Sorry, took a second to figure out how this thing works (Moderator can delete the previous post).
Presently a Chicago-pool NPCU is working on the Cascades route, equipped with a custom auxiliary Main Resovoir Compressor being tested as a method to hopefully alleviate some low main res pressure issues experienced by the Cascades Talgo Equipment. Since the NPCU is taken from the Chicago pool it was replaced in the pool with a Cascades NPCU for the duration of the test, I don't know how long this is expected to go on for but it's been about six months now.
In layman's terms Seattle and Chicago traded a pair of NPCUs to test some equipment, thus there's a PH-v NPCU working on the Cascades, and a Cascades NPCU working out of Chicago.