In which situation are alternative small wastewater treatment systems considered unnecessary?

Alternative small wastewater treatment systems are generally considered unnecessary in the situation where impervious formations are found at a depth of 10 feet. This is because an impervious layer, such as bedrock or clay, significantly hinders the movement of water and prevents the infiltration of wastewater into the soil. Since the wastewater cannot percolate through an impervious layer, traditional septic systems or other conventional wastewater treatment methods can effectively treat and contain the sewage without the need for alternative solutions.

In the context of this question, an impervious formation indicates that there is a physical barrier that protects the groundwater from contamination, making alternative systems redundant as the existing methods can be utilized without risk to the environment.

The other scenarios mentioned involve conditions that typically necessitate alternative treatment solutions: limited space and inadequate surface water suggest challenges for conventional systems; highly porous formations might lead to rapid wastewater dispersion and potential contamination; and high groundwater levels can cause problems with system failure or contamination of the water supply. Each of these conditions indicates a need for additional engineering solutions or alternative systems to ensure effective wastewater management.