## 4 Discussion
### Carrying Out a Mercury-Contaminated Soil Remediation Treatment on the Pilot Site  
For the remediation of mercury-contaminated soil at the pilot facility, a 100 m\({}^{2}\) site was selected within an industrial area. This site was first evaluated for the mercury content in the soil. The contamination in this area was localized and primarily concentrated around the blocking and bleeding systems. Preliminary investigations indicated that this area was contaminated with metallic mercury. The total mercury content in over 60% of the soil samples from this area was found to be 2 to 8.5 times higher than the acceptable mercury content for soils in industrial areas. Additionally, studies were conducted to determine the mercury content capable of emissions in the soil samples. The comparison of the obtained research results and measurements is presented in Figure 3.  
The analysis of the obtained measurement results revealed that soil samples from the area around the blocking and bleeding systems (contaminated area) contain significant amounts of mercury capable of emissions. In 57% of the examined samples, the content of emission-capable mercury was found to exceed 30 mg Hg/kg d.m. Mercury contamination was present in soil at depths ranging from 0 to 0.6 m below the ground. Field tests confirmed the presence of metallic mercury contamination. Measured mercury emissions to the air ranged from 21 to 2700 ng/h/m\({}^{2}\). The soil samples taken after remediation showed a significant reduction in mercury emissions across the entire remediation area. The estimated content of mercury capable of emissions in the soil decreased from over 600 mg/kg dry matter to less than 15 mg/kg dry matter. These results indicate that the metallic mercury in the soil was effectively bound and converted into stable mercury sulfide(II) after the addition of sulfur. The results of laboratory tests confirm the efficiency of the applied procedure of mercury immobilization in soil [21; 41; 46]. At the pilot facility where the remediation procedure was carried out, field measurements of mercury emissions into the air were also carried out using passive sensors and diffusion chambers. The results from these tests, performed in three measurement series, provided a basis for assessing the efficiency of the remediation procedure. This assessment was based on the analysis of the emission measurement results collected from the designated measurement points established at the beginning of the experiment. When evaluating the results of the measurements of mercury emissions into the air, it should be noted that during the remediation procedure, the entire soil contaminated with mercury was thoroughly mixed and displaced. For this reason, the results of tests and emissions measurements, despite the planned sampling scheme at the same locations, were difficult to compare directly. The results of the mercury emissions measurements to the air, carried out in the remediated area using passive sensors (Figure 4), indicated the following distribution before the remediation procedure:  
* At six out of seventeen measurement points (18% of the results), emissions were in the range of 50 to 100 ng/h/m\({}^{2}\);
* For 35% of the measurements, emissions ranged from 100 to 1000 ng/h/m\({}^{2}\);
* The remaining 47% of the results showed emissions ranging from 1000 to 5000 ng/h/m\({}^{2}\). Based on the results obtained, it can be concluded that the area to be remediated is unevenly contaminated, as is also confirmed by the laboratory testing of the soil samples from that area  
The measurements of mercury emissions into the air, conducted 21 days after the remediation procedure, showed the following distribution:  
* For 30% of the measurements, the mercury emissions ranged from 0 to 50 ng/h/m\({}^{2}\);
* In 59% of the measurements, the emissions were between 50 and 100 ng/h/m\({}^{2}\);
* A total of 18% of the results indicated emissions in the range of 100 to 200 ng/h/m\({}^{2}\).