Investigation of the source and occurrence of lead in the Brandon Water Supply System

Abstract

Lead concentrations in drinking water were found to exceed the provincial standard of 10 µg/L in Brandon, Portage la Prairie and Winnipeg, in some locations. Lead dioxide was identified in the scale coating the interior of lead pipes in the Brandon water distribution system. However, during periods of stagnation, free chlorine is used up by the elevated concentrations of natural organic matter (NOM) in the treated water, and lead dioxide is reduced back to more soluble divalent lead, resulting in release of dissolved lead. The removal of NOM and the targeted removal of aquatic humic substances (AHS), thought to be the most reactive fraction of NOM, were investigated as a means of decreasing the reduction of lead dioxide. Contrary to expected results, targeted removal of AHS was not found to have a significant impact on reduction of lead dioxide, while removal of 50% of the NOM non-preferentially was found to significantly decrease the reduction of lead dioxide. This indicates that AHS are not the most reductant fraction of natural organic matter in this particular water.