Last year’s drought had Boston worrying anew about a longstanding problem: The foundations beneath centuries-old homes and other buildings are at risk of rotting and crumbling.
It seems counterintuitive that a lack of water would be a problem for foundations, but this odd situation is the result of an unusual facet of Boston’s history: A large portion of the city sits on man-made land. Structures built on the landfill are supported by dozens of 30- to 40-foot-long wood pilings, similar to telephone poles, that reach down through the landfill to a harder layer of clay. These pilings sit entirely below the water table, which protects them from microbes that would attack them in dry air, causing rot.
Water leaking into sewers or tunnels can drop the water table below the pilings even in wet years. But last year’s drought brought the water table dangerously close to the tops of some of these pilings, putting them at greater risk. How did Boston end up in this situation? It all started in the 17th century, not long after the city was established.
When the Puritans arrived in 1630, much of the land that underlies some of the oldest parts of Boston didn’t exist. They settled on a small peninsula—called Shawmut by Native Americans—that covered less than 800 acres and was connected to the mainland by a narrow neck that became submerged during high tide. It had the advantage of a dependable supply of springwater, and it was well positioned for maritime commerce.