In which condition is it inadvisable to use the Wisconsin mound system?

Using the Wisconsin mound system is inadvisable in sites with restricted gravity flow absorption because this system relies on proper drainage and the ability for effluent to flow freely through the soil layers. The mound system is designed to elevate the distribution of wastewater above the natural ground level, where absorption occurs in the unsaturated soil layers. If the site has restricted gravity flow, it can lead to water pooling or inadequate treatment of the effluent, resulting in potential environmental impacts, odor issues, and system failure.

In contrast, hilly terrains, open fields, and areas with sandy soil may present challenges of their own, but these issues can often be managed through engineering solutions or specific design adaptations of the mound system. For instance, hilly terrains can still function if designed correctly to accommodate the slope, while sandy soil typically allows for good drainage, making it more suitable for absorption, albeit with careful consideration for the rate of percolation.