Roadway Runoff Water Quality from Milled and Unaltered Surfaces during Convective Storms

Abstract

Time series of total suspended solids, and total and dissolved copper, zinc, and lead concentrations were compared between milled hot-mix asphalt (HMA) roadway sections (n=6) and unaltered HMA roadway sections (n=6). Milled and unaltered road surface runoff water quality parameter values were within the ranges reported previously for unaltered rural and urban roadways. Event mean concentrations of suspended solids and lead were greater for milled roadway surfaces than for unaltered surfaces. No differences in copper and zinc concentrations were observed between road treatments. Contaminant mobilization was flow-driven, with incomplete wash-off of roadway constituents during the short-duration convective storm events. Storm precipitation intensity was not an indicator of storm-water quality. The presence of lead in runoff from milled roadway sections in this study indicated a road side soil source of the solids resulting from overland flow from adjacent land surfaces onto the roadway. Future milling operations should proceed with consideration not to create new hydraulic connections with the adjacent roadside.