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HomeMy WebLinkAboutPeer Review Letter-473 Station Ave 7.5.2023 westonandsampson.com 427 Main Street, Suite 400, Worcester, MA 01608 Tel: 508.762.1676 July 3, 2023 Yarmouth Conservation Commission C/O Brittany DiRienzo, Conservation Administrator 1146 Route 28 Yarmouth, MA 02664 Re: Engineering Review of Stormwater Management Permit Application 473 Station Avenue 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 Harrison French & Associates LTD, the “Engineer”, on behalf of the Colbea Enterprises LLC, the “Owner”. Weston & Sampson reviewed the following revised documents provided by the Engineer as they relate to the Stormwater Design.  Project Narrative, 4 pages, dated 2/23/2023  Stormwater Management Site Plan, one sheet, dated 2/23/2023  Site Detail Sheet, one sheet, dated 7/18/2022  Soil Erosion and Sedimentation Control Plan, 1 sheet, dated 8/22/2022  Construction Period Pollution Prevention and Erosion & Sedimentation Control plan, 7 pages, dated 2/23/2023  Existing Drainage Areas figure, 1 page, dated 1/30/2019  Proposed Drainage Areas figure, 1 page, dated 8/8/2019  Massachusetts DEP Checklist for Stormwater Report, 8 pages, dated 4/4/2023  Stormwater Report, 111 pages, dated 2/23/2023  Site Plan Review Comment Sheet, 3 pages, dated February 5, 2019 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 stated in the project narrative and in the stormwater report that “The site development has been minimized as much as possible and two Bioretention Areas are proposed for natural stormwater treatment.” This response does not appear to fully explain why other LID practices were not used on the project. We recommend that the engineer revise this response to document possible LID strategies for this site and why they were not used and why they would be inappropriate for this site. Page 2 westonandsampson.com 2.05(2) Good Housekeeping Procedures We have noted the following in our review related to this standard:  The Operation and Maintenance Plan found in the Stormwater Report makes reference to “carwash gutters” in the first paragraph under section 4. Plans do not show a car wash, and the project narrative states that no car washing will occur on the site, so this may be a typo.  The project narrative lists several procedures that are generally in keeping with the requirements of 2.05(2) (with the exception noted below) however they are not included in the Operation and Maintenance (O&M) Plan. This standard specifically states that these procedures should be included in the O&M plan.  The O&M requirements for fertilizers are lacking the detail and specificity found in 2.05(2)(d). We recommend that the engineer address the items noted above. 2.05(3) Stormwater Management Systems Design We have noted the following in our review related to this standard:  Plans do not indicate the material that is to be used for the proposed building roof. Under this standard there are specific pretreatment requirements for metal roofs. We recommend that the engineer clarify the type of roof being used.  Oil-Grit Separator No. 2 is designed to be an integral unit consisting of a catch basin grate combined with the separator unit, and the unit discharges to a bioretention area. These devices are given credit for 25% TSS removal in the MA Stormwater Handbook. However, 2.05(3) requires 44% TSS removal prior to discharge into an “infiltration device.” We recommend that the engineer address this.  Catch Basins are shown on the plans but there is no detail for these catch basins on the detail sheet that was provided. It is presumed that it is the intent of the engineer to use deep sump hooded catch basins that conform to the MA Stormwater Handbook since these are mentioned in the stormwater report. We recommend that the engineer confirm this and provide the applicable detail.  Under this standard, the applicant is required to demonstrate that post-development peak discharge rates do not exceed pre-development peak discharge rates for the 2, 10, 25, 50 and 100-year 24-hour storms. The stormwater report did not include an analysis of the 50-year storm peak discharge. We recommend that the engineer provide this.  The stormwater report indicates that the first chamber in Oil-Grit Separators No. 1 and 2 will have dimensions of 3 x 5 x 3.5 feet. The detail that was provided does not show all of these dimensions. Also, the 3-foot dimension is shown measuring to the middle of the baffle wall outlets whereas it should measure to the bottom in order to achieve full pool volume. We recommend that the engineer address these items.  This standard requires the use of NOAA Atlas 14 rainfall data for stormwater modeling, or alternative datasets at the discretion of the commission. Based on our independent review using the online NOAA Atlas 14 tool, the rainfall values that were used in the analysis do not appear to be consistent with NOAA Atlas 14 values, but appear to more closely align the dataset from Cornell University’s Northeast Regional Climate Center (with slight differences). The rainfall data used in this analysis uses slightly smaller rainfall values for storms up to the 25-year event and then uses a larger rainfall value for the 100-year event when compared against NOAA Atlas 14 rainfall values. If the engineer wishes to use a data set other than NOAA Atlas 14 then we recommend that the engineer cite the source of the data for the commission’s consideration. Page 3 westonandsampson.com  The engineer has provided a model of existing