Roofing as a Contributor to Urban Runoff Pollution

Development in sensitive watersheds continues to pose environmental problems for receiving waters. Materials, such as galvanized metal, concrete, asphalt and wood products, may release pollutants into urban runoff and snowmelt; however, the long term effect of commonly-used roofing materials on the environment has not been quantified. This lack of long-term testing poses a particular problem because roofing is ubiquitous in the urban environment and covers a comparatively large amount of the surface area available to generate runoff. Laboratory testing on common roofing materials indicated that the potential for release (primarily nutrients, hydrocarbons, pesticides, and metals) is substantial. Further testing on painted, galvanized roofing tiles that were exposed to the Pennsylvania climate for 60+ years indicated that material continued to be released from these panels — indicating a deeper reservoir than simply the loss of a sacrificial surface coating. The ongoing research project involves testing a variety of construction materials (roofing materials, treated and untreated woods) to determine their long-term pollutant release after typical installation and exposure to the weather. The goal is to develop a better understanding of how the aging and exposure processes will impact the release over time. Understanding the `release vs. time' of a pollutant from a material will be crucial for translating the laboratory results to the actual environment and to developing predictive models for evaluating new materials for their pollutant potential. To accomplish this, at PSH and UAB, intact sections of these materials were installed on outdoor frames in areas not subject to canopy cover. Initial testing showed that nutrient concentrations were elevated early in the materials' life, as were the metals. Now, over one year of installation and testing has occurred. For many of the pollutants, the concentrations have leveled off to much lower concentrations. For most pollutants, especially nutrients, periodic spikes in runoff concentrations can be correlated to noticeable degradation in the material itself. Preliminary metals results show that lead concentrations are just above the detection limit, while copper releases are much greater for many materials. Runoff concentrations of copper for asphalt shingles and the two treated wood panels exceeded 500 μg/L during the first two weeks of exposure (with multiple storms during that period to wash off any surface coating).