/7 m\({}^{3}\) soil) at approximately 8-9% by weight of the soil with a water-cement ratio of 40%, and the treated soil was then left as a construction earth material for two months in order to gain an equilibrium between cement and soil, before being reused in the area. The main goals in this process were the following:  
* Improve soil handling and physical characteristics;
* Minimize available surface area for the movement or loss of pollutants and limit fluid movement by the total hard matrix volume;
* Minimize the solubility of the contaminant into the amount of contaminated soil.  
The project was initiated on 16 January 2019 and lasted until 19 November 2019. The method of treatment included the following:  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Chemical Analysis**} & \multicolumn{2}{c}{**Results (\%)**} \\ \cline{2-3}  & **CEM II** & **OPC** \\ \hline SiO\({}_{2}\) & 20.04 & 20.17 \\ CaO & 61.84 & 63.11 \\ Al\({}_{2}\)O\({}_{3}\) & 4.37 & 4.22 \\ Fe\({}_{2}\)O\({}_{3}\) & 3.71 & 3.78 \\ MgO & 3.48 & 3.82 \\ SO\({}_{3}\) & 2.67 & 2.08 \\ Insoluble Material & 0.32 & 0.59 \\ Loss of Ignition & 3.05 & 1.55 \\ Line Saturation Factor & 0.87 & 0.96 \\ C\({}_{3}\)A & 5.3 & 4.79 \\ C\({}_{3}\)S & 42.09 & 63.94 \\ C\({}_{2}\)S & 25.72 & 9.79 \\ C\({}_{4}\)AF & 11.28 & 11.5 \\ \hline \hline \end{tabular}
\end{table}
Table 4: The physical and chemical properties of the CEM II and OPC.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Test**} & **H.5 (ppm)** & **BS\&W * (\%)** & **Total Sulphur (\%)** & **Salit (pb) ** & **Density (kg/m*)** & **API Gravity** & **Viscosity (mm*/s)** \\ \hline Standard & UOP 163 & ASTM D4007 [34] & ASTM D4294 [35] & ASTM D3230 [36] & ASTM D1298 [37] & ASTM D7042 [38] \\ Results & 41.3 & 0.6 & 2.22 & 229 & 863.1 & 32.29 & 12.8 \\ \hline \hline \end{tabular}  
* Basic sediment and water content of crude oils. **Pb** = pounds of salt per thousand barrels of crude oil.  
\end{table}
Table 3: The physical properties of the Khurmala crude oil.  
1. International drilling fluids and engineering services, a Qmax solutions company, waste management division, provided services of remediating and encapsulating all the pit's wastes, such as oily sludge and contaminated soil waste.
2. The remediation involves remediating the contaminated oil pit, reserve pit (Figure 3a), and overflow pit at the south production station, located at Khurmala Site, in the Erbil City.
3. The equipment and machinery were mobilized to the southern production plant site on 15 January 2019.
4. The contaminated soil in the oil pit was first treated by digging and treating all the soil contaminated with the existing crude oil (Figure 3b). The total volume of treated soil reached 2980 m\({}^{3}\).
5. The treated soil was stored beside the oil pit (Figure 3c) to be backfilled, after reconstructing and lining the pit, and prepared as a construction earth material.
6. When the test results of the oil pit's bottom and sides showed that it was cleaned of contaminant, the pit was reconstructed and lined up with a geosynthetic clay layer with high-density polyethylene liner to be backfilled with remediated soil (Figure 3d).
7. The oil pit was backfilled with treated soil, covered with a GCL liner on the top (Figure 3e), then backfilled to 3.5 m of fresh soil from the area around the pit, leveled, and compacted to the natural ground level.
8. The site underwent general clean-up and restoration. The procedures of the treatment are illustrated in Figure 3.