Estimations of copper roof runoff rates in the United States

Copper (Cu) concentrations in waterways of the United States are of widespread concern. Presently, 692 waterway segments around the United States are listed by the U.S. Environmental Protection Agency (USEPA) as having unacceptably high copper concentrations. As part of their water quality management strategy, the USEPA is mandated to understand and manage sources and impacts of nonpoint releases of chemicals of concern. One potential nonpoint source of Cu is the runoff of precipitation falling onto Cu used in external architecture (e.g., roofing). However, few studies of Cu roof runoff have been published. This article is intended to provide estimations of Cu runoff rates and concentrations across the United States. Copper runoff rates and concentrations are predicted at 179 locations with a recently developed model. The average and range (in parentheses) of annual Cu loading rates, based on roof area; Cu export rates, based on amount of precipitation; and Cu concentrations for the United States are 2.12 (1.05-4.85) g Cu/m2/y; 2.72 (0.69-16.48) mg Cu/m2/ mm; and 2.72 (0.69-16.48) mg Cu/L as total Cu, respectively. Statistics are presented that describe site-specific data distributions for use in probabilistic exposure and risk assessments. The effects of air quality as well as the potential fate and risks of Cu from roof runoff are discussed.