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The
equivalent of 56 pounds of table salt are discharged
into the drainfield soils each year from a household
of 3-4 users. Within 4-10 years, sodium discharge
begins to effect the ability of disposal soils
to treat and absorb domestic waste water. The
amounts of sodium used, the precise nature of
local soils, and the volume of drainage area in
the system vary, of course.
The
high sodium content of household products for
laundry, kitchen, bath and cleaning are a primary
source of soil failures. Addition of water softener
wastes or sodium content in local water supply
also contribute to the problem.
New
research pinpoints old problem
A
ten year study recently completed by Dr. Robert
Patterson contains the newest and most thorough
study ever undertaken on the contribution of sodiums
to septic system soil failures.
Dr.
Patterson's work sheds new light on the influence
of modern products on septic system drainage soils.
The detailed records and scientific laboratory
evaluations provided in this outstanding scientific
work by Dr. Patterson give us clear insights into
problems noted by leading scientists over the
years.
After
ten years of thoroughly documented research, Dr.
Patterson concludes: "The inevitable consequence
of continual addition of sodium in septic tank
effluent is a decrease in the soil's hydraulic
conductivity leading, in many cases, to drainfield
failure."
Clay
particles magnified by an electron microscope.
 |
If
a grain of sand were the size of a
basketball, then a piece of silt would
be the size of a marble, and a particle
of clay would be a pinpoint. Clay
particles are tiny, less than one
12,500th of an inch.
When
sodium is present in wastewater passing
through these tiny clay particles,
the particles tend to stick together
forming hardpan conditions in the
soil. |
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Three
causes of septic system soil failure
Septic
system soil failure may be physical, biological
or chemical. These three conditions often occur
in sequence. For instance, when chemical (cationic)
exchanges occur from sodium, fines or clay particles
may bond into a waterproof barrier, which in turn
causes the physical flooding, blockage of soil
passages and biological death of air-dependent
cleaning organisms in the soil.
Agricultural
soil and wastewater scientists have long recognized
that in time, sodium in irrigation waters will
cause finer soil particles to bond together into
impermeable layers. In agriculture, this chemical
change causes physical or structural changes in
the soil which ultimately leads to loss of biological
uptake of plant nutrients.
In
the septic system drainfield, problems begin when
a thin impermeable layer of bonded fines develops
directly under the leachlines or on the trench
floor or walls.
This
layer grows in density over time and soon a "waterproof"
barrier prevents access to the absorptive active
soil surfaces needed for maximum organism contact
and cleanup of wastes.
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Historic
recognition of sodium influence on soils
In
the late 1940s and early 1950s researchers working
at UC's Sanitary Engineering Research Lab (SERL)
in Richmond, California and at the Federal Security
Agency (FSA) facility in Cincinnati made a dozens
of presentations to environmental health professionals.
The
role of sodium in waste water was repeatedly mentioned
as a contributing factor in septic system leachfield
failures. Publications of SERL and Cincinnati
findings published over the next several years
made note of sodium influences on soils.
In
a 1953 speech entitled Clogging Characteristics
of Domestic Effluent, T.W. Bendixen outlined the
role of sodium to a series of audiences across
the nation.
He
observed, "It is generally considered that
waters containing 50 percent of total cations
(sodium, calcium, magnesium and potassium) as
sodium are potentially harmful to soil absorptive
characteristics. Even in sandy soils, waters of
85 percent or higher are likely to make soils
impermeable after prolonged use."
In
1973, Wastewater Treatment Systems for Small Communities,
published by the Commission on Rural Water, stated
that "High concentrations of sodium ions
exchange with calcium and magnesium ions in the
clay matrix. The exchanging ions alter the forces
that hold the clay together and cause it to lose
its structure ... the clay becomes tighter and
seals."
In
1984, University of Wisconsin scientists assigned
to study the effects of water softeners on septic
systems reported to the Water Quality Research
Council. The findings of these researchers led
them to recommend that, "Studies be initiated
to determine the effect of actual salt concentrations
in various zones of the septic tank, with and
without the addition of water softener wastes."
Many
field studies of septic system chemistry and structure
have historically noted the high sodium levels
where soils are used to drain domestic waste water.
In 1953, several studies were performed by Universities,
consultants, wastewater and soil laboratories
on methods for correcting or reducing sodium impact
on septic system soils. None of these studies
compare to the decade of documentation found in
the 1994 work of Dr. Patterson.
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How
soil failure contributes to health concerns
When
soils seal, aerobic organisms within the drainfield
"drown." Cleanup of wastewater effluent
slows or stops. As the soil area becomes more
and more limited, leach lines back up, the tank
surcharges, flow from the home is impeded and
eventually, building drains overflow exposing
residents to waste flow.
In
many cases raw sewage rises to the surface or
ponds on the ground. Children are attracted to
puddles of standing waste water which carries
diseases such as dysentery, hepatitis A or typhoid
fever. Wastes may be also be tracked into the
home, where further exposure may take place.
(Note:
Dr. Kevin Sherman (University of Florida) and
Dr. Charles Gerba (University or Arizona) have
each studied the potential for transmission of
HIV or AIDS viruses via septage or domestic wastewater
and independently concluded, due to the fragile
nature of these viruses, no danger could be found
from domestic septic wastes.
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How
to spot soil failures
Pumpers
often observe water falling back into the tank
from the field as the level is pumped down. This
is an important sign of soil failure. It is obvious
that the problem does not originate in the tank,
but in the drainfield.
It
is possible to restore soil structure and drainage
by chemically treating the soil to release the
cationic bond which locks clays and fines together.
This is called "reflocculating" the
soils, and the process is commonly used in agriculture
to provide better absorption of plant foods and
water in field application.
It
is not always easy to diagnose the cause of backups.
A recent issue of the EPA newsletter Pipeline
lists signs as "slowly draining sinks and
toilets, gurgling sounds in the plumbing, plumbing
backups, sewage odors in the house, or tests showing
the presence of bacteria in well water."
***Written
by Mary Gayman for an article in Pumper magazine.*** |
