Environmental Engineering Reference
In-Depth Information
Pathogens:
Types of microorganisms that can cause disease.
Perched groundwater:
Unconfined groundwater separated from an under-
lying main body of groundwater by an unsaturated zone.
Percolation:
The movement, under hydrostatic pressure, of water through
interstices of a rock or soil (except the movement through large
openings such as caves).
Perennial stream:
A stream that normally has water in its channel at all
times.
Periphyton:
Microorganisms that coat rocks, plants, and other surfaces on
lake bottoms.
Permeability:
The capacity of a rock for transmitting a fluid; a measure of
the relative ease with which a porous medium can transmit a liquid.
pH:
A measure of the acidity (less than 7) or alkalinity (greater than 7) of a
solution; a pH of 7 is considered neutral.
Phosphorus:
A nutrient essential for growth that can play a key role in stim-
ulating aquatic growth in lakes and streams.
Photosynthesis:
The synthesis of compounds with the aid of light.
Physical treatment:
Any water treatment process that does not produce a
new substance (e.g., screening, adsorption, aeration, sedimentation,
filtration).
Point source:
A discrete source of water pollutants.
Polar covalent bond:
Occurs when the shared pair of electrons between two
atoms are not equally held; thus, one of the atoms becomes slightly
positively charged and the other atom becomes slightly negatively
charged.
Polar covalent molecule:
Molecule containing one or more polar covalent
bonds; exhibits partial positive and negative poles, causing them to
behave like tiny magnets. Water is the most common polar covalent
substance.
Pollutant:
Any substance introduced into the environment that adversely
affects the usefulness of the resource.
Pollution:
The presence of matter or energy whose nature, location, or quan-
tity produces undesired environmental effects. Under the Clean
Water Act, for example, the term is defined as a manmade or human-
induced alteration of the physical, biological, or radiological integ-
rity of water.
Polychlorinated biphenyls (PCBs):
A mixture of chlorinated derivatives
of biphenyl, marketed under the trade name Aroclor, with a num-
ber designating the chlorine content (e.g., Aroclor 1260). PCBs were
used in transformers and capacitors for insulating purposes and in
gas pipeline systems as a lubricant. Further sales or new use were
banned by law in 1979.
Polycyclic aromatic hydrocarbons (PAHs):
A class of organic compounds
with a fused-ring aromatic structure. PAHs result from incomplete
combustion of organic carbon (including wood), municipal solid
