October 28, 2008
Mr. John OBrien
Boston Redevelopment Authority
One City Hall Square
Boston, MA 02201-1007
Subject: Prudential Center Expansion
Dear Mr. OBrien:
Thank you for the opportunity to comment on the Draft Project Impact Report for the 888 Boylston Street and Exeter Residences 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 reduced groundwater levels and to make recommendations for solving the problem. Therefore, my comments are limited to groundwater related issues.
I am pleased with the commitment that the proponent has made to meeting the requirements of Article 32 and the thought that has gone into fashioning a system that can meet the goals of the Groundwater Conservation Overlay District. I am also pleased that the proponent has continued to work on developing a more detailed plan during the PruPAC review process.
As stated in the DPIR, the recharge system for both buildings will need to be installed on the Exeter Street side of the Prudential Center because there is no space on the Boylston Street side between the edge of the original sheet piling wall surrounding the Center and the Green Line subway to install a system. Installing recharge inside the sheet piling wall would prevent the water from flowing outside the Center where it is needed. In addition, the nearest vulnerable wood piling supported buildings are on Exeter Street, and there is a history of low groundwater levels along that street and nearby Blagden Street.
The Boston Groundwater Trust has been monitoring the wells along Blagden Street consistently since 1999. There has been a consistent pattern during most of those readings showing levels dropping along the street from the Huntington Avenue intersection near Dartmouth Street toward Exeter Street. One possible explanation for this would be a breech in the sheet piling wall of the Prudential Center along Exeter Street that would allow groundwater to penetrate. The proponent should verify the integrity of the wall and take steps to eliminate any inflow that might be occurring. If there is none, it would be helpful if the proponent could suggest other potential causes of the low groundwater in the area.
I am pleased with the commitment in Michael Cantalupas October 2, 2008 letter to both you and me that, in the event that the Exeter Residences building is not constructed within five years of the issuance of a Certificate of Occupancy for 888 Boylston, Boston Properties will construct a recharge system on the Exeter Street side of the project to handle the recharge requirements related to the 888 Boylston project.
I am pleased, as well, with the preliminary designs that have been generated for the recharge system, with a tank sized to meet the requirements of Article 32 to be located on the Green Level of the parking garage and a leaching bed under the Exeter Street sidewalk.
The DPIR outlines the foundation methodology planned for both buildings. The structures will not extend below the existing parking garage. The deep foundations are planned to be constructed, according to the DPIR, with methods that will require minimal or no dewatering. I am pleased with the commitment, stated in the DPIR, to monitoring groundwater levels before and during construction using the existing substantial network of monitoring wells. The results of the monitoring should be shared shortly after the readings are taken with both the Authority and the Trust.
I look forward to continuing to work with the proponent and the Authority to assure that these projects can have only positive impacts on groundwater levels in the area.
Very truly yours,
Cc: Kathleen Pederson, BRA
Maura Zlody, BED