Mapping Heavy Metal Distributions in and around Riverside Park, Milwaukee, WI

A 2.5-mile impoundment sat behind the North Avenue Dam on the Milwaukee River for over 150 years, until it was breached in 1990. Upstream urban runoff and industrial pollution resulted in the deposition of heavy metal rich sediments in the slow moving waters of the impoundment. After the dam's removal, the river narrowed and returned to a more natural flowpath. The newly exposed riverbed was annexed as part of Riverside Park, enabling ecological recovery efforts on the river and riparian zones. However, these newly exposed soils are enriched with heavy metal contaminants, including Pb, Zn, Cd, Cu and Ni. In addition to metals deposited by the impoundment, soils are impacted by typical urban runoff including Pb from paints and gasoline. Previous work has shown that metal concentrations are typically near or below the EPA threshold of 400 ppm, though the metals are generally in highly available phases.

A field-portable x-ray fluorescence spectrometer (pXRF), coupled with a sub-meter accuracy GPS, is being used to create a geochemical map of heavy metal distributions throughout the park and surrounding neighborhoods. Sampling locations include the riparian zone along the Milwaukee River, urban forest land, athletic fields, a rails-to-trails corridor, a playground, school grounds and residential areas. In addition to field mapping of metal distributions, soil parameters including pH, LOI and XRD analyses will also be performed to further characterize the soils.

This study is being conducted in conjunction with the Urban Ecology Center, a nonprofit environmental organization located in Riverside Park that is dedicated to serving the local community and urban youth while restoring and protecting the natural areas along the Milwaukee River.