APPENDIX B: WATER QUALITY
According to the EPA, agriculture is the predominant source of water quality impairment in
lakes and rivers throughout the nation (USEPA, 1994). Siltation and nutrients are ranked
first and second for their role in impairment of rivers and streams in the United States.
Agriculture is said to be responsible for 72 percent of the river miles impaired by
pollution in the U.S. followed by municipal point sources at 15 percent and urban runoff
at 11 percent. Metals, nutrients, organic enrichment and siltation are the leading
pollutants responsible for lake impairment in the U.S. Agriculture is said to be
responsible for 56 percent of the lake acres impaired by pollution in the U.S. followed by
urban runoff at 24 percent.
Pesticides and Herbicides
Pesticides (particularly herbicides) from agricultural runoff cause most lake impairments
in Missouri (USEPA, 1994). This is a particularly critical concern in northern Missouri
because public drinking water supplies are largely dependent on surface water sources and
production agriculture is largely dependent on herbicides for weed control. Ten public
drinking water supplies in northern Missouri have received notices of violation for annual
running average atrazine concentrations based on quarterly samples that exceeded the 3
parts per billion (ppb) drinking water maximum contaminant level (MCL).
Approximately 140 water samples representing 95 streams and 21 major river systems in
northern Missouri were collected in April (pre-plant) and June (post-plant) of 1994
(Blanchard et al., 1994). The detection frequency in the June sampling was 100 percent for
atrazine, 98 percent for cyanazine, and 77 percent for metolachlor. Cyanazine exceeded the
1 ppb drinking water health advisory level (HAL) in 71 percent of the June samples and
atrazine exceeded the 3 ppb drinking water MCL in 59 percent of the June samples. For
information on how the EPA sets HAL's and MCL's see
Appendix A on
Human Risk Assessment.
Appendix A also has information on
Pesticide Regulation.
Nitrogen
Nitrogen is an important water quality indicator because it reflects the presence of
organic pollution as well as nutrient runoff from cropland. Prior to the development of
bacteriological tests for determining the sanitary quality of water, the form and
concentration of nitrogen compounds was used as an indicator of water purity. Organic
nitrogen in the form of proteins is present in plant and animal tissue and in animal feces.
When proteins are subjected to bacterial decay, the organic nitrogen compounds are
converted first to ammonia. Ammonia may be taken up directly by plants and converted back
to protein or it may be oxidized by nitrifying bacteria which convert it to nitrite and
subsequently to nitrate. Nitrates may also be taken up directly by plants or, under
conditions where oxygen is lacking, reduced to animonia or more commonly to nitrogen gas
that escapes to the atmosphere.
In addition to providing an indication of water purity, nitrogen compounds pose some
environmental risks of their own. High nitrate levels in drinking water are known to cause
a condition known as methemoglobinemia (commonly known as blue baby syndrome) that
reduces the oxygen carrying capacity of blood in infants. For this reason, the U.S.
Environmental Protection Agency has set a maximum containinant level requiring that the
nitrate-nitrogen content not exceed 10 parts per million (ppm) in public drinking water
supplies. The conversion of ammonia to nitrites and nitrates by nitrifying bacteria
requires oxygen and this process can reduce dissolved oxygen levels below that needed for
survival of fish and aquatic life. Ammonia gas dissolves in water to form ammonium
hydroxide that is toxic to fish and aquatic life at high pH.
Phosphorus
Phosphorus in surface waters arises from both soil loss and organic pollution.
Orthophosphate, the most common ionic form, is quickly fixed in the soil profile and
does not move easily with groundwater. Soil erosion results in the movement of fixed
phosphorus compounds with sediment. Domestic and agricultural wastes contain
phosphorus compounds from detergents and in the nucleic acids of decaying organic matter.
Wastewater treatment plants and failed septic systems are sources of phosphorus compounds.
The average total phosphorus content of effluent discharged from treatment plants with
secondary treatment is 10 ppm (Novotny, 1994).
