Urbanization and the Geoenvironment - Sustainable Practices in Geoenvironmental Engineering - page 229

Both the wastes themselves and the products they produce (such as leachates and emis-
sions) are health and geoenvironmental threats. Disposal of wastes in the ground, illicit
dumping, leaking underground storage tanks and others are all causes for concern. A
sampling of backyards in the Montreal area where wastes had been previously dumped
indicated elevated levels of the heavy metals lead and zinc (Figure 7.5).
Water entry into wastepiles in landills, together with dissolution processes result in the
generation of waste leachates. A liner and leachate collection system such as that shown in
Figures 1.11 and 3.12 in Chapters 1 and 3, respectively, is required to protect the ground-
water from fugitive leachates. A cap system is required also to prevent rain from entering
the wastepile and producing leachates. Typical leachates from landills include organic
chemicals (e.g., BTEX, PAHs, phthalates, ketones, dioxins, phenols, pesticides, solvents)
and inorganic components (e.g., mercury, cadmium, chromium, copper, zinc, lead, nickel).
The composition of leachates varies signiicantly depending on the age and type of waste
and landill technology used to contain the waste. The groundwater level and the nature
of the soil under the landill are important factors in managing leachate contamination
risks to the groundwater. Concentrations of both organic and inorganic components can
be high as shown in Figure 7.6.
In the past, quarries and other pits without proper barrier and liner systems were used
for waste disposal, for example, the Gloucester landill in Canada (Lesage et al., 1990).
From 1969 to 1980, hazardous wastes, including laboratory organic chemicals, were dis-
posed in this landill, which is situated on glacial outwash deposits with a semiconined
aquifer. The chemicals reacted with the explosive charges that were also in the waste pile,
and the leachate plume of more than 300 m in the aquifer in 1990 was found to contain the
unaltered and transformed chemicals from the wastepile.
Gaseous emissions from biodegradation of organic materials in landills also occur.
These gases generally contain both carbon dioxide and methane. More than 350 m 3 of

2500

Zinc

2000

Lead

1500

1000

500

0

1 2 3 4 5 6 7 8 9 10

Samples from an urban area

FIGURE 7.5
Lead and zinc concentrations of soil samples taken from various locations in the Montreal area (seven samples
from communal garden and three samples from locations near it). (Data from Huang Y.-T., Heavy Metals in Urban
Soils , MASc thesis, Concordia University, Montreal, Canada, 2005.)