Final Environmental Impact Report - Whittier Bridge/I-95 ...

Whittier Bridge/I-95 Improvement Project FEIR
Chapter 2.0: Response to Comments on the Environmental Assessment/Draft Environmental Impact Report
Amesbury Conservation Commission on March 19, 2012. If the commission votes to issue Negative
Determinations, the District would be able to perform that work within a month of receiving the
Negative Determinations. The timing may change due to site conditions but will be performed this
spring.
Amesbury-1A: Any expansion or improvements to I-95 must not impact the area as it is a statedesignated
40R priority development site. Of particular concern are drainage impacts to the existing
wetlands in the Golden Triangle.
Response: The comment is noted. The response to comment Amesbury-1B below describes the
potential impacts of increased stormwater runoff from I-95 to the Golden Triangle.
Amesbury-1B: The city had been informed by MassDOT that drainage from the I-95 corridor (Exit 58 in Amesbury to
the intersection of I-495 and I-95 in Salisbury) drained into wetlands in Salisbury, thereby alleviating Amesbury’s
concerns regarding any impacts of the proposed project to Amesbury residents and the Golden triangle. However,
the EA/DEIR indicates that most, if not all, of the drainage from I-95 in the aforementioned area runs into land in
Amesbury though a constricted pipe and stone box culvert at Rocky Hill Road and then down to the confluence of the
Powow and Merrimack Rivers.
Response: MassDOT provided additional information to the Salisbury Conservation Commission in
January 2012 to address the concerns expressed by the town in their comments on the EA/DEIR.
The information is summarized below.
The project will result in the incremental increase of approximately 1.0 acre of pavement tributary to
the Golden Triangle, and ultimately tributary to an existing culvert located in the vicinity of 289 Elm
Street. Stormwater improvements proposed as part of the project include Infiltration Basin 5 and
Infiltration Basin 6. These stormwater BMPs will provide water quality treatment, groundwater
recharge, and peak rate attenuation for surface water runoff generated from the ―new development‖
portion of the project in addition to portions of the ―existing development‖ portion of the project,
consistent with the Stormwater Management Standards of the Wetlands Protection Act.
Based on the stormwater analysis completed to date which includes revisions that have been
incorporated into the design based on comments received from the Salisbury peer review consultant
for the conservation commission, the following mitigation will be achieved for the Golden Triangle,
and consequently the southern culvert located at 289 Elm Street.
1. Post development peak runoff rates will be less than existing peak runoff rates for all storms
analyzed. This refers to design points DP-5 and DP-6, these stormwater discharges
ultimately converge within the limits of the Golden Triangle in a location up gradient of the
southern culvert located near #289 Elm Street.
2. Based on the recharge volumes proposed, post development runoff volumes will:
a. Result in a 35% decrease in runoff volume for a 1-inch storm event;
b. Approximate existing condition runoff volumes for a 2 year storm even; and
c. Result in an increase of approximately 4,343 CF for the 100-year storm event.
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