The Biological Mat
The bio mat is a black tar-like substance made up of organic material, microorganisms, and bacteria. As a drain field matures the bio mat grows along the walls and bottom of the trench containing the drain field. The billions of living organisms naturally occurring in the bio mat act as a filter for wastewater traveling through the drain field. While effluent passes slowly through the bio mat the bacteria living there act as a filter digesting the organic matter before it passes into the surrounding soil. When drain field soils flood, or the organic balance is upset the bio mat can grow into an impermeable barrier causing water to back up into the septic tank and eventually into the household plumbing.
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