What is one special design requirement for septic systems on high clay, group 4 sites?

Having two septic tanks in series is a special design requirement for septic systems located on high clay, group 4 sites. Clay soil has low permeability, which means it does not allow water to flow through it easily. This can lead to slow drainage and increased risk of system failure if the septic system is not designed appropriately.

Using two tanks in series allows for better treatment of wastewater. The first tank provides primary treatment, where solids settle to the bottom and scum rises to the top. The liquid effluent is then further treated in the second tank, allowing for additional breakdown of contaminants and improving overall effluent quality before it enters the drain field. This design is especially beneficial in high clay conditions because it helps manage effluent flow and minimizes the chances of backups or failures in the system.

This approach is also aligned with best practices for areas where soil conditions impede proper drainage and filter the effluent effectively before it reaches the groundwater or surrounding environment.