The YMCA has filed some early concept plans with Arlington County sketching its vision for replacing its Virginia Square facility with two structures — a new gym and an apartment building. This project at 3400 and 3422 13th Street N. represents the last of three developments concentrated within a seven-acre site along Washington Blvd, from N. Lincoln Street to Kirkwood Road. The first two have been approved: a 270-unit apartment building, “The Kirkwood,” for the southeast corner, where Kirkwood Road and Washington Blvd intersect, and an affordable housing project on the site of American Legion Post 139. The Y’s proposal is not only the last — at 4.39 acres, it is also the biggest.