Onsite Wastewater Management
These types of systems are generally used in rural areas where it would be costly to install a sewer system; they may be present in city limits.
Septic tanks are usually made of concrete, steel, fiberglass, polyethylene, or other approved material cistern that is buried in the yard. The tank can generally hold 4546.092 liters (1000 US Gal.) or more.
It is important to understand proper septic tank system maintenance, without this understanding and maintenance the tank could be significant threat to public health.
Some diseases to be aware of:
More information on Enteric disease: A major health concern in Canada
An example of why it is so important to maintain our wastewater treatment systems is the 1854 Broad Street cholera outbreak where Dr. John Snow recognized that the drinking water was contaminated due to improper handling of human waste.
The Treatment of Human Waste
Regardless of where you live, or if you have public or private wastewater treatment, that system should be disposing of the wastewater in a way that ensures the following:
- That the community or private potable water supply is not at risk of contamination.
- That direct human exposure is not possible.
- That the waste is not accessible to vectors (disease vectors), insects, rodents, or other possible carriers of disease.
- That all environmental laws and regulations are followed.
- That no odor or aesthetic nuisances are created.
Raw sewage or untreated domestic wastewater is primarily water with about 0.1% impurities that must be treated and removed. Raw sewage contains biodegradable organic materials with a high chance of pathogens. The purpose of the wastewater treatment system is to remove these impurities and let the effluent (clean water) back into the ground or a stream.
How do we treat and remove these impurities?
There are a few ways that this can be done:
- Centralized treatment plants that process water up to millions of liters per day.
- On-site treatment are septic tanks and absorption fields or any combination of.
- Stabilization ponds are a type of centralized treatment for populations of about ten thousand or less, or if the soil conditions are marginal and land space is ample.
Historically, there are two types of wastewater disposal systems: water-carrying and non-water carrying. Non-water carrying are things like a privy or compost toilet.
Decomposing Domestic Wastewater
Two processes happen when decomposing domestic wastewater: Anaerobic (no O2 required by bacteria) and aerobic (O2 required by bacteria). Anaerobic is preferred because it decomposes organic material faster and odors are less likely to occur. Most centralized wastewater treatment facilities will use the aerobic process and septic tanks use both.
Septic Tank Systems
Septic tank fields need to be maintained and operated within specific parameters; they’ll be able to treat wastewater for a few years but will need regular maintenance and eventual major repair or replacement.
Below is a diagram of a typical septic tank system. Image courtesy of InterNACHI®.
The absorption field has different names that include leach field, tile field, drain field, disposal field, and nitrification field. The effluent from the septic tank is sent to the absorption field for final treatment.
As you can see these systems are generally composed of a septic tank, distribution box, absorption field and leach field. The tank serves three purposes:
- Sedimentation of solids in the wastewater
- Storing solid waste
- Anaerobic breakdown of organic materials
Figure 1 – Provided by InterNACHI®
The placement of the septic tank is especially important, so it does not contaminate water wells, groundwater, or streams.
- The system should be at least 10 feet away from the house and other structures
- The system should be at least 5 feet away from the property
- The system should be at least 50 feet away from wells
- The system should be at least 25 feet away from streams
Depending on the area that you live in, there may be different or additional regulations that need to be followed. You should consult with your local health code authorities for the required distances.
Aerobic (or aerated) septic systems use a suspended growth wastewater treatment process and can remove suspended solids that are not removed by simple sedimentation. In the right conditions the aerobic process will provide some nutrification of ammonia, and significantly reduce pathogens in the water. This happens after some type of initial treatment. These systems are also designed to be continuous flow or batch flow systems.
The continuous flow type are the most commercially available units. Waste is always moving, sometimes by gravity sometimes with the use of a pump. The waste can be moved to a treatment/pre-treatment processing stage or to final treatment and disposal in a soil disposal system. Different types of pre-treatments can be used ahead of the aerobic units, that includes septic tanks and trash traps.
Batch flow systems stores and treats wastewater over a period and then drains the effluent at the end, then starts over.
Aerobic systems can be used in different situations from a single residence, a community, or a town. This process can be used before having the wastewater go through more treatments/pre-treatments before the effluent is released into the soil disposal system. The aerobic system is important in places where there isn’t a lot of space to put large soil disposal systems. Because these systems are so important, they must be maintained on a regular basis.
