What Septic System is Best?
A question that frequently comes up when a new home is being built or an existing septic system is being upgraded is ‘what septic system is best?’ The answer is not straight-forward as it depends on various factors.
The best septic system for one home may not necessarily be the best septic system for another. Some important points that need to be considered before deciding on what septic system is best for use at a particular site are outlined below.
Soil Type & Loading Rates
The best septic system for a property will largely be determined by the soil characteristics of the site and the amount of sewage that will be generated by the household.
The type of soil significantly influences percolation rates, and the amount of wastewater produced by the household is also a factor to take into account, as the septic system will need to be able to cope with the volume of wastewater produced.
In order for the wastewater to be properly treated, the effluent that flows into the drain field needs to be able to flow through the soil fast enough to prevent it from accumulating and rising to the soil surface, where it can pond and pose an environmental and human health risk.
By the same token, the effluent needs to pass through the soil slow enough to allow microbes in the soil to effectively break down the organic contaminants and pathogens before it reaches the groundwater.
Ultimately, the type and size of the septic system will be determined by the soil loading rate — the rate at which effluent is expected to pass through the soil (gallons per day / square foot) — which is influenced by both the structure and texture of the soil.
Secondly, there needs to be sufficient soil depth between the wastewater penetrating surface and the water table or any other restrictive layer or element, such as bedrock, restrictive soils or water bodies, to ensure effluent is properly treated by bacteria in the soil before it passes through to either the groundwater or a freshwater body.
If the depth of the soil that naturally occurs on site is inadequate, it will need to be artificially increased by installing a sand filter and/or an above ground sand mound to ensure proper treatment takes place before the effluent reaches the restrictive layer.
Poly Septic Tank vs Concrete Septic Tank
Another common quandary when deciding what septic system is best for a property is whether to opt for a concrete or plastic — polypropylene or high-density polyethene (HDPE) — septic tank. Both types are suitable, but there are advantages and disadvantages to both.
Plastic Septic Tanks
Plastic (polypropylene and HDPE) tanks are cheap, light-weight, and yet extremely durable — they are corrosion resistant and unlike concrete is watertight and not prone to cracking. They are cheaper to transport than concrete tanks and easier to manipulate on a site without the use of specialized equipment, which makes them cheaper to install.
Being so light, plastic tanks may be prone to floating to the surface of the soil in areas that have a high water table. If the tank isn’t bedded properly jagged rocks or surfaces could potentially penetrate the plastic causing leaks. Having access to large volume tankage is more difficult without customization and at times more than one tank could be required. Plastic septic tanks generally have a 2-3 foot burial depth maximum recommendation, and thus not work in certain situations where deeper depths are required.
Concrete Septic Tanks
Although concrete tanks come in various sizes, for much greater volumes there is more accessibility to larger manufactured tanks. They are also very durable, and because they are extremely heavy, they will not float to the surface. Concrete septic tanks can also withstand greater depths, often in cold regions tanks need to be deeper.
Because concrete is so heavy, these tanks are more tricky to install, requiring site access for a large delivery truck fitted with a crane, which in turn pushes up installation costs, making them more expensive than plastic tanks. As the lid of the tank is installed only after the concrete tank has been placed in the ground, if not properly sealed can result in major leaks. Concrete is also prone to cracking which can cause leaks to arise.
Alternate Septic Sytems
As developments get pushed further from city limits or let’s say lot sizes get more constrained as everyone pushes to get a great view of the lake…well this pushes septic systems outside the conventional.
As an example let’s say a property by the lake is purchased, it’s not a big lot, but the homeowner has a family and requires a large home. The soils have higher percentages of sands making it ideal for a conventional gravity septic system, but wait… The backyard is way too small to fit such a system and the front yard isn’t a consideration for any septic system to be dispersed into.
Well, in this case, the wastewater quality has to improve. You see with a conventional septic system the septic tank does the primary job of treatment, then the soils treat the rest. Since this type of system treats the wastewater less efficiently, a greater surface area is required as a safety measure. This type of system can be categorized as a Type 1 Septic system.
ATUs or Aerobic Treatment Units are then used in the case above to increase the quality of the effluent leaving the tank areas. This higher quality oxygenated wastewater allows us to conform to smaller space requirements. This type of system falls under the category of a Type 2 septic system.
Now there are other septic drain field technologies that produce a Type 2 effluent as well and often a Type 1 effluent septic system can be designed in a combination with a Type 2 Septic system…confused yet? There are many variant ways to categorize the right system for certain challenges, not every lot or home is the same.
If aerobic treatment still does not allow us to conform to the size of the yard, we then have to think about adding additional treatment, and this could be ultraviolet light or chlorination. This type of septic system can be categorized under a Type 3 Septic system.
With type 1 septic systems using gravity for dispersal isn’t always feasible. Often suitable land areas for the wastewater dispersal are located at higher elevations in accordance to the home. Also, very fast draining soils with shallow depths will not be suitable for gravity.
This is when a pressure distribution system can be more suitable. You see, our standards of practice require us to design a gravity septic system with a minimum of 4 feet of clearance from where the wastewater gets dispersed into (this is called the infiltrative surface) to limiting factor, and this could be high water, bedrock or restricting soil types.
To disperse the wastewater to higher elevations a pump will drive the wastewater to where it needs to go. The drain field will then perform the remaining treatment of the effluent leaving the tank area.
What is the Best Septic System?
There are many different types of septic systems available. They all have their merits and have been designed for use under specific conditions. When deciding what septic system is best, it is important to consider how much wastewater the household is likely to generate, together with limiting factors such as soil type and loading rates, and any restrictive layers present on the site.
Both plastic and concrete tanks have their strong points; ultimately the choice will depend on the wastewater practitioner and the homeowner’s preference and budget and/or whether they are approved for use in the area where the installation will take place.
Navigating through regulatory requirements and assessing the right septic system for the property can be a real challenge. Most jurisdictions in British Columbia require septic system approval prior to new construction, additions or upgrading a home.
It all starts with assessing the lot, the family or individual requirements and the size of the home. Giving quotations over the phone is very hypothetical. This is because without the proper data of soils, site and home it all becomes just guesswork.
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