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Water Pollution
Chapter 11 in textbook (Keller, 2000)
For this section, and all sections in this course, look up and study
all concepts and terms in various resources:
• other textbooks
• library books
• journal articles
• websites (in addition to the links in this presentation)
Diagrams in this presentation are from Keller (2000) and various other
sources, including the online version of this course.
S. Hughes, 2003
Water Pollution
Water pollution = Water contains an excess of a biological,
chemical, or physical compound that makes it harmful to
living organisms.
How much is excess?
It is any concentration level above that which is harmful. It is
a function of:
• size of the reservoir
• residence time within that system
• toxicity of the contaminant
• type of living organism harmed by pollutant
What may be highly diluted in a large reservoir may be
harmful or lethal in a small pond.
Pollution occurs in surface and subsurface water.
Subsurface contamination is more difficult to detect and
much more difficult to clean up than surface contamination.
Water Pollution
Common sources of groundwater pollution or contamination
-------------------------------------------------------------------------------------• Leaks from storage tanks and pipes
• Leaks from waste disposal sites such as landfills
• Seepage from septic systems and cesspools
• Accidental spills and seepage (e.g., trucks and trains)
• Seepage from agricultural activities such as feedlots
• Intrusion of salt water into coastal aquifers
• Leaching and seepage from mine spoil piles and tailings
• Seepage from spray irrigation
• Improper operation of injection wells
• Seepage of acid water from mines
• Seepage of irrigation return flow
• Infiltration of urban, industrial, and agricultural runoff
-------------------------------------------------------------------------------------(from Keller, 2000, Table 11.1)
Chloride is a good example of a pollutant that has many sources.
S. Hughes, 2003
Nutrients
Nutrients, such as nitrogen (N) and phosphorus (P), are
essential for plant growth. Plants lacking these elements lose
their color or are stunted. The concentrations of N and P are
related to land use. Agricultural areas contain the highest
concentrations, whereas forested regions have the lowest.
Agricultural land is often depleted in nitrogen and
phosphorus. Therefore, fertilizers containing such elements
are added to the soil for growing crops. Excess N and P
eventually filters into river systems.
Nutrients are also added to groundwater from feedlots, such
as these in the western U.S.
Nutrients
Relation
between land
use and average
N and P
concentrations in
streams (mg/L);
from Council on
Environmental
Quality, 1978.
(from Keller, 2000, Figure 11.3)
S. Hughes, 2003
Nutrients
Detergents are also pollutants. Phosphates were formerly
major constituents in detergents, so water pollution ocurred as
a by-product of phosphate-based detergents. Now, there is
restricted use of phosphates in the USA and Canada, except
for hospitals and institutions. Therefore, phosphate-based
detergents still contribute to water pollution.
Wastewater treatment plants also contribute to water
pollution. Although treatment reduces organic pollutants and
pathogens, nitrogen and phosphorus are discharged into
adjacent streams, lakes, or the ocean.
S. Hughes, 2003
Nutrients
High concentrations of N and P result in accelerated growth
of plant life, particularly algae. This process, known as cultural
eutrophication, causes thick mats of algae (algal bloom) to
grow on freshwater ponds and lakes. Eutrophication may kill
fish and aquatic animals.
Red Tide: A small number of algae
species produce potent
neurotoxins that can be
transferred through the food chain.
Eutrophication of red-pigmented
marine algae (dinoflagellates)
results in "red tide." Harvesting
shellfish (clams, oysters, scallops)
is prohibited during red tides due to
toxic effects from ingested algae,
S. Hughes, 2003
Nutrients
Ocean beaches lined with thick
layers of rotting seaweed (which is
marine algae) also indicate cultural
eutrophication in near-shore
environments. In tropical areas,
excess algae can cover coral beds,
damaging or killing it.
Sediment
Eroded sediment (either natural or man-induced) is probably
our greatest pollutant. It reduces water quality. It can choke
streams and fill ponds, lakes, and reservoirs. Sediment in a
useful setting is known as soil, which of course is a natural
resource.
S. Hughes, 2003
Oxygen-Demanding Waste
Bacteria are present everywhere. Some bacteria (including
stream types) are decomposers, consuming dead organic
material, a process that requires oxygen.
