Characterization of road runoff: A case study on the A3 Portuguese Highway

Abstract

Road runoff is a linear non-point source of pollution with a significant impact on water receiving bodies, but whose importance has been neglected in the past. The pollutants in road runoff can be responsible for both acute and chronicle effects.

Due to the processes involved in its formation, but also due to its intermittent nature, the characterization and prediction of road runoff quality is still a subject with limited scientific knowledge. Since the European Water Framework Directive demands a good ecological status for natural water bodies, there is an urgent need for controlling this source of pollution. The study of the highway runoff pollution load mass, the inter-event distribution and the estimation of event and site mean concentrations could contribute to increase the knowledge of the related phenomena, estimate its impacts and, therefore, contribute for the definition of mitigations measures for water resources protection or the enhancement of their quality.

In Portugal there is still a reduced knowledge on road runoff pollutants and also a lack of established procedures for the control of this source of pollution. A research project “Guidelines for Integrated Road Runoff Pollution Management in Portugal (G-Terra)” is evaluating, at a national level, road runoff pollution loads and distribution, in order to establish guidelines for road runoff assessment and management.

This paper describes the methodology and monitoring procedures of a case study on the A3 highway, at Santo Tirso, in the north of Portugal. At this site the average daily traffic is 43,000 vehicles. A total of 10 runoff events where monitored through discrete samples, taken along the duration of the runoff. The road site characteristics and the pollutants concentration in the different runoff events are presented and discussed.