Which aspect is critical for the design of mound systems in regards to stability and drainage?

The critical aspect for the design of mound systems in terms of stability and drainage is the slope ratio. The slope ratio is vital because it influences the stability of the mound, preventing erosion during intense rainfall and ensuring that water is distributed evenly across the system. A well-designed slope facilitates adequate drainage, allowing effluent to filter through the soil layers effectively. This helps prevent ponding, which could lead to system failure.

While the other factors, such as material composition, total area, and water source proximity, do play important roles in the overall effectiveness of a mound system, they do not have the same direct impact on stability and drainage as slope ratio does. Material composition affects how the effluent is treated but does not necessarily address how the mound itself holds up or how well it drains. Total area is significant for ensuring that there is enough space for effluent dispersal but does not influence the stability of the mound structure. Similarly, the proximity of a water source can affect drainage patterns and potential contamination but is not a primary factor in the structural stability of the mound itself.