PHOTO of sewage contamination leaking to a yard surface from a broken sewer pipe Septic system contaminants & pathogens
Identify water and soil contaminants produced by onsite waste disposal systems

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This document identifies the common contaminants found in onsite septic systems.

We discusses further the principal nitrogen contaminants produced by septic systems or on-site waste disposal systems.

This article discusses nitrogen and nitrate contaminants and links to sister documents discussing septic tank pathogens and other contaminants as well as to discussions of what to do about sewage backups in buildings and how to inspect and repair a septic system after flooding.

We include discussion of health or other concerns with soil and groundwater contamination and with measures adopted to address these problems.

The photo above shows what dirt and sewage effluent may look like in a yard where the sewer line between the house and septic tank is damaged and leaking. Nitrates, nitrites, and sewage pathogens leaking from a septic system to the soil surface and subsoil waters are potential health hazards.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

What are the Common Septic Tank & Onsite Septic System Contaminants & Pathogens?

Watch out: sewage spills contain contaminants that can cause serious illness or disease. Disease causing agents in raw sewage include bacteria, fungi, parasites, and viruses and can cause serious illnesses including bacterial infections, Tetanus, Hepatitis A, Leptospirosis, infections by Cryptosporidium & Giardia and gastrointestinal diseases.

For a detailed list of the pathogens found in common household wastewater such as a septic tank and drainfield, see also our discussion of pathogens in sewage at SEWAGE PATHOGENS in SEPTIC SLUDGE: what makes up the contents of residential sewage? Stated more simply, and according to various sources such as the Utah DEQ

"The major contaminant discharged from septic systems is disease-causing germs. These germs (bacteria and viruses) - can cause many human diseases.

Another contaminant discharged from septic systems is nitrogen in the form of nitrate. If the nitrate level of drinking water is too high, infants, up to the age of six months old, can develop a fatal disease called blue baby syndrome (methemoglobenemia).

Additionally, if toxic chemicals are disposed in a septic system, they can percolate through the drainfield and into the ground water."

Three Levels of Basic Septic System Treatment to Reduce Discharge of Contaminants to the Environment

  1. Initial wastewater sewage treatment occurs in the holding tank (or septic tank) where solids and some greases are separated for later removal by a septic cleaning or pumping contractor. These contaminants must be hauled to an approved disposal site and are regulated.
  2. The second phase of onsite waste treatment which also may occur in the holding tank or to some degree in soils of the absorption bed, is the removal of dissolved or emulsified contaminants.
  3. The third and final phase of onsite waste treatment is the processing of pathogens in the clarified effluent.

    At onsite waste systems (private septic systems using, for example, a leach field), liquid waste leaving the absorption bed seeps into the ground where it should be processed by a biomass of bacteria whose purpose is to digest certain pathogens, leaving the remaining effluent sufficiently sanitary as to not be considered a groundwater contaminant.

Septic System Operating Defects Prevent Successful Treatment of Sewage Contaminants

Not only are there defects which prevent adequate biomass treatment - thus releasing contaminated effluent into local soils, streams, and possibly wells, but further, as this water passes through local soils it may pick or contain up other contaminants not adequately processed by the biomass.

Of these nitrogen (discussed first below) is a major concern. Other contaminants that may be conveyed to nearby streams or wells includes soil particles, heavy metals, organic compounds, animal waste, and, if the system is in a more urban area, potentially oil and grease.

This article collects and discusses various contaminants that can be expected to escape the third phase of septic treatment just named. Separately we discuss the causes of septic system failure and their remedy. See More Information below.

NITROGEN CONTAMINATION: nitrogen discharge from sewage treatment plants

New York -- January 11, 2006. New York City will spend more than $700 million on advanced water treatment systems to help restore Long Island Sound's water quality by upgrading municipal sewage treatment plants over the coming decade in order to reduce the discharge of nitrogen.

Nitrogen in treated sewage effluent causes a number of problems including excessive algae growth, reduced oxygen in water, and the death of fish, shellfish, and plants. The project will address Jamaica Bay and other water systems in the area. -- New York Times, page B4, 1/11/2006.

NITROGEN REFERENCES - Nitrogen Contaminants in Sewage - Reference List & Excerpts

That nitrogen release is a worldwide concern is evident from these example reports on nitrogen and sewage treatment.

Israel: Evaluation of Pollution in the Gulf of Eilat [.DOC file] - Report For the Ministries of Infrastructure, Environment and Agriculture.

"There is consensus that the water clarity and coral reefs of Eilat are deteriorating. The widely suggested explanation for the degradation is that Eilat waters are suffering from sustained inputs of organic carbon and nutrients.

The International Expert Team (IET) was tasked to identify existing and potential sources of pollution; assess the carrying capacity of the Gulf for fish-farming; and formulate recommendations for minimization of pollution and environmental pressures. The IET considered 10 factors contributing to pollution in the Gulf: phosphate dust, sewage, fish-farms, groundwater inputs, siltation, marina activities, oil, tourist diving activities, water temperature, and port-ballast water.

