The streetcar track did go south along 8th from E St. The 1936 aerials aren't clear, but I think the track (it was single track here) went down the center of the street, not along one side.
Looking at the google streetview, there does appear to be a line of manholes on that side of the street, so I too am guessing this is a patch over a sewer (storm or sanitary I'm not sure) and not a patch over a streetcar track.
However, while the pavement is up you should check along the center of the street to see if you can find any other signs of rails or patches.