May 9, 2008
Ms. Kristin Kara, Project Manager
Boston Redevelopment Authority
One City Hall Square
Boston, MA 02201-1007
Subject: 30 North Margin Street
Dear Ms. Kara:
Thank you for encouraging me to comment on the supplementary information filed on this project. The Boston Groundwater Trust was established by the Boston City Council to monitor groundwater levels in sections of the City where the integrity of building foundations is threatened by lowered groundwater levels and to make recommendations for solving the problem. As such, my comments are limited to groundwater related issues.
According to the letter dated April 17 from McPhail Associates, the project intends to use slurry walls to act as the groundwater cutoff for construction of the project. While the letter does not address construction of the base slab, it was stated at the public meeting on March 4 that the project intended to use underdrains to relieve hydrostatic pressure on the foundation.
The letter states that "the planned design for the basement construction at 34 Cooper St (I assume that this is an alternate address) will not result in changes to the groundwater level outside the site". It is not clear whether this statement applies only to the construction period or during operation of the project. Under Article 32 of the Boston Zoning Code, projects in the section of the North End in which this building is planned to be located must demonstrate that they will have nonnegative impact on groundwater levels on their site or on adjacent lots. As we have seen from the Central Artery/Tunnel project, it is possible for slurry walls to have flaws which ultimately lead to leakage. In order to provide assurances for the long term, the proponent should commit that any leaks that develop in the walls will be sealed.
The proposed underdrains also present the possibility of creating a path that will cause withdrawal of groundwater and a lowering of groundwater levels on adjacent lots. The best way to prevent this is to construct the building using a waterproof pressure slab. Because the building has a relatively modest footprint, this is likely to be a practical solution.
I look forward to working with the proponent and the Authority to assure that the project cannot have a negative impact on groundwater levels in the North End.
Very truly yours,
Elliott Laffer
Executive Director
Cc: Kathleen Pederson, BRA
Maura Zlody, BED
