Impacts of Conventional Septic Tank on Ground Water

Septic Tank:

Septic Tank

A septic tank is a key component of the septic system, a small-scale sewage treatment system common in areas with no connection to main sewage pipes provided by local governments or private corporations. Periodic preventive maintenance is required to remove solids that remain and gradually fill the tank, reducing its efficiency. Maintenance requires regular pumping to remove these.

Those who disregard this requirement will eventually be faced with costly repairs when solids escape the tank and clog the clarified liquid effluent disposal system.

Like any system, a septic system requires maintenance. Although septic systems generally require less maintenance than communally connected sewage systems, the maintenance of a septic system is often the responsibility of the resident or property owner. Neglected or abused systems can pose the following problems:

Excessive dumping of cooking oils and grease can cause the inlet drains to block. Oils and grease are often difficult to degrade and can cause odor problems and difficulties with the periodic emptying.

Flushing non-biodegradable items such as cigarette butts and hygiene products such as sanitary napkins, tampons, and cotton buds/swabs will rapidly fill or clog a septic tank, so as in other systems, those materials should not be disposed of in that way.

As with all drainage systems, the use of garbage disposals for disposal of waste food can cause a rapid overload of the system with solids and contribute to failure.

Certain chemicals may damage the components of a septic tank, especially pesticides, herbicides, materials with high concentrations of bleach or caustic soda(lye) or any other inorganic materials such as paints or solvents.

As with communal sewage systems, roots from trees and shrubbery growing above the tank or the drainfield may clog and/or rupture them.

Playgrounds and storage buildings may cause damage to a tank and the drainage field. In addition, covering the drainage field with an impermeable surface, such as a driveway or parking area, will seriously affect its efficiency and possibly damage the tank and absorption system.

The flushing of salted water into the septic system can lead to sodium binding in the drainfield. The clay and fine silt particles bind together and effectively waterproof the leach field, rendering it ineffective.

Like communal sewage systems, excessive water entering the system will overload it and cause it to fail. Checking for plumbing leaks and practising water conservation will help optimize the system’s operation.

Very high rainfall, rapid snow melt, and flooding from rivers or the sea can all prevent a drain field from operating, and can cause flow to back up, interfering with the normal operation of the tank. High winter water tables can also result in groundwater flowing back into the septic tank.

Over time, biofilms develop on the pipes of the drainage field, which can lead to blockage. Such a failure can be referred to as “biomat failure”.

Septic tanks by themselves are ineffective at removing nitrogen compounds that have potential to cause algal blooms in waterways into which affected water from a septic system finds its way. This can be remedied by using a nitrogen-reducing technology, or by simply ensuring that the leach field is properly sited to prevent direct entry of effluent into bodies of water.

Environmental issues:

While a properly maintained septic tank poses no more environmental problems than centralised municipal sewage treatment, certain problems could potentially arise from a neglected installation.

The soil’s capacity to retain phosphorus is usually large enough to cope with the load through a normal residential septic tank. An exception occurs when septic drain fields are located in sandy or coarser soils on property adjoining a water body. Because of limited particle surface area, these soils can become saturated with phosphates. Phosphates will progress beyond the treatment area, posing a threat of eutrophication to surface waters.

In areas with high population density, groundwater pollution beyond acceptable limits may occur. Some small towns are facing the costs of building very expensive centralized waste water treatment systems because of this problem, owing to the high cost of extended collection systems. Ensuring existing septic tanks are functioning properly can also be helpful for a limited time, but becomes less effective as a primary remediation strategy as population density increases.


Groundwater comprises 97 percent of the world’s readily accessible freshwater and provides the rural, urban, industrial and irrigation water supply needs of 2 billion people around the world. As the more easily accessed surface water resources are already being used, pressure on groundwater is growing.

In the last few decades, this pressure has been evident through rapidly increasing pumping of groundwater, accelerated by the availability of cheap drilling and pumping technologies . This accelerated growth in groundwater exploitation—unplanned, unmanaged, and largely invisible—has been dubbed by prominent hydrogeologists ―the silent revolution.It is a paradox that such a vast and Groundwater has played a significant role in the maintenance of India’s economy, environment, and standard of living. India is the largest groundwater user in the world. Through the construction of millions of private wells, there has been a phenomenal growth in the exploitation of groundwater in the last five decades. The factors driving this expansion include poor public irrigation and drinking water delivery, new pump technologies, the flexibility and timeliness of groundwater supply, and government electricity subsidies. As a result, 29 percent of the groundwater assessment blocks in the country are classified in semi-critical, critical, or overexploited categories with the situation deteriorating rapidly.

