9. Groundwater pollution in urban areas

Abstract

The drinking water supply in Denmark is almost entirely based on groundwater. Approximately 1000 million m3 of groundwater are abstracted annually from subsurface reservoirs, approximately half of which are within, or close to, major urban areas. For Greater Copenhagen, which comprises the city and its suburbs, a yearly total of approximately 100 million m3 is abstracted. The main aquifer is a fractured Danian limestone/Senonian chalk. In most areas, the quality of the groundwater is good, but during recent years pollution has occurred in concentrations that have required the closing of several drinking water wells. In the Copenhagen area, 63 wells have been closed within the past few years, mainly because of pollution by chlorinated pollutants and other chemicals. In a further 28 wells traces of pollutants have been found. All wells have casing through Quaternary layers and are open in the limestone. In order to obtain control of and hopefully to preserve the groundwater resource, the independent municipality of Frederiksberg, which is in the middle of central Copenhagen, has initiated a comprehensive investigation and modelling of the hydrogeological conditions of the resource. Frederiksberg draws 2.5 million m3 of water from three wells within the upper fractured Danian limestone/Senonian chalk, which is covered by a 10–30 m layer of moraine and meltwater deposits. The catchment area is approximately 30 km2. Investigations Geology Hydrogeology Water balance Precipitation and changes of groundwater level Groundwater modelling Conductivity of the intact limestone Water exchange in the intact limestone Pollution