What type of soil generally allows for the slowest drainage in mound systems?

Clay soil is known for its fine particles and compact structure, which creates a tightly packed environment. This composition significantly impedes water movement, resulting in slow drainage. The small pore spaces between the clay particles restrict the speed at which water can pass through, leading to reduced infiltration rates. In mound systems, where effective drainage is crucial for proper wastewater treatment, clay's tendency to retain moisture can negatively impact the performance of the system, causing potential issues such as surface ponding or prolonged saturation. This characteristic makes clay soil the type that generally allows for the slowest drainage compared to other soil types mentioned.