Groundwater quality and pollution:

The groundwater quality dimension is addressed by describing pollution sources, namely

(a) groundwater salinity (inland and coastal),

(b) geogenic contaminants (arsenic, fluoride, and iron), and

(c) anthropogenic contaminants from mining, industrial, tanneries, land-fills and garbage dumps, agriculture, and poor sanitation and wastewater disposal.
The report highlights the need for groundwater quality management if groundwater use is to be sustainable.

How septic tank contaminates ground water :

The word “septic” comes from the Greek “septikos” which means “to make putrid.” Today it still means “causing putrefaction,” putrefaction being “the decomposition of organic matter resulting in the formation of foul-smelling products”. Septic systems are not designed to destroy human pathogens that may be in the human waste that enters the septic tank. Instead, septic systems are designed to collect human wastewater, settle out the solids, and anaerobically digest them to some extent, leaching the effluent into the ground. Therefore, septic systems can be highly pathogenic, allowing the transmission of disease-causing bacteria, viruses, protozoa, and intestinal parasites through the system.
One of the main concerns associated with septic systems is the problem of human population density. Too many septic systems in any given area will overload the soil’s natural purification systems and allow large amounts of wastewater to contaminate the underlying watertable.

A density of more than forty household septic systems per square mile will cause an area to become a likely target for subsurface contamination,
Septic tanks are enclosures that store and process wastes where no sewer system exists, such as in rural areas or on boats. Large portions of the population are still served by septic systems as opposed to public waste treatment facilities.

Contamination of water from septic tanks occurs under various conditions:

Poor placement of septic leachfields can feed partially treated waste water into a drinking water source. Leachfields are part of the septic system for land based tanks and include an area where waste water percolates through soil as part of the treatment process.

Badly constructed percolation systems may allow water to escape without proper treatment.

System failure can result in clogging and overflow to land or surface water.

High density placement of tanks, as in suburban areas, can result in regions containing very high concentrations of waste water. This water may seep to the land surface, run-off into surface water or flow directly into the water table.

What could the water be contaminated with?

Private wells can become contaminated with bacteria or chemicals such as nitrates.
Bacteria,Total Coliforms, E. coli,Nitrates & Herbicides and Pesticides

Dangers Of Contaminated Groundwater

Drinking contaminated groundwater can have serious health effects. Diseases such as hepatitis and dysentery may be caused by contamination from septic tank waste. Poisoning may be caused by toxins that have leached into well water supplies. Wildlife can also be harmed by contaminated groundwater. Other long term effects such as certain types of cancer may also result from exposure to polluted water.
In septic systems, wastewater drains from toilets and sinks into an underground tank, then through porous pipes in a leach field, where surrounding sand filters out bacteria and other pathogens.

Microbes in the dirt break down organic and inorganic wastes, such as nitrogen.
Fecal contamination can arise from sources such as combined sewer overflows, leaking septic tanks, sewer malfunctions, contaminated storm drains, animal feedlots, and other sources. During rainfalls, snow melts, or other types of precipitation, may be washed into creeks, rivers, streams, lakes, or ground water. When these waters are used as sources of drinking water will cause serious health effects
Onsite wastewater disposal systems used by homes, offices or other buildings that are not connected to a city sewer system.

Septic systems are designed to slowly drain away human waste underground at a slow, harmless rate. An improperly designed, located, constructed, or maintained septic system can leak bacteria, viruses, household chemicals, and other contaminants into the groundwater causing serious problems.
The health effects of drinking contaminated water can range from no physical impact to severe illness or even death.
Some of the effects of drinking contaminated water can be immediate, or not noticed for many years. These include gastrointestinal and stomach illnesses like: nausea, vomiting, cramps ,diarrhoea.

Many factors affect the possible impact on health such as:

  • the age and general health status of the person
  • the type of contaminant
  • the amount
  • how long the person has been drinking the contaminated water.