presumably your AS flights are SEA-PDX-EUG ... I'm sure you know that DL-->AS connections at SEA are entirely airside; worst case is that you will arrive on the South Satellite and depart from the North Satellite ... as long as DL will check your bag(s) at the origin (if in fact you need to avail yourself of that), you should be able to get AS BPs at any SEA Customer Service desk (opposite the C2 gates, near gate D3, or between Gates N1 and N16 in the N Satellite [which is at your 1 o'clock as you come up the escalator from the train])