Final answer:
The purchasers need to make an application for approval because they have a septic system.
Step-by-step explanation:
The purchasers will need to make an application for approval before adding the new bedrooms because they have a septic system. Adding bedrooms can increase the usage of the septic system, as more people will be using the facilities in the house. A septic system has a limited capacity, so any changes or additions to the house that could potentially affect the system's functioning require approval.