conditions runoff for purposes of establishing a pre- development peak discharge rate for comparison with the post-development peak discharge rate. The existing conditions analysis only accounts for the runoff from the 18,941 square foot portion of the property that is sloped toward the abutter and ignores the remaining 32,321 square foot portion based on the apparent assumption that this latter portion is retained on-site. A review of the site topography suggests that this assumption of existing on-site retainage may potentially be correct since the area drains to two localized depressions onsite where it may infiltrate into the ground. However, the analysis does not indicate whether these onsite depressions have sufficient capacity for the modeled storm events to retain the onsite stormwater. We recommend that the engineer revise the existing conditions model to factor in the capacity of the onsite depressions to confirm that they have adequate capacity to function as retention/infiltration basins under existing conditions.  In the proposed conditions model, certain areas are labeled “pervious retained on-site”, are evidently not accounted for in the model, and are assumed to simply infiltrate in-place. We recommend that the engineer revise the model to account for these areas, possibly with a combination of modeled infiltration and overflow to drainage structures to verify adequate retention capacity.  The subcatchments “Area to CB#1” and “Area to CB #2” in the model lists square footages that do not match the subcatchment map. We recommend that the engineer address this inconsistency. 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. The engineer has used this option and the design complies with this standard. 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. We recommend that the engineer provide this analysis or provide clarification for the commission’s consideration as to what alternative approach was 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 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 Page 4 westonandsampson.com 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, subject to the following comments:  The plan makes reference to temporary stockpiles being “seeded and/or stabilized”. Seeding may be impractical for temporary stockpiles, and the term “stabilized” is somewhat vague. We recommend that the engineer clarify how temporary stabilization will be accomplished.  The plan makes no reference to the handling dewatering discharges. Given the lack of groundwater that was observed at the time of test pits and the sandy soils it may be unlikely that dewatering will be required. That being said, it may be advisable to include a contingency plan for dewatering in the event that this needs to occur. We recommend that the engineer address this.  This standard requires a means to ensure that stormwater BMPs will be protected from compaction, siltation, erosion, etc. during construction. Siltation and erosion are addressed, but it may be advisable to provide some means of preventing equipment from compacting the proposed bioretention areas on the site. We recommend that the engineer address this. 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 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. Under these standards, compliance with the MA Stormwater Handbook is required. Compliance with the Handbook is further discussed below. Page 5 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, underground stormwater chambers with isolator rows and bioretention areas. 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-, and 100-years. The analysis indicates that the post-redevelopment peak discharge rates will be less than existing condition peak discharge rates. Some of the preceding review comments may impact compliance with this standard. We recommend that the applicant address the comments listed above. 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. This standard has been met. 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 recommend that the engineer address the preceding comments and in doing so this standard will be fully met. Standard 5: Land Uses with Higher Potential Pollutant Loads As a fueling facility, the proposed land use constitutes a land use with a higher potential pollutant load. The applicant’s engineer has proposed stormwater BMPs and O&M procedures that are generally in keeping with this standard, except that the preceding comments should be addressed in order to ensure full compliance. We recommend that the engineer address this. Standard 6: Protection of Critical Areas The applicant’s submission contains conflicting statement regarding whether or not the site is within a critical area. The project narrative states that the project is in an Aquifer Protection Overlay District, but the stormwater report states that the project is not in a critical area. Notwithstanding this conflict, the proposed stormwater BMPs are in keeping with what is required under this standard. We recommend that the engineer address the inconsistency between the narrative and stormwater report. Standard 7: Redevelopments This project qualifies as a new development. The applicant is required to fully comply with these standards. Standard 8: Construction Period Pollution Prevention and Erosion/Sedimentation Control Page 6 westonandsampson.com 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 An illicit discharge statement has been provided as required. 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