By: Tom Fletcher, CFP®
If you’ve ever been on one of those iconic sightseeing duck boats that drive around Boston before they dive into the Charles River, one of the things (between quacks) the guides always talk about is how Boston’s Back Bay used to be under water. I know these things, because it seems every time we have a visit from an out of town guest, the duck boat tour is one of our top ideas as a great way to get familiar with the city of Boston. Anyhow, it turns out when puritans arrived some 390 years ago, much of the city land we see today didn’t exist at all. Over the next 270 years, and mostly in the late 1800’s, to accommodate Boston’s growing population, engineers added significant amounts of landfill mostly from other
parts of the city to expand Boston’s metropolitan landmass footprint. And today Boston has the distinction of having the most “filled land” of any city in America. It’s not just Back Bay that received landfill, but also neighborhoods in Beacon Hill, Fenway, North End, South End, Chinatown and many others. In total the city’s footprint grew by over 5,000 additional acres!
Because filled land is too “squishy”, it generally can’t support a building. As a result when brownstones on this newly formed land were constructed, they required multiple wooden pilings to be driven through the filled land (which was full of water) and into the clay below in order to prevent these buildings from sinking. These 30-40 foot telephone pole like tree trunks literally have sat below the water level holding up the infrastructure of some of the oldest buildings in the city.
The miracle of these pilings is as long as they are submerged in water, they can last hundreds of years without decaying. However if groundwater levels drop and they become exposed to air, microbes attack the exposed piling wood which can gradually rot and potentially lead to structural building damage. Groundwater levels can drop for numerous reasons such as lack of rainfall, constructions projects, and leaks in sewers and subway tunnels. Conversely if water levels again rise, the rotting stops.
In the 1980’s after multiple historic buildings exhibited signs of structural damage related to rotting foundational pilings, the city established the Boston Groundwater Trust. This organization has drilled and currently monitors over 800 wells throughout the city to sample groundwater levels on a regular basis.
When the top of the pilings decompose there are generally two courses of action available to the owners of the building. They can wait for structural issues to develop such as doors and windows not being able to open or close, which eventually can lead to a building being condemned, or they can have their pilings “underpinned”. This means excavating the basement to expose all the pilings, and replacing the rotted tops with concrete and steel.
You’re probably reading this article and scratching your head wondering what I’m trying to get at here. It was partially to pique your interest in perhaps a little known history of Boston architecture, but also I’m quite familiar with this topic because the building where we live had to have all their piling tops replaced when we bought the place. Fortunately the water levels in our area are stable and the doors and windows in the house continue to open and close properly. If you’re ever in the neighborhood, feel free to pour a little water in a tree pit to preserve the pilings!