Determination of groundwater threshold values: a methodology applied to Gediz basin

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2019
Bulut, Onur Fatih
Turkish bylaw on Protection of Groundwater against Pollution and Deterioration requires the establishment of groundwater thresholds in groundwater bodies. According to this regulation, water status, as good or not, is to be determined based on the chemical status. Indeed, in a EU Project entitled “Background Criteria for the Identification of Groundwater Thresholds-BRIDGE”, in an attempt to the implementation of Water Frame Directive, a methodological framework has been developed to determine threshold values (TV) for pollutants which cause the groundwater body to be characterized as ‘at risk’. In this respect, Ministry of Forestry and Water Affairs of Turkey (MFWA) is in charge to determine the river basin based TV values for the priority and specific pollutants in Turkey. To this end, a methodology that would be followed in Turkey needs to be developed. A methodology developed by the BRIDGE has some flexibility as it allows countries to make some choices depending on the groundwater body characteristics and available monitoring data. In this study, taking the BRIDGE methodology as a basis, TVs will be determined for a pilot-basin, namely, Gediz Basin of Turkey. Basically, TV will be determined by comparing the natural background level (NBL) of a quality parameter in a basin with the appropriate reference value (REF). NBL is the value that represents a naturally occurring level or a level that could occur without human-caused changes in a river basin. This value will be determined through the statistical analysis of field measurements belonging to the target contaminant or quality parameter as suggested by BRIDGE. Whereas REF is the criterion value which is set by governmental authorities to regulate the water usage, depending on the intended use of water bodies. While determining TVs, groundwater monitoring data produced by the MFWA through three different monitoring campaigns were used. Statistical analysis was performed using “MATLAB” and “Excel”.