High concentrations of dead organic matter (by natural
processes, agriculture, or combined sewage-storm water runoff)
cause bacteria to multiply rapidly, reducing oxygen levels.
Aquatic organisms that require oxygen suffer and may die as a
result. Recovery time depends on the available oxygen supply
and the amount of pollution that has occurred.
Biochemical Oxygen Demand (BOD) = The amount of oxygen
used for bacterial decomposition. BOD is frequently used to
determine water quality.
High BOD = low O2 concentration and high decomposition
activity.
S. Hughes, 2003
Oxygen-Demanding Waste
BOD is measured as milligrams per liter of oxygen (mg/LO2)
consumed over a 5-day period at 20° C.
Relation between dissolved O2 and BOD in a stream following
the input of raw sewage.
(from Keller, 2000, Figure 11.2)
S. Hughes, 2003
Pathogenic Organisms
Cholera, typhoid fever, hepatitis A, and
dysentery are waterborne pathogenic
diseases. Such microorganisms can exist in
fecal waste. Certain strains of E. Coli are
associated with these diseases.
E. coli bacteria
E. Coli is one category of fecal coliform bacteria that live in the
lower intestines of all warm-blooded animals, including humans.
Fecal coliform bacteria, including many strains of E. Coli, are
harmless to humans. However, fecal coliform in streams or
other water supplies indicates contamination from fecal waste
and potential health risks for individuals exposed to this water.
Fecal coliform is measured using unfiltered water samples.
After the samples are incubated, the growth rate is determined.
The threshold concentration for declaring water to be
contaminated with fecal coliform is 200 cells per 100 mL water.
S. Hughes, 2003
Oil spills cause havoc in the environment. The worst spills
have resulted from oil-tanker accidents at sea. The Exxon
Valdez (in 1989) is an example of a crude oil spill into a
pristine marine environment. This environmental disaster had
a major impact on wildlife in the area.
Thermal pollution occurs when industrial plants emit
artificially heated water into natural water environments. The
effects may be positive or negative.
Heated water holds less oxygen than cooler water and may
cause changes in growth or respiration rates and may change
developmental rates of existing organisms. Some may become
more vulnerable to toxic pollutants in the water. Diseases and
parasites may become more effective at higher temperatures.
Some species that are intolerant to warm conditions may
actually disappear. On the other hand, warmer water may result
in better survival conditions for existing fish and plant life.
Toxic materials
Industry, mining activities, and agriculture are responsible for
releasing toxic materials into our environment. Relatively high
concentrations of such materials, present in some soil, water
and plants, have been associated with biological problems in
humans and animals. Serious pollution problems occur when
toxic materials are released into the environment. There are
two major types of toxic materials:
• Heavy metals = Industrial metals, such as lead (Pb), mercury
(Hg), cadmium (Cd), chromium (Cr), zinc (Zn), and nickel (Ni).
Even iron (Fe as soluble FeO or insoluble Fe2O3) can be
detrimental to water quality.
• Hazardous chemicals = Synthetic organic and inorganic
compounds that are toxic to humans and other living things.
Heavy metals and hazardous chemicals are also found in areas
of soil pollution, which is usually linked to water pollution.
S. Hughes, 2003
Mine Waste Pollution
Base metals such as zinc, lead, copper, and molybdenum,
are mined as sulfides. Most of these mines have abundant
iron sulfide (pyrite, FeS2) which is typically left behind in favor
of sulfides rich in other metals. Abandoned, old, or even
working sulfide mines often have seepage of water through
the mine and through spoils and tailings that oxidizes sulfide
to Fe2O3 and H2SO4 (sulfuric acid). This effect also occurs in
coal mines, where coal contains significant amounts of sulfide.
Sulfuric acid infiltrates soil and flows into streams and the
groundwater system. Acidic solutions are detrimental to
wildlife and often carry high concentrations of heavy metals
associated with the sulfide deposits. Water pollution can be
remediated only when the acids are neutralized and the mine
is reclaimed to eliminate infiltration of water to sulfides.
Review pH (website) and pH (Chemistry notes) to
understand more about acids and bases in water. S. Hughes, 2003
Common Chemicals Found at Superfund Sites
U. S. Environmental Protection Agency (EPA) designated
Superfund sites.
