What is the best type of drain field if there is a water table that raises 6 inches?

A humped, long, and narrow trench is the most effective type of drain field in conditions where the water table is prone to rising, as in this case where it raises 6 inches. This design allows for better drainage and more effective wastewater treatment. The humped configuration elevates the outlet of the trench above the fluctuating water table, helping to prevent the infiltration of groundwater back into the drain field, which can lead to system failure or less effective leaching.

A long and narrow trench shape maximizes the surface area available for effluent to disperse, which can improve absorption and treatment of wastewater as it moves through the soil. The shape inherently supports both aeration and filtration processes that are key in maintaining a healthy drain field.

The flatter and wider trench would not provide the same advantages, as it increases the risk of saturation from the rising water table, leading to reduced performance. Shallow and square areas can also be ineffective in managing water levels and may create conditions that impair drainage. A deep and wide trench could be beneficial, but if the water table rises, it may become difficult to maintain the necessary separation from the water table, rendering it less effective.