The work on the Nisqually Line could be utility work in advance of the rebuilding of the line between Lakewood and Nisqually as part of the Point Defiance Bypass project. I've seen similar ROW prep work in the Portland area when they've built new streetcar or light rail lines.

As I recall, the plan was to have the Nisqually Line rebuilt and in regular operation by 2017.

Food for thought -- I wonder how quickly Sound Transit would expand Sounder service past Lakewood once the line is rebuilt. It goes directly past Dupont's new town center, which already has a transit center and park/ride adjacent to the tracks.