 Acetone
 Lead
 Aldrin/Dieldrin
 Mercury
 Arsenic
 Methylene Chloride
 Barium
 Naphthalene
 Benzene
 Nickel
 2-Butanone
 Pentachlorophenol
 Cadmium
 Polychlorinated Biphenyls (PCBs)
 Carbon Tetrachloride  Polycyclic Aromatic Hydrocarbons
 Chlordane
(PAHs)
 Chloroform
 Tetrachloroethylene
 Chromium
 Toluene
 Cyanide
 Trichloroethylene
 DDT, DDE, DDD
 Vinyl Chloride
 1,1-Dichloroethene
 Xylene
 1,2-Dichloroethane
 Zinc
S. Hughes, 2003
National Primary Drinking Water Standards: Examples
Contaminant
Max. Level (mg/L)
Inorganic Chemicals
Arsenic
0.05
Cadmium
0.01
Lead
0.015
Mercury
0.002
Selenium
0.01
Asbestos
7 MFL*
Fluoride
4
Organic Chemicals
Endrin (pesticide)
Lindane (pesticide)
Methoxychlor (pest.)
2,4D (herbicide)
Silvex (herbicide)
0.0002
0.004
0.1
0.07
0.05
Problems
Highly toxic
Kidney
Highly toxic
Kidney, nervous system
Nervous system
Benign tumors
Skeletal damage
Nervous system, kidney
Nervous system, kidney
Nerv. Sys., kidney, liver
Liver, kidney, Nerv. Sys.
Nerv. Sys., liver, kidney
S. Hughes, 2003
National Primary Drinking Water Standards:
More Examples
Contaminant
Max. Level (mg/L)
Volatile Organic Chemicals
Benzene
0.005
Carbon Tetrachloride 0.005
Trichloroethylene
0.005
Vinyl Chloride
0.002
Microbial Organisms
Fecal coliform bact.
1 cell/100 ml
Problems
Cancer
Possible cancer
Probably cancer
Cancer risk
Indicator
disease-causing
organisms
(from Keller, 2000, Table 11.3)
* MFL = million fibers per liter with fiber length > 10 microns
NOTE: For additional information see the U.S.G.S National
Analysis of Trace Elements and Water Quality programs.
S. Hughes, 2003
Water Quality in the U.S.
Freshwater organisms
are used to help determine
water quality.
The concentration of
selected toxic metals (a)
and toxic organic
chemicals (b) in fish
tissue, measured at
monitoring stations by U.S.
Fish and Wildlife Service
between 1970 and 1986.
(from Keller, 2000, Figure 11.9)
S. Hughes, 2003
Surface water pollution
Pollution comes from point sources and non-point sources.
• Point sources = industrial sites and outflows for sewerstormwater runoff systems.
• Non-point sources = pollution runoff. Land uses (urban
and rural) and surface runoff factors (ex. geology, climate, and
topography) greatly affect pollution runoff. Everyday human
activities are also contributors. Driving automobiles and
trucks add to road grime. Fertilizing the lawn or garden,
washing the car, or even walking the dog are contributors as
well.
• Urban contributors = factories, parking lots, storage sites.
• Rural contributors = farming, forestry, mining.
• Rain causes pollutants to runoff and infiltrate over large
areas.
S. Hughes, 2003
Treating surface water pollution
Many rivers were once treated as dumping sites. Chemicals,
garbage, oil and gas discharge, and raw sewage were added to
rivers on a daily basis. Pristine rivers virtually became open
sewers. Conditions were so deplorable, some rivers were
considered dead, devoid of life. Humans now understand that it
is important to eliminate the source of pollution.
Treatment of polluted surface water takes many forms, for
example:
• Pass new laws (and enforce them!)
• Develop better technology to reduce pollution levels.
• Remove developments along rivers and lakes.
• Reconstruct natural habitats in riparian areas and along
shorelines.
• Build treatment plants to process water used in
agriculture and industry before release to the environment.
Groundwater pollution
Groundwater pollution results from harmful chemicals
infiltrating into groundwater systems. Groundwater pollution
is an ongoing problem in many urban and industrial areas
especially, but it can occur anywhere. A pollution plume
occurs when toxic wastes are released into the environment.
