We’re having trouble getting funding to change the structure of our CSOs.
When I had a similar situation, I used the city of Spokane, WA as an example. They haven't completely separated their CSOs, but they've taken care of most of them and it reduced their overflow volumes by up to 85%. Of course it cost $50 million to do that, which is not always available... anyway, they have a complete review of their process on their city website. Hope you find it as helpful as I did.
There have been funding options in place since 1995 from the EPA in regards to upgrading combined sewer overflows. Have you seen that guidance memo they produced? If not, it’s online: https://www3.epa.gov/npdes/pubs/owm0249.pdf
I know its old, but the info is still good. Cleveland used SRF loans successful. South Portland, ME used general obligation bonds. There are federal grants, state grands, and numerous loan programs available as well. It sounds like you’re trying to convince the powers that be to proceed with a specific funding option??? I might look at every option in that link, put together a few proposals, and then submit some to get real answers that you can then use to create an initiative to get your funding.