444SUBSTANCE: Material with definite chemical composition.
SULFATE: Will readily dissolve in water to form an anion. Sulfate is a substance that occurs
naturally in drinking water. Health concerns regarding sulfate in drinking water have been raised
because of reports that diarrhea may be associated with the ingestion of water containing high
levels of sulfate. Of particular concern are groups within the general population that may be at
greater risk from the laxative effects of sulfate when they experience an abrupt change from
drinking water with low sulfate concentrations to drinking water with high sulfate concentrations.
SULFIDE: The term sulfide refers to several types of chemical compounds containing sulfur in its
lowest oxidation number of -2. Formally, "sulfide" is the dianion, S2-, which exists in strongly
alkaline aqueous solutions formed from H2S or alkali metal salts such as Li2S, Na2S, and K2S.
Sulfide is exceptionally basic and, with a pKa > 14, it does not exist in appreciable concentrations
even in highly alkaline water, being undetectable at pH < ~15 (8 M NaOH). Instead, sulfide
combines with electrons in hydrogen to form HS, which is variously called hydrogen sulfide ion,
hydrosulfide ion, sulfhydryl ion, or bisulfide ion. At still lower pH's (<7), HS- converts to H2S,
hydrogen sulfide. Thus, the exact sulfur species obtained upon dissolving sulfide salts depends
on the pH of the final solution. Aqueous solutions of transition metals cations react with sulfide
sources (H2S, NaSH, Na2S) to precipitate solid sulfides. Such inorganic sulfides typically have
very low solubility in water and many are related to minerals. One famous example is the bright
yellow species CdS or "cadmium yellow". The black tarnish formed on sterling silver is Ag2S.
Such species are sometimes referred to as salts. In fact, the bonding in transition metal sulfides is
highly covalent, which gives rise to their semiconductor properties, which in turn is related to the
practical applications of many sulfide materials.
SUPERNATANT: The liquid layer which forms above the sludge in a settling basin.
SURFACE WATER SOURCES: Surface water sources such as a river or lake are primarily the
result of Runoff.
SURFACE WATER: Water that is open to the atmosphere and subject to surface runoff;
generally, lakes, streams, rivers.
SURFACTANT: Surfactants reduce the surface tension of water by adsorbing at the liquid-gas
interface. They also reduce the interfacial tension between oil and water by adsorbing at the
liquid-liquid interface. Many surfactants can also assemble in the bulk solution into aggregates.
Examples of such aggregates are vesicles and micelles. The concentration at which surfactants
begin to form micelles is known as the critical micelle concentration or CMC. When micelles form
in water, their tails form a core that can encapsulate an oil droplet, and their (ionic/polar) heads
form an outer shell that maintains favorable contact with water. When surfactants assemble in oil,
the aggregate is referred to as a reverse micelle. In a reverse micelle, the heads are in the core
and the tails maintain favorable contact with oil. Surfactants are also often classified into four
primary groups; anionic, cationic, non-ionic, and zwitterionic (dual charge).
SUSCEPTIBILITY WAIVER: A waiver that is granted based upon the results of a vulnerability
assessment.
SYNCHRONY: Simultaneous occurrence; synchronism.
T
TALC: A mineral representing the one on the Mohs Scale and composed of hydrated magnesium
silicate with the chemical formula H2Mg3(SiO3)4 or Mg3Si4O10(OH)2.
TASTE AND ODORS: The primary purpose to use potassium permanganate in water treatment is
to control taste and odors. Anaerobic water undesirable for drinking water purposes because of
color and odor problems are more likely to occur under these conditions. Taste and odor
problems in the water may happen if sludge and other debris are allowed to accumulate in a
water treatment plant.
TCE, trichloroethylene: A solvent and degreaser used for many purposes; for example dry
cleaning, it is a common groundwater contaminant. Trichloroethylene is a colorless liquid which is
used as a solvent for cleaning metal parts. Drinking or breathing high levels of trichloroethylene
may cause nervous system effects, liver and lung damage, abnormal heartbeat, coma, and
possibly death. Trichloroethylene has been found in at least 852 of the 1,430 National Priorities
List sites identified by the Environmental Protection Agency (EPA).