Volunteers with sufficient experience and skills can do reconstruction work too.
Hand tools are the norm.
Powertools are used for some projects. I'll pass it on to the appropriate local PCTA or agency contact. Each year the PCTA, other groups and agencies offer a number of great short term, volunteer projects. Other projects involve 2-4 days while camped at trailheads, roadside campgrounds or at backcountry sites. The PCTA and other groups, in cooperation with land managing agencies, also sponsor a variety of longer projects that draw volunteers from around the US and beyond.