water pollution

Chapter 12

WATER POLLUTION

12_T01

Groundwater contamination

Sources of contamination

Common Pollutants (1)

•Pollutant: Any substance that, in excess, is known to be harmful to desirable living organisms

•Oxygen-demanding waste (common organic waste)

•Pathogenic waste (pathogenic microbes)

•Nutrients•Petroleum (oil)•Toxic waste (chemicals, heavy metals, radioactive

waste)•Sediment•Thermal plumes

Oxygen-demanding waste

•Dead organic matter decomposed and consumed by aerobic bacteria, which need oxygen to live

•BOD (Biochemical Oxygen Demand) is the amount of oxygen used for bacterial decomposition

•High BOD, associated with a high level of decaying organic matter in water, reduces O for other healthy organisms

•Sources of oxygen-demanding waste: Natural processes, agricultural applications (33%), urban sewage, and runoff

12_01 Several thousand factory-style hog farms in NC

12_02 Ruptured hog waste lagoon in Pitt County NC as a result of Hurricane Flyod

Pathogenic microbes (need microscope to see them)

•Fecal coliform bacteria•Harmful risks (diseases and death ) of E. coli

which leads to disease and death in humans•Billions exposed to waterborne diseases,

especially in poor countries•Outbreaks do occur in developed countries, e.g.,

400,000 cases in Milwaukee WI, in 1993 of cryptosporidiosis (parisitic micro-organism)

•Epidemic risks of waterborne diseases during natural disasters (earthquake, flood, hurricane)

Nutrients Two important nutrients: N, P, from fertilizers,

detergent, and sewage-treatment products

Major problems caused by high concentrations of nutrients: Cultural eutrophication (well-fed by nutrient) - which leads to growth of algae bloom, triggering biological oxygen demand (BOD) problem

The algae covering the surface of water, block sunlight to plant below and consuming oxygen, killing the underlying plants.

Algae kill coral in tropical areas

Major sources for nutrients: Fertilizer, feedlots, and discharge from wastewater treatment plant

12_04a Algae contaminated beaches in Hawaii (brown line along the beach!). They rot and stench! Ocean front condominium on the island Maui.

12_04b Algae pileup on the beach, Maui

12_04c Condos have small wastewater-treatment plant providing primary and secondary treatment, which do not remove P and N that encourage growth of marine algae

12_05 Cultural eutrophication - Dead zone in Gulf of Mexico, Summer (July) 2001 with bottom water < 2 mg/l dissolved oxygen, killing shell fish and crabs where blooms of algae occur. This is caused by the Mississippi bringing agricultural N from fertilizer.

Oil

Major problems: Polluted water, ecosystem damage, interrupted socioeconomic conditions of a community

Major sources: Oil spills from tankers and pipelines, on- or offshore oil production, war (e.g., Persian Gulf War; 1989 Exxon Valdez)

Toxic Waste

•Hazardous chemicals, synthetic organic or inorganic compounds toxic to living things

•Serious pollution problems occur when these are introduced accidentally into surface/subsurface waters

– e.g., Love Canal, MTBE (methyl tertbutal ether; an oxygen additive to gasoline; leaked from gas stations to GW & SW)

– Groundwater with MTBE smells like fresh paint and is nauseating to some people. It may be carcinogenic!

12_07

Diagram showing the movement of MTBE, a gasoline additive, and other volatile hydrologic compounds in the hydrologic cycle of an urban environment

Toxic Waste … Heavy Metals: Pb, Hg, Zn, Cd – often deposited at the

bottom of stream channels If deposited in floodplains will be incorporated into

plants, crops and animals Examples:

Mercury contamination of aquatic ecosystems; sourced: from volcanoes and erosion of natural mercury depositsBurning coal, incinerating waste, processing metals

Lead to e.g., lead or mercury contamination

Radioactive materials

Toxic waste

12_08 Input and changes of mercury in the aquatic ecosystem

Yucca Mountain Nuclear Repository

Sediment pollution

Sand and smaller particles Polluted streams, lakes, reservoirs, even ocean

water

Major sources: Soil erosion, dust storms, floods, and mudflows

Greatest pollutant by volume

12_11 Examples of water pollution causing health hazards. (a) Ditch carries sewage and toxic waste to the Rio Grande in Mexico. (b) Sediment, overflowed from nearby stream, being removed by heavy equipment after the 1995 flood in Goleta CA deposited it in a car dealership.

Thermal Pollution

•Artificial heating of waters, primarily by hot-water emission from industrial operations and power plants.

