Each level of treatment (Type 1, Type 2, and Type 3) results in different levels of effluent quality. As the treatment level increases, the overall size of the dispersal field can be reduced, and with proper engineering design, it may also allow for smaller minimum horizontal setbacks from watercourses.
Type 1 effluent is produced by a septic tank that holds three days' worth of daily wastewater flow before the effluent exits the tank into either a pump chamber or distribution box. A common misconception is that Type 1 systems are always gravity-based, but many Type 1 systems are pressurized. Since regulatory changes in 2005, it has become more difficult to find locations where gravity systems are still permitted.
According to BC Sewerage System Regulations, Type 2 effluent must have a Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS) concentration greater than 45 mg/L. This level of treatment is usually achieved with an air pump and media in a separate chamber within the tank, providing an environment where bacteria can grow and treat the wastewater more effectively. Keeping the system aerobic allows organisms that would typically not survive in a conventional septic system to thrive and improve treatment. Using Type 2 effluent can help reduce the size of the dispersal field.
Type 3 systems can only be designed by engineers and must be installed under their direct supervision. According to BC Sewerage System Regulations, Type 3 effluent has a BOD greater than 0 mg/L, TSS greater than 10 mg/L, and a median fecal coliform density exceeding 400 colony-forming units per 100 ml. Type 3 systems are similar to Type 2 systems but typically include additional disinfection, such as an ultraviolet (UV) lamp or chlorine, to further treat the effluent before it enters the pump chamber. These components require annual maintenance and can be more expensive to operate than Type 1 or Type 2 systems. However, Type 3 systems allow for a further reduction in the dispersal field size compared to Type 2 systems.