Trace metal geochemistry of peat under a sanitary landfill-a reconnaissance

Abstract

Core samples were taken at two sites from a peat deposit buried by a sanitary landfill operated by the city of Vancouver since the 1960s and from a third site where the same peat bed is not covered by landfill. Twenty-nine subsamples from the three cores were analyzed by a variety of techniques to determine the concentration of as many as 34 constituents. The content of heavy metals, the principal object of this investigation, is highest in the lower part of the peat succession, in which there is a significant amount of interbedded inorganic sediment, rather than in the upper clean bog peat. Individual layers as little as 2.5 cm thick can hold concentrations of heavy metals ten times that of the nearby layers. The heavy metal contents show a high positive correlation with those of iron and manganese and a very low correlation with sulfur. Iron from the landfill has been transported by downward percolating groundwater in solution or colloidal suspension into the lower layers of peat deposit where the passing heavy metals were sorbed. A comparison of the amounts of heavy metals stored in the peat alone with the amount leaving the whole landfill annually suggests that some metals, notably lead and arsenic, might be retained in the peat for very long periods, whereas other metals such as zinc and mercury might be quickly lost.