Characteristics of Natural and Urban Soils - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 124

contains contaminated agents like cyanides (Genske 2003 ). The sludge fields create
bad conditions for plants due to contamination as well as physical impacts such as
high soil density and platy soil structure. Fly ash fields consisting of 40% silt and
60% fine sand and indicating an alkaline pH value, underline the same negative
impacts, deflation in dry conditions and strongly reduced root penetration result-
ing from the cement-like substance after reaction with lime (Bullock and Gregory
1991 ).
2.6 Physical Characteristics with Reference
to Contaminated Sites
In urban areas, a lot of deposited soils are covered with sealing material to make an
urban lifestyle possible. Therefore, apart from the areas covered with buildings, a
high percentage of areas are covered with asphalt, concrete, or alternative mate-
rial with a high load bearing capacity. In regard to town planning processes, in
particular de-sealing and Brownfield redevelopment, some soils may be altered,
e.g., excavated and transported off-site. Thus, the currently sealed surfaces can
also be rehabilitated, and consequently should be taken into account in relation to
contaminated site assessment.
The degree of sealing depends upon the utilization of the site. The degree of
sealing in construction areas ranges between 35 and 80% and at roads and squares
the values are higher than 60%. Results from investigations in the Southeast district
of Moscow have revealed that industrial sites are usually >75% sealed, followed by
residential areas (50-75%) and the natural areas (urban forest, agriculture) (<25%)
(Stroganova et al. 1998 ).
Even outside the sealed areas water infiltration is often reduced, since the sur-
rounding areas are influenced by compaction due to trucks and other vehicles, in
particular caused during the construction phase. The compaction results from soil
displacement and transportation and destroys soil structure. Moreover, the revital-
ization process of the soil is reduced, due to the low organic matter content as
structure-forming agent. The reduced humus content results from mixing processes
involving both topsoil and subsoil. The bulk density of the soil in refilled areas is
increased by the passage of heavy traffic. In New York's Central Park, the bulk den-
sity in subsoil varies between 1.52 and 1.96 g cm − 3 (Bullock and Gregory 1991 ).
Still higher values are feasible, if the use of the sites requires drainage and high
load-bearing capacity such as playgrounds and footpaths.
Craul ( 1992 ) mentioned water infiltration rates of 6.6 cm h − 1 (sidewalk areas),
19.6 cm h − 1 (baseball fields), 0.9 cm h − 1 (areas with small slabs), while unsealed
sites had values of 179.9 cm h − 1 (abandoned pineapple field) and 61.7 cm h − 1
(golf course). In contrast, deposits of technogenic materials like construction rubble
or slag can have a very high saturated hydraulic conductivity, explained by their
typical skeleton structure, leading to increased pore capacity between and within
the material (e.g., pores in brick and slag) (Meuser and Blume 2004 ).