In DC, they're storing the combined runoff+sewage until it can be treated: https://dcist.com/story/23/09/18/new-anacostia-river-tunnel-online-sewage-overflows/

In DC, they're storing the combined runoff+sewage until it can be treated: https://dcist.com/story/23/09/18/new-anacostia-river-tunnel-online-sewage-overflows/ https://dcist.com/story/23/09/18/new-anacostia-river-tunnel-... As expensive as this project is, separating the storm drains from the sewage lines (https://en.wikipedia.org/wiki/Combined_sewer https://en.wikipedia.org/wiki/Combined_sewer) in an existing system is much more costly.