Regarding mound fill depth, what is the required minimum and maximum fill depth?

• A. 4 inches minimum and 24 inches maximum
• B. 6 inches minimum and 24 inches maximum
• C. 6 inches minimum and 36 inches maximum
• D. 8 inches minimum and 30 inches maximum

Answer: (C)

In mound systems, the fill depth refers to how thick the soil cover around the mound’s components must be. This depth is chosen to balance effective treatment and protection with practical, maintainable construction.

Six inches of fill minimum ensures there’s enough soil above the system to provide proper filtration, warmth, and protection from freezing and surface disturbances. If the fill is shallower, the system can freeze or be damaged and may not treat wastewater adequately.

Thirty-six inches of fill maximum keeps the mound from becoming excessively tall, which could hinder drainage, reduce air exchange, increase loading on the system, or create maintenance challenges. Too much height can also complicate installation and structural stability.

So the required range is six inches minimum and thirty-six inches maximum, which is why that option is the best fit.