This study provides guidance on vehicle emission factors (VEFs) for loads of copper and zinc discharged in road runoff, and the performance of stormwater treatment devices for removing these metals and total suspended sediments (TSS).
Between February 2008 and June 2009, a field programme comprising the measurement of road runoff volumes and the collection and analysis of runoff samples was conducted at four sites, of differing traffic characteristics, in the Auckland Region. Concentrations of copper and zinc were higher at a congested site than at two sites at which traffic generally moved freely. Substantially lower TSS and metal concentrations were measured at a moderately congested site, counter to expectations and possibly reflecting the recent resealing of the road surface at this location with open-graded porous asphalt (OGPA). VEFs estimated using a contaminant accumulation/wash-off model provided the basis for determining a set of guideline copper and zinc VEF values for (1) congested roads and intersections and (2) 'normal' roads.
The performances of a stormwater pond, a grass swale and a roadside drainage channel for treating road runoff were assessed in terms of contaminant removal efficiencies and comparisons of treated runoff quality with water quality guideline values and criteria. The roadside drainage channel was the most effective method and the pond was the least, because of its ineffectiveness at removing dissolved metals. The results provided a basis for determining a set of guideline load-reduction factors (LRFs) for the removal of contaminants by these types of system.