## 3 Data and Methodology  
The most widely used salinity indicators of coastal aquifers are chloride and sulfate concentrations in groundwater and the value of electrical conductivity [25]. Data for the analyses were collected by operational and surveillance monitoring of the water-supply company Zadar (Table 1) [13]. In the Bokanjac-Policnik catchment area, salinization occurs most often, almost every year, at two water supply facilities, Golubinka and Boljkovac (Figure 3). This occurs in situations when Golubnika spring yield decreases during the dry season, and in the Boljkovac in conditions of significant precipitation after dry periods. Increases in salinization due to pre-exploitation also occur at the Jezerce water intake, but only in extremely dry years. Due to the difference, chloride concentrations are shown for all case study wells (Figures 3 and 4). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Monitoring Point**} & **Number of Analyses** & **Minimum (mg/L)** & **Maximum (mg/L)** & **Average (mg/L)** \\ \hline Bokanjac B-4 (chlorides) & 123 & 11.00 & 61.00 & 25.89 \\ \hline Bokanjac B-4 (sulfates) & 33 & 9.08 & 95.00 & 28.50 \\ \hline Bokanjac B-5 (chlorides) & 104 & 15.33 & 87.00 & 23.34 \\ \hline Bokanjac B-5 (sulfates) & 25 & 9.11 & 72.00 & 20.04 \\ \hline Jezerce (chlorides) & 223 & 27.00 & 66.00 & 48.01 \\ \hline Jezerce (sulfates) & 53 & 11.57 & 125.46 & 57.70 \\ \hline Boljkovac (chlorides) & 134 & 36.60 & 1.953.00 & 442.15 \\ \hline Boljkovac (sulfates) & 33 & 39.12 & 678.86 & 122.83 \\ \hline Golubinka (chlorides) & 150 & 25.30 & 5.006.00 & 593.63 \\ \hline Golubinka (sulfates) & 40 & 13.86 & 372.50 & 78.14 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Monitoring data for the period 1 January 2017–1 October 2019. Standard to ensure protection against short-term exposure to pollution, the Maximum Allowable Concentration (MAC) of the substance concerned, i.e., the maximum for any single measurement, is proposed in order to ensure protection against short-term exposure, i.e., pollution peaks [23]. Occurrences of increased seasonal chloride contents above  
Figure 4: Chloride concentrations on wells B-4, B-5, and Jezerce in the period from 1 January 2017 till 1 October 2019. Figure 3: Chloride concentrations on wells Boljkovac and Golubinka in the period from 1 January 2017 till 1 October 2019.  
the MAC values at water supply sources from the Bokanjac-Policnik catchment area characterize all water supply sources except wells B-4 and B-5, where slight increases in chloride content occur very rarely and are far below the MAC limit. Existing regulations in Croatia for the MAC content of chloride in drinking water is 250 mg/L, and the electrical conductivity is 2500 us/m at 20 \({}^{\circ}\)C [26]. Increases in chloride content occur during long dry periods in the form of gradual increases in chloride content or when significant precipitation appears during long dry periods. Such precipitation causes increased inflows in parts of karst aquifers, and there are sudden changes in hydraulic conditions which are manifested in changing the boundaries of salt and freshwater and pushing saline water from deeper and more distant parts of aquifers through their lowest hydraulic resistance. According to the chemical composition, the water from wells B-4 and Jezerce belongs to the Ca-HCO\({}_{3}\) and CaMg-HCO\({}_{3}\) hydrorochemical types [27]. However, sometimes waters of Jezerce belong to Ca-HCO\({}_{3}\)Cl hydrochemical type due to seawater intrusion. The results of several hydrochemical analyses indicate that the Golubinka and Boljko-vac wells are under the constant influence of seawater, while at the Jezerce water pumping station salinization occurs occasionally [13; 20; 28]. Given analysis shows that the wells of the Bokanjac water pumping station are in the zone of influence of the sea water and, due to over-pumping, can also lead to an increase in chloride concentration [28].