Boston has been urbanized for a very long time, and along with urbanization comes a growing problem: storm water flooding. In Boston, the Back Bay area was also filled in for development in the late 1800’s. More than 100 years later, the shrinking water table in Boston has created some issues with the stability of the fill and the buildings that rest on top of that.
On natural land, rainwater is reabsorbed into the ground where it is filtered through the soil and eventually returned to the underground water reservoirs. In the city, buildings and driveways, roads and other structures cover much of the surface and interrupt the natural recharging process that would otherwise keep the water table at a relatively constant height.
To accommodate the loss of natural land, cities like Boston have extensive storm sewer systems that aggregate storm run-off and discharge it back to rivers, lakes and reservoirs. While it’s good to get water off the streets, storm drains don’t provide an ideal solution. By redirecting water to lakes and rivers, the water levels in rivers and lakes tend to rise, sometimes beyond what the waterway would normally hold. At the same time, storm sewers reduce the water table in urbanized areas.
Reduction of the local water table has been particularly bad for areas like the Back Bay, which was constructed on landfill. Untreated wood pilings that support buildings in this area and were supposed to be submerged under water are now exposed because the water table has fallen. This exposure has made the pilings more susceptible to decay and has compromised the stability of these buildings.
Each permanent structure in the city reduces the amount of land that is available to reabsorb rainwater, and places additional strain on the remaining natural land. Municipalities and homeowners alike are now looking for ways to recharge the local water table by returning storm water runoff to the ground in highly urbanized areas.
One way to accomplish this is through the use of a dry well. Dry wells have been used in Boston for a long time to help reduce storm water flooding. A dry well is a special structure that is designed to collect run-off and return it to the ground, primarily through infiltration.
A dry well consists of a pit that is filled with gravel or other coarse material. Runoff from building roofs is directed into the dry well where the water is returned to the surrounding soil through perforated pipes. Dry wells are designed to distribute any overflow that might occur following a significant storm or melt. Dry wells can be custom-engineered on site or can be made from pre-fabricated components that can safely discharge 25 gallons or more of water at one time.
A dry well must be constructed deep enough to avoid freezing in the winter, but not so deep that it sits below the local water table and ends up acting as a groundwater reservoir instead. Dry wells are constructed completely underground so they do not significantly alter the visible landscape of a property. Properly maintained dry wells can last between 30 and 100 years!
The location and construction of dry wells is exceptionally important because an improperly constructed dry well can cause damage to foundations or flooding in areas adjacent to the dry well. Certain areas are not good for dry well construction, including land where clay and other non-porous soils are prevalent.
If you would like more information about installing a dry well for your home, or you have a dry well that is in need of maintenance or rebuilding, please contact Boston Standard Plumbing & Heating at (617) 288-2911 to schedule a consultation.
In the right circumstances, dry wells in Boston can make a significant difference in the long-term health, well-being and value of your home. They can also help preserve the local water table and provide an ideal solution for controlling rainwater runoff.