What Is Septic Systems in Clay Soil?
To separate solid waste from liquid wastewater, septic tanks employ a filtration mechanism. The liquid is released onto a drainage field after passing via a soak away system. lay is incredibly thick, and the spaces between the particles in the soil are too small to enable liquid to pass through. As a result, the water cannot be properly absorbed by the soil for subsequent treatment.
As a result, most septic tanks are unsuitable for soil with a high clay concentration. If you are unclear whether you have clay soil, a percolation test can be performed to evaluate whether the soil of a site is suitable for a drainage field. The drainage field system, which is a critical component of septic tanks, is not supported by clay soil. As a result, septic tanks are rendered ineffective when built on clay-rich soil.
If your property has clay soil, it is suggested that you upgrade to a comprehensive sewage treatment system. These offer complete treatment within the system tank, and the leftover liquid is of sufficient quality to be discharged straight into water sources.
To discharge water from a sewage treatment facility, you won’t need a permit in the vast majority of cases.
However, a number of requirements must be met, including that the system be built and operated according to the manufacturer’s instructions, that system maintenance be performed by a qualified person, and that the discharge not pollute ground or surface water.
As a result, it’s always a good idea to double-check with the Environmental Agency to ensure that your system and disposal technique are up to code.
Impact of Expanding Clay Soils on Septic System Performance
Septic systems on clay soils, particularly expansive clays, may provide a number of problems and hassles for any homeowner with a clay-based property. There can be several issues with expanding clays, not just with home foundations but also with septic systems.
It is critical to understand different sorts of clays so that the proper technique can be utilised to alleviate future fundamental problems. The capacity of the soil to filter wastewater naturally as it travels through the soil particles limits the effectiveness of a septic system.
Obviously, soil factors such as type, texture, structure, and mineral content will impact a septic system’s effectiveness in the long run. Septic wastewater infiltrating clay soils with even relatively modest quantities of expansive clay minerals (5-10%) will cause the soil to expand as a result of the moist circumstances.
In turn, this lowers the amount of pore space in the soil structure and, as a result, the drain field’s ability to absorb wastewater. Due to their poor drainage, clay soils with limited absorption capabilities will not be able to effectively treat wastewater effluent from septic systems.
Reduced performance or even failure of a septic system results, causing sewage to collect on the surface. As a result, expanding clay soils with a COLE value of more than 0.06 (i.e. soils that are susceptible to swelling and shrinking) can cause structural damage to septic systems, requiring costly repairs.
Effects of Shrink-Swell Soils
Here, the effects of shrink-swell soils are as follows.
- As a result of the clay’s capacity to attract and absorb water, the clay shrinks and expands. Some soils have been observed to expand by 150 times their original dimensions. Expanding clay may be quite sticky while wet. It fractures when dried.
- This means that during dry seasons, cracking on the top of the soil might be a sign of shrinking or swelling of soil.
- Their size makes them a threat to the stability of building foundations, as well as causing significant infrastructural difficulties.
- The economic harm that these sorts of soils create is felt all across the world. More damage to structures and pavement is caused by these expanding soils than any other natural catastrophe. Nelson (Nelson, 1992).
- The hydrology of these soils may drastically alter the landscape, creating underwater ponding conditions and allowing water to flow through fissures.
- As a result, water contaminants such as wastewater from septic systems, herbicides, and pesticides from agricultural land may be transported.
- Of course, this has implications for groundwater quality since pollutants can run easily through the gaps and into aquifers, streams, and ponds.
- It’s difficult to manage these sorts of expansive soils since swelling isn’t determined by a single source.
- Swelling and shrinking are influenced by the amount of clay, the kind of clay mineral, organic matter, moisture, and (CEC) cation exchange capacity.
Alternative Options for Septic Systems in Expanding Clay Soils
You can choose from the following alternatives for extending clay-based land:
- Prior to being discharged into the drain field, an aerobic treatment unit (ATU) helps filter sewage so that soil particles do not become stuck.
- There are still numerous places in North America where sand filtration is still necessary above ground (sand mound septic system).
- An above-ground sand mound septic system with a drain field/filtration bed where wastewater is treated.
- Any silts or clay residues must be removed from the medium before it can be used. Standards and regulations allow just a limited number of sand medium types.
- This is because a wider drain field provides a broader assimilation system to compensate for the lower drainage rate. The drain field may be extended across a greater region using this method, which is low-tech and very inexpensive if you have the space available on your site. In many parts of North America, this is no longer acceptable.
- Dry Wells and Cesspools: In the past, this was a typical procedure for many different types of septic systems. This wastewater dispersal solution is still used in many parts of Europe.
- Because of the inadequate effluent treatment, much of North America has moved away from this type of wastewater dissemination. Because these types of systems are still in use, several water sources have seen elevated nitrogen concentrations.
Septic Tanks and Expanding Clay Soils
1. Septic Tank Problems in Clay
Here, the septic tank problems in clay soil are as follows.
- The risk of a concrete septic tank cracking when placed directly in the expanding clay is one issue. Expanding clay, like foundations, can wreak havoc on septic tanks.
- The continual shrinking and swelling of the concrete septic will develop cracks over time. Enough bedding sand will be available to support the concrete septic tank if the excavation is larger and longer.
- This will provide enough of a buffer to relieve pressure on the concrete tank immediately.
- Placing a polyethene septic tank directly onto expansive clays can jeopardise the tank’s structural integrity.
- Plastic septic tanks might bow or cave in due to significant side strain from clay expansion. Many of the septic tank’s plastic risers can also become ovular in shape, causing the lids to no longer fit properly.
- If you’re using poly septic tanks with expansive clays, bedding the tank with the right amount of sand will help relieve the pressure, as long as the tank isn’t more than 3 feet deep.
2. Some of the Science Behind Expanding Clays
- Clay soils are made up of layers of mineral sheets that are layered on top of one other. The structural makeup of these layers dictates whether or not they will expand.
- During dry seasons, when soils shrink, expanding clay soils commonly produce extensive fractures. During the wet season, these wide cracks allow water to enter deep into the earth.
- The negatively charged clay particles inside the soil attract positively charged water molecules, allowing water to travel between the mineral layers and causing the soil to swell.
- The pores between soil particles shrink as the soil swells. Restricting the flow of water through the earth.
- As the soil dries out, water trapped between the clay mineral layers evaporates, causing the soil to shrink and fracture on the surface.
- Areas having a distinct wet and dry season are more likely to undergo faster shrinking and swelling as the soil expands.
- In order to calculate the coefficient of linear extensibility (COLE), which is the shrink-swell potential of the soil’s natural fabric, complete soil core samples are taken in three samples and the volume change of the core must be recorded in both damp and dry circumstances.
- An engineering counterpart of COLE measures the change in length after drying a dried ground soil sample. This may be accomplished by creating a cylindrical worm while the clay is still damp, then oven baking the sample until it is dry.