Groundwater pollution considered as a continuous injection of tracers

The Bavarian Geological Survey has been investigating for more than 10 years the extent and range of groundwater contaminants derived from a domestic and industrial refuse tip. The results of investigations have shown that contaminated groundwater travelled at least 5000 m. The investigation involved a general survey of electrical conductivity and groundwater temperature as well as supporting evidence of pollution by analysis for chloride, permanganate value and nitrate. The sampling points were so placed that some gave slight and variable indications of possible contamination and others none at all. As results showed, the chloride components increased sharply in groundwater passing under the tip. Chloride in the underflow cannot be removed and its concentration is reduced only by dilution. The investigations showed a relationship between electrical conductivity of groundwater and chloride concentration. On this basis, the chloride concentration, as indicated by electrical conductivity, allowed the path of the pollution to be traced throughout the zone in which the organic components and the nitrate were decaying or already decayed. A comparison of the direction of groundwater flow with the distribution of chloride and electrical conductivity shows very good agreement. Increased electrical conductivity could always be followed along a line of observation points. A comparison of electrical conductivity and its variation at different times shows the change of flow direction for a certain period. The investigation established that the direction of groundwater flow and its changes could certainly be traced over a distance of more than 5000 m. The hope of thus being able to follow certain maxima from bore to bore and hence to obtain an indication of the flow velocity, was not fulfilled