I visited this place a number of times before I had talked to enough people to actually find the best access. It's hard to tell you that you will have to violate some protocols to visit this place. No way in but down on the tracks. I found a trail that leads from State St. (WV 7) down onto the tracks. Overall it's an easy walk. The hard part comes when you get there and try to find a good vantage point to take photos from. There's a lot of debris in front of the falls and a lot of dead wood and briars on the hill opposite. But I'm sure you'll manage.
Follow WV 7 into Terra Alta. Look for a trailer park on your right (39.451978, -79.552012). There's a row of mail boxes near the entrance. Park just past that and if you see anyone out ask them for permission just to be nice. Right where you park and off to the right, you'll see a traill that leads down to the tracks. I'm not telling you to go that way because it's not legal, but that's the only way to get to the falls short of sliding down the hill in back of Ball Auto and I doubt you would enjoy that even if they would let you. Down the tracks to the right about 1/4 mile.