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Home My WebLink About2023-02-28 Stormwater Review SPR Page February 23,2023 Town of North Andover Planning Board C/o Ms. Jean Enright, Planning Director 120 Main Street Nortlil Andover,MA 01845 Re: Summary of Plan Changes Extra Space Storage Site Plans 1701 Osgood Street North Andover,MA ALLEN ENGINEERING Dear Chairman Goldberg and Members of the Board: &AssocIATES, INC. Civil Engineers,Surveyors& Allen Engineering&Associates, Inc. providing the Board with a summary of the Land Development Consultants changes inade to the site plans to date. The plans were initially submitted to the Board on November 3 d. There were two subsequent reviews conducted by the Board's peer review consultant,Horsley Witten Group. The plans were revised as follows based on the peer reviews and comments received from the North Andover Fire Department: 0 Revision#1, dated December 28,2023 ADDRESS ® Revision#2, dated February 17, 2023 140 Hartford Avenue East Hopedale, A 3 d and final peer review was issued by Horsley Witten Group, dated February 20, MA 01747 2023. It appears that no additional plan changes are required as a result of this review and that all comments have been reconciled. PHONE Summary of plan revisions: (508)381-3212 L Additional field survey data was obtained and added to the plans, including: topography for the upper elevations of the site for watershed analysis purposes;pipe sizes, material and inverts for all drainage infrastructure; the headwall and outlet pipe was added on the opposite side of Osgood Street. WEB SITE 2. Snow storage areas were added. www.allen-ea.com 1 The proposed parking was modified as requested by the Fire Department, The initial plans depicted twelve (12),head-in parking stalls along the front of the proposed building. The parking was revised to provide seven (7) spaces in a combination of head-in and parallel parking,which provides an additional 4 feet of pavement for fire tnick maneuvering. 21 total parking spaces are proposed as compared to the initial 26 spaces. 4. The proposed hydrant on the north side of the site was moved closer to the new building and a second standpipe was added per the request for the fire department. 5. A separate Erosion and Sedimentation Control Plan was added to the plan set to highlight measures to control sediment laden runoff and address construction sequencing. In addition to the above plans changes,there was significant effort put forth on the site drainage analysis, subsequent to the initial submission, to demonstrate that the existing(as-built) site conditions are designed and functioning per the MassDEP Storrnwater Management standards. The additional drainage analysis resulted in only minor plan changes in the form of notes and call-outs. Page 1 2 Please feel free to contact me at(508) 381-3212 with any questions. Sincerely, ALLEN ENGINEERING ASSOCIATES, INC. Michael J. Dryden,RLA Senior Project Manager Cc: Greg Susko,Applicant John Smolak,Esq., Smolak&Vaughan LLP ----------------------------------- --------------------- 140 HARTFORD AVENUE EAST - HOPEDALE, MASSACHUSETTS 0 1747 (508) 381-3212 WWW.ALLEN-EA.COM Stormwater Long-Term Operation & Maintenance Plan 1701 Osgood Street, North Andover, MA Date: December 28, 2022 Rev: February 17, 2023 The proposed stormwater management system and the Best Management Practices (BMP's) are to be constructed in accordance with the approved site design plans. During the construction process the general site contractor and property owner, Extra Space Storage, shall be designated as the owners of the BMP's and will be responsible for their operation and maintenance. Once the BMP's are constructed they are to be protected from sedimentation until the site is stabilized and vegetated. Inspections should be performed routinely and after every major storm event. Any accumulated sediments and debris are to be removed and any eroded areas are to be re-graded and re-vegetated. Post-Development Phase Ownership: After the completion of the site construction, the entire drainage system will be the responsibility of the property owner— Extra Space Storage Emergency Fuel Spill Response: In the event of a fuel spill the responsible party shall call 9-1-1. They shall follow local and state removal procedures for the contaminant. The responsible contractor shall also call the North Andover Board of Health. Any contaminated soil must be completely removed from the property and be delivered to a certified land fill. Operation & Maintenance: The following are the minimum maintenance criteria for the proposed BMP's. Responsible parties should however review the Mass DEP Stormwater Handbook for further explanation. Grass Swale These swales shall be inspected 4 times a year and shall be cleaned of debris, silt and/or any vegetation. The grass swale shall be cut regularly to prevent grass from entering the yard drain grate and/or Cultec system. Cultec Stormwater System The Cultec System includes all of the plastic chambers and the PVC pipe that feed the systems. The systems should be inspected at least twice per year to ensure that it is operating as intended. Inspections should be conducted during the spring and fall seasons. The Cultec System shall be cleaned out if a minimum of six inches of material has accumulated as viewed and measured through the inspection port. Inspections shall also include verifying adequate soil cover is maintained over and around the system. This area shall be free of permanent structures. Fertilizers, Pesticides & Insecticides Pesticides and Insecticides shall not be stored on site. Fertilizers and other landscape products may be stored on site provided they are kept indoors. Estimated Operation & Maintenance Budget The estimated cost to maintain the above referenced stormwater system will be $3,000- $5,000 per year. Supplimental Information Inspection Log Forms BMP Site Plan Cultec Manufacturer's Operation & Maintenance Sheets Stormwater BMP Inspection and Maintenance Log Facility Name: Extra Space Storage Address: 1701 Osgood Street,N. Andover, MA Begin Date End Date Date BMP BMP Description Inspected Cause for Exceptions Noted Comments and by: Inspection Actions Taken Instructions:Record all inspections and maintenance for all treatment BMPs on this form.Use additional log sheets and/or attach extended comments or documentation as necessary.Submit a copy of the completed log with the annual independent inspectors'report to the municipality,and start a new log at that time. • Inspected by—Note all inspections and maintenance on this form,including the required independent annual inspection. • Cause for inspection—Note if the inspection is routine,pre-rainy-season,post-storm,annual,or in response to a noted problem or complaint. • Exceptions noted—Note any condition that requires correction or indicates a need for maintenance. Comments and actions taken—Describe any maintenance done and need for follow-up. F+RERAREO FOR: Extra Space Properties 104 LLC c/o Storage&Distribution Group,LLC 31 Border Street Cohasset,MA 02025 TrrLE. BMP Plan 1701 Osgood Street LOT AREA. a�' &016*AC. N.Andover,MA BMP-1 (131,385*SF) _._...............-- sr,Al. Cultec Inflltretionvt e System /c oN0 471 "t fgcrste��w i seraent V 1 wRewnR .�,� _.... {a"1,�r, PREPARED Rv iJ - " AL.LEN ENGINEERING &AsSCCiATES,INC. Development C.. BMP-2 LCivilCLngtneers Surveyors N; � Grass Swale p Consultants 140 Hartford Avenue East Hopedale,Ma 01747 �.} (08)381-3212 wwwalk.r.can pp��''yyg,7pp77 ~V'�}ti'Aa"Jd27 SCALL......_. 1'- 40 FEET Be DATE: _ December 28,2022 __m...— REVISIONS D.ATE DESCRIPTION INI JOB NO, SHEET; 00447 f 1 a iomiomrACTOR@ � RIECI-11ARGE !mmf ��mm a annim -STORMWATER MANAGEMENT SOLUTIONS kL �e y, / f:l�fl tAPYt'�Ni� f I � I u1�i ��'n ��fil��uf V� J� i f;liM P, ,7 '✓ w� n R/flr Ju)�+ r zs(� i, I � �« r, %F/rN �/ � it % art ,,�''su* ,{l n a� ,✓ "�r, h i2 U� rr ,,,r 1,J p//r.i.�;7�lJrr/ „� M, V. f �, rrl� � {r � ..,ur'✓�fi�;��I rj�Tr`�� l' 1 >i// �r lh�/f0 r �� ",r �s /f ,' /, ,I ::u��l/hl�r/� r`�fl�� rl�� /li r r/✓r �li'v l/ 'r ,. r / �' �i',,^✓r �d u� �%/. � �%r /�°� ,�G„4��i iJ ��/.i �r /rj I %r^; l; i7: � ` i - � r r e�� -. ,�, u..„ .��.. t�. ` ��,fu�1l%�. ir11�/i iij%/{r% ✓��1.,!�%%�� r s� y W "wu w / r r ,u,., p. �� l'iGirBk�a, n��•N N�"'��. °s. � �� .,. wre,.."' a 'ky✓��rr//t� i f��ur��l��J{j�'... ,r K� a / r h. 