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
design increases the limiting hydraulic cross-sectional area within the Regulatory Floodway by
reducing the number of piers at a given section within the Merrimack River from four to three.
The findings of the hydraulic analysis are included in section 1.4.6. Insertion of the two existing
Whittier Bridge cross sections into the ―Duplicate Effective‖ HEC-RAS model resulted in 0.1 to 0.2
foot increase in the river‘s Base Flood Elevation (BFE) profile upstream of the I-95 crossing location.
This result is reasonable and indicates that, most likely, the total energy head loss a 100-year flood
event will sustain as it passes through the existing bridge waterway opening is relatively minor.
The BFE profiles computed with the ―Pre-Project (Existing) Conditions‖ and ―Post-Project (Revised)
Conditions‖ HEC-RAS models are virtually identical. This result directly infers that the construction of
the preferred replacement bridge type will meet applicable NFIP base floodplain development
performance standards and thereby assure overall project compliance with the terms of EO 11988.
This result also directly infers that implementation of this alternative will not necessitate further
project coordination with FEMA pursuant to revising existing NFIP base floodplain mapping products
for the Merrimack River.
The final bridge hydraulic analysis is included in Appendix B.
EEA-12: The FEIR should indicate that the local Conservation Commissions have been notified of any changes to
resource area delineations and that ORADs have been appropriately modified to reflect these changes.
Response: MassDEP has confirmed that the ORADs issued for the project remain valid and there
have been no changes to resource area delineations.
EEA-13: The FEIR should clarify whether the project will require dredging as indicated in MassDEP's comments.
Response: Dredging and excavation will be required in order to construct the new Merrimack River
bridges. Section 1.4.7 includes information included in the Section 401 Water Quality Certification on
dredging location, volume, and characterization.
EEA-14: The FEIR should indicate if measures will be implemented to reduce impacts to resource areas as a result
of flooding during the construction period.
Response: Section 1.4.8 includes information on procedures to be included in the design/build
contract to be followed in the event of flooding events during construction.
EEA-15: The FEIR should describe consistency with Chapter 91 licensing requirements, as applicable. The FEIR
should include information to support a Public Benefit Determination (PBD) pursuant to 301 CMR 13.02.
Response: Section 1.4.10 includes a description of the project‘s compliance with the applicable
performance standards of the Waterways Regulations and also includes the requested public benefit
review, per 301 CMR 13.03(1): ―describing the nature of the tidelands affected by the project and the
public benefit of the project, including the purpose and effect of the project, the impact on abutters
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