What happens with the septic exactly?
If your septic tank has a concrete lid it may just need new 'tar rope' to create a new seal on it. Most of the time that is why the older ones get water in them. Otherwise the tank may need to be pumped out and possibly patched due to roots breaking it.
Yeah, I am hoping they are just expanding some. Thankfully there is no chance of a housing development going in. Everything here is zoned for agricultural use but I doubt that is what they are up to.