The exact location of Vault 111 would be a little Northwest of https://www.google.co.uk/maps/place/394+Monument+St,+Concord,+MA+01742,+USA/@42.47163,-71.3496119,1199m/data=http://forums.bethsoft.com/topic/1529938-skill-perk-line-up-speculation/!3m1!1e3!4m2!3m1!1s0x89e39a25b5066e99:0x7b4c7a3fe91aad35!6m1!1e1 marker, most likely where we see the huge circular driveway. The bridge next to the marker is the one we see raiders crossing in the footage, and the Minute Man Monument has been relocated to the other side of the river, immediately South of the marked building. The lake in question is the one seen to the East. Note that if you zoom the map out a little, you can see Concord to the Southeast, exactly as we see it in the footage.
Also, the escape route would not have been designed as a conventional emergency exit. It would have been deemed as classified due to the sensitive nature of the tech inside the vault, as well as the nature of the experiment itself. Once the experiment was completed, should the main exit have become blocked or damaged, for example by a 747 or equivalent dropping out of the sky following an EMP blast, then the vault scientist/s would activate the emergency exit protocol and would then allow access to the tunnel. And the reason that the tunnel would be filled with water and connected to the nearby lake would be to prevent anyone from attempting unauthorised access into the vault, and to keep it's location a secret.
This would also be aided by the fact that, when the cryo tech inside is fully active, the internal pressure of the vault would instantly kill anyone not inside one of the pods. The inclusion of the tunnel would also perfectly explain how the Institute were able to gain access to the vault, by sending in a recovery team consisting of modified amphibious synths, designed to swim up and into the compression chamber under the vault, who would then be unaffected by the crushing pressure inside. Once in the vault itself, they would remove the pod containing the protagonist's spouse and child and place it into a portable containment system to maintain the pressure inside in order to keep it's inhabitants alive. If the pressure were to be removed, any water inside the pod, including 70% of the body mass of both Shaun and his parent, would instantly expand, killing them both.
With regards to my definition of V.A.N.S., the Pip-Boy already has a built in targeting and navigation system. My suggestion of it being a nautical system would mean that both of these are replaced with an equivalent that will function perfectly when underwater. Add to this the fact that, should a nuclear war actually occur (which it did), you would need individuals capable of recovering any useful resources to ensure ongoing survival, and one huge potential source of recoverable resources that would remain relatively untouched would be the rivers and lakes in the surrounding area, as well as the sea itself. This is one of the many reasons why I believe that every single person intended for entry into vault 111, including our protagonist and their spouse, would have been either in the US Navy or the Marine Corps. Because by definition, they would have recieved specialist training in underwater survival skills.
Finally, with regards to the http://www.gamesas.com/topic/1526246-the-glowing-sea, I think that Todd has pulled another "200 years" on us by showing the 'yellow haze' in the area with the deathclaw. These look to be nothing more than the beginnings of sandstorms, as seen http://allpics4u.com/www/slike/place/sydney_storm/sydney_storm6.jpg. When you consider how much moisture would be required to whip up a storm capable of unleashing radioactive lightning strikes, as Todd has told us, the only location in the area of the Commonwealth that would be capable of generating such storms would be Boston Harbor, exactly as I have explained in my theory.
EDIT: the above details regarding V.A.N.S. would also suggest that there would be a huge number of underwater collectibles to discover and then salvage, just as there are in GTA V. This could involve sunken ships, boats, submarines, and even aircraft, as well as a ton of other possibilities. Note that if the concept art is anything to go by, we will be seeing some massive underwater enemies, including the giant squid that has already been shown, and of course the submarine mines that kicked the Great War off in the first place...