The biomat is a bacteria layer which forms in soil below and around drainfield trenches/beds where septic effluent or wastewater is discharged. In standard or conventional drainfield systems, this layer is critical in the processing of fine biological solids and pathogens in the effluent. Without the biomat the septic system will not be adequately treating the effluent. Inadequately treated effluent released into the ground risks contamination of nearby surface water, springs, wells, etc.

Septic effluent (wastewater) is discharged into a drainfield from the septic tank. The septic tank retains all large solids. The job of the soil in the drainfield is to treat the effluent to reduce the level of biological solids and pathogens to a level acceptable for movement of the liquid into the underlying soils.

As the effluent is discharged into the drainfield, bacterial growth develops beneath the distribution lines where they meet the soil. The biomat is also known as the “clogging layer.” The biomat eventually reduces infiltration of wastewater into the soils by filling the pore spaces within the soil.