Geochemical and statistical interpretation of the Dutch national ground water quality monitoring network

Abstract

Data bases and environmental research Concern for the environment has grown rapidly in the last decade(s). Many potential threats to our surroundings have been recognized. The precise effects of these threats are often not known, and much research is needed. Considerable effort is put into the acquisition of data in time and space to evaluate the influence of anthropogenical processes in the environment. One of the tools used is monitoring by networks. Large numbers of samples are collected and their analysis by modem analytical methods produces very sizeable data bases. Fortunately, with the appearance of personal computers for the data storage and interpretation no costly investments have to be made. Compared to the considerable effort and capital put into the data acquisition, the investment made for (sophisticated) interpretation of this enormous amount of data is often limited. In many cases the evaluation focuses on answering questions put forward by governments. However, environmental data sets should be studied extensively by scientists, in order to extract more knowledge from the data, which may set new perspectives for environmental policies. The Dutch National Ground Water Quality Monitoring Network Quality monitoring of ground water in the Netherlands basically started in the nineteenth century, with the regular examination of extracted drinking water. A systematic approach on a national scale was implemented in 1979, when the Dutch National Institute of Public Health and Environmental Protection (RIVM) initiated the Dutch Groundwater Quality Monitoring Network (LMG). The national network has been designed to keep track of the shallow ground water quality down to 25 m below surface, with an average monitoring site density of 1 per 100 km2• Site selection criteria were mainly based on soil type, land use and on the hydrogeological situation (van Duijvenbooden, 1987). Samples are collected every year and are analyzed for all macrochemical parameters and a selection of trace elements. The available data set contains over 7500 chemical analyses. A first official evaluation was made in 1989 to support formulation of the Dutch environmental policy (van Duijvenbooden, 1989). Aims of this thesis In 1989 ten years of data from the LMG became available for scientific study, which resulted in this thesis. A combined statistical and geochemical approach was taken, focused on an understanding of the fundamental controls of ground water quality. The aims of this thesis are: (1) to derme an efficacious geochemical framework for the interpretation of shallow ground water compositions of the Netherlands. (2) to determine the short- and long term geochemical processes, that change and/or threat the ground water quality. (3) to discuss the merits and limitations of national monitoring networks and to recommend additional tools for the study of ground water quality threatening processes. In pursuing these aims, this thesis serves to illustrate how a large data set can be surveyed and interpreted in a detailed and sophisticated way.