## 3 Results and Discussion
### Hydraulic Conductivity of Soil--Semi-Technical Scale Test  
On a semi-technical scale, a study was carried out to assess the hydraulic conductivity of soil exposed to sodium chloride using constructed filter columns (see Figure 4). During the course of this experiment, 84 days, i.e., 12 weeks of operation of the water softener system, working together with the septic tank, were simulated. As designed, a salt solution was injected into the second group of columns every 10 simulated days (Figure 3; 2a, b, c). In order to assess the potential difference between the effects of the treated wastewater, brine from the grey water and water on the ground, four hydraulic conductivity tests were carried out on all columns, which were each performed on the fourth simulated day after the regeneration of the water softener. Figure 12a-c shows the changes in height difference between the initial water level and the level after 60 min during the hydraulic conductivity tests for each group of filter columns. The linear trends in Figure 12a-c are mostly decreasing. However, in Figure 12b, which shows the columns supplied with treated wastewater and brine, there are more leading trends. This may be due to the increased salt content of the soil. It is likely that the NaCl may have influenced the swelling of the soil and reduced the water-permeable surface area [22]. The coefficient of determination relating to the first group of columns (treated wastewater, Figure 12a) reached values above 55% in two cases (Column 1a and 1b), while it was below 10% for Column 1c. Regarding the second group of columns (treated wastewater + brine, Figure 12b), variable X had an influence of more than 80% on the value of variable Y in two cases, while the remaining third had an influence of less than 70%. The coefficient of determination R2 in the third group of columns (tap water, Figure 12c) ranged from 56% to 68%. When comparing all three column variants, it was found that for column group 2 (i.e., the column variant supplied with treated wastewater and brine), the decrease in the height difference between the initial water level and the level after 60 min (\(\Delta\)H), was  
Figure 11: Changes in temperature of the treated wastewater in sample weeks of (**a**) the summer period and (**b**) the winter period. most evident. In this case, the trend lines (Figure 12b) show the greatest decreases, while the coefficients of determination were the highest compared to the others (Figure 12a,c), with column group 1 distinguished by the lowest decrease in \(\Delta\)H.  
Table 1 presents the values of water level differences during hydraulic conductivity testing. On the basis of the Shapiro-Wilk test of normality [44], it can be deduced that the distribution follows a normal distribution--there are no grounds to reject the null hypothesis \(p=0.827>\alpha=0.01\) (\(p\)--test probability, \(\alpha\)(n)--tabulated test coefficient for sample size n (see Figure 13)). The next step was to check for the homogeneity of variance [44] in order to select an appropriate statistical test for the significance of differences between the results. A \(p\)-value \begin{table}
\begin{tabular}{c c c} \hline \hline
**Column Marking** & **Solution** & **Differences in Liquid Level** \\  & **Type** & **(cm**\(\cdot\)h\({}^{-1}\))** \\ \hline
1a & & 0.3 \\
1b & Wastewater & 0.3 \\
1c & & 0.1 \\ \hline
2a & & 0.6 \\
2b & Wastewater + brine & 0.9 \\
2c & & 0.7 \\ \hline
3a & & 0.4 \\
3b & Water & 0.8 \\
3c & & 0.6 \\ \hline \hline \end{tabular} Explanation: Differences between the period after 1 regeneration and after 8 softener regenerations were considered; h—hour.  
\end{table} 
Table 1: Summary of water level differences during hydraulic conductivity testing.