## 3 Results and Discussion
### A Source Control Measure Based on the Optimal Combinations of Purification Materials  
To develop effective control measures for treating pavement runoff pollution, four pollution situations were determined based on the analysis above. The first situation, denoted as A, contains high concentration SS and small amounts of other pollutants. The second situation, denoted as B, contains high concentration heavy metals Pb and Zn. Pavement runoff with high concentration dissolved pollutants TN and TP belongs to the third situation, C. If the concentrations of all pollutants are at approximate level, it is viewed as the last situation, D. The removal rates, calculated by Formula (2), of six purification materials on different pollutants are listed in Table 6.  
\[(|C_{\rm 2 min}-C_{0}|/C_{0})\times 100\% \tag{2}\]  
In Formula (2), \(C_{0}\) is the initial concentration and \(C_{\rm 2 min}\) is the concentration 2 min after the beginning of infiltration experiment. Because of differences in pore structure, pore size and mineral composition the six materials have different removal rates for different pollutants. Each pollutant corresponds to an optimal purification material. Since it is impossible to use one purification material that has a better effect in treating pavement runoff [30], combinations of purification materials applicable for different pollution situations would be of great significance in processing the pavement runoff more efficiently. Figure 8: The correlation curve between time and concentration of SS. The combination including two purification materials was taken as an example in this paper. In each column of Table 6, the top two removal rates are marked with asterisk. For the pollution situation containing only one kind of high concentration pollutant, the purification materials corresponding to the top two removal rates would be the best for this pollution situation. Therefore, the best combination for A (SS) includes scoria and slag. For the pollution situation containing two or more high concentration pollutants, the combination should be determined by considering mutual complementation of purification materials. Thus, for B (Pb and Zn), zeolite and ceramsite were selected. Finally, the optimal combinations of purification materials applicable for different pollution situations are listed in Table 7.  
Based on the RRS runoff pollution characteristics, the advantages and disadvantages of various control measures, we referred to the three-stage treatment system [23] to integrate different purification materials into a source control measure to process the pavement runoff. The measure was designed as a portable device shown in Figure 9. To ensure the growth of plants, the container cover was made of glass. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Purification Materials**} & \multicolumn{6}{c}{**Removal Rates (\%)**} \\ \cline{2-7}  & **SS** & **COD** & **TN** & **TP** & **Zn** & **Pb** \\ \hline Fine sand & 95.1 & 34.7 & 8.6 & 43.1 * & 36.4 & 47.3 \\ Zeolite & 96.4 & 48.5 * & 45.7 & 40.3 * & 55.9 * & 56.0 \\ Slag & 97.3 * & 45.2 * & 45.3 & 20.8 & 36.4 & 10.8 \\ Ceramsite & 94.6 & 40.1 & 27.4 & 20.8 & 73.4 * & 78.7 * \\ Diatomite & 88.9 & 42.3 & 50.6 * & 31.9 & 21.9 & 26.0 \\ Scoria & 99.5 * & 30.4 & 56.9 * & 15.3 & 34.0 & 84.7 * \\ \hline \hline \end{tabular} Note: In each column, the top two removal rates are marked with *.  
\end{table} 
Table 6: Results of the infiltration experiment. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Pollution Situations** & **A** & **B** & **C** & **D** \\ \hline Combination & Slag + Scoria & Zeolite + Ceramsite & Zeolite + Diatomite & Zeolite + Scoria \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Optimal combinations of purification materials applicable for different pollution situations. Figure 9: A Portable Device of Pollution Control Measures. The runoff went through the permeable pavement or other media, was collected by PVC tube and flowed into the processing chambers.