August 13, 2014

Arlington and Belmont Commissions still using out of date rain data
Anne Marie Lambert

Ms. Tourneau,

Thank you for distributing my letter and for listening to my concerns at last night's meeting, when an order of conditions was granted for this project.

With regard to Fish Migration, I was encouraged to hear that for the transmission line installation the proponent is considering trench-free construction techniques which would be less likely to disturb the migration. I look forward to the future hearing when permitting for the transmission line will be reviewed, likely in October timeframe.

With regard to Stormwater runoff calculations using outdated precipitation data, the confirmation that 50-year-old precipitation data from TP-40 were being used was discouraging (see "Stormwater Report for Belmont Municipal Light Department 115 kV Substation Project, October 29, 2013" page 3, which cites TP-40 as a data source and the 1961 figure of 6.5" as the rainfall depth for a 100-year storm event). This figure was used as input into all the hydrograph charts and calculations in Appendix A.

However, as a redevelopment project which includes a reduction in impervious surface and the installation of a sedimentation forebay with sufficient storage area to detain 1109 cubic feet of water (Appendix C), it is clear that this project at least incrementally improves upon existing conditions on this site with respect to peak discharge rate (SW Standard No. 2) and recharge to Groundwater (SW Standard No. 3). My understanding from TetraTech is that the volume of the forebay is sufficient to handle the first 1/2" of stormwater, five times as much as the 1/10" required by WPA.

Unlike redevelopment projects, the difference between using TP-40 1961 data rather than NRCC 2011 data is much more significant for new development projects. I encourage the Conservation Commissions of both Belmont and Cambridge to consider the flooding risk associated with permitting new development projects using such outdated data. It will not be easy to recover from the detriment to the well being of our citizens and our wildlife, not to mention to our economy, should these risks continue to rise unmitigated.

Anne-Marie

August 10, 2014

Jennifer Letourneau
Director, Cambridge Conservation Commission:

I am writing with two concerns about the following agenda item for your meeting on Monday, August 11, 2014: "Notice of Intent from the Belmont Municipal Light Department for Proposed Electric Substation and Installation of Transmission Line." My first concern is about the annual fish migration by the proposed project, and my second concern is about stormwater runoff calculations using outdated precipitation data.

Fish Migration: Every spring, alewife herring migrate up Wellington Brook into Blair Pond. I am concerned about the potential for this project to interfere with this annual migration. The project involves installing a transmission line for high voltage electric power under Wellington Brook, and an electric substation on the shores of Blair Pond. When DCR dredged Blair Pond two years ago, the construction schedule was delayed so much that the stage which included depleting and redirecting the waters of the Wellington Brook into large plastic pipes occurred during peak migration season. Alewife herring could be seen flipping around and dying in the depleted brook. I request that the conditions for the substation project include a specific ban on any construction during alewife migration season, and that this be enforced. I also request that adequate study is made of the affect of high voltage transmission lines on fish migration longer term. When I raised this issue with the Belmont Conservation Commission during the NOI hearing for the Belmont portion of the project, I was told that this issue was under the jurisdiction of the Cambridge Conservation Commission, since Wellington Brook was in Cambridge, not Belmont.

On a related note, there is an ongoing menace from the invasive Asian carp in this water body. As we read about recent efforts to control Asian carp in our nations Great Lakes, I suggest that this project creates an opportunity to control the population of Asian carp in Cambridge and Belmont.

Stormwater runoff calculations using outdated precipitation data: I urge the Conservation Commission to require that the Belmont Light Department report on whether the proposed project safely handles stormwater from current NRCC estimates of a 24-hour 100-year flood, and not solely on TP-40 estimates based on precipitation data collected only through 1958.

Extreme precipitation events are now known to have dramatically changed for the worse. In particular, the 24-hour 100-year storm event on this site is now known to be over two inches more severe than was assumed prior to a significant report issued by the Northeast Regional Climate Center (NRCC) in 2011. The 24-hour 100-year storm is now estimated at 8.8. inches instead of the 6.5 inches estimated in 1961. It is my understanding that the stormwater management design of the proposed project was made to accommodate 6.5 inches of rain, an event which is now known to occur every 30 years instead of every 100 years.

In 2011, the Northeast Regional Climate Center (NRCC) and the Natural Resources Conservation Service (NRCS) published updated models of extreme precipitation which take into account precipitation data collected through 2008. More information about NRCC, NRCS, and these results can be found at precip.eas.cornell.edu. The fact that WPA regulations make reference to Technical Paper 40 (TP-40), which was published in 1961 based on data collected through 1958, does not change the simple fact that, for this site, it is now known that there is a lot more rain during a 24-hour 100-year storm. More robust stormwater management is required to ensure the type of safety and mitigated flood risk that my constituents and a robust economy require.

I therefore request that the number of additional cubic feet of rain that will fall on the impervious surface of the proposed project during a 24-hour 100-year storm be calculated. I further request that the proposed project handle extreme precipitation estimates that include 50 years of precipitation data missing from TP-40.

I urge you to find a way to protect my constituents, to protect residents in low-lying parts of Cambridge and Arlington, and to protect our waterways during this time of climate change. The urgency of mitigating the type of damage witnessed during Hurricane Sandy in New York and New Jersey is great. The urgency is especially great for a new public utility project.

Respectfully,

Anne-Marie Lambert
Belmont Town Meeting Member, Precinct 8
Founder, Belmont Stormwater Working Group