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

Whittier Bridge/I-95 Improvement Project FEIR
Chapter 3.0: Mitigation and Commitments
3.7 WATER RESOURCES
Areas of soils would be exposed during construction and could erode into, and cause sedimentation
of, adjacent water bodies and wetlands if controls are not established. The control of soil erosion and
sedimentation from the site during construction would be based on the regulations, guidelines, and
conditions set forth by the EPA in its Final Notice of the National Pollutant Discharge Elimination
System (NPDES) General Permit for Stormwater Discharges from Construction Sites. The MassDEP
stormwater management standards will also be used as a guideline.
Storm Water Pollution Prevention Plan. Controls during construction will be incorporated in a
SWPPP that complies with the NPDES requirements for construction. An SWPPP will be prepared
for the project prior to initiating earth-disturbing activities. The SWPPP will establish the project‘s
approach to controlling water pollution during construction and would list structural and nonstructural
Best Management Practices (BMPs) that will be employed to control stormwater pollution
associated with construction. The SWPPP will also identify stormwater control measures remaining
after the construction is complete. Control methods such as minimizing areas of disturbance,
maintaining existing vegetated areas, and employing non-structural and structural stabilization
methods will be included. BMPs will include, but not be limited to, seeding, mulching, geotextiles,
bonded fiber matrices, permanent vegetative cover, turf reinforcement mats, bioengineering,
armoring, outlet stabilization, vehicle sediment tracking, dewatering, dust control, management of
hazardous materials and stockpiling. Velocity dissipation methods such as surface roughening,
diversion swales, check dams, earth dikes, and level spreaders will also be included as appropriate.
Measures for sediment capture techniques such as hay bales, silt fences, sedimentation basins,
deep sump catch basins and water quality inlets, filter berms, and sediment tanks will be detailed as
applicable. Finally, the SWPPP will clearly outline training, inspection, and reporting responsibilities.
The SWPPP is conceptual at this stage of design. A final SWPPP will be prepared by the
design/build contractor before the start of project construction and final details may vary somewhat
from the draft SWPPP included in this report.
An engineered stormwater management system will be constructed for the project. This system will
improve water quality for stormwater discharges to the Merrimack River, Meader Brook, and other
project-area surface waters compared to No Build conditions. The proposed stormwater
management includes:
Eight infiltration basins;
One wet basin;
Two extended detention basins;
An outlet control structure installed over existing drainage located in the Route 110 Loop Ramp;
Eleven sediment forebays (one per basin);
Water quality swales (in the median where space is available); and
Deep sump catch basins.
No adverse impacts to water quality are anticipated and no post-construction mitigation measures
would be required.
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