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
3. The incremental increase in runoff volume for the 100-year storm event represents
approximately 0.12% (4,343 CF / 3,672,000 CF) of the total volume of stormwater tributary to
the culvert located at 289 Elm Street. Although we have calculated an increase in runoff
volume of 4,343 CF, the total amount of attenuation has been conservatively modeled at
13,530 CF for this storm event.
In summary, the project will comply with the DEP Stormwater Management Standards and will not
result in an increase to off-site flooding as a result of peak discharges from the 2, 10, or 100‐ year
storm events.
Amesbury-2: The city requests that the applicant provide additional information on possible impacts to the wet
meadow from the increase of the pre-development watershed water volume to the post development watershed
water volume and the subsequent decrease of peak flow to this area. The change in duration and quantity of flooding
over time could have a detrimental effect on the conditions of the wet meadow.
Response: MassDOT notes that the proposed stormwater management system is designed to
address the impacts of the project within the limits of the I-95 ROW and the regulatory requirements
of the stormwater performance standards as contained in the Wetlands Protection Act. Compliance
with the stormwater performance standards is designed to ensure minimal impacts to existing
hydrology along the ROW. MassDOT has no information on the location, size, or hydrology of the
referenced wet meadow, located outside of the ROW.
Amesbury-3: While the storm water management plan will attenuate the peak runoff flows for the drainage system
that runs through the Golden Triangle area, will the addition to the overall volume of water within the watershed, due
to the increased duration of the water flow, be significant enough to cause a shift in the characteristics of the existing
intermittent stream
Response: MassDOT notes that the proposed stormwater management system is designed to
address the impacts of the project within the limits of the I-95 ROW and the regulatory requirements
of the stormwater performance standards as contained in the Wetlands Protection Act. Compliance
with the stormwater performance standards is designed to ensure minimal impacts to existing
hydrology along the ROW. MassDOT has no information on the location, watershed or hydrology of
the referenced intermittent stream, located outside of the ROW. Existing topographic mapping does
not show an intermittent stream in the area. The Golden Triangle report prepared for the city by
VHB, Inc. indicates that the stream nearest I-95 is largely perennial with a minimal length designated
as intermittent.
MassDOT supplied additional information to the Amesbury Conservation Commission in January
2012 which concluded that no adverse effects to the Golden Triangle would occur. See the
response to Amesbury-1B above for additional information.
Amesbury-4: Within the DEIR, the applicant indicates that two storm water basins (Basins 3A and 3B) are to be
constructed directly behind Martignetti Enterprises, Inc., at 32 Merrill Street Extension. The ground surface behind
the building appears to be sloping down from I-95 to the back of the existing building. Basin 3B is proposed to be an
extended detention basin and Basin 3A is proposed to be an infiltration basin. Has the applicant given thought as to
what effects these basins may have on the Martignetti property during construction and with the operation and
maintenance of the basins Given that the area is shallow to bedrock they are likely to be detrimentally impacted by
the increased groundwater.
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