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Washington State’s Department of Ecology Releases Findings on Stormwater Roof Runoff

By Joe Gorsuch,  Copper Development Association (CDA), Manager, Health, Environment and Sustainable Development

The Washington State Department of Ecology (Ecology) recently released a report highlighting the preliminary results of a stormwater roof runoff study. Ecology researchers sampled stormwater runoff after 10 rainstorm events February – April 2013, and a second 10 events from October – February 2014, on roofing test panels near Olympia, Washington.  Stormwater comes from rain or melting snow that runs off surfaces – roofs, paved roads or fields. The stormwater can pick up pollutants or certain chemicals as it travels into a body of surface water, like a stream, bay or lake.

A task force made up of roofing manufacturers, contractors and associations, including the CDA, regulators and NGOs, helped design the study by identifying chemicals of concern and the 14 most common types of roofing used in the Pacific Northwest. The goal of the study was to determine if roofing materials were the potential source of toxic chemicals found in the Puget Sound basin. Preliminary results of the new metal roofing material were as anticipated with copper and zinc present in roof runoff at concentrations observed in published studies.

Stormwater is collected from the copper roof and passes through bioretention planters and biofiltration swales. These treatment measures reduce the amount of copper in runoff by 88 to 99% and alter its chemistry as it passes through.

The leached copper results from the ecology study were similar to those reported by researchers at Towson University, which proved that by the simple use of planter boxes and swales (through which roof runoff is diverted) the amount of copper could be significantly reduced – some 83-99%. Though Department of Ecology researchers did not use these planter boxes and swales in their study, Towson has proved that stormwater management practices can control the amount of copper released from roofing materials in urban environments, and copper can be used as a safe and sustainable building material.

Read the full report  from the Washington State Department of Ecology. Results from the second round of this study will be available in late spring. Learn more about the misclassification of copper in building construction.

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