Stressors and Soil Contamination - Sustainable Practices in Geoenvironmental Engineering - page 34

long periods. The two sets of issues are (1) high temperatures and (2) freezing tempera-
tures, and their impacts include:
• Water and vapor transfer in soils (e.g., evapotranspiration) resulting in changes in
soil properties and behavior (could be adverse or beneicial impact).
• Types and rates of chemical reactions and biological processes resulting in changes
in the nature and energy status of the affected soil—consistent with soil weather-
ing processes (could be adverse or beneicial impact).
• Soil freezing and developed frost heaving pressures, as discussed under the
mechanical group of stressors.
• Freeze-thaw phenomena and development of ice lenses in frost susceptible soils
with water availability and thaw subsidence from disappearing ice lenses (adverse
impact).
2.2.1.4 Chemical
Some of the natural stressors classifying under the grouping of chemical include acid rain,
organic acids obtained from decomposing suricial organic matter, and the natural chemical
constituents in soils. Waste landills, discharge of contaminated wastewater, acidic leachates
from mine heaps, acid rain, etc., are stressors attributable to human activities. Note that we
include acid rain under both natural and human activities inasmuch as emissions into the atmo-
sphere from production facilities are seen to be the principal contributors to the acid nature
of rain and snow. The impact of actions and/or events in the chemical environment in soils
will be felt, over time, in terms of changes in the nature and properties of the soil because of
changes in (a) the nature of the soil fractions themselves, e.g., transformation of montmoril-
lonite to illite or mixed layer clay mineral, (b) interactions between soil particles and between
particles and water and soil-water energy characteristics, (c) biological processes in the soil,
leading to changes in the nature and character of the soil, and (d) chemical reactions and pro-
cesses, e.g., a decreasing pH (as would happen with acid rainfall onto and into the soil) could
dissolve carbonates in the soil, thereby not only destroying carbonate cementation bonds
between particles but also raising the possibility of releasing CO 2 from the affected soils.
2.2.1.5 Geochemical
In respect to soils, the stressors in the geochemical category are leachates or contaminants
from mine heaps, constructed facilities, and excess fertilization in agriculture. The impacts
from these stressors generated in a soil mass are (a) decomposition of soil minerals and
chemical constituents in soils and (b) changes of soil particle surface functional groups.
These decompositions and changes result in alteration of soil structure and chemical con-
stituents in soil mass, thus affecting water, solute, and heat transfer phenomena in soils.
2.2.1.6 Biologically Mediated
The stressors in this category are microorganisms in the soil. The impacts of their interac-
tions with soil constituents and other energy sources are decomposition of organic matter and
alteration or decomposition of clay minerals and chemical constituents of soil. In turn, the out-
come would be changes in nature of the soil—resulting in corresponding changes in not only
hydraulic, mechanical, and thermal phenomena in soils but also the relevant soil properties.