HomeMy WebLinkAboutResponse Letter 2.9.2026
53 Southampton Road • Westfield, MA 01085-5308 • Tel 413.562.1600
www.tighebond.com
C-5200-001
February 9, 2026
Yarmouth Conservation Commission
C/O Joe Jerolimo, Conservation Agent
1146 Route 28
Yarmouth, MA 02664
Re: 127 Whites Path – South Yarmouth LNG Response to Peer Review Comments
Dear Commission Members:
We are in receipt of administrative review comments regarding the South Yarmouth LNG
Stormwater Permit submitted to the South Yarmouth Conservation Commission on January
15, 2026 by Tighe & Bond, Inc. on behalf of National Grid. Comments have been provided by
James I. Pearson, PE of Weston & Sampson via electronic mail and dated February 4, 2026.
The comments are reiterated below in italic font in the order in which they were received. For
comments requiring a response, a bold text response follows the respective comment.
Weston & Sampson Comments
Section 2.04 Stormwater Management Site Plan
The applicant has submitted all of the items required for submission under this section, subject
to the comments presented below.
Section 2.05 Stormwater Management Performance Standards
2.05(1) Low Impact Development
Under this standard the applicant is required to “document in writing why LID strategies are
not appropriate when not used to manage stormwater.” LID examples cited in this standard
include infiltrating roof runoff at the source, planting large canopy trees over impervious areas
and using porous paving materials, etc. where feasible. The applicant has provided a brief
statement indicating that it is their belief that LID strategies have been implemented to the
maximum extent practicable. The engineer has cited sediment forebays and an infiltration
basin as LID measures. While most definitions of LID measures do not include sediment
forebays and infiltration basins, it is noted that the engineer has oversized these features to
ensure capture of storms up to the 100-year event and a case can be made that oversizing
constitutes an LID approach. We offer no objection to the brief statements presented by the
applicant on the topic of LID, this standard appears to be met.
2.05(2) Good Housekeeping Procedures
The engineer has incorporated, verbatim, the requirements of this standard into the Long
Term Pollution Prevention Plan (Appendix F of the Stormwater Report) This standard has been
met.
205(3) Stormwater Management Systems Design
We have noted the following in our review related to this standard:
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The Engineer has shown that peak discharge rates do not exceed pre-development discharge
rates for the 2, 10, 25, 50 and 100-year 24-hour storm events. Runoff from all areas of
onsite improvement discharge to either an above-ground stormwater infiltration basin. This
retains runoff from stormwater events including the 100-year event with no offsite runoff
from the basin. This standard has been met.
This section includes a standard requiring pretreatment of runoff from metal rooftops if the
site is discharging to a Zone II or interim wellhead protection area. The proposed project
does not include the construction of a new rooftop. This standard has been met.
This standard requires the use of NOAA Atlas 14 rainfall data for stormwater modeling, or
alternative datasets at the discretion of the commission. It does not appear that the Engineer
has used NOAA Atlas 14 data in the analysis. We recommend the Engineer revise the
calculations to reflect the NOAA Atlas 14 data.
NOAA Atlas 14 data has been used for the hydraulic analysis of this project. A copy
of the NOAA Atlas 14 rainfall events is provided in Appendix D of the stormwater
report. The second page of the existing conditions and proposed conditions
HydroCAD reports contain the rainfall depths for each design storm, and those
events match the rainfall data from Atlas 14.
2.05(4) Stormwater Management System Pollutant Removal Requirements (new
development)
We have noted the following in our review related to this standard:
Stormwater management systems for new developments shall be designed to meet an
average annual pollutant removal equivalent to 90% of the average annual post-construction
load of TSS AND 60% of the average annual load of TP AND 30% of the average annual load
of TN related to the total post-construction impervious area on the site. The Engineer has
routed all trafficked impervious areas through pretreatment into infiltration practices and is
infiltrating more than inch multiplied by the total post-construction impervious surface area
on the redeveloped site. This standard has been met.
