Dartmouth Street: A Tale of Two Sewers
Coordination with the Boston Water & Sewer Commission was essential in solving the depressed groundwater levels in this area of the City.
The Boston Water and Sewer Commission (BWSC) manages the largest and oldest system of its kind in New England, providing drinking water and sewer services to more than one million people daily. BWSC was created by the Massachusetts Legislature in 1977, replacing separate water and sewer divisions of the city’s Public Works Department. BWSC is overseen by a three-member Board of Commissioners that is appointed by the Mayor with the approval of the City Council. Source: https://www.bwsc.org/about.
In response to low groundwater levels reported by the BGwT, BWSC conducted several investigations of their infrastructure along Dartmouth Street in the area between Marlborough and Beacon Street in the Back Bay neighborhood of Boston.
BWSC map with sewers in red and purple, storm drains in green, and manholes in black cirlces.
BWSC installed two groundwater injection wells in the area. Using these wells they injected potable water and green dye to perform dye tests. The method is simple. If the green dye showed up in their sewers and/or manholes that would indicate groundwater intrusion from a leak within their infrastructure. Several leaks were identified, with particular problems in a manhole near the Public Alley No. 418 between Beacon and Marlborough Streets and a sewer line that lead to the West Side Interceptor under Beacon Street was found to have several leaks.
Green dye seeping into a manhole (left) and joints in a brick lined sewer along Dartmouth street (right).
Leaks in the manhole were grouted, and the manhole was also lined. In addition, the sewer was lined in two sections. During this time the BGwT had a series of automated data loggers installed in 8 different observation wells recording the water level in each well every hour.
BGwT Observation Well and BWSC Recharge Well Locations
BWSC groundwater contour map showing groundwater levels below El. 3' BCB.
BWSC relined manholes and sewers in this area. That infrastructure was roughly at El. 3' Boston City Base (BCB). The above groundwater contour map aided BWSC by helping them understand where the depressions in groundwater were and where to look for possible sources of inflow into manholes or sewers.
The data logger plot and groundwater contours below show the increase in groundwater from El. 3' to 3.5' BCB. For the better part of a year, the groundwater fluctuated but never consistently rose above El. 3.5' BWSC continued their investigations in the area; looking closely at all infrastructure in the area at El. 3.5' and above.
BGwT Logger Data increased from El. 3' to 3.5' BCB.
BWSC groundwater contour map showing groundwater levels at approximately El. 3.5' BCB.
BWSC searched high and low for a leak but could not find any additional points of groundwater infiltration. BWSC Chief Engineer John Sullivan instructed his staff to divert flow in a sewer which the bottom was at El. 3.5' BCB. Once that sewer was free of all flow a giant hole in the bottom of it was discovered with groundwater bubbling up from below.
Groundwater observed bubbling up from a sewer along Dartmouth street.
The same sewer as the above image now grounted and relined.
Groundwater levels recovered within 24 hours of the repair and were sustained since the source of groundwater withdrawal was no longer present. The data below indicated a rise in area groundwater levels of 1.5'+ in 4 of the 8 observation wells closest to the leak. The remaining 4 wells further away from the leak also rose around 1'+.
BGwT Logger Data increased from El. 3.5' to 5'+ BCB.
And since then our manual readings and BWSC contours below have indicated a consistent, positive trend.
BGwT manual reading data for 10 observation wells.
BWSC groundwater contour map showing groundwater levels above El. 5' BCB.
