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HomeMy WebLinkAboutSECOND Review Letter-473 Station Ave 7.31.2023 westonandsampson.com 427 Main Street, Suite 400, Worcester, MA 01608 Tel: 508.762.1676 July 31, 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 provided review comments in a letter dated July 3, 2023 for the following 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 The Engineer subsequently submitted additional and/or revised documents in response to the review cited above. The revised documents are as follows:  Code Comment Response narrative, 9 pages, dated 7/11/2023  Boundary & Topographic Survey, one sheet, dated 11/28/2018  Site Detail Sheet (SD-3), one sheet, dated 7/10/2023  Stormwater Report, 167 pages, dated 7/5/2023  Operation and Maintenance Plan, 10 pages, dated 7/10/2023  Soil Erosion and Sediment Control Plan (ER-1), 1 sheet, dated 7/10/2023  Site Landscape Plan (L-1), 1 sheet, dated 8/22/2022  Stormwater Management Site Plan (C-2.1), 1 sheet, dated 7/10/2023 Our previous comments from our July 3, 2023 letter are reproduced below, with updated comments inserted thereafter to reflect our review of the latest submission. 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. Page 2 westonandsampson.com Section 2.05 Stormwater Management Performance Standards 2.05(1) Low Impact Development Previous Comment: 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. Updated Comment: The Engineer has provided a LID narrative in the Stormwater Report (5 th page of the electronic submission) outlining the use of bioretention, justification for the location of infiltration measures away from the building, provision of large-canopy trees, and reasons for not using porous pavement. The narrative appears reasonable. Our previous comment has been addressed. 2.05(2) Good Housekeeping Procedures Previous Comment: 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. Updated Comment: The Engineer has revised the O&M plan. Our previous comment has been addressed. 2.05(3) Stormwater Management Systems Design We have noted the following in our review related to this standard:  Previous Comment: 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. Updated Comment: The Engineer has indicated in the Code Comment Response that the building roof material will be architectural asphalt shingle. Our previous comment has been addressed.  Previous Comment: 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. Updated Comment: The design has been revised to provide a separate catch basin and oil-grit separator to provide the required 44% TSS removal. Our previous comment has been addressed. Page 3 westonandsampson.com  Previous Comment: 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. Updated Comment: The Engineer has provided a catch basin detail that conforms to the requirements of the MA Stormwater Handbook for a deep sump hooded catch basin. Our previous comment has been addressed.  Previous Comment: 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. Updated Comment: The Engineer has updated the Stormwater Report to include an analysis of the 50- year storm peak discharge for the Proposed Conditions model. However, it has been omitted from the Existing Conditions model. During review it was also noted that the peak discharges in the Existing Conditions model do not match the values listed in the peak discharge summary table (page 4 of the electronic report). We recommend that the Engineer address these issues.  Previous Comment: 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. Updated Comment: The Engineer has revised the Oil-Grit separator detail to provide the requested dimensions. Our previous comment has been addressed.  Previous Comment: 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. Updated Comment: The Engineer has stated in the Code Comment Response that the rainfall data used for the stormwater modeling has been changed to NOAA Atlas 14. The rainfall values listed in the updated report do not appear to have changed from the previously submitted report. The Engineer is using rainfall values for the 2, 10, 25, 50 and 100-year storm events of 3.26, 4.74, 5.88, 6.97 and 8.15-inches, respectively. Our review of the NOAA Atlas 14 online tool indicates values of 3.35, 4.88, 5.83, 6.55 and 7.30-inches, respectively. Our previous comment remains unaddressed.  Previous Comment: 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 Page 4 westonandsampson.com 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. Updated Comment: The Engineer has provided an existing conditions model in which the cover page indicates that existing depressions were added to the model as ponds but the model itself is missing the technical output for these. We recommend that the Engineer revise the report to include this missing information.  Previous Comment: 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. Updated Comment: The Engineer has generally addressed this comment. However, in reviewing the calculations for the proposed conditions model, it was noted that the sum of the areas on the proposed drainage areas map was 51,262 square feet whereas the sum of the areas in the model is 51,374 square feet. Furthermore, the proposed drainage areas map seems to indicate 633 square feet of pervious area contributing to subcatchment CB3 whereas the model indicates 2,197 square feet. Finally, it was unclear where the “pervious area to bio area #2” (1,452 square feet) was being accounted for in the model. We recommend that the Engineer address these issues.  