What is the Biomat Clogging Process?
Biomats tend to restrict the flow of effluent through the drainfield, but are crucial because they filter out viruses and pathogens. As the biomat develops, the soil infiltration rate decreases. Once the hydraulic loading rate exceeds the soil infiltration rate, ponding starts. At some point wastewater will either back up into the home or break out onto the soil surface. Septic loading and dye tests look for this “breakout” of effluent on the soil surface – a condition which will occur when the biomat has become so thick that septic effluent no longer percolates through it to the soils below. If you dig a neat cross section of a traditional leach field trench, and if it was properly constructed, you’ll see the perforated effluent pipe surrounded first by gravel, and then the sides of the trench as it was originally cut through the soil. You will also see a 1cm (about 1/2″) to 5cm (about 2″) thick gray band around the perimeter of the trench – this is where the soil clogging has occurre
