In the initial period (up to 16 months of operation), the Cl concentration in the MP leachate
was directly proportional to the rainfall depth because of the leaching effect. Subsequently, the tracer concentration tended to increase up to 2198 mg Cl/dm3 and was negligibly affected by
rainfall. This observation can be explained by the on-site pretreatment of wastewaters generated by the SU and CU, which, along with the concentrate generated by RO units, are pumped back to the
MP (Fig. 1).