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sodium contributes to septic system failure

How Sodium Contributes to Hardpan Soil Conditions

The equivalent of 25 kg 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.

Particles of clay soil magnified.
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 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.***

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