Previous Comment: 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.  Updated Comment: The model has been revised as requested. Our previous comment has been addressed. 2.05(4) Stormwater Management System Pollutant Removal Requirements (new development) We have noted the following in our review related to this standard:  Previous Comment: 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.  Updated Comment: No further comment. 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:  Previous Comment: 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 Page 5 westonandsampson.com this analysis or provide clarification for the commission’s consideration as to what alternative approach was used.  Updated Comment: The EPA tool has been used to evaluate average yearly pollutant removal. Our previous comment has been addressed. 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  Previous Comment: 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.  Updated Comment: The Engineer indicated in the Code Comment Response that a SWPPP has been prepared. No SWPPP was found in the materials submitted. Unless the Engineer made a separate submission that was not provided to us, our previous comment has not been addressed. 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:  Previous Comment: 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.  Updated Comment: The Engineer has revised the notes on the plan. Our previous comment has been addressed.  Previous Comment: 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.  Updated Comment: The Engineer has revised the notes on the plan. Our previous comment has been addressed.  Previous Comment: 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 Page 6 westonandsampson.com advisable to provide some means of preventing equipment from compacting the proposed bioretention areas on the site. We recommend that the engineer address this.  Updated Comment: The Engineer has revised the notes on the plan. Our previous comment has been addressed. 2.06(4) Erosion and Sedimentation Control Plan Content We have noted the following in our review related to this standard:  Previous Comment: 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.  Updated Comment: The existing conditions plan has been revised to note tree locations and size. Our previous comment has been addressed.  Previous Comment: A description of procedures for construction vehicle fueling, temporary chemical storage and construction vehicle washing/washout was not found. The engineer should address this.  Updated Comment: The Engineer has indicated that there will be no vehicle fueling or washing onsite. Our previous comment has been addressed. 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:  Previous Comment: There are comments noted farther above that the applicant should address related to the O&M plan.  Updated Comment: See updated comments above.  Previous Comment: 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.  Updated Comment: The Engineer has created a standalone O&M plan. Our previous comment has been addressed. Page 7 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 Previous Comment: 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. Updated Comment: No further comment. Standard 2: Post Development Peak Discharge Rates Previous Comment: 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. Updated Comment: Certain comments above need to be addressed which may impact this standard. We recommend that the Engineer address the comments above and ensure that this standard is still met. Standard 3: Recharge to Groundwater Previous Comment: 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. Updated Comment: No further comment. Standard 4: Total Suspended Solids (TSS) Removal Previous Comment: 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. Updated Comment: No further comment. Standard 5: Land Uses with Higher Potential Pollutant Loads Previous Comment: 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. Page 8 westonandsampson.com Updated Comment: No further comment. Standard 6: Protection of Critical Areas Previous Comment: 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. Updated Comment: A revised project narrative was not submitted, but the stormwater report still correctly identifies that the project is within the Aquifer Protection Overlay District. We have no further concerns on this topic since the stormwater BMPs are adequate for the critical area. The commission may at its discretion decide whether to require a revised project narrative. Standard 7: Redevelopments Previous Comment: This project qualifies as a new development. The applicant is required to fully comply with these standards. Updated Comment: No further comment. Standard 8: Construction Period Pollution Prevention and Erosion/Sedimentation Control Previous Comment: 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. Updated Comment: No further comment. Standard 9: Operations & Maintenance Plan Previous Comment: 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. Updated Comment: No further comment. Standard 10: Illicit Discharge Compliance Statement Previous Comment: An illicit discharge statement has been provided as required. Updated Comment: No further comment. Page 9 westonandsampson.com 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