## 2 Materials and Methods
### Rainfall Simulator Study  
Chemical analysis of the studied materials: Granules of calcareous material (granular material), containing mainly particles with 5-10 mm sizes, were obtained from Modiim Quarry Ltd, Israel. These calcareous granules are used as a cover layer on the unpaved roads. The brine solution and secondary TWW were obtained from the Dead Sea Works and the Taoz treated wastewater plant near the city of Beit-Shemes in Israel, respectively. These solutions were used in the rainfall simulator experiment. A sample of the brine solution was obtained a couple of days before the beginning of the experiment, and the TWW samples were taken <48 h before their uses in the experiment. Filtrated samples of <0.45 um of the brine and TWW solutions were analyzed using the following standard methods: (i) Electrical conductivity (EC) and pH values by standard EC and pH meters, respectively. (ii) Cl concentration by Digital Chloridometer, 442500, Labconco, Kansas City, MO. (iii) Concentrations of Na by flame photometer model 420 Clinical Flame Photometer, Sherwood Scientific Ltd, Cambridge, UK. (iv) Concentration of various elements by Dual-View High-Resolution ICP-OES Plasma Quant 9000 Elite, Analytik Jena, Germany. The chemical properties of the brine and TWW solutions that were used in the rainfall simulator study are presented in Table 1.  
The treatments: The granular material was packed and leveled in metal trays with a perforated bottom and dimensions of 0.3 \(\times\) 0.5 m\({}^{2}\) area and 0.02 m depth for each tray. The trays with the granular material were treated by the following treatments, with 4 replicates (4 trays) for each treatment:  
1. Control: four trays with untreated granular material were subjected to 3 consecutive rainstroms by a rainfall simulator, 1 storm a day, as described below. After each rainstrom, the trays were left for 3 days in a net house for drying to air-dry. 2. TWW treatment: four trays with the granular material were sprayed 10 times with 4 mm of TWW in each time. After each spray, the trays were left for 3 days in a net house for drying to air-dry. Three days after the last TWW application, the trays were subjected to 3 consecutive rainstroms, with no further TWW addition between the rainstroms, as described above for the control treatment. 3. Brine treatment: four trays with the granular material were sprayed 1 time with 4 mm of brine solution, and then were left for 3 days at a net house for drying to air-dry. After the drying period, the trays were subjected to 6 consecutive rainstroms, with 3 days of drying between the rainstroms, as described above for the control treatment, and with no further brine addition between the consecutive rainstroms. Simulated rainstroms runs: A laboratory rotary disc-type rainfall simulator [14] was used to determine the leakage of the ions, Cl, Na, and Ca+Mg (the studied ions), from the pretreated granular materials during consecutive rainstroms. Before each rainstrom, 4 trays with the pretreated granular materials were placed in a carousel below the rainfall rotary disc. Each tray was placed at a 9% gradient on an 8 cm layer of coarse gravel in a box. The trays were exposed to a rainstorm of 50 mm of deionized water, with the following mechanical parameters: rain intensity = 48 mm h\({}^{-1}\), raindrop mean diameter = 1.9 mm, \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Treatment** & **pH** & **EC** & **Cl** & **Ca** & **Mg** & **Na** & **K** & **HCO3** \\ \cline{2-8}
**Solutions** & \multicolumn{3}{c}{**dS m\({}^{-1}\)**} & \multicolumn{3}{c}{**mg/L**} & \\ \hline Brine & 6.0 & 130 & \(250\times 10^{3}\) & \(23.2\times 10^{3}\) & \(62.2\times 10^{3}\) & \(2.5\times 10^{3}\) & \(2.8\times 10^{3}\) & \(13.7\times 10^{3}\) \\ \hline TWW & 7.8 & 1.6 & 233.4 & 34.4 & 11.2 & 72.7 & 41.3 & 1018.7 \\ \hline \hline \end{tabular}
\end{table}