What must be available when conventional subsurface sewage disposal systems are installed?

When installing conventional subsurface sewage disposal systems, having an additional area for expanding the disposal field is essential. This requirement arises from the need to ensure that if the initial disposal area becomes ineffective or saturated, there is a backup space available for extending the system. This flexibility helps maintain the functionality and efficiency of the septic system over time, allowing for adjustments if the soil conditions change or if the system needs to be expanded due to increased household waste.

The other options may contribute to overall system planning and installation but do not address the critical need for an expansion area directly related to the function and longevity of the sewage disposal system. For example, while a detailed survey of the area can be useful for site assessment, it does not provide the redundancy necessary in the system design. Access to a public sewerage system isn't applicable for conventional septic systems, which are self-sufficient. Lastly, a backup generator may be beneficial in certain situations where power is needed for pumps but is not a fundamental requirement for the installation of the septic system itself.