Abstract

In an open pit mining lake in the Central-German lignite district, untreated pyrolysis water from lignite smouldery was disposed of for < 15 years. The water is highly contaminated with phenols, ammonium, and polyaromatic hydrocarbon, resulting in an extremely high dissolved organic carbon content. Several aquifers are in danger of being polluted by leaking wastewater. Since 1993, the water in up to 24 wells around the lake in different Quaternary and Tertiary aquifers was monitored two to six times per year for organic and inorganic pollutants. Isotope data (deuterium, oxygen, tritium, nitrogen) and hydrochemical investigations were used to assess the influence of lake water on groundwater. Data gathered to date shows <5% of contaminated lake water in the downstream groundwater. Nevertheless, this leakage water has a sustainable influence on the groundwater quality at least locally. Furthermore, isotope data suggest lower flow velocities within the underlying aquifer than was expected.