Environmental geology outline -
groundwater quality and contamination
might people want to know about the water they drink and use (water
Science of aqueous geochemistry a critical
Aquifer contribution to groundwater chemistry:
- 3 important factors: rock type, time, water
chemistry (e.g. pH).
- limestone and hard water.
- pH typically 7-8.2
- if > 80 -100 ppm then hard.
- can also be high in SO2
- water softeners typically used: exchange
Na for Ca, Mg ions.
- pH 6.3-7.9.
- Na and K predominant ions, Fe common also.
- sandstones: generally low TDS, high quality.
- time factor: the older the higher the TDS,
old formation waters essentially brines.
Groundwater contamination sources:
Contaminant plume geometry and clean up:
Above is a simple schematic of point source, its associated
contaminant plume and contours on the water table of a simple
unconfined aquifer. This is a basic approach geohydrologists often
use in some form. What direction is the groundwater flowing? Given
the scale, and a ten year time span since the point source was
created, at about what speed are the contaminants moving? How
long before they might reach the surface drainage (stream)? Note
that contours on the plume are sub-perpendicular to those of the
ground water table.
- maps of groundwater surface and contaminant
plume - how compiled?
- observation well samples and contours of
- reaction fronts, sinkers and floaters, and
a 3-D approach.
are some clean up methods?
- cost-benefit analysis and clean-up standards.
The above is a schematic graph showing the relationships between
cost and the level of clean-up. It is a very useful initial framework
for considering the question of what level of clean-up should
be undertaken for a given contaminated site. Perhaps consider
two different perspectives: that of someone living next to the
site, and that of the administrator with a fixed budget who has
the responsibility of cleaning up many more sites than he has
money for. Most important to note that it may be several times
the cost to clean up the last 5% or so of contaminant. More recently,
faced with large costs and limited resources, clean-up fund administrators
are taking a cost-benefit approach. The basic trade off is between
cleaning up a few sites to pristine levels versus cleaning a larger
number of sites to lower levels.
- major groups of contaminants: pathogenic
organisms, inorganic compounds, organic compounds, radioactive
- common organic compounds (solvents, lubricants,
- stability and residence time?
- hydrocarbons: gasoline one of the most common.
- chlorinated organics: powerful solvents and
- PCE: perchloroethylene (used in drying cleaning).
- TCE: trichloroethylene (common grease cutter).
- DCE: dichloroethylene
- all carcinogenic.
- floaters and sinkers (DNAPLs - dense non-aqueous
- vinyl chloride: used in plastic production,
angiosarcoma, mostly a concern to workers.
- up to 1000 new industrial chemicals invented
- radioactive material/nuclides of concern?
- strontium-90, cesium-137, iodine-131, radon-222,
- will cover more in context of nuclear power.
Legal and regulatory framework. This framework is extensive and complex, to the point
that some people make a living just at helping industry stay in
compliance. Below are just a few of the highlights, major pieces
- Water Pollution Control Acts (1956,65,72)
- National Environmental Policy Act (1969):
requires EIS, environmental impact statements
- Comprehensive Environmental Response, Compensation
and Liability Act (1980): also known as Superfund,
National Priority List
- Resource Conservation and Recovery Act (1988):
for better record keeping, permitting and database formation.
- Nebraska Department of Environmental Quality. This is our lead agency for environmental issues
in Nebraska. Each state has an equivalent agency.
Some clean-up case histories
We will return to some of these considerations
when we talk about waste disposal and landfill design in the next
part of the course.
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