## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**IPZ Index**} & \multirow{2}{*}{**Vulnerability**} & \multicolumn{2}{c}{**Vulnerability for Groundwater State Defined in Years:**} \\ \cline{3-5}  & & **1999–2013** & **2003** & **2011** \\ \cline{3-5}  & & & **Area (km\({}^{2}\))** & \\ \hline
75–100 & Very low & 1.20 & 1.85 & 1.11 \\
101–125 & Low & 138.80 & 160.27 & 141.11 \\
126–150 & Medium & 193.21 & 216.26 & 197.99 \\
151–175 & Medium high & 231.87 & 190.75 & 221.75 \\
176–200 & High & 5.68 & 2.12 & 9.29 \\ \hline Mean IPZ & 142.7 & 139.5 & 142.99 \\ Standard deviation & 19.33 & 18.77 & 20.54 \\ IPZ scope & 80.5–181 & 76.5–180 & 80.5–185 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Statistics of IPZ index and occurrence of vulnerability classes on research area. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multirow{2}{*}{**“Theoretical”** Weight} & \multirow{2}{*}{**“Theoretical” Weight (\%)**} & \multirow{2}{*}{**“Effective”** Weight} & \multicolumn{4}{c}{**“Effective” Weight (\%)**} \\ \cline{3-5}  & & & & **Mean** & **Minimum** & **Maximum** & **Standard** **Deviation** \\ \hline D & 5 & 21.74 & 7.4 & 32.28 & 20.47 & 59.52 & 6.63 \\ R & 4 & 17.39 & 2.4 & 10.37 & 2.44 & 23.81 & 3.54 \\ A & 3 & 13.04 & 2.7 & 11.58 & 0 & 17.33 & 3.13 \\ S & 2 & 8.70 & 2.2 & 9.59 & 5.78 & 19.88 & 1.89 \\ T & 1 & 4.35 & 1.6 & 6.99 & 4.3 & 11.9 & 1.15 \\ I & 5 & 21.74 & 4.4 & 19.3 & 0 & 28.88 & 5.21 \\ C & 3 & 13.04 & 2.3 & 9.89 & 1.94 & 23.76 & 3.71 \\ \hlineFigure 6: Comparison of original and effective weights of parameters. Figure 7: IPZ index after optimization by single parameter sensitivity analysis for groundwater state defined in years: (**a**) 2003; (**b**) 2011; (**c**) 1999–2013. The study area is characterized by low concentrations of chlorides, which reach values from 4.2 to 111 mg/L, with an average of 28.2 mg/L (median: 17.6 mg/L). The lowest concentrations occur on dune areas, while the highest are in drainage zones near the canals. Validation of vulnerability as an expected high dependence of chloride concentration and IPZ index was found as the reverse. For low values of Cl\({}^{-}\) ions, the highest IPZ indexes were calculated (Figure 8). This results from the lack of source of groundwater contamination and intensity of infiltration. Intense recharge in the area of dune belts causes a slight transformation of precipitation water. In drainage zones, due to the long residence time of water in the system, processes such as evaporation result in much higher chloride concentrations. The results of the correlation analysis indicate a better adjustment of the trend line to the results of the DRASTIC method with the original weights, where lesser importance is attributed to depth, and higher to the recharge and lithology of the aquifer and the vadose zone. Figure 8: Correlation of chloride concentration and IPZ index in selected piezometers. \begin{table}
\begin{tabular}{c c c c c c c c} \hline  & & & \multicolumn{3}{c}{**Class Area after**} & \multicolumn{3}{c}{**Class Area Changes according**} \\  & & & \multicolumn{3}{c}{**Optimization (km\({}^{2}\))**} & \multicolumn{3}{c}{**to Original IPZ (\%)**} \\ \cline{3-8}
**IPZ Index** & **Vulnerability Class** & & & & & & \\  & **Class** &