Encyclopedia of Environmental Science and Engineering, Volume I and II

GROUNDWATER RESOURCES 445

the destruction of the ecological system and natural resources

but also present a danger to public health. Pollutants have

been broadly classified into eight categories by the U.S.

Public Health Service.

1. Oxygen-demanding wastes: These include domes-
   tic and industrial wastewaters, leachates from land-
   fill, and any other wastes containing biodegradable
   organic material. These wastes are stabilized by
   microorganisms and will remove dissolved oxygen
   from water.


2. Infective agents: Bacteria, virus, protozoa, and
   other infectious agents may be present in domes-
   tic wastewaters. Those that reach drinking water
   or even recreational waters represent a health
   hazard to humans.


3. Plant nutrients: Mineral substances, particularly
   nitrates and phosphates, stimulate the growth of
   plants. However, nitrates in groundwater poten-
   tially infiltrating through heavily fertilized soil
   can be a public health hazard.


4. Organic chemicals: Chemicals such as insecti-
   cides, pesticides, and detergents are toxic at low
   concentrations and can cause significant changes
   in groundwater quality.


5. Other minerals and chemicals: This group con-
   sists primarily of materials found in industrial
   wastes, including chemical residues, petrochemi-
   cals, salts, acids, etc. New chemical substances are
   being created at the rate of 400 to 500 compounds
   per year. Many of these substances are known to
   be toxic, although very little is known about their

biological action. Almost nothing is known about

the possible long-term effects of these chemical

compounds.

6. Sediments from land erosion: These materials
   have little effect on groundwater quality since
   they would be filtrated out in the first stages of
   percolation.


7. Radioactive substances: Expected increases in
   the use of nuclear reactors for power generation
   indicate that radioactivity may be a serious prob-
   lem in the future. The extremely long half-lives of
   some radioactive materials make the disposal of
   radioactive wastes difficult. Once a radionuclide
   reaches the groundwater it remains a hazard for
   a long time. One rule is that a radionuclide is no
   longer dangerous after nine half-lives.^


8. Heat: Heat from industry and power generation
   is considered a serious pollutant. Its effect on
   groundwater is limited to reducing the value of a
   groundwater source for cooling water.

In addition to the eight categories of pollutants used by

the U.S. Public Health Service, oil can be considered a ninth

category, since oil spills in coastal waters have found their

way into groundwater supplies near the coast.

The quality of water required for industrial-process

usages varies widely with the type of industry and the

type of process used. For example, the recommended total

solids concentration in boiler feed waters varies from 50 to

3,000 mg/l depending on the design of the boiler and the pres-

sure of operation. The quality of water used for agricultural

operations also varies considerably. Range-cattle-use water

Rainwater contains dissolved

organics and minerals, suspended

particles, virus, bacteria

Rainwater

Biological Action

Sedimentation

Filtration Ion

Exchange

Aerobic Zone

Biological Action

Removal of Organics Oxidation of NH 3

Filtration Ion Exchange

Rock Strata

Groundwater

FIGURE 6 Effect of water movement on water quality.

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