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Home My WebLink About06/14/2018 - A&M 1st Response - - 1429 OSGOOD STREET ' � V H,��. , �� ..�•,�mow, "�° � 1 wig 100 Commerce Way P.O.Box 2118 Woburn,MA 01888-0118 June 14, 2018 Tel:(781)935-6889 Fax:(781)935-2896 Horsley Witten Group, Inc. Re: A&M Project#: 2351-02 Janet Carter Bernardo, P.E. Site Plan and Drainage Report Review Senior Project Manager 294 Washington Street Suite 801 Boston, MA 02108 Dear Ms. Carter Bernardo, This letter provides responses to the Horsley Witten Group, Inc. review letter dated May 2, 2018 for the proposed development at 1429 Osgood Street,North Andover. The original comment is listed with A&M's response in bold italics. The numbering is consistent with your letter. 1. Standard 1 states that no new stormwater conveyances may cause erosion in wetlands of the Commonwealth. a. The existing site currently sheet flows in three directions: • West from the Project site into an existing catch basin that appears to be associated with the drainage system in Osgood Street, also known as Rte 125, a Massachusetts State Highway; • Northwest towards an existing low point at the property boundary; and • Southwest towards the unnamed stream and BVW delineated at the edge of the existing parking lot. The Applicant is intending to maintain these three discharge points and has proposed best management practices (BMPs)to provide additional treatment. To verify that the proposed grass swale located along the southwest property line will not cause erosion at the existing headwall HW recommends that the Applicant provide the velocity calculations for the grass swale. Response: The Drainage Report will be updated to include velocity calculations for the narrowest section of the grassed swale. 2. Standard 2 requires that post-development runoff does not exceed pre-development runoff off-site, for a redevelopment project per MassDEP this standard must be met to the maximum extent practicable. The Applicant has reduced impervious cover to all three discharge points and the HydroCAD modeling calculations provided indicate that the post-development peak discharge rates do not exceed the pre-development discharge rates. The proposed HydroCAD model does not include the proposed BMPs, including the rain gardens and grass swales proposed for water quality treatment. This is a reasonable methodology to verify compliance with Standard 2. HW has the following comments regarding the HydroCAD model: a. The Existing and Proposed Watershed Plans indicate that the existing building has specific breaks in the roof runoff. HW recommends that the Applicant provide a narrative explaining how the roof divide was determined. Response:ABM walked the entire interior of the building to note roof drain locations as well as roof drain building exit locations. Most of the roof drain lines were visible. All building drain exit locations are above grade on the exterior of the building. ABM verified the information gathered on the inside of the building with the visible drain exits on the civil & structural engineers • land surveyors • environmental consultants • landscape architects exterior of the building. A&M then compared the roof drain locations with aerial images to determine which parts of the roof drain to which drain exit locations. The majority of the roof drains to the south, but a portion of the building drains to the north. c. Furthermore, in accordance with Section 7.2 B.b) of the Stormwater Regulations the Applicant should provide the analyses for the 1/2 inch storm. HW recommends that the Applicant provide these additional calculations. Response: The Drainage Report will be updated to include the %"Storm. 4. Standard 4 requires that the stormwater system be designed to remove 80% Total Suspended Solids (TSS) and to treat 0.5-inch of volume from the impervious area for water quality. b. In accordance with Section 7.2 D. b) and c)of the Stormwater Regulations the Applicant should provide the water quality volume for the 1/2 inch storm, however it appears that the Applicant has not provided sizing calculations for the rain gardens or provided the 1/2 inch storm analysis. HW recommends that the Applicant provided the sizing calculations for the rain gardens in accordance with Volume 2, Chapter 2,page 26 of the MSH. Response: The Drainage Report will be updated to include sizing calculations for the rain gardens. These calculations show that the proposed rain gardens do not meet the sizing criteria of 5% to 7% of the area draining to it, as provided on the referenced page 26 of the Stormwater Handbook. However, as described in Volume 2, Chapter 3,Page 6 of the Stormwater Handbook, the rain gardens have been sized to be as large as possible and remove TSS to the maximum extent practicable and are an improvement to the existing condition. c. HW recommends that the Applicant provide a detail for the pea stone diaphragm. Response:A detail for the Pea Stone Diaphragm has been added to the detail sheets (Detail 8 on sheet C-502). 5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads (LUHPPL). a. The Applicant has noted that the proposed land use is not considered a LUHPPL; however the Layout&Materials Plan indicates that open storage bins are proposed. HW recommends that the Applicant clarify the proposed use of the property as well as document what material will be placed in the storage bins. Response: The property will be a mixed-use development consisting of office space, warehouse and contactor's yard. A portion of the site will be used for parking. The remaining area within the fenced off area will be used for exterior material storage for a contractor's yard, ranging from gravel to crushed stone, to granite block, to precast concrete curbing to loam. The intent of the storage bins is they are constructed of large freestanding walls and contain the material stored in them (crushed stone,gravel, loam, etc.). 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation or other pollutant sources. b. In accordance with Section 8.0 of the Stormwater Regulations, if a SWPPP is required per the NPDES General Permit the Applicant is required to submit a complete copy of the SWPPP as part of its application for a Land Disturbance Permit. HW recommends that the Applicant provided the SWPPP to the Town for review and verify that the Erosion and Sediment Control Criteria listed under Section 8.2 of the Stormwater Regulations is clearly referenced. Response:A copy of a SWPPP will be prepared for review. c. HW recommends that the size of the Fiber Roll be added to Detail 7 on Sheet C-501. Furthermore HW recommends that the size of the siltation fence be added to the detail. civil & structural engineers • land surveyors • environmental consultants • landscape architects Response: The size of the fiber roll and the siltation fence have been added to Detail 7 on sheet C-501. 9. Standard 9 requires a Long Term Operation and Maintenance (O &M)Plan to be provided. a. The Applicant has included an O&M Plan in accordance with Standard 9. HW recommends that the Applicant provide additional information related to the maintenance of the grass swale and pea stone diaphragm. Furthermore the Applicant may choose to separate the narrative for the bioretention area and the grass channel so that the plants in the rain gardens are not mowed. Response: The Drainage Report will be updated to include the maintenance of the grass swale and pea stone diaphragm. 13. Miscellaneous Comments: a. The proposed plan set including the Layout&Materials Plan, the Grading&Drainage Plan, and the Utilities Plan illustrate subsurface trenches in the area of the existing catch basin and Bioretention Area#2. It is not clear what these trenches are. HW recommends that the Applicant clarify the purpose of these trenches. Response: The trenches shown were the reserve area for the septic system. This system has since been revised and the reserve trenches are now shown between the primary trenches. b. As noted previously Osgood Street is a state highway and the Applicant is discharging stormwater into the state drainage system. HW recommends that the Applicant document to the Planning Board that permission to continue to discharge into the Massachusetts Department of Transportation(MassDOT) drainage network will be received prior to construction. The Applicant is reducing the flow to this catch basin as well as providing water quality as will be required by MassDOT. Response:Allen &Major has reached out to MassDOT to inquire what will be needed to obtain permission to continue to discharge. Any permits necessary will be obtained. We look forward to reviewing these comments and responses at the next Conservation Commission and Planning Board meeting. Please feel free to contact me at my direct line of(781) 305-9434 with any questions. ALLENp, M JOR ASSOCIATES,INC. Wayne KeelLer, .E.,PTOE, LEED AP Senior Project Manager June 14, 2018 Date civil & structural engineers • land surveyors • environmental consultants • landscape architects