Determination of Groundwater Threshold Values: A Methodological Approach Applied to the Gediz River Basin (Western Turkey)

Dilek, Filiz Bengü
Yetiş, Ülkü
Duru, Burcu
Bulut, Onur Fatih
Cakmak, Özgür
Gunhan, Ozgur
The purpose of the EU Groundwater Directive (2006/118/EC) is to prevent and control groundwater pollution. For this purpose, it requires member states to assess groundwater chemical status. To evaluate the chemical status of a groundwater body, threshold values (TVs) of the relevant risk-posing parameters should be established. In addition, TVs should be implemented in the river basin management plan to prevent or limit inputs of pollutants into groundwater. In the present study, TVs of the substances (12 metals, 5 metalloids and 5 ionic species) observed in the groundwaters of the Gediz Basin (Western Turkey) were determined using one-year seasonal water quality monitoring data from groundwater wells and springs in the basin. The procedure to determine TVs comprised three steps: determining natural background levels (NBL), choosing reference values (REF) and establishing TVs. The NBL determination involved a pre-selection step based on a set of criteria developed by the EU countries within the framework of the project called “Background cRiteria for the Identification of Groundwater thrEsholds (BRIDGE)”, and a data selection step using Box & whisker plots. Then, three different methods were applied to determine NBL, which are probability plot, 2-σ Iteration and distribution function methods. The results indicated that these three approaches provided different estimates of NBL almost for all the parameters. However, the method of 2-σ Iteration provided the most conservative NBL values for almost all parameters. Following the determination of NBLs, TVs were determined considering the REF values selected based on the intended use of groundwater in the basin.


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Citation Formats
F. B. Dilek, Ü. Yetiş, B. Duru, O. F. Bulut, Ö. Cakmak, and O. Gunhan, “Determination of Groundwater Threshold Values: A Methodological Approach Applied to the Gediz River Basin (Western Turkey),” 2018, Accessed: 00, 2021. [Online]. Available: