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HomeMy WebLinkAbout2023-07-17 Storm Water Response to Comments_YarmouthEngineeringReviewCommentsResponsesYarmouth 1705 S. Walton Blvd, Suite 3 Phone: 479.273.7780 Bentonville, AR 72712 Fax: 888.520.9685 Code Comment Response Project: Colbea Enterprises 473, 478 & 479 S. Yarmouth S. Yarmouth, MA 02664 Arch. No.: 42.21.20002 Date: 07/11/2023 The information below is in response to the comments received by our office from Weston & Sampson, Plan Reviewer, of Yarmouth, MA regarding the above referenced project. Engineering Review of Stormwater Systems Section 2.05 Stormwater Management Performance Standards Comment 1: 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 application has stated in the project narrative an in the stormwater report that “the site development has been minimized as much as possible and two Boretention 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 are not used and why they would be inappropriate for this site. Response 1: Since this development includes a drive-thru, and due to the location of the new septic system, it was not feasible to infiltrate the building roof runoff right at the source. The project does provide eleven (11) large canopy trees including Red Maples and Pin Oaks planted over impervious surfaces. The use of porous pavement was not considered appropriate for this site, since the use is a LUHPPL and it is located in the Aquifer Protection District. 2.05(2) Good Housekeeping Procedures – Comment 2: We have noted the following in our review related to this standard: a) 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 carwash, and the project narrative states that no car washing will occur on the sire, so this may be a typo. b) The project narrative lists several procedures that 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. 1705 S. Walton Blvd, Suite 3 Phone: 479.273.7780 Bentonville, AR 72712 Fax: 888.520.9685 c) The O&M requirements for fertilizers are lacking the detail and specifically found in 2.05(2)(d). We recommend that the engineer address the items noted above. Response 2: The reference to carwash gutters has been removed, as it was a typo. Additional procedures have been added to the O&M plan, including requirements for fertilizers as specifically found in 2.05(2)(d). 2.05(3) Stormwater Management Systems Design - Comment 3: 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. Response 3: The building roof surface material proposed is an architectural asphalt shingle, which does not require pretreatment for the runoff to be infiltrated. Comment 4: 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. Response 4: The plan has been revised to provide a separate deep sump hooded catch basin that discharges to oil-grit separator, which provides the 44% TSS removal prior to discharge to the Bioretention Area. Comment 5: 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 details. Response 5: A detail for the deep sump catch basin has been added to the detail sheet. Comment 6: Under this standard, the applicant is required to demonstrate that Dost-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. Response 6: The stormwater report has been updated to include an analysis for the 50-year peak discharge. Comment 7: 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 details that were provided does not show all of these dimensions. Also, the 3-foot dimension is shown measuring to the middle of the baffle wall 1705 S. Walton Blvd, Suite 3 Phone: 479.273.7780 Bentonville, AR 72712 Fax: 888.520.9685 outlets whereas it should measure to the bottom in order to achieve full pool volume. We recommend that the engineer address these items. Response 7: The oil-grit separator details have been revised to include all chamber dimensions, and dimension to the bottom of the baffle wall outlet to achieve full pool volume. Comment 8: 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 due 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. Response 8: The rainfall data used for the stormwater modeling has been changed to NOAA Atlas 14. Comment 9: 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. Response 9: The model of the existing conditions has been updated to include the capacity of the depressed areas to infiltrate the runoff into the ground. Comment 10: 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. Response 10: The proposed conditions model has been revised to include the pervious areas at the front of the site flowing to the catch basins at the front of the site. The one area to the north side will infiltrate on-site. 1705 S. Walton Blvd, Suite 3 Phone: 479.273.7780 Bentonville, AR 72712 Fax: 888.520.9685 Comment 11: The sub catchments “Area to CB#1 ” and “Area to CB #2" in the model lists square footages that do not match the sub catchment map. We recommend that the engineer address this inconsistency. Response 11: The sub-catchment areas in the model have been revised to match the drainage areas map. 2.05(4) Stormwater Management System Pollutant Removal Requirements (new development) Comment 12: 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. Response 12: No action required. 2.05(5) Stormwater Management System Pollutant Removal Requirements (new development) Comment 13: This standard is not applicable since the site is a new development. Response 13: No action required. 1705 S. Walton Blvd, Suite 3 Phone: 479.273.7780 Bentonville, AR 72712 Fax: 888.520.9685 2.05(6) Stormwater Management System EPA Tool Analysis Comment 14: 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. Response 14: The EPA Region 1 BMP Accounting and Tracking tool has been utilized to evaluate the average yearly pollutant removal for the BMPs, and a summary report has been exported, and is now included in the stormwater report. 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 Comment 15: 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. Response 15: A SWPPP has been prepared, and a copy is included in the re-submission. 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: Comment 16: 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. Response 16: The note has been updated to specify stabilization through the use of a protective cover. Comment 17: The plan makes no reference to the handling dewatering discharges. Given the lack of groundwater that was observed at the time of test oils 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. 1705 S. Walton Blvd, Suite 3 Phone: 479.273.7780 Bentonville, AR 72712 Fax: 888.520.9685 Response 17: A note has been added to the plan specifying if de-watering is needed, it shall be pumped to a frac truck and disposed of at a facility offsite. Comment 18: 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 Conducting the proposed bioretention areas on the site. We recommend that the engineer address this. Response 18: A note has been added to the plan specifying the Bioretention Areas are to be protected from grading equipment during construction to avoid compaction. 2.06(4) Erosion and Sedimentation Control Plan Content Comment 19: This standard calls for the identification of “trees with a caliber 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. Response 19: The existing trees have been identified on an updated survey which will be included in the re- submittal. The existing trees to remain have been identified on the landscape plan. Comment 20: A description of procedures for construction vehicle fueling, temporary chemical storage and construction vehicle washing/washout was not found. The engineer should address this. Response 20: As noted in the O&M, there will be no vehicle fueling or washing taking place on the site. Any temporary storage of chemicals on the site will be in a secure, covered container. 2.07 Operation and Maintenance (0&M) Plan 2.07(1) Stand-alone 0&M plan requirements Comment 21: 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. Response 21: The O&M plan has been updated and separated from the stormwater report to be a stand- alone plan. 1705 S. Walton Blvd, Suite 3 Phone: 479.273.7780 Bentonville, AR 72712 Fax: 888.520.9685 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 t he Massachusetts Stormwater Handbook are adopted by reference. These standards are listed below, followed by our review comments. Standard 1: L/untreated Stormwater No new point discharges of untreated stormwater are proposed. The proposed stormwater improvements for the site include deep sumo 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 areas. 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 1705 S. Walton Blvd, Suite 3 Phone: 479.273.7780 Bentonville, AR 72712 Fax: 888.520.9685 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 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 statements 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 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. 1705 S. Walton Blvd, Suite 3 Phone: 479.273.7780 Bentonville, AR 72712 Fax: 888.520.9685 Standard 10: Illicit Discharge Compliance Statement An illicit discharge statement has been provided as required. End of Code Comment Response Rich DeFusco Sr Landscape Architect Harrison French and Associates