IMPACTS OF URBANIZATION ON GROUNDWATER IN SOUTHEASTERN MICHIGAN

Adverse impacts on groundwater from more than 100 years of urbanization were studied over a period of several years. A subset of the data collected from over 3,000 sites of environmental contamination from within the Rouge River watershed in southeastern Michigan was analyzed for the presence of dissolved heavy metals in groundwater. A total of 1,140 groundwater samples were collected from 126 sites of varying use, including residential, commercial and industrial properties. Sample collection was spatially dispersed throughout six near-surface geological units of the watershed, and collected from 1990 to 2000. Sample collection over a period of 10 years helped average the variability of heavy metal concentrations caused by the constantly changing urban region. The metals evaluated for this study included As, Ba, Cd, Cr, Cu, Pb, Hg, Ni, Se Ag, and Zn. The results indicated significantly elevated metal concentrations were found at 32 percent of the sites sampled, which suggests groundwater contamination by heavy metals is widespread throughout the watershed. Other significant findings include the occurrences of elevated concentrations of heavy metals within a sand unit, with the mean concentrations of Cr, Cd, and Pb exceeding the Maximum Contamination Level by 20, 12, and 10 times, respectively. Additional analysis of the groundwater contamination in this watershed was obtained by analyzing the pattern of remediation costs at 89 contaminated sites. The findings indicate that at geologically vulnerable locations contamination is more likely to migrate through larger-grained materials (sand and moraine), reach groundwater, and be more costly to remediate than units that are less vulnerable to contamination (clay and silty clay soils). From public health and environmental perspectives, the contamination of the regional groundwater along with potential damage to the hydraulically connected Great Lakes ecosystem poses significant challenges for watershed management efforts and underscores the need to protect groundwater.