Variations in Highway Stormwater Runoff Quality and Stormwater Treatment Performance in Relation to the Age of Porous Friction Courses

Abstract

A program of highway runoff sampling was conducted at four sites in Auckland, New Zealand. Concentrations of suspended solids, particulate copper, and zinc were significantly lower in runoff from a highway paved with a 1-year-old porous friction course (PFC) than in runoff at the other sites. Differences in total metal concentrations were less marked, reflecting relatively high concentrations of dissolved copper and zinc in runoff from the 1-year-old PFC. Runoff quality at a highway site that had been paved with a PFC 6 years previously was similar to that discharged from two impermeable roads, indicating a reduction over time in the quality of runoff discharged from PFCs. Runoff from the highways paved with 1- and 6-year-old PFCs was treated by a grass swale and wet pond, respectively. Both treatments were effective, the former predominantly through the lowering of dissolved metal concentrations and the latter through the lowering of particulate metal concentrations. These results indicate that stormwater treatment can improve the quality of runoff discharged from PFCs, irrespective of their age, provided that treatment is targeted to the predominant contaminant phase present.