RIVER SEDIMENTS CONFIRM LOCATION OF CONTAMINATED GROUNDWATER DISCHARGE

Oil refineries operated in Alma, Michigan, for most of the twentieth century. A local environmental concern is whether heavy metals associated with petroleum refining have polluted the Pine River, which runs through the center of town close to refinery operations. Analysis of ground water discharging to the river indicated somewhat higher metal concentrations from sampling sites near the refinery, but did not provide convincing evidence that pollution from the refinery was reaching the river by this mechanism.

Subsequent analysis of heavy metals in river sediments provided more credible evidence that contamination originating from the refinery has indeed reached the river by way of ground water discharge. Metal concentrations are highest (up to eighty times background levels) in river sediments down gradient from the refinery. The greatest enrichment is observed for metals most closely associated with the local refinery: lead, nickel, zinc, and barium. Concentrations of these metals are also highly correlated to one another in sediments. At other sites along the river, which flows past a variety of industries, sediment metal concentrations exceed background levels, but at much lower degrees of enrichment and in different proportions than those near the refinery.

These results support the hypothesis that a plume of contaminated ground water originating from the refinery did enter the river at some time in the past, although it appears that ground water is no longer transporting significant quantities of metals to the river. The elevated concentrations in sediments do not pose an immediate threat to the river’s water quality, but if sediments were resuspended metals could be mobilized and re-introduced to the ecosystem.