2.05(5) Stormwater Management System Pollutant Removal Requirements (redevelopment)
We have noted the following in our review related to this standard:
Stormwater management systems for redevelopments shall be designed to meet an average
annual pollutant removal equivalent to 80% of the average annual post-construction load of
TSS AND 50% of the average annual load of TP AND 30% of the average annual load of TN
related to the total post-construction impervious area on the site. The Engineer has routed all
trafficked impervious areas through pretreatment into infiltration practices and is infiltrating
more than 0.8 inch multiplied by the total post-construction impervious surface area on the
redeveloped site. This standard has been met.
2.05(6) Stormwater Management System EPA Tool Analysis
We have noted the following in our review related to this standard: The applicant has not
used the EPA Region 1 BMP Accounting and Tracking Tool to evaluate average yearly pollutant
removal for the BMPs. Under this standard, applicants are required to provide this analysis
or are otherwise allowed to use other federal or state approved performance standards when
the EPA tools are not applicable for the proposed BMPs. Under 2.05(4) the Engineer is using
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more than 1-inch of retention as a means of satisfying the nutrient removal standards, so the
EPA Tool Analysis would not be required. This standard has been met.
2.05(7) Discharges to water bodies subject to TMDL
The site does not discharge to a water body subject to a TMDL.
Section 2.06 Erosion and Sediment Control Plan Standards
2.06(1) Contents of Erosion and Sediment Control Plan
The applicant has submitted plans for Erosion and Sediment Control which are substantially
complete, subject to further comments below.
2.06(2) Stormwater Pollution Prevention Plan (SWPPP) Submission
The project will disturb more than one acre of land, therefore it will be subject to coverage
under the NPDES Construction General Permit. Under this section, the applicant is required
to submit a complete copy of the SWPPP for the project. We recommend that the applicant
submit a copy of the SWPPP. Alternatively, the commission may wish to consider adopting a
condition of approval requiring the submission of the SWPPP prior to any ground disturbing
activity since the contractor will ultimately be the party responsible for the SWPPP.
The applicant does not have all the information required for a SWPPP (contact
information, schedule, etc.), because a contractor has not yet been selected for the
project. The applicant respectfully requests that the Commission require a SWPPP
submission as a condition of approval.
2.06(3) Design of erosion and sediment controls
The applicant’s erosion and sediment control plan substantially conforms to this standard.:
2.06(4) Erosion and Sedimentation Control Plan Content
The engineer has provided an erosion and sediment control plan within the plan set, and also
in narrative form within the stormwater report. These documents appear to form a complete
set of requirements that address the conditions required under this standard. This standard
has been met.
2.07 Operation and Maintenance (O&M) Plan
2.07(1) Stand-alone O&M plan requirements
The engineer has submitted a comprehensive stand-alone O&M plan. The plan appears to
include all of the items required under this standard. This standard has been met.
Under these standards, compliance with the MA Stormwater Handbook is required.
Compliance with the Handbook is further discussed below.
Massachusetts Stormwater Handbook Compliance Review
Under Section 2.04(1) of the Yarmouth Conservation Commission Stormwater Management
Regulations, the standards of the Massachusetts Stormwater Handbook are adopted by
reference. These standards are listed below, followed by our review comments.
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Standard 1: Untreated Stormwater
No new point discharges of untreated stormwater are proposed. The proposed stormwater
improvements for the site include deep sump hooded catch basins, drain manholes, a
hydrodynamic separator and an infiltration basin. The design proposed no new outfalls for
stormwater to leave the site and proposes to retain stormwater up to and including the 100-
year storm event. This standard has been met.
Standard 2: Post Development Peak Discharge Rates
The stormwater report analyzed the site for storm events with recurrence intervals of 1-, 2-,
10-, 25-, 50-, and 100-years. The analysis indicates that the post-redevelopment peak
discharge rates will be less than existing condition peak discharge rates. We offer the
following comment:
The Hydrocad report indicates that for Pond 8P (Trench Drain), the peak stormwater elevation
exceeds the rim elevation of the trench drain for the 50 and 100 year storm events. This may
lead to stormwater bypass into the adjacent part of the site with not all runoff being captured
and directed to the proposed infiltration basin as claimed in the calculations. We recommend
that the engineer address this item.
