Monitoring methyl tertiary butyl ether (MTBE) and other organic micropollutants in groundwater: Results from the Danish National Monitoring Program

The paper presents results of analyses of 7671 groundwater samples collected from 1115 screens in the period 1993 to 2001 for the Danish National Groundwater Monitoring Program. In Denmark groundwater is widely used for drinking water and the objectives of the monitoring program is to describe the present conditions, the development of, and the impacts on the groundwater. The design of the Danish National Groundwater Monitoring Program is described and data are provided. Data originate from monitoring areas and are supplemented with data from the waterworks' control of nearly 6000 water supply wells. In addition to pesticides there is a series of other organic compounds that must be considered in relation to possible groundwater contamination. Sources of these compounds and their importance in relation to groundwater contamination is discussed on the basis of the monitoring data. The organic micropollutants monitored are grouped according to chemical properties: aromatic hydrocarbons, chlorophenols, detergents, halogenated aliphatic hydrocarbons, ethers (MTBE), phenols, and phthalates. The most frequently found compounds were toluene (18.7%), phenol (14.6%), xylene (10.9), trichloromethane (9.5%), and benzene (in 8.8% of the screens monitored). The five compounds most frequently found at a concentration above the maximum residue limits (MRL) for drinkingwater were: dibuthylphthalate (28%), phenol (14%), 2,4-dichlorophenol (10%), trichloromethane (10%), pentachlorophenol (7% of findings exceeding the MRL for drinkingwater). Overall, one or several compound was observed at least once in 57.8% of the 1115 screens monitored within the period 1993-2001. On a yearly basis the median finding frequency was 19%.