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Determination of environmental quality standard -based discharge limits and mixing zones for tersakan sub-basin of Yeşilirmak river

Çelebi, Sarp
The control of point source discharges to rivers has become more elaborate since the establishment of environmental quality standards (EQSs). Many countries including Turkey have set EQS values for various contaminants of concern (CoCs) i.e. maximum concentration limits that would not cause detrimental effects on the health of the human-beings or the overall environment. One important challenge of achieving these EQSs is to reconcile the effluent limits that are technically and economically achievable with the ones that are required to accomplish the EQSs. Tersakan Sub-basin of Yeşilırmak River acquires good examples of this challenge due to the intense industrial and agricultural activities present. In this study, an approach to help this compromise is developed and implemented for all suitable discharge points within the sub-basin. The foundation of this approach is that effluent discharges may mix and become diluted within negligibly short distances from the point of discharge where exceedance of EQSs can be permissible. The approach developed, modularly combines different analytical solutions of the advective-dispersive mass transport equation that are applicable under different mixing conditions and estimates maximum allowable discharge concentrations of CoCs. The results of the case study which included all 20 instances, indicate that none of these discharges need load reduction to achieve EQSs. However, in various points tridecane, nickel, bis(2-ethylhexyl) terephthalate, NH4-N, total phosphorus, and free CN have consumed ≥10% of their discharge quotas estimated by the mentioned approach. Therefore, these six CoCs and their corresponding two discharge points may require more attention in the future.