Hazard Level: 5

The last tunnel section of the drain has fallen completely off (as can be seen in the small picture above, and in the full size verion lower down on this page). The next section has also broken partly away from the rest of the tunnel, and looks as though it may have an old length of 2"x8" board under the end to help keep it from breaking the rest of the way off.

Once we've carefully climbed up into the tunnel (hoping that our extra weight is not enough to break off the cracked section) we find that the entire length of this leg of the tunnel has eroded down to the rebar cribwork in the center where the water flows. This is an overflow/runoff tunnel, so there is only a constant flow of water when the system overflows; but the tide comes partialy into the tunnel so this area likely always has a little water stuck in the eroded sections of the tunnel. The gurgling rush of water in the main tunnel can be heard from the entrance / overflow tunnel.

The overflow tunnel leads into the type of area we call an "overflow control" room. We're not sure if that's the real name for this type of room, but it describes it's function well. When the sewage and stormwater system gets more water than it can handle, the water backs up into this type of room until it gets to a certain level, at which point it flows over some form of dam or weir and out the overflow tunnel to the river. We're no experts in drain engineering, but that's the way we figure it works. We have found several types of these overflow control rooms, all mostly different but similar in the way they function. This one is an octagonal room with an inverted V shaped dam or weir across the middle. The weir is five or six feet tall, with about a 45 degree grade on each side. Steps are built in to make it easier to climb over. At the base of the up-stream side of the weir, water from the main tunnel flows into a gutter and out through a small tunnel towards downtown.

Two steringes were found washed up on the area at the base of the weir. Another danger of this area could be dangerous gases near the ceiling of the overflow room above the weir. We noted the air did not smell so good up there, and there was no vented shaft directly above this room.

A round cement tunnel continues on with a thin stream of greywater running back to flood control. It goes a short ways before coming to a vented shaft. The tunnel continues on, offset slightly to the side and several feet higher on the other side of the room. It looks as though the next leg was built atop the remains of an older oval-shaped brick tunnel, with parts of the older brick tunnel still in place creating a slippery obstacle to climb over. There are also the remains of other old brick walls that were incorporated into the construction of this area.

The next leg of the tunnel is about the same length as the last, and comes to a juncture/manhole room with a crawlable but very wet tunnel going towards downtown. More crumbling brick and concrete walls here. it looks as though they used a bulldozer to shape the end of the small side branch, and a dry green plastic pipe juts out from one corner. We don't bother with the small side branch since it is half full of sewage, opting instead to continue on up the main line.

The next juncture we find is a room made mostly of brick, with a vented grate above. The main line continues on to the right (away from downtown); and there are two small tunnels, not large enough to fit through. One is level with the floor, and made of brick. looking into that one, it seemed to go to a small brick room with a small arched tunnel on the other wall.. this tunnel did not look like much flowed through it. The other small tunnel is on the wall above the brick one is made of cement and has a goodly amount of water flowing from it. It goes in just a few feet and turns to the right.

The main line continues on with the sound of traffic above... we are now under Hancock St. We went a short ways up this tunnel and saw that the water got a bit deeper further up. We went up to the point where we could see a metal pipe jutting down from the ceiling, and faint light from a vented juncture far up ahead. The collapsed remains of "Old Outflow #8" must be somewhere around/under this area, but we had to turn back because we knew that it would not be long before the tide came back into the overflow tunnel.