Which of the following is true of an intermittent sand filter?

An intermittent sand filter indeed serves multiple important functions in wastewater treatment, and all of the statements provided highlight different essential characteristics concerning its operation.

The use of an intermittent sand filter for secondary wastewater treatment is pivotal because it effectively removes contaminants that primary treatment may not fully address. This process enhances the overall quality of the effluent, making it safer for discharge or further use.

In terms of the loading rate, the statement regarding the maximum surface loading rate of 1.2 gallons per day per square foot is significant. This specific measurement is critical for maintaining the effectiveness of the filter and ensuring that it operates efficiently without overwhelming the system, which could lead to clogging or reduced treatment efficacy.

The requirement for at least 24 inches of filter media that complies with specifications, such as ASTM C-33, ensures that the materials used in the filter provide adequate treatment capacity and longevity. Proper filter media not only facilitates effective filtration but also supports the biological processes necessary for treating the wastewater.

By encompassing all these accurate statements, the correct answer reflects a comprehensive understanding of the operational parameters and requirements for an intermittent sand filter in the context of on-site sewage facilities. Each point addresses a key aspect that contributes to the overall effectiveness and safety of the system.