OSSF surface application always requires:

In the context of OSSF surface applications, secondary treatment and disinfection are essential requirements. Secondary treatment effectively removes a greater amount of organic matter, pathogens, and nutrients from the wastewater compared to primary treatment, which primarily focuses on settling solids and reducing floating materials. This is crucial because when effluent is applied to the surface, it has a direct interaction with the environment, including soil, plants, and possibly water sources.

Disinfection following secondary treatment ensures that any remaining pathogens are effectively reduced to safe levels, protecting public health and the environment. This combination of treatment processes is critical in minimizing contamination risks and complying with regulatory standards designed to safeguard water quality and ecological integrity.

While primary treatment is a vital step, it does not provide adequate purification for surface applications since it may leave higher concentrations of contaminants in the effluent. Therefore, relying solely on primary treatment, even if coupled with disinfection, would not meet the necessary safety standards for surface application. Tertiary treatment, while beneficial for achieving even higher water quality, is not a strict requirement for all surface applications, making secondary treatment and disinfection the foundational components necessary to ensure the safety and efficacy of this practice.