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

chemical, or physical excess

of a

biological,

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.

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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

(from Keller, 2000, Figure 11.3) Relation between land use and average N and P concentrations in streams (mg/L); from

Council on Environmental Quality, 1978

.

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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.

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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

.

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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 O 2 activity. concentration and high decomposition S. Hughes, 2003

Oxygen-Demanding Waste

BOD is measured

as milligrams per liter of oxygen (mg/L O2 ) consumed over a 5-day period at 20 ° C.

Relation between dissolved O 2 the input of raw sewage.

(from Keller, 2000, Figure 11.2) and BOD in a stream following 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

releasing

toxic materials

are responsible for 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 Fe 2 O 3

)

detrimental to water quality.

can be •

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.

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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, FeS 2 ) 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 Fe 2 O 3 and H 2 SO 4 (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)

understand more about acids and bases in water.

to S. Hughes, 2003

Common Chemicals Found at Superfund Sites

U. S. Environmental Protection Agency (EPA) designated Superfund sites.

               Acetone Aldrin/Dieldrin Arsenic Barium Benzene 2-Butanone Cadmium Carbon Tetrachloride Chlordane Chloroform Chromium Cyanide DDT, DDE, DDD 1,1-Dichloroethene 1,2-Dichloroethane               Lead Mercury Methylene Chloride Naphthalene Nickel Pentachlorophenol Polychlorinated Biphenyls (PCBs) Polycyclic Aromatic Hydrocarbons (PAHs) Tetrachloroethylene Toluene Trichloroethylene Vinyl Chloride Xylene Zinc S. Hughes, 2003

National Primary Drinking Water Standards: Examples

Contaminant Max. Level (mg/L) Problems Inorganic Chemicals

Arsenic 0.05

Highly toxic Cadmium Lead Mercury Selenium Asbestos Fluoride 0.01

0.015

0.002

0.01

7 MFL* 4 Kidney Highly toxic Kidney, nervous system Nervous system Benign tumors Skeletal damage

Organic Chemicals

Endrin (pesticide) Lindane (pesticide) Methoxychlor (pest.) 2,4D (herbicide) Silvex (herbicide) 0.0002

0.004

0.1

0.07

0.05

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 Carbon Tetrachloride 0.005

0.005

Trichloroethylene Vinyl Chloride 0.005

0.002

Problems

Cancer Possible cancer Probably cancer Cancer risk

Microbial Organisms

Fecal coliform bact.

1 cell/100 ml 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 sewer stormwater 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

areas.

causes pollutants to runoff and infiltrate over large 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

shorelines.

in riparian areas and along •

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

S. Hughes, 2000

Groundwater Pollution Plumes

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 non aqueous phase liquids

(LNAPL)

.

• Compounds with a specific gravity

higher below the water

than water

sink

(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 filtering

,

air stripping

(oxidation), (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

added to the vadose zone or saturated zone.

and •

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

aeration tank

-- Wastewater moves into the 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 point source 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 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