Contaminant migration will follow the flow paths of
groundwater, typically perpendicular to water table contours,
and move in the direction of decreasing concentration.
NOTE: Pollution plumes in groundwater are much like plumes
of smoke emitted from smokestacks. Although the fluid media
are different (atmosphere vs. aquifer, and smoke goes up, not
down), groundwater pollution plumes behave in much the
same way as smoke plumes. Both are subject to variations in
flow rate and dispersion.
S. Hughes, 2003
Groundwater Pollution Plumes
S. Hughes, 2000
Specific concentration data (measured by sampling
groundwater from wells and then analyzing it) is used to
construct a contaminant isoconcentration map. Like a flow
net, these maps join lines, or contours, of equal concentration
called isopleths. An idealized isoconcentration map of a
pollutant plume depicts the pattern of relative concentration
levels at increasing distance from a continuous source.
SEE PLUME NOTES (PDF file)
Idealized isoconcentration map
1
0.9
0.5
0.1
0.01
Point source (1 = max. concentration)
Other plume shapes
Salt Water Intrusion
Natural Conditions
Pumping Conditions
A groundwater
system near the coast
may be contaminated
with salt water when
freshwater is pumped
from wells. Intense
pumping will cause a
cone of ascension to
become drawn
upwards, delivering
salt water to the well.
(from Keller, 2000, Figure
11.7)
S. Hughes, 2003
Groundwater Treatment
Groundwater pollution cannot be avoided; therefore, we must
be prepared to help nature clean up our problems. Before actual
clean up procedures begin, it is vital that the geological and
hydrological characteristics are understood. It is also essential
to know which contaminants are being dealt with, as well as
their transport processes.
Insoluble contaminants form a separate, non-aqueous phase.
• Compounds with a specific gravity lower than water float
on water (example = gasoline), and are called light nonaqueous phase liquids (LNAPL).
• Compounds with a specific gravity higher than water sink
below the water (example = trichoroethylene/TCE), and are
called dense non-aqueous phase liquids (DNAPL).
Soluble contaminants (example = salts) flow with the water.
S. Hughes, 2003
Groundwater Treatment
Four methods are used for treating contaminated
groundwater and vadose zone water:
• Extraction Wells -- Contaminated water is pumped out
of the aquifer and then treated by aeration (oxidation),
filtering, air stripping (volatilization in an air column), or
biological processes.
• Vapor Extraction -- The contaminant is removed while it
is in a vapor phase, usually in the vadose zone.
• Bioremediation -- Microbes degrade the contaminants.
The microbes either exist naturally (nutrients and oxygen are
injected), or they have to be prepared in a bioreactor and
added to the vadose zone or saturated zone.
• Permeable Treatment Beds -- Filters are used to treat
contaminants by physical, chemical, or biological processes
while water flows through a treatment bed.
S. Hughes, 2003
Groundwater Treatment
Vapor phase
pollution exists in
most urban areas.
Older service stations
commonly have
cracked and leaky
underground gasoline
storage tanks.
Seepage filtrates
down through the
vadose zone onto the
water table.
Leaking underground storage tanks (LUST) add gasoline to
groundwater and gasoline vapors to the vadose zone where
they can infiltrate underground structures.
S. Hughes, 2003
Groundwater Treatment
Dewatering wells
and vapor
extraction wells
are used to remove
the offending gas
contaminant.
Pollution from leaking underground storage tanks can be
remediated, but this type of remediation is expensive and can
be difficult.
S. Hughes, 2003
Wastewater treatment
The USA has laws stating that wastewater (industrial,
municipal, and sewage) must be treated before releasing it into
the environment. Septic tank disposal systems are common in
rural areas. Urban communities generally have municipal
systems collecting wastewater for treatment in a central location.
Diagram of a
septic-tank
sewage disposal
system for a
single house.
(from Keller, 2000,
Figure 11.10)
S. Hughes, 2003
Septic tank systems
Almost 30% of the U.S. population uses septic tank systems
for sewage disposal. Unfortunately, not all locations are
suitable for this method. Local geology is the key.
