WATER QUALITY - Water Quality Engineering in Natural Systems - page 19

Radium. Naturally occurring radium is leached into
groundwater from rock formations, so it is present
in water sources in areas where there is radium-
bearing rock. It may also be found in surface water
as a result of runoff from mining and industrial
operations, where radium is present in the soil.
The two isotopes of radium of concern in drinking
water are radium 226, which emits primarily
alpha particles, and radium 228, which emits beta
particles and alpha particles from its daughter
decay products. radium is chemically similar
to calcium, so about 90% of ingested naturally
occurring radium goes to the bones. Consequently,
the primary risk from radium ingestion is bone
cancer.
Uranium. Naturally occurring uranium is found in
some groundwater supplies as a result of leaching
from uranium-bearing sandstone, shale, and other
rock. uranium may also occasionally be present in
surface water, carried there in runoff from areas
with mining operations. uranium may be present
in a variety of complex ionic forms, depending on
the pH of the water. The primary adverse effect of
uranium is toxicity to human kidneys.
Radon. radon is a naturally occurring radioactive
gas. It cannot be seen, smelled, or tasted. radon
comes from the radioactive decay of uranium and
is the direct radioactive decay daughter of radium
226. The highest concentrations of radon are found
in soil and rock containing uranium. Significant
concentrations, from a health standpoint, may be
found in groundwater from any type of geologic
formation, including unconsolidated formations.
The problem with radon from a public water
supply viewpoint is that if radon is present in the
water, a significant amount of the gas will be liber-
ated into a building as the water is used. Showers,
washing machines, and dishwashers are particu-
larly efficient in transferring radon gas into the air.
The radon released from the water adds to the
radon that seeps into a building from the soil,
adding to the health danger. Inhaled radon is con-
sidered to be a cause of lung cancer.
Artificial Radionuclides. Significant artificial radio-
nuclide levels have been recorded in surface
waters as a result of atmospheric fallout following
nuclear testing, leaks, and disasters. Otherwise,
surface water typically contains little or no radio-
activity. If an accidental discharge of artificial
radionuclides occurs from nuclear power plants,
waste disposal sites, or medical facilities, the ele-
ments most likely to be present are strontium 90
and tritium.

2.3.8 pH

The pH of water is defined as the negative log of
the hydrogen-ion activity (in mol/l), and commonly
expressed as

pH = − log [ H

+

] (2.18)

10

The pH of natural water bodies affect biological and
chemical reactions, control the solubility of metal ions,
and affect natural aquatic life. For example, the viability
of fish species such as brook trout and lake trout is
significantly diminished below a pH of 5.5, and most fish
species cannot survive in waters with a pH below 5.0.
As the pH in a river is lowered, more metallic ions will
be held in solution. For fish, it is often the level of dis-
solved aluminum that is critical for their survival in low
pH waters (Davie, 2008). The desirable pH for freshwa-
ter aquatic life is in the range 6.5-9.0 and 6.5-8.5 for
marine aquatic life. Most natural waters have a pH in
the range of 6-9.
Drainage and runoff from mining operations and dis-
carded mine wastes have long been major sources of
acid loadings on streams, lakes, and rivers. Coal mining,
for example, releases sulfur-bearing minerals that form
dilute sulfuric acid when contacted with process water
used in the mining operation, or with rainfall that
leaches acidic materials from waste piles and carries
them to nearby surface waters (rubin, 2001).
Acid deposition from the atmosphere directly into
surface waters or onto surrounding lands is another
important source of acid waters. The northeastern
united States and Canada frequently record rainwater
pH values in the range of 4-5, and this acid rain has
caused a complete eradication of some fish species, such
as brook trout, in hundreds of lakes in the Adirondaks.
Most rainwater not affected by acid-rain-causing anthro-
pogenic emissions has a pH of approximately 5.6, due
to the presence of dissolved carbon dioxide from the
atmosphere.

2.4 BIOLOGICAL MEASURES

Biological measures of water quality can be divided into
two broad categories: (1) measures that are related
directly to the health of humans that are likely to come
in contact with the water; and (2) measures that are
related to the health of ecosystems within the water
body. The first category is related to the concentrations
of pathogenic microorganisms in the water body, and
the second category is related to the ability of the water
body to support and maintain species composition,
diversity, and functional organization comparable with