It is my understanding that a properly functioning septic tank can remove about 75% of the suspended solids, oil, and grease from effluent. Now, the waste is generally in the tank for 24 hours or less, it will not cause a significant decrease in pathogenic bacteria in the effluent. These bacteria will be removed in the drain field. Keep in mind, that there are soils and conditions that prevent the field from absorbing the effluent.
As we use the tank, sludge builds up on the bottom of the tank (as shown above). The only way for us to know how much sludge is to use a probe from the inspection port. This needs to be done regularly, DO NOT ignore this. Excessive build up, in my understanding, will lead to damaging the absorption field – which is expensive to repair. The buildup happens slower in warmer climates, but quicker in colder climates like Ottawa.
There is also a buildup of scum on the surface of the water in the tank. This must be monitored as well, if the scum makes its way into the absorption field, there will be problems. The scum needs to remain below the outlet (exiting the tank to the absorption field), the scum also should not be near the bottom or below the baffle – this indicates the tank needs to be cleaned.
When building an absorption field, it’s been made simple as there are laws that govern the installation of septic systems and absorption fields. Before one can get a permit though, the site needs to be evaluated by a:
- Local environmental health specialist
- Soil expert
- Private contractor (occasionally)
With the information gathered on-site, and historical information, a proper system can be designed. Factors to consider when choosing where to put the septic tank are:
- Landscape position
- Soil texture
- Soil structure
- Dept to restrictive horizons (like rocks)
- Usable area (how much we need versus how much is available)
Absorption Field Trench
Absorption field trenches (or rock lateral system) is the most common system you will find on level land or land with little slope with enough dept above the water table or restrictive horizons. The effluent leaves the septic tank and than flows through the distribution box or straight into the absorption field. The effluent flows through perforated pipes into gravel-filled trenches and subsequently seeps through the gravel into the soil.
Local regulatory agencies will need to be consulted with, when installing a septic system. There are some general guidelines:
- In some locations, the bottom of the trench can be up to 4 feet above the groundwater source.
- The dept of the field trench should be about 18 to 24” deep.
- The absorption field pip should be flat.
- There should be at least 12-18” of acceptable soil below the trench before reaching a restrictive horizon.
- Trench pipes should not be longer than 100 feet if using a distribution box.
Serpentine systems can be hundreds of feet long, filled with clean gravel in the bottom 6” of the trench. Perforated 4” diameter pipe is laid on the gravel and covered with 2” of rock and leveled for a total of 12”. The trench is covered with a geotextile (like landscaping felt, but much better) or a biodegradable material like straw, this prevents topsoil from getting in between the stones and clogging the system.
To make it easier for homeowners to inspect their trenches, there should be monitoring ports installed in the absorption area extending to the bottom of the gravel to be able to measure the liquid depth in the gravel. This is important, as it also allows for further testing of adequacy of the system.
Generally, serpentine systems maximize the efficiency of the square footage available, works better and facilitates a longer lasting ground absorption disposal system.
Alternate Septic Tank Systems
The prices of land are increasing as the availability of suitable land is decreasing. This has led people to develop land that is unsuitable for standard septic tank systems because the soil on these lands is poor and do not drain very well (marginal soil).
The trouble with septic tank systems is treating the effluent in marginal soil. Low-water-use devise help in these situations – usually when required as a larger effort to develop a usable alternative sewage disposal system.
The mound system is achieved by raising by placing sand fill material on top of the best native soil available. There must be at least one foot of native soil for this type of system to function properly. It is also important to minimize water usage at the property to make sure that effluent doesn’t leak through the sides of the mound.
In a standard septic tank system, you have the septic tank, the distribution box, and then to the absorption field – all of this is done by gravity. In mound systems, we have a septic tank, a pump chamber which pushes the effluent up to the absorption field. The pump mechanism works like your sump pump, once the effluent reaches a certain level a float switch activates the pump and then automatically shuts off. An alarm/monitoring system should be installed to make sure that if the pump fails, that it can be addressed immediately.
Figure 2 – Provided by InterNACHI®
Advantages of the mound septic system:
- Can be used in places with high ground water, bedrock, or clay near the surface.
