Environmental Engineering Reference
In-Depth Information
downward colloid-transport of heavy metals
[15, 16]
. Seasonal and temporal varia-
tions in runoff quality, such as spreading of de-icing salts may have an important
impact on the colloidal matter in the runoff waters and in the sediment (aggrega-
tion, adsorption/desorption of pollutants). Several studies highlight the partitioning
of trace metals in runoff waters between particulate and dissolved-bound fractions,
the “dissolved” fraction being operationally defined by filtration through a 0.45-mm
pore size membrane
[7, 17]
. But, only few studies have begun recently to investi-
gate the colloidal fractions of metals in runoff waters (nanometer to micrometer
size range)
[9, 18]
.
A peri-urban experimental site was chosen to sample highway runoff waters.
The objective was to study the distribution of selected trace metals (Cd, Cr, Cu,
Ni, Pb, Zn) among dissolved, colloidal and particulate fractions, in relation to
potential constituents of colloidal and particulate matter (Al, Fe, Mn, Si, organic C).
The relationship between physico-chemical water characteristics and chemical
elements was investigated and the fractionation of trace metals was quantified by
filtration and ultrafiltration.
Experimental
Highway Study Site
The experimental site is located on the south bypass motorway of Nantes (Loire-
Atlantique, France), where it crosses the Loire River at the Cheviré Bridge
[14]
.
Opened in 1991, the Cheviré Bridge supports nowadays an average total daily traf-
fic of 90,000 vehicles. The bridge is 1,500 m long and 24.6 m wide. Carriageways
consist of three lanes in each direction, separated by a central reservation and the
pavement consists of a conventional asphalt surface. The runoff waters of the
19,000 m
2
contribution area are collected in gulleys and flowed in aluminum
collectors. Then, they are gathered in a detention-infiltration basin. Nantes has an
oceanic climate with a mean annual rainfall of 820 mm over the last 50 years.
Between August 2004 and May 2006, runoff waters were sampled in a concrete
pipe, at the inlet of the basin, with an automatic sampler to take mean samples
according to time during rain events. Twenty one samples were taken over the year
(three events in spring, seven in summer, nine in autumn and two in winter).
Analysis of Runoff Waters
The physico-chemical characteristics (pH, conductivity, suspended solids (SS))
were measured according to French and EU standard methods, either on site or
after sampling at the laboratory on mean composite samples. Total concentrations
