If you look up "Passport in Time" you will find entries about working on the tunnel. Look up Past events.
Passport in Time is a program of the USDA Forest Service. The various National Forests and Grasslands have projects that they list on the PIT website. Your application goes to the person in charge of that particular event along with the rest. That way everyone has an equal chance of being chosen.
I have helped dig up 1,300 year old camps and helped rebuild a National Historic site from the 1940's.
Each state is listed that is having an event.