Environmental Engineering Reference
In-Depth Information
contaminants can be traced to mitigate contamina-
tion of the urban aquatic environment at source.
100%
90%
80%
5.4.1 Sources of particulate-associated
pollutants in urban areas
70%
60%
50%
40%
30%
20%
10%
0%
Many studies around the world have identifi ed the
principal sources of contaminants in urban centres
in association with heavily traffi cked areas (Jansson
2002; Charlesworth
et al.
2003a; Adachi & Tainosho
2005), municipal wastewater systems (Gromaire
et al
. 2001; Pardos
et al
. 2004; Brown & Peake
2006), construction activities using materials such as
bricks, gravel, sand, and concrete (OMEE 1993;
Tucci 2003), and industry. Construction sites have
been considered one of the urban land uses with high
pollution potential, especially because of erosion of
unprotected soil surfaces (Wolman & Schick, 1967;
Sonzogny
et al.
1980; Harbor 1999; Burton & Pitt
2002).
However, non-point sources such as emissions
from vehicles, by defi nition are diffi cult to investi-
gate. For instance, the toxic effects of Pb are well
known, and where there is one identifi able source of
Pb, for example Pb-based paints or leaded petrol, it
can be legislated for. However, low-level environ-
mental exposure to Pb can be associated with multi-
ple sources (petrol, industrial processes, paint, solder
in canned foods, water pipes) and pathways (air,
household dust, street dirt, soil, water, food).
Evaluation of the relative contributions of sources is
therefore complex and likely to differ between areas
and population groups (Von Schirnding 1999; Tong
et al.
2000). In a study by Poleto (2007), the princi-
pal sources of sediment to a small urban catchment
in Brazil included the river channel itself, paved and
unpaved streets. Three suspended sediment samples
were collected at hourly intervals during the storm
event. Figure 5.4 shows how the relative importance
of these sources changes with time with that from
paved street declining while both unpaved streets
and the river channel increase in importance.
Studies such as that by Stigliani
et al.
(1993) found
that contaminated sediments deposited in the River
Rhine were dominated by diffuse sources. And in a
study of an urban stream in Oahu, Hawaii, Sutherland
(2000) found that the sediments were signifi cantly
polluted with Pb and less so with Ba, Cd, and Zn,
sources of which were directly attributable to the
15:00
16:00
17:00
Paved streets
Stream channel
Unpaved streets
Fig. 5.4
Sediment sources in a small urban watershed.
From Poleto
et al
. (2009).
wear of vehicles, wear of tires, spillages of fl uids, and
exhaust emissions. Further, owing to the predomi-
nance of impervious surfaces in the urban environ-
ment, when there is a storm or sudden snowmelt,
surface runoff fl ows rapidly across the urban catch-
ment because infi ltration and storage are greatly
reduced (Robinson
et al
. 2000). This was shown in
Poleto & Merten's (2007) study of Pb, Zn, and Cr
removal from paved streets in Brazil, which showed
the transport downstream of these pollutants in asso-
ciation with stormwater fl ow and their distribution
in the basin (Fig. 5.5).
This rapid runoff will carry with it what Robinson
et al
. (2000) term a “cocktail” of associated contami-
nants whose concentrations increase with increasing
imperviousness. These contaminants are then carried
into storm sewers and thence to receiving waters
where they have been identifi ed as the cause of deg-
radation in urban watercourses (Pitt
et al
. 1993). In
Eastern England, Perdikaki & Mason (1999) found
that most of the problems associated with contami-
nant-rich run-off from urban areas were associated
with particulate material. The importance of water
as the transport medium for particulate-associated
material is further emphasized during storms when
pollutants are fl ushed out into the stream, while
overall discharge remains unaffected (Brinkmann
1985). This “fi rst fl ush” effect is virtually unique to
