Environmental Engineering Reference
In-Depth Information
The extraction processes leave voids behind that may cave in slowly leading to a
long-term overburden subsidence. Subsidence can lead to collapsed buildings and
wetted depressions creating new ponds or lakes. Additionally, subsurface mining,
like hard coal mining, requires sites used for mining waste depositing. In the past,
they were constructed as barren cones or flat-topped heaps. Nowadays, spoil heaps
with natural-like topography and full vegetation are created. Analogously, surface
mining, e.g., applied to lignite coal mining, means a greater extent of Greenfield
consumption combined with changes of the morphology based on excavation and
refilling operations. The terrain becomes completely devastated, creating horrible
scars in the landscape (Genske 2003 ).
2.7 Case Studies
In most developed countries environmental assessments that include soil and
groundwater analyses not infrequently turn up elevated concentrations of heavy met-
als and metalloids or other trace elements, like boron, that exceed the official Soil
Quality Standard for defined ecological and human health impacts and hence cre-
ate concerns about human health and ecological risk. In many cases these concerns
are unwarranted because the contaminants are part of the natural geochemistry and
inert. Risk Assessment would benefit greatly if high level soil science is called upon
to analyse these situations. Unfortunately, there are few soil scientists involved in
this work. A few examples may illustrate this.
2.7.1 The Soil as a Chromatogram - Barium
The expansion of Melbourne's urban land to the west required an environmental
assessment of land that had never been used for anything else than grazing sheep
and cattle. All of the western area is in McBride's “Strongly alkaline, confined envi-
ronments” where basalt-derived soils are dominated by smectite clays and Na, Ca,
and Mg salts accumulate. Most of these heavy clay soil profiles have slightly acidic
top soils, but pH rapidly increases with depth. Calcium carbonate as soft accretions
or hard nodules are ubiquitous at about 0.5-0.6 m depth.
The 2006 soil assessment (Wrigley et al. 2006 ) was carried out by grid sampling
with more than 100 auger holes of a 15 hectare site near Deer Park, an outer suburb,
with samples taken as per official prescription at the soil surface 0-0.1 m, 0.5 m
depth and 1.0 m depth. A number of the 0.5 and 1.0 m samples showed elevated
barium concentrations varying between 320 and 900 mg
kg dw 1 , thus exceeding the
National Environmental Protection Measure (NEPM) for Ecological Impact Level
(EIL) of 300 mg
·
kg dw 1 . The whole process of preparing the site for residential
development came to a sudden halt, while in the meantime the cost of interest on
the borrowed capital continued unabatedly.
Barium is likely to concentrate in intermediate and acid magmatic rocks, linked
with alkali feldspar and biotite, although in this case the barium is derived from
mafic (or “basic”) rocks. Commonly, the concentration range is 400 mg
·
kg dw 1 to
·
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