Environmental Engineering Reference
In-Depth Information
remediation industry in Australia will grow by 27% per annum. This is
well reflected in the current market for contaminated site assessment and
remediation with the industry growing from $300 million per annum in
1999 to >$3 billion per annum in 2012.
Contamination frequently affects more than surface soils. Although the
focus of the CEI was contaminated soils, it is well recognized that once con-
taminants are in soils, they can leach into the groundwater with recharge
waters (i.e., rainfall or surface water) when they come into contact with
contaminated soil. Subsequently, contaminants travel in a more horizontal
direction creating a dispersion plume. Shallow aquifers are usually impor-
tant sources of groundwater. These upper aquifers are also the most suscep-
tible to contamination. Contaminants may enter an upper aquifer in one of
the following ways: (1) artificial recharge or leakage through wells; (2) infil-
tration from precipitation or irrigation return flow through the vadose zone
above the water table; (3) induced recharge from influent streams and lakes
or other surface water bodies; (4) inflow through aquifer boundaries and
leakage from overlying or underlying formations; and (5) leakage or seepage
from impoundments, landfills, or miscellaneous spills.
Groundwater contamination is now well recognized as an integral com-
ponent of contaminated sites and its assessment and remediation can pose
significant technical and financial challenges. Sources of groundwater con-
tamination include
a. Leaching of contaminants from contaminated soils especially due to
inadvertent releases, spills, or leaks of liquid wastes
b. Leaking underground storage tanks
c. Landfills that were not engineered or designed to hold leachates
d. Poorly constructed injection wells
e. Anthropogenic activities that enhance release of geogenic contami-
nants such as arsenic
1.2.1 Groundwater Contamination Fate and Transport
Contaminant interactions with phases in the subsurface may reduce the
rate of their transport; and because most geologic materials have surfaces
that possess a net negative charge, contaminants in cationic form are fre-
quently observed to interact with solid surfaces, at least to some degree.
The fate and transport of contaminants through soil to groundwater is
influenced by many variables such as properties of the contaminant itself,
soil conditions, and climatic factors. Some organic contaminants can
undergo chemical changes or degrade into products that may be more or
less toxic than the original compound. Metallic and metalloid contami-
nants cannot break down, but their characteristics and chemical states
may change.
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