Environmental Engineering Reference
In-Depth Information
Effects of Atmospheric Salt Deposition
on Highway Runoff Characteristics - A Pilot
Case Study
Pedro Baila Antunes and Ana Estela Barbosa
Introduction
Monitoring studies of road runoff, from two different sites (highways A25 and IP6),
located on coastal areas of Portugal
[6-8]
detected high levels of salinity and
Carbon Oxygen Demand (COD). Table
1
compares results for these two sites, dis-
playing interesting similarities between the parameters connected to salinity and
COD. On the other hand, pollutants typical for highway runoff characterization,
such as total suspended solids (TSS) and the heavy metals zinc (Zn), copper (Cu)
and lead (Pb) clearly indicate different levels of traffic pollution.
[5, 7]
proposed
that such evidences should be related to the vicinity of the Atlantic Ocean, since the
non-coastal Portuguese roads did not show this same pattern.
Multivariate exploratory statistical techniques, applied to a set of coastal and non-
coastal Portuguese roads indicated different patterns for the two groups, in terms of
salinity, conductivity and chlorides, as expected, but also of COD concentrations
[7]
.
According to
[16]
the marine aerosol can be transported to large distances. In
areas with high salinity and where evaporation is systematically superior to the
precipitation, the salts crystallization at the top surface of pavement materials tend
to provoke a significant degradation of the road pavement, with structural conse-
quences relevant to road engineering
[17]
. The bituminous material is lifted and its
adhesion to the road base is destroyed.
In coastal areas, under climate conditions such as the Portuguese ones, maritime
salts transported by the atmosphere are deposited and may remain in the road pave-
ment and crystallize during dry periods between rainfall events, eventually, leading
