Quality of roof runoff for groundwater infiltration

The assumption that roof runoff can be considered as non-polluted stormwate r that can be discharged directly into natural water bodies without impairi ng their quality and use was examined in a field study. Concentrations of major ions; total C, N, and P; heavy metals (Cu, Zn, Pb, Cd, Cr, Mn, Fe) and pesticides (triazines, acetamides, phenoxy acids) were measured in runoff from an inclined tile roof, an inclined polyester roof a nd a flat gravel roof. Runoff from the: first two roofs showed initially ve ry high concentrations declining rapidly to lower constant levels. This fir st-flush effect was modelled using a first-order rate law (wash-off functio n). For most constituents, concentrations were in the range of the wet depo sition after the first few mm runoff depth and total loads in the runoff co rresponded approximately to the total (dry and wet) atmospheric deposition load. The flat gravel roof depicted a different behaviour. Rainwater was fi rst retained before it overflowed. Consequently gravel will be weathered an d most pollutants were partially retained in the gravel layer. However, cor rosion of Cu in drains (rate about 5 g m(-2) y(-1)) produced such high Cu c oncentrations thai direct disposal of runoff is questionable. (C) 2000 Else vier Science Ltd. All rights reserved.