Geoscience Reference
In-Depth Information
11.5.2 Urban Runoff
Urban (municipal) runoff contaminants like surfactants, pesticides, and pharma-
ceutical products and contaminants associated with highway construction and
maintenance are nonpoint sources that contribute significant amounts of pollution
to the land surface and thus, indirectly, to the subsurface. Runoff pollution is
associated with rainwater or melting snow, which washes impermeable urban
surfaces as roads, bridges, parking lots, and rooftops. Suspended solids carried by
runoff water represent the major source of urban contamination. For example,
Wiesner et al. (
1995
) estimates that over 40 % of the suspended solids entering
Galveston Bay (Texas) are of urban origin. Particle size distributions in runoff,
taken under storm and ambient conditions, show that more than 90 % of the
particles are between 0.45 and 2 lm. The particulate phase includes 1-10 %
organic carbon, with heavy metal functional groups containing detectable levels of
Fe, Ba, Cu, Mn, Pb, and Zn. Zinc and barium were distributed bimodally with
respect to the size fractions, while lead and iron were associated almost exclu-
sively with the largest size fraction. These results show that suspended particles
from runoff include heavy metals. The association of heavy metals with different
sizes of suspended particles may affect their spatial distribution on the disposal
areas.
A wide range of transport models are available for predicting water contami-
nation and flow under urban runoff. Models based on conventional methods for
runoff generation and routing were reviewed critically by Eliott and Trowsdale
(
2007
). These authors suggest that future models on urban runoff should include a
broad range of contaminants and improve the representation of contaminant
transport.
References
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