Effect of age and rainfall pH on contaminant yields from metal roofs.
Metal roofs are recognized for conveying significant metal loads to urban streams through stormwater runoff. Metal concentrations in urban runoff depend on roof types and prevailing weather conditions but the combined effects of roof age and rainfall pH on metal mobilization are not well understood. To investigate these effects on roof runoff, water quality was analysed from galvanized iron and copper roofs following rainfall events and also from simulating runoff using a rainfall simulator on specially constructed roof modules. Zinc and copper yields under different pH regimes were investigated for two roof materials and two different ages. Metal mobilization from older roofs was greater than new roofs with 55-year-old galvanized roof surfaces yielding more Zn, on average increasing by 45% and 30% under a rainfall pH of 4 and 8, respectively. Predominantly dissolved (85-95%) Zn and Cu concentrations in runoff exponentially increased as the rainfall pH decreased. Results also confirmed that copper guttering and downpipes associated with galvanized steel roof systems can substantially increase copper levels in roof runoff. Understanding the dynamics of roof surfaces as a function of weathering and rainfall pH regimes can help developers with making better choices about roof types and materials for stormwater improvement.
University of Canterbury, Hydrological and Ecological Engineering, Department of Civil and Natural Resources Engineering, Private Bag 4800, Christchurch 8140, New Zealand E-mail: tom.cochrane@canterbury.ac.nz.
Daniel
D
Wicke
University of Canterbury, Hydrological and Ecological Engineering, Department of Civil and Natural Resources Engineering, Private Bag 4800, Christchurch 8140, New Zealand E-mail: tom.cochrane@canterbury.ac.nz.
Thomas A
TA
Cochrane
University of Canterbury, Hydrological and Ecological Engineering, Department of Civil and Natural Resources Engineering, Private Bag 4800, Christchurch 8140, New Zealand E-mail: tom.cochrane@canterbury.ac.nz.
Aisling D
AD
O'Sullivan
University of Canterbury, Hydrological and Ecological Engineering, Department of Civil and Natural Resources Engineering, Private Bag 4800, Christchurch 8140, New Zealand E-mail: tom.cochrane@canterbury.ac.nz.
Simon
S
Cave
University of Canterbury, Hydrological and Ecological Engineering, Department of Civil and Natural Resources Engineering, Private Bag 4800, Christchurch 8140, New Zealand E-mail: tom.cochrane@canterbury.ac.nz.
Mark
M
Derksen
D003252:Construction Materials / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D008670:Metals; D011891:Rain / Q000737:chemistry*; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000737:chemistry*
D008670:Metals; D014874:Water Pollutants, Chemical