Loading...
HomeMy WebLinkAboutFIRST REVIEW 2.4.2026 westonandsampson.com 427 Main Street, Suite 400, Worcester, MA 01608 Tel: 508.762.1676 February 4, 2026 Yarmouth Conservation Commission C/O Joe Jerolimo, Conservation Agent 1146 Route 28 Yarmouth, MA 02664 Re: Engineering Review of Stormwater Management Permit Application 127 Whites Path Dear Commissioners: In accordance with your request, Weston & Sampson is pleased to present our review of the above referenced application. The purpose of this letter report is to provide comments on the proposed stormwater drainage as it currently relates to regulatory compliance with the Town of Yarmouth Conservation Commission Stormwater Management Regulations (Effective July 1, 2021) and the Massachusetts Stormwater Handbook as referenced therein. Our review is based on information submitted to the Town by Tighe & Bond, the “Engineer”, on behalf of Boston Gas Company DBA National Grid, the “Owner”. Weston & Sampson reviewed the following revised documents provided by the Engineer as they relate to the Stormwater Design.  A document entitled “Stormwater Management Permit Application,” dated December 2025 (15 pages)  A plan set entitled “South Yarmouth LNG,” dated November 12/8/2025 (8 sheets)  A report entitled “Stormwater Management Report,” dated December 2025 (266 pages)  A document entitled “Administrative Checklist, Stormwater Management Permit Application,” undated (1 page)  A document entitled “Town of Yarmouth Stormwater By-Lay Ch. 145 Stormwater Management Permit Application,” dated 12/11/2025 (2 pages)  Abutter mailing labels and scanned copies of envelopes with certified mail labels (7 pages)  A document entitled “Section 2 Project Description,” undated (5 pages)  A document entitled “Site Plan Review Comment Sheet,” dated 12/2/2025 (2 pages)  A document entitled “Long-Term Pollution Prevention and Stormwater Management System Operation and Maintenance Plan,” dated December 2025 (19 pages) Town of Yarmouth Conservation Commission Stormwater Management Regulations Compliance Review 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. Page 2 westonandsampson.com 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. 2.05(3) Stormwater Management Systems Design We have noted the following in our review related to this standard:  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. 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: Page 3 westonandsampson.com  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 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. 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. Page 4 westonandsampson.com 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. 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. 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. 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 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. 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. Page 5 westonandsampson.com 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. Weston & Sampson appreciates the opportunity to present our findings. We are available at your earliest convenience to discuss our report. Please contact me if you have any questions. I may be reached at (978) 532-1900 or pearsonj@wseinc.com. Sincerely, WESTON & SAMPSON ENGINEERS, INC. James I. Pearson, PE Technical Leader