Loading...
HomeMy WebLinkAbout Peer Revew 8.16.2024 westonandsampson.com 427 Main Street, Suite 400, Worcester, MA 01608 Tel: 508.762.1676 August 16, 2024 Yarmouth Conservation Commission C/O Brittany DiRienzo, Conservation Administrator 1146 Route 28 Yarmouth, MA 02664 Re: Engineering Review of Stormwater Management Permit Application 770 Route 28 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 Conserv Group, Inc. and Atlantic Design Engineers, Inc., the “Engineer”, on behalf of Mash Realty, LLC., the “Owner”. Weston & Sampson reviewed the following revised documents provided by the Engineer as they relate to the Stormwater Design.  A Stormwater management Permit Application, dated 7/1/2024 (2 pages)  A plan set entitled “Site Plans for Cape & Islands Nissan”, dated June 28, 2024 (10 sheets)  A report entitled “Storm Water Drainage Analysis for Cape & Islands Nissan”, dated June 21, 2021 (202 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 as much as feasible, and that such measures include the planting of as many grassed/landscaped areas as possible. We offer no objection to the rationale presented by the applicant, but the commission may wish for the applicant to further discuss what other LID approaches may have been considered for this site. 2.05(2) Good Housekeeping Procedures We have noted the following in our review related to this standard:  This standard requires provisions for car washing to occur “on lawns or pervious areas using biodegradable and phosphate free detergent.” This is not discussed in the O&M plan. We recommend that the engineer address the item noted above. Page 2 westonandsampson.com 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 basin or subsurface chambers. These retain runoff from stormwater events including the 50-year and 100-year event with no offsite runoff from these BMPs. These standards have 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 Engineer is proposing to discharge roof runoff into the subsurface infiltration system with no pretreatment, but the site does not appear to be within the areas described above. 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 appears that the Engineer has used NOAA Atlas 14 data in the analysis. This standard has been met. 2.05(4) Stormwater Management System Pollutant Removal Requirements (new development) We have noted the following in our review related to this standard:  Under this standard, the engineer is given the option to provide a retention volume equal to or greater than one inch multiplied by the impervious area of the site. It is presumed that the engineer intends to meet this standard via the option for retaining the volume of runoff equivalent to or greater than 1-inch multiplied by the post-construction impervious surface, and this standard is likely met since the systems retain the 100-year storm event. That being said, a calculation of water quality flow was provided, but a calculation of static (i.e. not taking into account dynamic recharge) water quality volume (required vs proposed) was not found. We recommend that the Engineer provide this. 2.05(5) Stormwater Management System Pollutant Removal Requirements (redevelopment) This standard is not applicable since the site is a new development. 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. If the presumption stated under 2.05(4) is correct and the Engineer is using 1-inch of retention as a means of satisfying the nutrient removal standards, then the EPA Tool Analysis would not be required. We recommend that the Engineer clarify the approach being used. 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 Page 3 westonandsampson.com 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. 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 We have noted the following in our review related to this standard:  This standard calls for the inclusion of 100-year flood elevation information based on FEMA mapping, this was not found on the plan. The engineer should address this.  This standard calls for a description of how fueling of vehicles/equipment and fuel/chemical storage will be conducted. This was not found on the plan. The engineer should address this.  This standard calls for the identification of “trees with a caliper twelve (12) inches diameter breast height or larger, noting specimen trees and forest communities.” This was not found in the submitted materials. We recommend that the applicant either clarify whether this is applicable, submit the applicable information, or request a waiver from the commission if that is the applicant’s intent.  A description of procedures for construction vehicle fueling, temporary chemical storage and construction vehicle washing/washout was not found. The engineer should address this. 2.07 Operation and Maintenance (O&M) Plan 2.07(1) Stand-alone O&M plan requirements We have noted the following in our review related to this standard:  There are comments noted farther above that the applicant should address related to the O&M plan.  The O&M plan is currently formatted as a chapter within the stormwater report. The commission may wish to advise whether it is desirable to have it separated as a “stand-alone” report. Page 4 westonandsampson.com 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. 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, underground stormwater chambers, hydrodynamic separators 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 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. This standard has been met, subject to comments under the heading of other standards below. 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 onsite stormwater BMPs have been designed to retain and recharge far above the minimum required recharge volume. The Engineer has shown test pit data for the site, and adequate separation to groundwater appears to be provided for the subsurface infiltration system. The following issues were noted:  The test pit data for one of the test pits (TP-5) could not be found in the report, so adequate separation to seasonal high groundwater could not be confirmed.  The subsurface chambers are called out as proprietary precast structures from Shea Concrete. While we are familiar with this product and the design appears to be consistent with the product, we would recommend that a detail/cross section for the chamber system should be in the plans for clarity. We recommend that the Engineer address the items above. 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 believe that this standard has been met. 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. Page 5 westonandsampson.com Standard 7: Redevelopments This project qualifies as a new development. The applicant is required to fully comply with these 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. 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. Provided that the applicant addresses the preceding comments, this standard from the Handbook will be satisfied. 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. Provided that those comments are addressed, this standard from the Handbook will be satisfied. Standard 10: Illicit Discharge Compliance Statement The Engineer has stated that an Illicit Discharge Compliance Statement will be signed by the responsible party prior to the start of construction. The Commission may wish to include this as a condition of approval for the project. 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