I found a two other images of ACW era pile drivers in my files. Both of these shots show scenes near the railroad wharf in Alexandria.
The first shows the railroad wharf with the pile driver on the south side of the wharf. The men in the foreground are constructing one of Haupt's "Arks."
The second shot shows the railroad wharf from Battery Rodgers later in the war. We know this because the car ferry transfer gallows have been reinforced with additional posts and beams. In earlier shots there is only one row of posts. The sheds on the wharf are also considerably improved from the earlier images.
Also note that there are two pile drivers visible in the image, but both are on the north side of the wharf. Also of interest is the box car and caboose on the wharf. I need to build a couple of those cabooses (also called conductor cars).