Civil Engineering Reference
In-Depth Information
high-molecular-weight aliphatic and aromatic hydrocarbons. Humics can also serve as
precursors for formation of trihalomethanes and other organohalogen oxidation prod-
ucts during disinfection. Organics can also be contributed by such sources as waste-
water effluents, agricultural and urban runoff, and leachate from contaminated soils.
Many of the organics of greatest health concern come from these sources. The con-
centrations of naturally occurring organics is often in the mg / L range, while the syn-
thetic
organics
from
sources
of
contamination
are
often
in
the
microgram-
or
nanogram-per-liter range.
2
Organic contaminants can also be formed during water treatment, including trihalo-
methanes, such as chloroform, haloacetonitriles, and aldehydes. As water passes
through the transmission system, organic materials, such as polynuclear aromatic
hydrocarbons, can be leached from pipes, coatings, linings, and joint adhesives. Table
6-2 summarizes information on the organic constituents with known health effects.
The best available treatment technology often does not recognize that oxidation is a
viable treatment technology for several organic compounds, such as atrizine.
Taste and odor together is not addressed as an organic contaminant, but is a critical
contaminant for the acceptability of a treated water. The individual treatment chapters
on coagulation, activated carbon, and oxidation discuss taste and odor control.
RADIONUCLIDES
Radioactive atoms break down and release radioactivity in the form of alpha radiation
consisting of large, positively charged helium nuclei; beta radiation consisting of elec-
trons or positrons; or gamma radiation consisting of electromagnetic, wave-type en-
ergy. Alpha particles are massive, travel at extremely high speeds, and can be very
damaging when ingested. The smaller size of beta particles allows greater penetration
but creates less damage. Gamma radiation has tremendous penetrating power but lim-
ited effect at low levels.
Radiation can be naturally occurring or manmade. Naturally occurring radiation
comes from elements in the earth's crust or from cosmic ray bombardment. Manmade
radiation comes from three major sources: nuclear fission (weapons testing), radio-
pharmaceuticals, and nuclear fuel processing and use.
Based on occurrence in drinking water and related health effects, the naturally
occurring radionuclides (radium 226 and 228, uranium, and radon 222) are of greatest
concern. Radium 228 is a beta emitter, while the others and the decay products of
radium 228 are alpha emitters. Table 6-3 summarizes information on radionuclides of
greatest concern.
MICROBIAL CONTAMINANTS
Pathogenic species of bacteria, virus, and protozoans are of concern. Some pathogenic
microbes, including bacteria and protozoans, are found in natural waters, but the most
significant sources are human and animal feces that may enter a water supply from a
variety of sources, including inadequately treated sewage and surface runoff.
Bacteria of concern and the related diseases include
Salmonella
(typhoid or para-
typhoid fevers),
Shigella
(dysentery),
Yersina enterocolitica
(acute gastroenteritis),
Campylobacter
jejuni
(acute
gastroenteritis),
Legionalla
(pneumonic
illness),
