The maximum grade for drain lines in a disposal field is ___ per 100 feet.

The maximum grade for drain lines in a disposal field is ___ per 100 feet.

• A. 1 inch per 100 feet
• B. 2 inches per 100 feet
• C. 3 inches per 100 feet
• D. 4 inches per 100 feet

Answer: (C)

In a disposal field, drain lines rely on gravity to move effluent through the laterals and into the surrounding soil, so they must have a gentle, uniform slope. A slope that is too steep would cause the liquid to flow too quickly, reducing contact time with the soil, risking uneven distribution, erosion, or bypass of the treatment process. The maximum allowed grade for these lines is three inches of rise per one hundred feet of run, which is a 0.25% slope. This keeps the flow slow enough for the soil to absorb and treat the effluent evenly along the entire length of the lateral.

In a disposal field, drain lines rely on gravity to move effluent through the laterals and into the surrounding soil, so they must have a gentle, uniform slope. A slope that is too steep would cause the liquid to flow too quickly, reducing contact time with the soil, risking uneven distribution, erosion, or bypass of the treatment process. The maximum allowed grade for these lines is three inches of rise per one hundred feet of run, which is a 0.25% slope. This keeps the flow slow enough for the soil to absorb and treat the effluent evenly along the entire length of the lateral.