Percolation tests (commonly called a perc test) are used to
determine septic tank suitability. Water movement through the
soil (absorption field) is the determining factor. Good drainage
purifies the water as it percolates down through the soil into the
groundwater system. Anything else results in polluted water!
When a septic system fails, waste may rise to the surface
above the drainage field. The problem is easily visible, but
processes beneath the ground are difficult to see. If extensive
leaching of waste occurs, then groundwater resources may
become polluted, especially around failed septic systems that
serve small commercial and industrial activities (which
dispose more nutrients, heavy metals, and organic chemicals).
Wastewater treatment plants
Obviously, the purpose of a wastewater treatment plant is to
remove contaminants. This is typically a 2- or 3-step process.
Primary treatment -- removes mucky sediment or sludge
(30-40% of the wastewater pollutants) using screens, a grit
chamber and sedimentation tank, from which the sludge goes
to a digester.
Secondary treatment -- Wastewater moves into the
aeration tank where air is pumped in and aerobic bacteria
break down organic material. The water goes to a final
sedimentation tank which allows more sludge to settle out.
• Digester uses anaerobic bacteria to digest organic
compounds left in the sedimentation tanks and produces
methane in the process. The methane can be used to run
equipment or to cool/heat the processing plant.
• Disinfecting the water, usually with chlorine, is the final
step in the secondary process.
S. Hughes, 2003
Wastewater treatment plants
(from Keller, 2000, Figure 11.11)
NOTE: If heavy metals, nutrients, or certain chemicals are present,
advanced treatment is needed. Chemicals, carbon filters, or sand
filters are used for advanced treatment. Wastewater that has undergone
advanced treatment is called reclaimed water, which can be used for
watering parks, golf courses, farm fields, or wildlife habitats.
S. Hughes, 2003
Wastewater Renovation
After wastewater has been processed, it is perhaps 95%
clean. The sludge has been removed. Many communities now
consider wastewater and sludge to be recovered resources,
and they recycle it.
The process of recycling liquid waste is called the wastewater
renovation and conservation cycle. Treated wastewater is
(1) returned to crops by sprinkler systems; (2) water is
renovated by slow percolation downward to become naturally
purified and recharge the groundwater resource; and (3) water
is pumped out of the ground for reuse by industrial, municipal,
institutional, or agricultural purposes.
Sludge is used to improve soil texture and soil quality. It is
used in mining reclamation projects and other landfill
processes.
S. Hughes, 2003
Resource-Recovery Wastewater Treatment
Idealized system of recovering resources during wastewater
treatment: methane from anaerobic beds, ornamental
flowers, and more. (from Keller, 2000, Figure 11.13)
S. Hughes, 2003
Water Pollution Questions to Think About:
• What are the three most common forms of water pollution in
your local community?
• How severe are these water pollution problems?
• What potential and actual pollution-related harms exist?
• What is being done to correct these problems?
• What five ways could you help?
• Is cultural eutrophication a problem near your home?
• Can you identify point and non-point pollution sources?
• Visit a wastewater treatment plant sometime; are biological
processes being used there? What are the advantages and
disadvantages of using biological systems (such as plants) in
the treatment process?
• How safe is your water supply? If you drink bottled water,
how safe is it? What is the basis for your answer?
S. Hughes, 2003
Water Pollution Exercise
The Magic Gulch Water and Waste Problem
This exercise involves water table contours, flow lines and
a simple flow net. Calculations are made based on
Darcy’s Law and all work must be shown. Use separate
sheets if necessary. Answers to questions require general
knowledge of pollution and groundwater systems. Use all
information and knowledge that will help provide a
meaningful assessment of the problem.
Help will be provided if necessary.
S. Hughes, 2003
Terms to Understand
acid mine drainage
algae
bacteria
biochemical oxygen demand
bioremediation
carbon filter
contamination
cultural eutrophication
detergent
dinoflagellate
extraction well
fecal coliform bacteria
fertilizer
groundwater
non-point source
nutrient
organic pollutant
pathogen
point source
pollution
primary treatment
reclaimed water
reservoir
residence time
salt-water intrusion
sediment
secondary treatment
septic tank
subsurface
thermal pollution
treatment bed
vadose zone
vapor extraction
wastewater
wastewater treatment
water quality
S. Hughes, 2003