It's going just under orbital velocity at separation
I don't have the exact figure handy, but I'm pretty sure separation happens within about 200 feet per second of orbital velocity. Separation occurs at an altitude of approximately 120 kilometers. The OMS engines fire at that time to achieve orbital insertion.
Here's some reference info on the ETs. They impact somewhere in the Indian Ocean. Since they don't have heat shielding, there probably isn't a lot that makes it to the surface.