There is a reload in Sumas WA, here: [www.google.com]
... that sure seems to have open top garbage containers on the lot. The business name is Mountain View Reload, and they clearly do a considerable business in lumber reloading, but they seem to be virtually non-existent as far as a web presence.

I suspect that is where at least some Whatcom County trash goes to get on rail. There are no open landfills in Whatcom County, so trash has to go somewhere else.

Also of interest is Point Roberts WA in Whatcom County, but Point Roberts has no land or bridge connection to the rest of the county, and AFAIK there is no ferry either. Point Roberts does have a land connection to Canada. And, Point Roberts does have a trash transfer station. I suspect that Pt Roberts trash gets trucked through Canada to reach the main part of Whatcom County and goes to that reload, along with some other Whatcom County trash.

Whatcom County does have another trash reload in Ferndale, here: [www.google.com]