Characteristics of Natural and Urban Soils - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 118

• humus accumulation leading to the formation of new A horizons;

• weathering processes, such as swelling-shrinkage, thawing-freezing, and acidifi-

cation;

• reductomorphology caused by impeded water, human-made compactness, and

reductive gases;

• carbonate and salt formation resulting in calcium-crusts and salt-crusts (in

relation to some technogenic materials indicating high calcium carbonate con-
centrations as well as enhanced electrical conductivity);

• turbation by fauna, but also by swelling-shrinkage processes, e.g., in sludge

fields.

However it should be kept in mind, that the soil weathering processes become
less intensive because of higher temperatures (0.3-3.0 ◦ C higher), reduced freezing-
thawing processes and other climatic effects in urbanized areas.
Apart from the deposited soils, former industrial sites can occupy originally nat-
ural soils. Nevertheless, their contamination potential may be very high, since there
are specific contaminant losses during industrial processes in the course of time.
A typical example is that of gas works areas, where one can find residues contain-
ing ferric ferro cyanides and coal tar enriched with benzene, toluene, xylene, phenol
and PAH. Another example is scrap yards, where dismantling of vehicles and other
machinery takes place, producing contaminants as PCBs derived from break-up of
electrical equipment, and waste oil needed to run conveyor belts, sorting machines,
etc (Bullock and Gregory 1991 ; Genske 2003 ). Besides, soil contamination of indus-
try sites often results from handling, storage, and transport of potentially polluted
products and by-products.
Additionally, in urban environment underground leakages of e.g. wastewater
tubes and gas pipelines causing dispersion of soluble contaminants or reductive
gases are another source of soil contamination. In case of leakage, different kinds of
damage are possible. For instance, corrosion, swelling effects of loamy or clayey
soils, traffic influence or subsidence present in mining areas are able to initiate
losses of wastewater or gas. Thus, spills of liquids containing e.g. ammonia, sul-
phate, or heavy metals are typical results of leakages indicating contamination to
soil. Furthermore, gases like methane derived from corroded gas pipelines may be
vulnerable to explosion.

2.4.2 Additional Sources of Contamination

The introduction of technogenic materials is one mode that can contaminate
soils, but additional contamination factors can overlap each other (Fig. 2.10 ). It
is well-known, that natural soils without any visible disturbance or presence of
anthropogenic artefacts can be highly contaminated due to different sources of
contamination:

• atmospheric precipitation (dust deposition);

• flood occurrences in alluvial floodplains resulting in contaminated particle

sedimentation during or after the flood;