– Major sources: Hot-water discharge from industrial operations, power plants, abnormal ocean currents

•Heated water causes several problems: Heated water contains less O than cold water leads to adverse changes to the habitats of

organisms favors growth rate of undesirable organisms

Surface Water Pollution and Treatment (1)

•Point sources of pollution Point sources are discrete, confined, and more

readily identifiable

Common sources: Landfills, discharge from wastewater treatment plants, discharge from

industries, power plants, storm water runoff, etc.

Identify sources, on-site treatment and mitigation, prevention

Contamination by septic tanks

Reversal of flow by pumping


•Nonpoint sources of pollution Nonpoint sources are diffused, intermittent,

and hard to specifically identify

Causes of non-point pollutions often regional, cumulative and compound


•Non-point sources of pollution (continued)

Multiple factors: Land-use, climatic, hydrologic, topographic, geologic

Pollution reduction needs comprehensive and regional studies

Reservoir contaminationSan Juaquin Valley CA

Groundwater Pollution and Treatment (1)

•Why care about ground water pollution? Most abundant freshwater source Growing dependency on GW ~ 50% of people in U.S. depend on GW for drinking water Triggers other environmental problems, subsidence,

saltwater intrusion, etc.


•GW pollution hazard impact depends on: Amount of contaminant discharged Chemical concentration or toxicity Degree and duration of exposure of people or

other organisms to the pollution


•GW pollution vs. SW pollution Residence time difference Environmental conditions: Inflow, flow rate,

Dissolved oxygen, sunlight Harder to track pollution sources More difficult and expensive to clean up May pose long-term risks


•Saltwater intrusion More than half of the world’s population lives in or

near the coastal zones GW pollution from saltwater intrusion is not a

local isolated problem Causes major water supply problems in NY, FL, CA Case History: Long Island


•Saltwater intrusion mechanism Water table is inclined oceanward Wedge of saltwater is inclined land ward Overpumping of GW Severe drawdown of GW causes saltwater

ascension

11_01ab

12_13ab

Saltwater Intrusion

(a) Natural environment

(b) A well with both a cone of depression and a cone of ascension

If pumping is intensive, the cone of ascension may be drawn upward delivering saltwater to the well

Salt water Intrusion in Florida

Salt water intrusion by excessive pumping

GW Treatment (1)

•Pretreatment studies Identify contaminants and their characteristics

of transport behavior Identify the characteristics of aquifer geology

(factors controlling GW flow—physical dimensions, structure)

Determine the hydrologic characteristics of polluted aquifer(s)—flow direction, flow

rates, discharge and recharge conditions Select possible treatment strategies and methods

Contamination

Movement of a contamination

Comtamination movement

GW Treatment (2)

Decontamination by pumping

Water Quality Standards

•MCLs—Maximum Contaminant Levels

•Permissible limits for 83 contaminants

•MCLGs—Maximum Contaminant Level Goals

•The maximum level at which no adverse health effects from a lifelong exposure

•SMCLs—Nonenforceable limits for contaminants that affects aesthetic qualities in drinking water

Waste Water Treatment

•Law: Used waste water must be treated

•Break the potential vicious cycle of waste water entering the general water cycle

•Tier treatment and reuse system Septic system—rural residential areas Water treatment plant for towns and urban cities Innovated ways for recycling and reclaiming

waste water New technologies for innovative waste water

treatment

12_12

River basin studied to monitor and describe water quality. Delaware River Basin with physiographic provinces

12_14ab

Septic tank sewage disposal system for a home

(a) plan (map) view;

(b) cross section

12_15 Activate sludge sewage treatment with or without advanced treatment

12_16

Wastewater renovation and conservation cycle

12_B Boston harbor and Massachusetts Bay showing old sewage outfalls (red squares) and new outfall (green rectangle) 15 km offshore.

Applied and Critical Thinking Topics

•What can individual citizens do to reduce GW pollutants?

•Does surface water contamination automatically trigger GW pollution of a given location?

•What are the major threats to your community water supplies?

•What current water laws and legislation are you familiar with? Are there any problems with them?

Critical Thinking Answers:

• 1. A student addressing this assignment will need to examine land uses in the area and identify the pollution sources. Ideas regarding reduction of pollution from those sources should address environmental impacts of the pollution, the costs and benefits involved with reduction, and the willingness of the public, community leaders, and business owners to address pollution reduction.

• 2. An answer to this question will depend largely on local conditions and wastewater treatment processes. If there is a geologically and biologically suitable area for wastewater renovation and recovery, a likely use for renovated wastewater, money available for such a project, and some limitation on water resources that would make water recovery beneficial, the concept might be useful. Use of biological systems would also depend on the situation and the contaminants of concern

• 3. A student addressing this question will need to consider the sources of their perceptions regarding their drinking water. An informed answer requires knowledge of the water supply source, possible natural and human threats to water quality at that source, the quality of the water delivery system, and other factors.

End of Chapter 12