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
Table 2-1:
Stormwater Outfalls (continued)
Description of
Discharge
Salisbury (cont’d)
Sheet flow on east side
28
of NB
Sheet flow on west side
29
of SB
Baseline
Station
Reference
ST 68 to ST
72 Right
ST 85 to ST
95 Left
Nearest Down
Gradient
Resource Area
Isolated Wetland
U
Wetland 5
30 Existing 48" Outfall ST 105 Right Wetland 2
Notes: Refer to Stormwater Management Plans dated November 16, 2011 (Revised through February 2012)
(Excludes discharges from the proposed bridge scuppers associated with Whittier Bridge)
Comments
Existing drainage pattern to remain, BVW
immediately adjacent to roadway
Existing drainage pattern to remain, BVW
immediately adjacent to roadway
Discharge contains a mix of existing and proposed
flows. Portion of flow includes treatment provided in
median swale and deep sump CB's.
Response: MassDOT has submitted a table (Table 2-1) to each conservation commission that
identifies every stormwater discharge within the project limits. The proposed TSS removal rates for
every subcatchment area and resultant level of TSS removal achieved at each resource area with a
distinction between New Development and Redevelopment has also been tabulated and included in
the Stormwater Report.
DEP-11: While the 80% TSS removal rate requirement may be met using the macro-approach, all new
discharge points must receive at least some level of TSS treatment to comply with 310 CMR
10.05(6)(k)(I) and 314 CMR 9.06(6)(a)(l) and disproportionate impact to any one receiving wetland
or water must be avoided for both redevelopment and new development drainage.
Response: All proposed discharge points will receive at least some level of TSS treatment, with the
exception of bridge scuppers as discussed in the previous DEP comment. The proposed stormwater
management system has been designed such that at least 80% TSS removal will be achieved for
the new development portion of the project as evaluated at each resources area. This methodology
was specifically incorporated into the design in an effort to avoid disproportionate impacts to any
individual resource area. Additional treatment measures are incorporated for redevelopment portions
of the project to the maximum extent practicable and improve existing conditions.
DEP-12: The Merrimack River is designated as a shellfish growing area (where taking of shellfish is currently
prohibited) on easterly side of the Whittier Bridge. As such, the Merrimack River is a critical area for purposes of
stormwater discharges pursuant to 310 CMR 10.05(6)(k)(6) and 314 CMR 9.06(6)(a)(6). MassDOT should explore
opportunities to increase stormwater treatment from landside drainage directed to the Merrimack River to comply with
310 CMR 10.05(6)(k)(6) and 314 CMR 9.06(6)(a)(6) requirements. All headwalls, splash pads, aprons, or preformed
scour holes for stormwater management may not be located in land under water, bordering vegetated wetlands, or
salt marsh pursuant to wetland regulations at 310 CMR 10.05(6)(k).
Response: The proposed stormwater management system for this section of the project includes a
proposed infiltration basin located on the east side of I-95 in Newburyport. The proposed basin will
provide water quality treatment for a portion of the projects total discharges to the Merrimack River,
which has been identified as immediately upstream of the shellfish growing area. The proposed
infiltration basin will be sized to include an equivalent amount of water quality volume that represents
at least 1-inch of water quality treatment for the New Development portion of the project tributary to
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