Stable lead isotopes as tracers of groundwater pollution in the water supply for a small village

High lead (Pb) concentration has been measured in the incoming water to the water supply for a small Swedish village since the 1990s. There are several sources of the contamination and the objective of this study was to identify these by analysis of Pb isotopes. Lead has four stable isotopes in nature (204Pb, 206Pb, 207Pb, 208Pb) and the relative proportions of these vary according to their geological source. The study showed that two anthropogenic sources of Pb, a glassworks deposit and a highway, had similar Pb isotope ratios and thus it was not possible to separate them. However, the very high Pb concentration in the glassworks deposit suggested that this is the main source of the very high concentrations observed occasionally in low flow conditions. The soil in the recharge area of the most important well for the water supply had elevated Pb concentrations compared with background values in soils. Moreover, the Pb ratios in this soil differed from those in the anthropogenic sources. Several sites of mineralisation or natural enrichment have been identified in outcrops about 14 km northwest of the site and several anomalies in Pb exist in the glacial till. The conclusion was that Pb originating from the soil in the recharge area generally dominates and leads to Pb concentrations in water of 1–2 µg L−1. However, at higher concentrations, e.g. around 10 µg L−1, water transported in cracks and fissure from the glassworks deposit becomes more important.