How is minimum liquid capacity (V) calculated for systems under 500 gallons?

The minimum liquid capacity (V) for on-site sewage facilities systems under 500 gallons is calculated as approximately 3 times the daily flow in gallons per day (Q). This calculation is based on the need to ensure that the system can adequately handle the wastewater generated in a way that promotes effective treatment and reduces the risk of overflow or backup.

Using a factor of 3 allows for sufficient retention time, enabling solids to settle and biological processes to occur, which is essential for treating wastewater effectively. This capacity helps to mitigate issues such as clogging or under-treatment, which can lead to environmental contamination or system failure.

The other calculations provided—such as using 2, 4, or a fixed capacity of 200 gallons—do not align with the recognized standards for wastewater treatment needs and can lead to less effective systems that do not meet regulatory requirements for public health and safety. In particular, a fixed capacity of 200 gallons would not variably adjust to account for different daily flows encountered in smaller systems, making it insufficient for variable usage patterns.