(1) Individual on-site wastewater disposal systems may be approved in an area where individual on-site wastewater disposal systems otherwise would not be approved because of the availability or feasibility of connection to a centralized wastewater treatment system only after a contract has been awarded or other definite commitments as are deemed sufficient to the department are formalized for the construction of a centralized wastewater treatment system that upon completion will adequately serve the property. Individual on-site wastewater disposal systems shall only be approved when the centralized wastewater treatment system will be completed and available for use within thirty-six (36) months. The department may approve the installation of a system under these circumstances only if the system will comply with the requirements of Section 41-67-5(1) and comply with all construction requirements of the department. The system may be installed only after the developer has signed a written agreement with the centralized wastewater treatment provider stating that the developer will connect to the centralized wastewater treatment system when it becomes available, and the provider of the centralized wastewater treatment system being constructed certifies that the centralized wastewater treatment system will have adequate capacity to accept the sewage to be produced by the individual on-site wastewater disposal systems. The developer shall install an internal sewage collection system from each lot to the connection point to the centralized wastewater treatment system as he develops the streets of the subdivision. Upon completion of the construction of the centralized wastewater treatment system, all individual on-site wastewater disposal systems shall be abandoned and all residences, buildings or facilities connected to the centralized wastewater treatment system.

(2) The department may approve the use of a sewage holding tank for the purpose of providing sewage services. The department shall require the proper abandonment and removal of the sewage holding tank and connection to a centralized wastewater treatment system when that system is available, or the usage is no longer needed.