The outlet pipe from the trench drain has been increase to 18” to convey runoff
through the 100-year storm event. The trench drain is designed such that the peak
stormwater elevation will not exceed the rim elevation for the 50- and the 100-year
storm events. See sheet C-104 REV4 in the project drawings for drawing changes
and Appendix D in the stormwater report for hydraulic analysis updates.
Standard 3: Recharge to Groundwater
This standard requires that the site infiltration mimic preconstruction conditions for small
storms based on the proposed increase in impervious area. The engineer has submitted
calculations showing that the proposed infiltration basin has been designed to retain and
recharge far above the minimum required recharge volume. The Engineer has shown
geotechnical boring data for the site with static groundwater readings. We offer the following
comments:
The stormwater narrative references a calculation that was performed using the the Cape Cod
Commission adjustment method for estimating seasonal high groundwater. A blank
groundwater calculation sheet was found on page 120 of the PDF document of the stormwater
report. We assume that this was intended to be the referenced groundwater calculation. We
recommend that the engineer address this item.
The Cape Cod Commission seasonal high groundwater sheet can be found at the end
of Appendix C in the revised stormwater report.
Standard 4: Total Suspended Solids (TSS) Removal
The town standards for TSS removal and stormwater quality treatment are more stringent
than this standard. Compliance with the town’s standards is discussed in the preceding
comments. We offer the following comment:
The detail for the stormwater sediment forebay shows forebay check dams that appear to
consist of a stone layer over a soil berm. The forebay check dam should consist of a free-
draining stone material all the way down to the elevation of the bottom of the forebay to allow
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for water to drain out of the forebay and into the infiltration basin, otherwise the forebay itself
will function as an infiltration basin. We recommend that the engineer address this item.
The forebay design detail has been updated to have free draining stone material all
the way down to the bottom elevation of the forebay. See sheet C-202 REV3 in the
project drawings.
Standard 5: Land Uses with Higher Potential Pollutant Loads (LUHPPLs)
The Engineer has indicated that the proposed development is not a LUHPPL. We agree with
this assessment.
Standard 6: Protection of Critical Areas
The applicant’s submission indicates that the site is not within a critical area. Even so, the
proposed stormwater BMPs are in keeping with what is required under this standard. This
standard has been addressed.
Standard 7: Redevelopments
This project qualifies as a redevelopment. The applicant has taken the approach of fully
meeting the stormwater standards. This standard has been addressed.
Standard 8: Construction Period Pollution Prevention and Erosion/Sedimentation Control
The engineer has provided an erosion and sedimentation control plan and narrative. Due to
the fact that the site will disturb more than one acre, a Stormwater Pollution Prevention Plan
(SWPPP) will be required to obtain coverage under the NPDES Construction General Permit.
The town’s standards related to this are more stringent. This standard has been met.
Standard 9: Operations & Maintenance Plan
A long-term pollution prevention and operations and maintenance plan have been provided.
Further comments that related to this standard are provided above under the analysis of the
town’s similar standard. This standard has been met.
Standard 10: Illicit Discharge Compliance Statement
The Engineer has provided a copy of a signed illicit discharge compliance statement. This
standard has been met.
General Comments:
A constructability issue was noted at CB-2. This structure has a 24” outlet pipe and the
distance from rim elevation to invert of the pipe appears to be too small to allow for the catch
basin construction as a precast concrete structure. We recommend that the engineer address
this.
The outlet of that structure was lowered to allow for a precast concrete structure to
be used. See C-104 REV4 for the updated inverts and pipe information.
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Should you have any questions or require additional information, please contact Timothy
Grace at (
Very truly yours,
TIGHE & BOND, INC.
Timothy J. Grace, PE
Senior Engineer
Copy: Matthew Wozniak, PE - National Grid
Attachments:
1 Stormwater Report (Revised February 2026)
2 Project Drawings (Revised February 2026)
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