The IET recognizes that there have been multiple stressors on the coral reefs of Eilat over the past 25 years, and these are discussed and ranked in the report. Presently, environmental pressures include: 1) continued inputs of nutrients from Aqaba phosphate dust, Aqaba sewage, and fish farms; 2) siltation from construction; 3) diving activities and, perhaps, 4) increased water temperature."

" In the past 25 years, total nitrogen in the water of the northern Gulf appears to have doubled, but varies seasonally. The large seasonal fluctuations are approximately equivalent to all the nitrogen input from fish-farms over the last 10 years and one-fourth of all the nitrogen input from sewage over the last 30 years;..."

China: The Problems and Countermeasures on Agricultural Sewage Irrigation in China - [website] Yang Jifu (Irrigation and Drainage Department,IWHR)

"Abstract Due to the lack of agricultural water resources and the continuously increasing volume of sewage discharging all over the country, sewage has already become an important water resources for agriculture irrigation in the suburbs near many big cities in the North.In 1991 sewage irrigation area has reached 3 million hectares about 6%of the total irrigation area.

On the one hand, sewage irrigation alleviates agricultural water shortage, and on the other hand, it reduces the harmful impact on water environment by discharging sewage. However,three big problems on sewage irrigation have been existing for many years. They are the low water quality, the blind development on irrigation area and the backward research and management.

Thus, the sewage irrigation has become one of the three sources of water environment worsening in the village.It has been jeopardizing not only the quality of food and drinking water in the irrigation area, but also the food safety of 1.6 billion populations until the 21 st century.The following suggestions and countermeasures are provided in the Paper."


See SEWAGE PATHOGENS in SEPTIC SLUDGE for a list and discussion of of the common pathogens and other contaminants in residential sewage.




and also our discussion of pathogens in sewage at SEWAGE PATHOGENS in SEPTIC SLUDGE: what makes up the contents of residential sewage?

Anyone working on or around or owning a septic tank should be sure to see SEPTIC & CESSPOOL SAFETY.

Reader Question: what are the risks of human infection by parasites traced to a septic system drainfield or soakaway bed?

My question is whether any of the microscopic larvae that is in the toilet water or effluent? will find their way to the leach field. By doing so, they hatch within 1-2 days, mature into the infective stage within a week and last for 3-5 months in the infective stage. Anyone who's skin comes into contact with this larvae will in turn get the hookworms.

There are two types and one of them can be transferred by ingestion or drinking contaminated water. Which brings me to the next question, and that is, can these larvae somehow infect the water source for a well. Would normal weather changes such as melting snow, flooding, heavy rains bring them down into the water source. - Dr. M.K., 4/17/2013

Reply: Risk of parasitic infection from human passage over proprly-working septic system drainfields


I interpret "microscopic larvae" to mean parasites of various forms. In sum, references cited below generally emphasize illnesses ascribed to drinking water contamination from sewage, or illnesses ascribed to direct contact with untreated sewage, say from a sewage backup into a building, area flooding and storms, or a septic tank backup and spill onto an outdoor yard area. It may also be pertinent to note that there are ample opportunities for parsasites borne by animals other than human to find their way to the ground surface in outdoor areas.

Significantly, Robertson (1999) reported on this question as follows:

Some research indicates that some sewage treatment processes may result in relatively high removal efficiencies of some intestinal protozoa, whereas other data indicate that the concentration of cysts and oocysts discharged in sewage effluent may be in the order of several thousand per litre.

Note that the authors are discussing contamination sewage effluent, not the level of pathogens that might be found on the ground surface. In the case of a properly working septic system (not discharging effluent to the surface) or a properly functioning aerobic septic system that discharges highly-treated, disinfected effluent directly to the ground surface one would expect the presence of these pathogens to be much lower - at a lefel accepted by a public health department as safe for the public.

Taylor (1981) performed research suggesting that the principal pathogenic risk is in drinking water contamination not a person's passing over dry ground over a working drainfield.

If there is a specific illness, parasite, and issue with which you are concerned, it would be important to tell me what that parasite and illness are, and how people believe it was contracted. As you'll see even in the mere abstracts above, parasites protected by their existence in cyst or oocyst form are difficult to kill - a problem reflected in our discussion of emergency and regular water purification system choices.

Repeating what I said to you by telephone, you will not be likely to find general public health warnings to people to not walk across septic system drainfields provided the septic system is working properly - in particular, that there is no sewage or effluent breakout to the ground surface, though there are studies reporting such effects including the NRC (1993) cited in turn by Grimes et als (undated).

You might want to see the citations I give below in response to research on parasites in septic drainfields, parasites in septic systems, parasites in sewage, as well as our own articles and their individual citations at

References & research citations on the risk of parasitic infection from passage over working septic system drainfields

Some more useful pertinent citations discussing parasites in sewage and septic effluent include

The ability of a septic system to handle parasites was also discussed two years earlier in Robertson (1997)

Note again that the authors are talking about groundwater, not pathogens on the ground surface

Note that in this report illness was NOT caused by walking on a drainfield; there was direct water contamination of the water source from the septic system. Quoting "Drinking water was most likely contaminated by back-siphonage through a cross-connection between the school's well and septic tank. This contamination occurred approximately 24 to 36 hours before the outbreak developed.

Septic & Sewage Pathogens and Contaminants, References & Research Articles


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