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Is Boston Sinking?

Updated: Jan 14, 2019

If you’re buying or selling in the city of Boston, you may be surprised to know that many areas have endured an ongoing battle with structural settlement over the years. Whether you’re a potential buyer, seller, or agent facilitating a transaction, you need to be aware of this potentially expensive problem.

The affected areas include Back Bay, South End, parts of South Boston, Fenway area, Bay Village, parts of Beacon Hill, North End, parts of East Boston, and several other areas. The repairs can cost hundreds of thousands, and are not to be taken lightly.

To understand the issue, first we need a little background context…

Originally Boston was quite small and difficult to access as compared to today. However the city was expanded around 1820 by back-filling the surrounding salt marshes. This mission to create more land would undoubtedly violate a number of environmental regulations by today’s standards, however the need for valuable real estate far outweighed any environmental concerns at the time. The project would also deal with a sanitary problem the city was facing, due to sewerage accumulation in the Back-Bay mud flats.

The city was expanded in all directions, and landfill was acquired from all over. When it came to creating what is now known as the Back Bay area, the closest place which could supply this much suitable back-fill was Needham, so a railway system was constructed for the sole purpose of accomplishing this task. It ran 24hrs a day for about 50 years.

However, a heavy brown-stone building would undoubtedly sink into the man-made land and marshy earth underneath. To avoid this, large wooden pilings were driven deep into the earth past the landfill and organic silt, down into the more stable marine clay. It could be 20 feet or more before the stable soil was reached. The pilings were simply tall trees with the limbs chopped off, tipped upside-down and driven into the earth (Southern Yellow Pine was most commonly used). The structures could then be built on top of the pilings.

This marsh is located in Winthrop Ma, minutes outside of East Boston. This is what the majority of Boston looked like back in the early 1800's, before it was filled in.

After being driven into the ground, the tops of the pilings were leveled by chopping off the excess, and large granite blocks placed on top. This process would create the foundation for what are now considered some of the most well-kept historical buildings of this time period in the entire country. This was very labor intensive, and a very impressive undertaking especially when you consider the time period of mid-to-late 1800’s.

So what’s causing the sinking?

The pilings were intentionally installed so that 100% of the wood would remain submerged below the groundwater. This technique was not new, and had already been used in other parts of the world for hundreds of years. As long as the pilings remain completely submerged everything is fine.

Unfortunately the groundwater level did not remain consistent. Over the years it has dropped in certain areas due to Boston’s aging infrastructure. As groundwater leaks into the aged sewer pipes, tunnels, basements, etc., the solution has been to pump it away. This also happens every time a new tunnel, highway, or giant structure is built and the groundwater needs to be pumped away while construction takes place.

It is this pumping of leaking groundwater on a city-wide scale which has lowered the groundwater table, thereby exposing the wood pilings to the air. To amplify the problem, the natural recharging of groundwater levels through precipitation is stifled due to the lack of permeable ground which allows water to infiltrate back into the earth. When’s the last time you saw a lawn on Newbury St? Recharging systems and permeable roads are now being implemented to help cope with this issue, but that’s a subject for another article.

Once the groundwater becomes lowered, bacteria, mold, fungus, worms, and other organisms have the opportunity to flourish by using the wood as food. As the exposed tops of the pilings become deteriorated, the heavy structures which they support begin to sink.

The solution is not cheap….. potentially $250K on the lower end (depending on how many piles are damaged).

To create a proper work environment for the repairs, the pilings have to be exposed below the water table by several feet. This of course is challenging since the pilings sit directly underneath the building. The process goes as follows: access the piling, temporarily support the structure above, remove the decayed portion of piling, install a steel column to replace the section of damaged wood, and then pour concrete to encase the steel column up to the base of the granite foundation block. As each adjacent piling is replaced and encased, a wall of concrete begins to slowly grow. This is the new acting foundation for the structure. It could take months to fix an entire building.

What can one do?

Do your research before you buy. Most buildings have a condo association which will take account of any ongoing issues with the building and discuss how to spend the reserves (if there are any). The content of the meetings is often documented, and the minutes made available to the owners. Ask to see the minutes, and inquire(in writing) about any issues with past or present settlement.

During your home inspection, look for evidence of settlement. Although you will almost always find some degree of settlement, anything more than “normal” should be seriously scrutinized. Consider hiring a structural engineer for a more fine-tuned look into the structural integrity of the building.

Monitoring well located on Appleton St in the South End.

Look for monitoring wells in the sidewalk near the property. These wells are installed all throughout the city as a means to physically check and record the groundwater levels. They look not unlike a metal cap for a water or gas connection, except they say Monitoring Well on the top. You can check the Boston Groundwater Trust website (Monitoring Well & Logger Data page; also check out Project Lightwell page to find locations of Bluetooth enabled monitoring wells), and search the groundwater data on specific streets to see if there are any issues documented.

Additionally, make sure the homeowner’s insurance policy for the building has a supplemental ryder which specifically states coverage for failed underground pilings. This ryder will cost more to add to the policy, however it’s worth it’s weight in gold for piece of mind. Otherwise, it’s unlikely the average policy will automatically cover this.

So do you still want to live in the city? I’m sure the answer is YES! Just make sure you cover your bases by doing your own due diligence.

If you have any questions about my inspection process, or would like to know more about some additional considerations when buying in the city, please don’t hesitate to reach out!


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