bio mat is a naturally occurring tar-like
substance that forms on the bottoms
and sides of the drainfield trenches.
It is made up of living anaerobic
(without oxygen) organisms, which
feed on organic matter in the wastewater.
As the biomat matures it grows thicker
slowing down the flow of wastewater
to the surrounding soil. As the wastewater
passes through the biomat pathogenic
organisms and viruses are removed.
On the outside of the trench, beyond
the biomat where the soil is not saturated,
are living colonies of aerobic (with
oxygen) bacteria. These aerobic bacteria
colonies feed on the biomat and keep
it from becoming so thick that wastewater
will no longer pass through.
soil floods these aerobic bacteria
colonies will die off and no longer
keep the biomat in check. The biomat
will grow too thick and drainage will
stop. Further, as these colonies die
off they leave behind sulfides, which
over time will clog soil passages
stopping the flow of water. When the
biomat grows too thick a waterproof
barrier develops and absorption stops.