For many decades the east side of Alma, Michigan, has been home to an oil refinery. Local citizens are concerned by the existence of a benzene plume and petroleum contamination in the surface aquifer. Although governmental agencies are working to clean up the refinery site, an unresolved aspect of the problem is whether groundwater is transporting contaminants to the nearby Pine River.

The hypothesis investigated is that contamination from the refinery has affected the quality of groundwater discharging to the Pine River. To test this hypothesis, seepage meters and mini-piezometers were installed in the river bed to measure groundwater flux rates, determine hydraulic gradients, and collect groundwater samples. Groundwater and river water were analyzed for heavy metals that are associated with crude oil and petroleum refining operations. Although metals from the refinery pose a potential environmental threat, little is known about their concentrations or distribution in this system.

Preliminary results show heavy metal concentrations are elevated in groundwater compared to river water, and, for many metals, the highest concentrations occur in groundwater directly down-gradient from the refinery. These results confirm that groundwater is indeed transporting metals to the Pine River. Concentration ratios of heavy metals in groundwater are distinctive for individual sites, indicating that such ratios may serve as geochemical fingerprints for metal sources. Total fluxes of metals to the river from the aquifer depend on hydrologic conditions, but metal concentrations are generally below state drinking water quality limits.

Acknowledgements: This work was funded by the Council on Undergraduate Research Student Summer Research Fellowships in Science and Mathematics, sponsored by CUR’s Undergraduate Researcher’s Graduate School Registry. Additional support was provided by Central Michigan University’s Research Excellence Funds program.