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Bulfinch - Notice of Intent (NOI) comments
Mystic River Watershed Association, August 20, 2004

MYSTIC RIVER WATERSHED ASSOCIATION
20 ACADEMY STREET, SUITE 203
ARLINGTON, MA 02476

August 20, 2004

City of Cambridge
Conservation Commission
344 Broadway
Cambridge, MA 02138

FAX: 617-349-4633

Dear Commissioners:

The Mystic River Watershed Association (MyRWA) is a non-profit organization dedicated to protecting and restoring the watershed's water quality, open space, and habitat. The Mystic River Watershed includes the Little River, which is the site of the proposed Cambridge Discovery Park redevelopment. MyRWA has reviewed the Notice of Intent (NOI) submitted by The Bulfinch Companies for this project, and has the following comments that we hope the Commission will consider for review.

The proposed redevelopment is located adjacent to Little River and immediately upstream of Alewife Brook, which are areas of special concern to us because of their important role in water quality, flooding, and future recreational uses. The poor water quality and flooding problems that plague the Alewife area now are the result of many poor land use planning decisions in the past. These decisions have not taken into account the flat topography of the area and the poor condition of much of the sewer infrastructure. Each decision about development can be portrayed as a minor contributor to the overall problems. The cumulative effects have been dramatic, however. It is clear that the area's wastewater infrastructure and capacity to control flooding are already inadequate, and the affected municipalities are just now beginning to deal with the high costs of past development decisions.

MyRWA believes that the proposed redevelopment of Cambridge Discovery Park can offer important economic benefits to the community, and also provide an opportunity to improve water quality, reduce flooding, and reclaim open space. Many sites developed in the past did not meet adequate standards for stormwater and wastewater management, and provided little open space benefit to the public. Well-designed redevelopment can correct these past errors, and contribute to the recovery of local watershed resources.

Hydrologic and Hydraulic Analyses

MyRWA is concerned that the hydrologic and hydraulic analyses performed by the Applicant are not sufficiently detailed to assess the flooding potential at the site. Pipe sizing calculations were performed using HydroCAD. HydroCAD is typically used to perform rainfall-runoff modeling, and does not necessarily provide adequate hydraulic information to assess the surcharge/flooding potential of a storm sewer system. In accordance with Massachusetts Highway Department recommendations, the Applicant should check the hydraulic grade line (HGL) of the proposed systems to identify if they will surcharge during the 10-year design storm. Furthermore, the pipe design assumes free discharge for the system. Given the sensitivity of this area to flooding, MyRWA believes a more conservative design, assuming a 10-year flood elevation in Little River, is warranted.

The above comments are also pertinent to the design of the 30-inch HDPE pipe. The design of this pipe was performed using open channel hydraulics that do not account for pipe surcharge or head losses. The hydraulics of this system should be studied in detail to assess the surcharge potential of this system and the adequacy of the 30-inch pipe.

Nevertheless, MyRWA is pleased to see that the Applicant has used the more conservative Northeast Regional Climate Center Atlas of Precipitation Events for the Northeastern United States and Southeastern Canada in its hydrologic analyses. This study reports up to a 29 percent increase in rainfall amounts for each frequency. In general, the greatest disparity between values occurs with the more extreme events, which are those most likely to cause flooding. Given the serious flooding issues experienced in the City, MyRWA urges the Cambridge Conservation Commission to adopt a local by-law or ordinance to require the use of the more conservative Cornell data in hydrologic and hydraulic calculations.

Site Recharge

MyRWA encourages the Conservation Commission to require the Applicant to investigate additional methods of recharge at the site to further reduce stormwater volumes. According to the Applicant, high groundwater limits the use of recharge at the site. Nevertheless, there is an existing dry well that collects runoff from building 46. The consultant should assess whether this existing dry well is functioning properly, and reconsider the use of rooftop infiltration at other nearby locations. Could roof drains be tied in to leaching catch basins with adequately sized overflows to the proposed storm drainage system?

Operation and Maintenance

Best Management Practices (BMPs) are only effective if they are properly maintained. We recommend that the Site Engineer and/or manufacturer's representative perform an initial walk-through with site maintenance staff to ensure they are adequately trained in inspection and maintenance of the BMPs. We also recommend that a member of the Conservation Commission attend this training. Inspection and maintenance forms for use by the maintenance staff should be provided, and these forms should be submitted to the Conservation Commission on a semi-annual basis, along with any receipts for street sweeping, catch basin cleaning, or other BMP maintenance.

Water Quality Monitoring

Given the water quality concerns associated with Little River and Alewife Brook, MyRWA recommends the Applicant provide a water quality monitoring plan for the site. Sampling stations would be established at each downstream discharge point, as well as at the stormwater detention basin inlet. Sampling would be performed during construction and annually for the first five years following construction. We would be happy to discuss this plan in further detail with the Conservation Commission.

Restoration of Former MDC-Parking Lot

Phase I of the project calls for abandonment of the former MDC parking lot. It is not clear what this abandonment entails. If the parking lot is merely abandoned, no increase in recharge or reduction in impervious area will be attained. Removal of impervious surfaces alone will not provide the open space, recreational, and habitat benefits of the land. MyRWA encourages the Conservation Commission to require full restoration of the former MDC parking lot to increase site recharge during Phase I of the project. Restoration should be consistent with the Alewife Master Plan.

Thank you for considering these comments and questions. Please contact myself or Nancy Hammett, our Executive Director, if you have any questions about this letter, or if MyRWA can be of further assistance in your review of this project.

Sincerely,


Matthew Shuman
Chair, Policy Committee

PHONE: 781-316-3438 o FAX: 781-641-2103 o WEBSITE: WWW.MYSTICRIVER.ORG