Whenever the governing body of a locality or a combination of governing bodies of two or more localities is using the authority of this chapter to construct a new sewage treatment plant, or a hydraulic expansion or major upgrade of an existing sewage treatment plant, the facility shall be designed and constructed so that it has the capability to treat the septage from all onsite sewage disposal systems, which are not adequately served by another approved disposal site, located in the area of the locality or combination thereof to be served by such plant. However, the locality or combination thereof may limit the amount of septage that the sewage treatment plant is designed to accept in order to eliminate or reduce a disproportionate engineering, design, or fiscal burden that may be placed on the sewage treatment plant or its users, to utilize cost-effective regional approaches, or to address engineering design considerations including protection of biological treatment processes. The locality or combination thereof shall notify the Department of Environmental Quality of the septage treatment capability of the sewage treatment plant prior to the Department’s issuance of a state certificate to construct for such new, expanded, or upgraded facility. The locality or combination thereof shall provide a copy of such notification to the Board of Health to assist the Board of Health in its long-range planning pursuant to § 32.1-163.2. This notification requirement shall not apply to any new project for which a preliminary engineering report has been submitted to the Department of Environmental Quality on or before December 31, 2008.