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Draft Environmental Impact Report - Belmont Office/R&D Building
Response from Bruce Jacobs, Jacobs Consulting Services
May 5, 2003
Ellen Roy Herzfelder
Secretary, Executive Office of Environmental Affairs
251 Causeway Street, 9th Floor
Boston, MA 02114
Subject: Comments on DEIR for Belmont Office/ R&D Building, EOEA #12376R
Dear Ms. Herzfelder:
At the request of the Friends of Alewife Reservation (FAR), I have reviewed the Draft Environmental Impact Report for the Belmont Office/R&D Building (EOEA #12376R). I have an extended relationship with FAR having served both on the board and as treasurer. I participated in a shoreline survey of the receiving waters of the proposed office building and have worked with several north Cambridge clients addressing local flooding problems as well as the regional flooding issues facing north Cambridge. Given this experience and my professional credentials as a Civil Engineer, I am well aware of the environmental problems facing the already stressed Little River - Little Pond watershed as well as the flooding problems in north Cambridge.
Environmental Stresses. The Little River and Little Pond area are already environmentally stressed environments, necessitating special care when siting new shoreside development. Little Pond receives stormwater from a large urban area, taking in nutrients, pesticides, motor oils, sediment and salts that are typically mixed in with urban stormwater. Through personal observation, I have noticed that the northern part of the pond that receives water from Spy Pond and indirectly from Route 2 is very shallow possibly due to the impact of sand used in deicing operations on Route 2. Further, sewage cross-connections and sewer overflows have been well documented resulting in elevated E. Coli counts. The large carp population along Little River is indicative of the stream's poor water quality.
Propensity for Flooding. An increase in the frequency of flooding has been noted by north Cambridge and Arlington residents. This is in part due to the long-term reduction of pervious surfaces in the watershed that increase runoff and peak discharges. Many of the homes bordering the Alewife River in north Cambridge and Arlington are built in low-lying flat areas making them particularly sensitive to flooding and overtopping of the banks of the Alewife River. The most recent storm events in the 1990's did not cause overtopping of these banks, yet many homes and fields were flooded and Route 2 was under water for an extended time. It is important to remember that a recurrence of storms of the depth and intensity of those experienced in 1938 and 1955 would cause flooding in these areas of a type not previously encountered in living memory.
Given the potential for intense flooding, the Cambridge Department of Public Works requires that applicants for new storm discharges reduce the 25-year storm event peak discharge to that of the existing 2-year event. This development is located in Belmont, so it is not within the jurisdiction of the City of Cambridge, however since the receiving water flows through portions of Cambridge it is highly advisable that development in this area be held to this higher standard.
Design Issues. I have reviewed the stormwater management design for the proposed development. The project design is in general of a professional nature, however I have particular concern that adequate precautions have not been taken to ensure that the infiltration basin will work as intended. This basin is an integral component of the stormwater management system. Its failure could potentially cause the introduction of peak off-site discharges far greater than projected in the design calculations. It is standard practice in siting of infiltration facilities to require a 2-foot clearance between the bottom of the basin and the elevation of the seasonal high groundwater elevation. This requires spring-time observations and checks for soil mottling in boreholes at the infiltration facility that are evidence of frequent flooding of soils. The DEIR notes that the highest observed groundwater elevation was 3.7 feet below the bottom of the infiltration facility. It is not noted where and when this observation was taken. This is not the same as a seasonal high water elevation measurement.
The infiltration basin performance is predicated on an assumed infiltration rate of 0.52 inches per hour. This was apparently determined based on a soil classification noted from a state-wide soil survey. Site specific information is necessary for siting of an infiltration facility to make sure that it will accept the intended water infiltration.
Given the importance of this basin in the stormwater design, I would recommend that additional investigations be performed to ensure that the site is appropriate both from the perspective of the seasonal high water elevation and the infiltration rate of the receiving soils.
Summary of Findings. The Little River-Little Pond environment is an already stressed ecosystem necessitating a cautious attitude in siting of new development to ensure that habitat is preserved and water quality is not further diminished. Downstream communities have faced frequent flooding due in part to long-term trends in development of the watershed area. The presence of homes in low-lying areas, potentially subject to future significant flooding events, further necessitates additional caution in the application of stormwater regulations. Elevated standards, such as those used in Cambridge for approval of stormwater discharge permits, are highly advisable. The stormwater management plan meets the Commonwealth stormwater standards, however a large infiltration basin is called for without appropriate field testing. Approval of the development should be contingent on receipt of more detailed field testing showing the adequacy of the infiltration basin site.
I have been informed that the developer has let it be know that he may decide in the future to retract the existing plans and put forward an alternative proposal for residential development. In this event, I would respectfully advise that the existing DEIR not serve as the DEIR for the new proposal. The impacts are likely to be of a different nature and should entail a fresh review of development at the site.
Jacobs Consulting Services
Cc: Ernie Kirwan, Friends of Alewife Reservation