How much separation is required between the trench bottom and a soil wetness condition in sandy soil?

The correct answer is 18 inches, which is the required separation between the trench bottom and a soil wetness condition in sandy soil. This specification is aligned with septic system regulations that ensure adequate drainage and to prevent the potential for contamination of groundwater. The 18-inch separation helps maintain a safe barrier between the effluent and the water table, facilitating proper absorption and treatment of wastewater in sandy soils.

Sandy soils are known for their rapid drainage capabilities; however, they also can become quickly saturated during heavy rain or flooding conditions. Therefore, the requirement for this specific separation distance is crucial. It accounts for fluctuations in groundwater levels, ensuring that even in wet conditions, the septic system remains operational without causing adverse environmental impacts. The 18-inch clearance helps mitigate the risk of effluent surfacing or reaching the saturated zone, which could lead to pollution of nearby water sources.

Other choices present either insufficient or excessive separation distances that do not comply with current septic system design standards for sandy soils.