Geology Reference
In-Depth Information
domestic uses. Persons having an abnormal sodium
metabolism should consult their physicians concerning
the planning of a sodium-free diet if the supply of
drinking or culinary water has a high sodium content.
A concentration of sodium in excess of 500 mg/L,
when combined with chloride, results in a salty taste.
Concentrations in excess of 1,000 mg/L are unsuitable
for many purposes. On the other hand, some com-
munities use water containing more than 4,000 mg/L of
dissolved solids because other supplies are not available.
Generally the more highly mineralized the water, the
more distinctive its taste.
effluents. Chloride may combine with sodium to
produce a salty taste; the chloride content of public
water supplies should not exceed 250 mg/L (Table 13.2).
This recommended limit is based solely on taste.
Throughout nearly all the land masses, fresh water is
underlain by salt water. The depth to the freshwater-
salt-water interface may range from a few to several
hundred feet. Highly mineralized water from a deep
well could reflect the underlying salt water. In
addition to sewage, major sources of contamination by
wastes of high chloride content include disposal of
hydrochloric acid, leaching of oilfield brines, and road
salting.
Hydrogen-Ion Concentration (pH)
FLUORIDE (F).
Most fluoride compounds have a low
solubility; hence, fluoride occurs only in small
amounts in natural water. Fluoride in drinking water
has been shown to reduce the formation of dental
caries if the water is consumed during the period of
enamel calcification; it may also cause mottling of the
teeth under certain conditions. Former recommended
fluoride concentrations for public water supplies
The pH of water is a measure of alkalinity or acidity.
A pH of 7 indicates a neutral solution; a pH greater
than 7 indicates an alkaline solution and a pH less than
7 indicates an acidic solution. The pH is related to the
corrosive properties of water. Low pH water is most
corrosive. Acidic water may have a sour taste. Most
water has a pH between 5.5 and 8. The recommended
range is 6.5-8.5. A low pH may be related to the dis-
charge of acid water from coal mining regions or dis-
posal of spent acids by certain industries.
TABLE 13.2 Secondary Maximum Contaminant
Levels
1
Other Inorganic Chemicals
Contaminant
Level
2
Other inorganic chemicals, often present in trace quan-
tities, are also important water quality factors and
some have implications for human health. Limits on
several inorganic chemicals are given in Table 13.1
Aluminum
0.05-0.2 mg
/L
Chloride
250 mg/L
Copper
1.0 mg/L
Fluoride
2.0 mg/L
SULFATE (S0
4
).
Sulfate is dissolved from rocks
containing sulfur compounds, such as gypsum and
pyrite (Hem, 1985). Sulfate, when combined with other
elements, may produce a bitter taste. Large amounts of
sulfate may produce a laxative effect in some people;
therefore the U.S. Public Health Service (1962)
recommended that the sulfate concentration in public
supplies should not exceed 250 mg/L. Although high
sulfate concentrations may reflect natural background
conditions, various industrial activities may cause
severe contamination. In the extensive coal-mining
region of Appalachia, much of the surface water
contains high levels of sulfate. This is the result of
weathering of abundant iron sulfides associated with
the coal deposits and the leaching of the water-soluble
products into streams. This activity is largely responsible
not only for the high sulfate, but the acid condition of the
streams as well, since it forms sulfuric acid. Several
industries, particularly steel mills, use large amounts of
sulfuric acid, which in the past in North America was
dumped into streams after it was used. High sulfate
content may also indicate sewage pollution.
Foaming Agents
0.5 mg/L
Iron
0.3 mg/L
Manganese
0.05 mg/L
Silver
0.10 mg/L
Sulfate
250 mg/L
Total Dissolved Solids (TDS)
500 mg/L
Zinc
5.0 mg/L
Color
15 color units
Corrosivity
noncorrosive
Odor
3 threshold odor number
6.5-8.5
PH
1. Secondary Maximum Contaminant Levels (SMCLs) are federally
nonenforceable and establish limits for contaminants in drinking water
that may affect the aesthetic qualities (e.g., taste and odor) and the pub-
lic's acceptance of drinking water.
2. These levels represent reasonable goals for drinking water quality.
The states may establish higher or lower levels, which may be appropri-
ate dependent upon adverse effect on public health and welfare and
upon local conditions such as unavailability of alternate source waters
or other compelling factors. Some contaminants appear in both primary
and secondary standards.
CHLORIDE (CI).
Although chloride is dissolved from
rocks and soil, its presence may indicate contamination
by human and animal sewage as well as industrial
