What percentage of the liquid depth should the depth to the invert of the opening between compartments be?

The correct choice reflects a widely accepted industry standard for the design of septic tanks and related systems. The depth to the invert of the opening between compartments is crucial for ensuring effective treatment and flow stability within a two or more compartment septic tank. By maintaining this opening at approximately 40% of the liquid depth, there is an optimal balance that allows for adequate separation of solids and liquids.

This positioning helps facilitate the settling of solids in the first compartment while allowing a clear flow of clarified effluent into the next compartment for further treatment. If the opening were placed higher or lower than this percentage, it could disrupt the intended separation process, possibly leading to the carryover of solids into subsequent compartments, which would hinder the system's effectiveness. Additionally, this design maintains a sufficient hydraulic head, ensuring that the flow through the system is managed effectively, promoting better overall performance of the septic system.

Understanding these design parameters is essential for private sewage contractors to ensure compliance with regulations and to provide effective sewage treatment solutions.