Urbanization and the Geoenvironment - Sustainable Practices in Geoenvironmental Engineering - page 255

every hectare of brownield restored. Land use is more compact, thus increasing city
competitiveness. The Revi-Sols program in Montreal and Québec, Canada led to the
cleanup and development of 153 projects for a total of 220 ha of land by the year 2004.
The tax revenues in Montreal increased by $25.6 million and 3400 new housing units
were established.
One example of the restoration of a former contaminated site is the Angus Shops in
Montreal (NRTEE, 2004). Between 1904 and 1992, the site was used as an area for rail-
way and military maintenance and the construction of new equipment. Approximately
one-third of the sites (309 acres out of 1240 acres) were contaminated with heavy met-
als, petroleum hydrocarbons, and PAHs. All hazardous wastes were disposed of off-site.
Recyclable materials, all debris and contaminated soil were removed. Backill consisted of
clean on-site soil. The cleanup cost a total of $12 million. Five hundred houses, a supermar-
ket, and an industrial mall have been built, with a biotechnology center under construc-
tion. Property taxes have increased to $2.2 million a year and more than $391 million has
been invested by private parties.
To restore urban contaminated sites, various parameters need to be considered. These
include the characterization of the soil (mineral, texture, geochemical characteristics),
the factors inluencing fate and mobility of the contaminants such as dilution, sorption/
desorption, biodegradation, and transformation, and other factors such as climate, hydrol-
ogy, and microorganisms present. As a irst step in the remediation of land for redevelop-
ment, an investigation will be required to determined underground heterogeneity and
hidden object and obstacles. This can be accomplished by studying historical records and
conducting geophysical surveys. Sewers, cables, underground tanks, pipelines, founda-
tions, etc., must all be identiied. They should be grouped according to their ease of extrac-
tion. For example, large foundations cannot be easily extracted and may require blasting,
whereas tanks and other similar objects are not dificult to remove. Another factor is
the type of material. Wood piles can be cut off, brick foundations may be extracted, but
concrete foundations require special procedures. Various strategies could also be used
to reduce redevelopment costs and promote sustainability. These are summarized in
F i g u r e 7.1 7.
As noted in Chapter 3, a variety of remediation techniques exist. They include excava-
tion, contaminant ixing or isolation, incineration, or vitriication, and biological treat-
ment processes. In situ processes include (a) bioremediation, air or steam stripping, or
thermal treatment for volatile compounds, (b) extraction methods for soluble components,
(c) chemical treatments for oxidation or detoxiication, and (d) stabilization/solidiication
with cements, limes, resins for heavy metal contaminants. Phytoremediation is a devel-
oping technique (Mulligan, 2002). The most suitable types of plants must be selected
based on contaminant type and recovery techniques for disposal of the contaminated
plants.
In Copenhagen, a soil treatment plant of 45,000 tonnes/year was recently established,
mainly for oil-contaminated soils, with requirement for reduction of levels of 700 to
2000 mg/kg to below 50 mg/kg (Cooper, 1999). The treatment procedures call for green
waste to be added to the soil in a 50:50 ratio and placed in a 1.5-m high windrow. Turning
every week is required to maintain the temperature above 15°C even in the winter. Because
of better air permeability characteristics, sandy soils are much easier to treat than clay
soils. If the treatment is successful, the remediated soil can be used to grow vegetation
in embankments or in construction projects. If the treatment fails or does not meet the
required criteria, the soil must be sent to a special landill.