Flow dynamics of groundwater and soil water in the former heap Gessenhalde at the uranium mining area of Ronneburg: a stable isotope approach

Stable isotopes, 2 H water , 18 O water as well as 18 O sulphate and 34 S sulphate , were used to study the flow system of shallow groundwater and soil water at the base area of a former leaching heap at the uranium mining area of Ronneburg, Germany. The flow paths and water‐retention times were estimated by comparison of δ 2 H and δ 18 O values in groundwater and soil water to the δ 2 H and δ 18 O signature of precipitation, giving distinctive inputs of summer or winter precipitation. The points of measuring the groundwater were divided into three categories with different flow conditions: rapid flow, stagnant conditions and a transition zone by hierarchical cluster analysis of δ 2 H and δ 18 O values of groundwater. The transit time of groundwater in the rapid flow area is less than 6 months, whereas water in the stagnant zone is stored for at least 1 year. In soil water, a clear response to different input signals is detectable only in the 30‐cm horizon (retention time is about 6 months), whereas at deeper levels a mixing with older water is taking place. The isotopic composition of the dissolved sulphate was used to identify oxidation of sulphides as the source of sulphate. Copyright © 2010 John Wiley & Sons, Ltd.