| Summary: | The aim of remediation of impoundments with sulfide-rich tailings is to prevent oxygen transport to the tailings and thereby inhibit the oxidation of sulfides. Over time, remediation usually leads to decreasing contents of elements such as metals and sulfur in the groundwater of the impoundments. This has been the progress in most parts of impoundment 1 in Kristineberg mining area in northern Sweden. The studied impoundment was exposed to weathering during 50 years before remediation. A protective cover of one meter of till was applied on the tailings, and by sealing off ditches the groundwater level was raised. Fresh groundwater flowing in from the surrounding hills has resulted in a wash out of released elements from most parts of the impoundment, and subsequently the concentrations of metals in the groundwater has decreased. The geochemistry in the northwestern part though, shows a rather different behaviour than the rest of the impoundment, with much higher concentrations of metals and sulfur in the groundwater. The aim of this study is to find an explanation to the high content of metals in this part. The study evaluates data from sampling during five years, 1998 – 2002. The data consists of analyses of the groundwater, analyses of the solid tailings and measures of groundwater levels. The evaluation of the groundwater data in this study focuses on four groundwater pipes, two installed in the northwestern part (pipes H and I) and two pipes installed in the middle of the impoundment (pipes F and G). The pipes have been installed on different depths in the tailings. The result shows that the concentrations of metals and sulfur in the groundwater are highest in the deeper pipe H in the northwestern part of the impoundment than in any other pipe. During year 2002 the average value for Fe in pipe H was 17 350 mg/l, while in pipe F the average value was 156.9 mg/l. The average value for Zn in pipe H was 2 510 mg/l , in pipe F the average value for Zn was 0.882 mg/l. In pipe I, F and G the pH of the groundwater ...
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