## 3 Results and Discussion
### Surface Laaching
The average value of the three samples is used to draw a statistical trend line which was used to calculate the equation for the expected leaching of TBT within one year. The threshold limit specified for TBT is standard for the concentration parameter. The variations  
Figure 6: Cumulative leaching of nickel (Ni) over time in tested soil specimens. in the TBT concentration can be affected by the dilution due to matrix disturbances, limited sample quantity, or low dry matter content. The threshold limit of chemical substances was estimated following the analytical method which evaluates the lowest level of concentration at which the contaminants are detected in a soil sample. \[y=0.0001\ln(time)+0.0002 \tag{4}\]  
For evaluation of the obtained results, a comparison has been completed between the results for surface leaching received in the present study against those from other studies [94; 95; 96]. More specifically, ref. [97] demonstrates similar results on leaching of As, Pb, and Sb; the immobilisation of Cr, Cu, and Zn were assessed by [98]. Furthermore, ref. [99] reports the leaching of diverse heavy metals from remediated soil. The removal of PHB that is a waste product from the aluminium industry is reported in [100] using stabilization and neutralization methods. Table 7 summarises the values of leaching recorded in samples from Oslo (O), Arendal (A), and Timra (T). The results are based on the measurements performed after 9 days of soil testing, and show surface leaching of contaminants (heavy metals and TBT, mg/m\({}^{2}\)) from soil after 9 days of testing, as shown in Table 7. The threshold limits of contaminant concentration of TBT and heavy metals with regard to the content of binder (water-binder ratio) were evaluated in soil samples as a collective designation for the highest levels of the substances in samples and compared for various test locations, as shown in Table 7. The analysis of Table 7 indicates that the amount of As is slightly higher in Kongshavn Port of Oslo (O) than for Arendal (A) and Timra (T); however, the content of Cd, Cr, and Ni is lower. Similar results were reported earlier in the study on the immobilisation of Mg, Cu, Zn, Al, and K which were evaluated in Swedish soils in Timra [101]. As for TBT, the levels are significantly lower in Oslo than for the corresponding sample in Arendal. The TBT was not analysed in the Timra project, and, therefore, could only be compared between the sampling results from Oslo and Arendal. The threshold limit for for contaminants was determined as a quantification limit of seven types of heavy metals, PAH-16, TBT, and PCB. The applied methodology was optimised to evaluate and report the concentration values in the contaminants from soil stabilised with various binder proportions. The specimens were treated using geotechnical and environmental engineering tests and then evaluated using quantitative methods of the statistical analysis. Figure 7: Cumulative leaching of PAH-16 in tested soil samples. The comparison of the leaching levels was performed using estimated levels over time as accumulative leaching compared to the background level of toxic contaminants.