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Posted on 17-Feb-2019

GroundStone Wastewater Services

Impact of Expanding Clay Soils on Septic System Performance


Septic systems in clay soils, especially expansive clays can bring certain challenges and headaches to any homeowner living with a backyard that consists of clay.

With expanding clays there can be many challenges with not only house foundations but with septic systems, it is important to recognize these types of clays to ensure the right strategy is being used to relieve potential integral problems.



Since the efficiency of a septic system is limited by the ability of the soil to filter wastewater naturally as it passes through the soil particles.

It stands to reason that the overall performance of a septic system will be affected by soil properties such as soil type, texture, structure and mineral composition.

When wastewater effluent from a septic system infiltrates clay soils that have even relatively low levels (5-10%) of expansive clay minerals, the wet conditions will cause the soil to expand.

This reduces the pore space within the soil structure, which will, in turn, diminish the ability of the soil in the drain field to absorb wastewater and hence its drainage capacity.



Clay soils with poor drainage will, therefore, have a reduced capacity to absorb effluent from a septic system, and will not be able to process wastewater effluent efficiently.



The result is a reduced performance of the septic system, or even system failure, which can cause effluent to pool on the surface.
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