1. Lecture 18
Water quality

2. Water Resources: U.S. Withdrawal

3. Pollution Source terminology
Point source = pollution comes from single, fixed, often large identifiable sources
smoke stacks
discharge drains
tanker spills
Non-point source = pollution comes from dispersed sources
agricultural runoff
street runoff

4. Types of Water Pollution
Sediment
logging, roadbuilding, erosion
Oxygen-demanding wastes
human waste, storm sewers, runoff from agriculture, grazing and logging, many others
Nutrient enrichment = eutrophication
N, P from fertilizers, detergents
leads to increased growth in aquatic systems, ultimately more non-living organic matter

5. BOD
As micro-organisms decompose (through respiration) organic matter, they use up all the available oxygen.
Biological Oxygen Demand (BOD) Amount of oxygen required to decay a certain amount of organic matter.
If too much organic matter is added, the available oxygen supplies will be used up.

7. Eutrophication
Eutrophic – well-fed, high nutrient levels present in a lake or river
Oligotrophic – poorly-fed, low nutrient levels
Water bodies can be naturally eutrophic or oligotrophic, but can also be human-caused

8. Types of Water Pollution (con’t)
Disease-causing organisms
from untreated sewage, runoff from feed lots
Toxic chemicals
pesticides, fertilizers, industrial chemicals
Heavy metals
lead, mercury
Acids (to discuss later)
Elevated temperatures = Thermal Pollution
water is used for cooling purposes, then heated water is returned to its original source
any increase in temperature, even a few degrees, may significantly alter some aquatic ecosystems.

9. Groundwater Pollution
Agricultural products
Underground storage tanks
Landfills
Septic tanks
Surface
impoundments

10. Oil Spills
Exxon Valdez released 42 million liters of oil in Prince William Sound, contaminating 1500 km of Alaska coastline in 1989
Deepwater Horizon oil spill in 2010 released 800 million liters (210 million gallons) in Gulf of Mexico
Was the cleanup effective?
Most marine oil pollution comes from non-point sources:
runoff from streets
improper disposal of used oil
discharge of oil-contaminated ballast water from tankers

11. Water Quality ● Contamination of the water supply ● lead pollution
● radioactive wastes
● microorganisms in water
● other chemical contaminants

12. Water Quality: Human Contamination

14. ● Reversing contamination ● easier if recharge rate is fast
Water Quality
● Reversing contamination
● easier if recharge rate is fast
● usually costly and very slow
● decontamination after pumping
● in-ground water treatments