ABSTRACT
The EU Water Framework Directive demands the achievement of a good qualitative status for all groundwater bodies. Therefore, a reference for the natural background values in groundwater is needed. The German Geological Surveys have established such background values based on previously determined hydro-geochemical units, based on a method using probability nets. The probability net displays normal or lognormal distributions as straight lines and mixtures of distributions as sequences of straight line segments. Through an iterative process of excluding the present anomalies, a trend line can be fitted to the bulk of data, considered as background population. With the line’s slope and intercept, which are equivalent to the underlying populations’ standard deviation and mean, every percentile can be calculated, using the 90th or the 95th the as upper limit of the background population. In order to accelerate and facilitate the process of calculation, an Excel application has been developed with extensive graphical and statistical controls.
