(a) Shall be for the replacement or major rehabilitation of an existing collection system which was not build with Federal funds awarded on or after October 18, 1972, and shall be necessary to the integrity and performance of the complete waste treatment system; or

(b) Shall be for a new cost-effective collection system in a community in existence on October 18, 1972, which has sufficient existing or planned capacity to adequately treat such collected wastewater and where the bulk (generally two-thirds) of the expected flow (flow from existing plus future residential users) will be from the resident population on October 18, 1972. The expected flow will be subject to the limitations for interceptors contained in § 35.2123. If assistance is awarded, the grantee shall provide assurances that the existing population will connect to the collection system within a reasonable time after project completion.