Phosphorus, along with nitrogen, is an essential nutrient for the growth of minute aquatic
plants called algae. These consist primarily of free-floating phytoplankton and attached
algae called periphyton. Nutrient enrichment in a lake can trigger massive nuisance
growths of algae called blooms. These blooms are most noticeable in the way they reduce
water clarity, giving a pea soup appearance in severe cases. The green color results from
a plant pigment called chlorophyll. The chlorophyll content is often used to quantify the
level of algae in a water sample. Because algae are green plants, they derive energy from
the sun through photosynthesis giving off oxygen in the process. At night or when light is
limited these plants respire, consuming oxygen from the water. Since warm water holds less
oxygen than cold, fish kills due to oxygen depletion by algal blooms commonly occur early
in the morning on hot summer days when water the temperature is warm and respiration has
occurred all night.
Algal blooms can also cause toxicity, taste, and odor problems. Many microorganisms
engage in a sort of chemical warfare by excreting substances that are toxic to their
competitors. Blue-green algae synthesize both nerve and liver toxins that can be fatal to
humans, although confirmed human poisonings are rare. The appearance of these toxins is
unpredictable. Every year dozens of cattle and hogs die from drinking water containing
toxins produced by common blue-green algae while millions of others drinking water
containing the same algae suffer no ill effects. What circumstances actually cause these
algae to produce such potent toxins is not known. Some algae also secrete compounds such
as geosmin and MIB (2-methyl-isoborneol) that impart a musty taste and odor to water. Like
toxins, there is no apparent reason for the production of these compounds. They are a
nuisance in water supply systems and require oxidation or activated carbon filtration for
removal.
The nitrogen to phosphorus ratio (N:P) can be used to estimate which nutrient is limiting
algal growth. As a rule of thumb (Home, 1994), nitrogen is the limiting nutrient if N:P is
less than 10 and phosphorus limits if N:P is greater than 10. Either or both can limit
algal growth if N:P is near 10. Typically, the total phosphorus content of the water must
be reduced below 10 ppb to significantly improve water clarity.
Soluble phosphorus is in high demand from microorganisms living in lakes and is recycled
rapidly in the water column. Natural phosphorus loss from the water column occurs as dead
organisms and chemically formed precipitates settle to the bottom. As these sediments
accumulate, they become a source for internal phosphorus loading. Internal loading occurs
as deep waters become anoxic causing chemically fixed phosphorus compounds to be
released. When the lake turns over, the phosphorus is distributed through the water column.
Internal loading can be a significant phosphorus source and, in fact, can mask watershed
external loading reductions until internal sources are depleted.
Nutrient and Sediment Regulations
The Federal Water Pollution Control Act commonly known as the Clean Water Act is the
primary law goveniing the regulation of both point and non-point pollution sources. Point
sources are those originating from a pipe or other geographically definable source. The
point source control program empowers the U.S. EPA to delegate authority to approved
states to issue permits to municipal wastewater treatment facilities and industrial waste
dischargers. Permittees are held to minimum effluent and water quality standards
established by the EPA although individual states may be more restrictive.
Section 319 of the Clean Water Act, enacted in 1987, established a national program to
control non-point sources of pollution. Non-point source pollution results primarily from
runoff, drainage, or seepage of contaminants. The major pollutants responsible for
non-point source impacts in the U.S. are sediment and nutrients. Section 319 created a
three-stage national program to be implemented by the States with Federal approval and
assistance. States were to address non-point source pollution by (1) developing non-point
source assessment reports, (2) adopting non-point source management programs, and (3)
implementing the management programs over a multi-year timeframe (USEPA, 1994).
Septic System Regulations
On-site septic systems are regulated at both the state and county level. The Missouri
septic system law states:
"No person or property owner may operate an on-site sewage disposal system or transport
and dispose of waste removed therefrom in such a manner that may result in the
contamination of surface waters or groundwater or present a nuisance or imminent health
hazard to any other person or property owner and that does not comply with the
requirements of sections 701.025 to 701.059 and the on-site sewage disposal rules
promulgated under sections 701.025 to 701.059 by the department." -Revised Statutes
of Missouri 701.029.
On-site septic systems are generally considered to be "no-discharge" systems. As such there
are no effluent standards or discharge permits for these systems. Individual counties may
establish their own septic system requirements but they can not be any less restrictive
than state requirements.
Back to Plan Index... |