- It uses space more efficiently when compared to rock lateral systems (absorption fields).
- Can be used in areas unsuitable for rock lateral systems.
- Won’t be harmed by water softener wastes, common household chemicals, and detergents.
Disadvantages of the mound septic system:
- Needs to be installed on leveled lots.
- Distribution network requires regular flushing (regular maintenance).
- These systems can be expensive.
- The system needs to be designed for each lot, which means that some lots are harder to design for than others. Great care needs to be taken during the design phase to avoid future problems.
- System, components, and controls must be inspected on a regular basis, issues should be addressed immediately.
Low-Pressure Pipe (LPP) Systems
These systems, like the mound system, can be used where the soil profile is shallow. These systems are installed usually at depts of 12” to 18” and consist of a septic tank, high-water alarm, pumping tank, supply line, manifold, lateral line, and submersible effluent pump.
Figure 3 – Provided by InterNACHI®
When the pump is activated, it will push the effluent through to the supply line and distribution laterals. The laterals have small holes usually 3 to 8 feet apart, which allow the effluent to move into the soil and be treated. This is called dosing; it usually happens once or twice a day. An alarm/monitoring system should be installed to make sure that if the pump fails, that it can be addressed immediately.
Advantages of the LPP System:
- Takes ups approximately 50% less space than conventional septic tank system.
- Can be installed in areas with an irregular shape and size.
- Can be installed in shallower soil.
- It alternates the dosing and resting periods.
- Sites are left in their natural condition.
Disadvantages of the LPP System:
- Regular maintenance is required.
- Electrical components.
- Designing and installing this type of system can be difficult.
Plant-Rock Filter Systems for Wetlands (Constructed Wetlands)
These systems are relatively new but have been a simple part of nature for a very long time. These systems generally consist of a two-compartment septic tank, a rock filter, and a small absorption field (or overflow lateral). The rock filter is a trench (3-5’ wide, 60-100’ long) that is built with a leak-proof material (much like how they build a pool), they fill it with 2-4” clean crush stone with larger stones near the inlet and the outlet.
Figure 4 – Provided by InterNACHI®
Advantages of Constructed Wetlands:
- Takes about 33% of the space used by a conventional septic system.
- Can be placed almost anywhere.
- Can be used in places with shallow water tables, high bedrock, or other restrictive horizons.
- Relatively low maintenance required.
Disadvantages of Constructed Wetlands:
- Installations costs vary and may cost more to install.
- Effluent needs to be disinfected.
- Experienced installers may be difficult to find.
- New technology, life span of system is unknown.
- People think it’s ugly.
Dos and Don’ts for maintaining your system
|Do conserve water.||Do not run water continually when brushing teeth or shaving|
|Do fix dripping faucets/leaky toilets||Do not install a garbage disposal|
|Do avoid disposing of the following down your sink/toilet: Chemicals Sanitary Napkins Tissues Cigarette butts, Grease, cooking oil Pesticides Cat litter Coffee grounds Diapers Stockings/Nylons||Do not use septic tank additives or cleaners.|
|Do avoid taking long showers|
|Do laundry or run the dishwasher only when there is a full load.|
The following are signs that the septic system is having problems:
- Drains/Toilets backing up with sewage (Black liquid, harsh odor)
- Slow drains/flushing toilets (possibly a clogged air-vent)
- Wastewater near the surface. What happens is that liquid will seep out and away from the septic tank along the surface, and you may see liquid pooling of various colours (clear to black) with almost no odor.
- Lush green grass over the absorption field. This indicates that there is too much water in the field and that it is being pushed up instead of flowing down.
- If there are nitrates or bacteria in the drinking water from a well, it may indicate that water from the septic is making its way into the drinking water via underground or surface routes.
- If you have a lake/pond near your home and notice aquatic weeds or algae seem to be flourishing in abundance, it may indicate that the septic system waste is leaching into the surface water. This will most likely affect your drinking water and could be as minor as a being an inconvenience or causing health problems.
- Sewer odors in or around the home. This may be a venting problem.
As homeowners, the most important step if you are having any, some, or all these issues is to have a Septic System Specialist inspect, repair, and maintain your septic system.
Thanks for reading!
Thank you InterNACHI® for the excellent training material and images that I used in this article.