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Box 280 878 Federal Road Brookfield, Connecticut 06804 USA www.cultec.com Cop aright hiloflce @ 2019 CULTEC, Inc. All rights reserved. Printed in the USA. This document and any accompanying CULTEC products are copyrighted by CULTEC, Inc. Any reproduction and/or distribution without prior written consent from CULTEC, Inc. is strictly prohibited. Dis6laiiners: The drawings, photographs and illustrations shown in this document are for illustrative purposes only and are not necessarily to scale. Actual designs may vary. CULTEC reserves the right to make design and/or specification changes at any time without notice at CULTEC's sole discretion. CULTEC, the CULTEC logo, RECHARGER, CONTACTOR, HVLV, PAC, STORMFILTER, STORMGENIE and The Chamber with The Stripe are registered trademarks of CULTEC, Inc. Chamber of Choice, HD, 100, 125, 150, 150XL, 180, 280, 330, 330XL, 360, VS, 902, Field Drain Panel, C-1, C-2, C-3, C-4, EZ-24, Landscape Series are trademarks of CULTEC, Inc. @ Copyright on all drawings, illustrations, photos, charts - CULTEC, Inc. All rights reserved. Pirotected by oine our. rnore t)f the foiHiowilng Ill. ateints owned by 0,fltec, [inc.: U.S. Patents 6,129,482; 6,322,288; 6,854,925; 7,226,241; 7,806,627; 8,366,346; 8,425,148; U.S. Designs D613,819; D638,095; D668,318; Canadian Patent 2,450,565; 2,591,255; Canadian Designs 129144; 135983; 159073; 160977; and/or other U.S. or Foreign Patent(s) or Patent(s) Pending. Contact Inforimabon: For general information on our other products and services, please contact our offices within the United States at (800)428-5832, (203)775-4416 ext. 202, or e-mail us at custservice@cultec.com. For technical support, please call (203)775-4416 ext. 203 or e-mail tech@cuItec.com. Visit www.cuItec.com/downloads.htmI for Product Downloads and CAD details. Doc ID: CLT057 01-20 January 2020 These instructions are for single-layer traffic applications only. For multi-layer applications, contact CULTEC. All illustrations and photos shown herein are examples of typical situations. Be sure to follow the engineer's drawings, Actual designs may vary. .................................................... .............................................................. 2 .............................. For more information, contact CULTEC at (203) 775-4416 or visit www.cultec.com. @ CULTEC,Inc.CLT057 01-20 CULTEC STORMWATER CHAMBERS C CULTEC This manual contains guidelines recommended by CULTEC,Inc. and may be used in conjunction with, but not to supersede, local regulations or regulatory authorities. OSHA Guidelines must be followed when inspecting or cleaning any structure. lnl,]-oductiol,i The CULTEC Subsurface Stormwater Management System is a high-density polyethylene (HDPE) chamber system arranged in parallel rows surrounded by washed stone. The CULTEC chambers create arch-shaped voids within the washed stone to provide stormwater detention, retention, infiltration, and reclamation. Filter fabric is placed between the native soil and stone interface to prevent the intrusion of fines into the system. In order to minimize the amount of sediment which may enter the CULTEC system, a sediment collection device (stormwater pretreat- ment device) is recommended upstream from the CULTEC chamber system. Examples of pretreatment devices include, but are not limited to, an appropriately sized catch basin with sump, pretreatment catchment device, oil grit separator, or baffled distribution box. Manufactured pretreatment devices may also be used in accordance with CULTEC chambers. Installation, operation, and maintenance of these devices shall be in accordance with manufacturer's recommendations. Almost all of the sediment entering the stormwater management system will be collected within the pretreatment device. Best Management Practices allow for the maintenance of the preliminary collection systems prior to feeding the CULTEC chambers. The pretreatment structures shall be inspected for any debris that will restrict inlet flow rates. Outfall structures, if any, such as outlet control must also be inspected for any obstructions that would restrict outlet flow rates. OSHA Guidelines must be followed when inspecting or cleaning any structure. Q��)eratJbn and 114ai loans nance I. Operation CULTEC stormwater management systems shall be operated to receive only stormwater run-off in accordance with applicable local regulations. CULTEC subsurface stormwater management chambers operate at peak performance when installed in series with pretreatment. Pretreatment of suspended solids is superior to treatment of solids once they have been introduced into the system. The use of pretreatment is adequate as long as the structure is maintained and the site remains stable with finished impervious surfaces such as parking lots, walkways, and pervious areas are properly maintained. If there is to be an unstable condition, such as improvements to buildings or parking areas, all proper silt control measures shall be implemented according to local regulations. II. Inspection and Maintenance Options A. The CULTEC system may be equipped with an inspection port located on the inlet row. The inspection port is a circular cast box placed in a rectangular concrete collar. When the lid S removed, a 6-inch (150 mm) pipe with a screw-in plug will be exposed. Remove the plug. This will provide access to the CULTEC Chamber row below. From the surface, through this access, the sediment may be measured at this location. A stadia rod may be used to measure the depth of sediment if any in this row. If the depth of sediment is in excess of 3 inches (76 mm), then this row should be cleaned with high pressure water through a culvert cleaning nozzle. This would be carried out through an upstream manhole or through the CULTEC Storm Filter Unit (or other pre- treatment device). CCTV inspection of this row can be deployed through this access port to deter mine if any sediment has accumulated in the inlet row. B. If the CULTEC bed is not equipped with an inspection port, then access to the inlet row will be through an upstream manhole or the CULTEC StormFilter. 1. Manhole Access This inspection should only be carried out by persons trained in confined space entry and sewer inspection services. After the manhole cover has been removed a gas detector must be lowered into the manhole to ensure that there are not high concentrations of toxic gases present. The inspector should be lowered into the manhole with the proper safety equipment as per OSHA requirements. The inspector may be able to observe sediment from this location. If this is not possible, the inspector will need to deploy a CCTV robot to permit viewing of the sediment. For more information, contact CULTEC at (203) 775-4416 or visit www.cultec.com. @ CULTEC,Inc.CLT057 01-20 OPERATIONS AND MAINTENANCE GUIDELINES CULTEC 2. StormFilter Access Remove the manhole cover to allow access to the unit. Typically a 30-inch (750 mm) pipe is used as a riser from the StormFilter to the surface. As in the case with manhole access, this access point requires a technician trained in confined space entry with proper gas detection equipment. This individual must be equipped with the proper safety equipment for entry into the StormFilter. The technician will be lowered onto the StormFilter unit. The hatch on the unit must be removed. Inside the unit are two filters which may be removed according to StormFilter maintenance guidelines. Once these filters are removed the inspector can enter the StormFilter unit to launch the CCTV camera robot. C. The inlet row of the CULTEC system is placed on a polyethylene liner to prevent scouring of the washed stone beneath this row. This also facilitates the flushing of this row with high pressure water through a culvert cleaning nozzle. The nozzle is deployed through a manhole or the StormFilter and extended to the end of the row. The water is turned on and the inlet row is back-flushed into the manhole or StormFilter. This water is to be removed from the manhole or StormFilter using a vacuum truck. III. Maintenance Guidelines The following guidelines shall be adhered to for the operation and maintenance of the CULTEC stormwater management system: A. The owner shall keep a maintenance log which shall include details of any events which would have an effect on the system's operational capacity. B. The operation and maintenance procedure shall be reviewed periodically and changed to meet site conditions. C. Maintenance of the stormwater management system shall be performed by qualified workers and shall follow applicable occupational health and safety requirements. D. Debris removed from the stormwater management system shall be disposed of in accordance with applicable laws and regulations. IV. Suggested Maintenance Schedules A. Minor Maintenance The following suggested schedule shall be followed for routine maintenance during the regular operation of the stormwater system: Monthly in first year Check inlets and outlets for clogging and remove any debris, as required. Spring and Fall Check inlets and outlets for clogging and remove any debris, as required. One year after commissioning and every third Check inlets and outlets for clogging and remove any debris, as required. year following B. Major Maintenance The following suggested maintenance schedule shall be followed to maintain the performance of the CULTEC stormwater management chambers. Additional work may be necessary due to insufficient performance and other issues that might be found during the inspection of the stormwater management chambers. (See table on next page) 4 ...... uuuuu For more information, contact CULTEC at (203) 775-4416 or visit www.cultec.com. @ CULTEC,Inc.CLT057 01-20 CULTEC STORMWATER CHAMBERS CULTEC ............ ............... Inlets and Outlets Every 3 years 0 Obtain documentation that the inlets, outlets and vents have been cleaned and will function as intended. Spring and Fall & Check inlet and outlets for clogging and remove any debris as re- quired. CULTEC Stormwater 2 years after commis- • Inspect the interior of the stormwater management chambers Chambers sioning through inspection port for deficiencies using CCTV or comparable technique. • Obtain documentation that the stormwater management chambers and feed connectors will function as anticipated. 9 years after commis- • Clean stormwater management chambers and feed connectors of sioning every 9 years any debris. following • Inspect the interior of the stormwater management structures for deficiencies using CCTV or comparable technique. • Obtain documentation that the stormwater management chambers and feed connectors have been cleaned and will function as intend- ed. 45 years after com- • Clean stormwater management chambers and feed connectors of missioning any debris. • Determine the remaining life expectancy of the stormwater man- agement chambers and recommended schedule and actions to reha- bilitate the stormwater management chambers as required. • Inspect the interior of the stormwater management chambers for deficiencies using CCTV or comparable technique, 0 Replace or restore the stormwater management chambers in accor- dance with the schedule determined at the 45-year inspection. • Attain the appropriate approvals as required. • Establish a new operation and maintenance schedule. Surrounding Site Monthly in 11tyear • Check for depressions in areas over and surrounding the stormwater management system. Spring and Fall • Check for depressions in areas over and surrounding the stormwater management system. Yearly Confirm that no unauthorized modifications have been performed to I the site. For additional information concerning the maintenance of CULTEC Subsurface Stormwater Management Chambers, please con- tact CULTEC, Inc. at 1-800-428-5832. For more information, contact CULTEC at(203) 775-4416 or visit www.cultec.com. @ CULTEC,Inc,CLT057 01-20 OPERATIONSr MAINTENANCE GUIDELINES Cu EC WQMP Operation & Maintenance (O&M ) Plan Project Name: Prepared for: Project Name: Address: City, State Zip: Prepared on: Date: 1N1010 For moreinformation,contact CULTECat (203) 775-4416 or visit www.cultec.com. @ CULTEC,Inc.CLT057 01-20 CULTEC STORMWATER CHAMBERS CULTEC This O&M Plan describes the designated responsible party for implementation of this WQMP, including: operation and maintenance of all the structural BMP(s), conducting the training/educational program and duties, and any other necessary activities. The O&M Plan includes detailed inspection and maintenance requirements for all struc- tural BMPs, including copies of any maintenance contract agreements, manufacturer's maintenance requirements, permits, etc. 8.1.1 Project Information Project name Address City, State Zip Site size List of structural BMPs, number of each Other notes 8.1.2 Responsible Party The responsible party for implementation of this WQMP is: Name of Person or HOA Property Manager Address City, State Zip Phone number 24-Hour Emergency Contact number Email 8.1.3 Record Keeping Parties responsible for the O&M plan shall retain records for at least 5 years. All training and educational activities and BMP operation and maintenance shall be documented to verify compli- ance with this O&M Plan. A sample Training Log and Inspection and Maintenance Log are included in this docu- ment. 8.1.4 Electronic Data Submittal This document along with the Site Plan and Attachments shall be provided in PDF format. AutoCAD files and/or GIS coordinates of BMPs shall also be submitted to the City. For more information, contact CULTEC at(203) 775-4416 or visit www.cultec.com. '7 @ CULTEC,Inc,CLT057 01-20 OPERATIONS CULTEC Appendix BMP SITE PLAN Site plan is preferred on minimum 11" by 17" colored sheets, as long as legible. N For more information,contact CULTEC at (203) 775-4416 or visit www.cultec.com. @ CULTEC,Inc.CLT057 01-20 CULTEC STORMWATER CHAMBERS C CULTEC BMP OPERATION & MAINTENANCE LOG Project Name: Today's Date: Name of Person Performing Activity (Printed): Signature: For more information, contact CULTEC at(203) 775-4416 or visit www.cultec.com. O CULTEC,Inc.CLT057 01-20 ,,i C OPERATIONS AND MAINTENANCE GUIDELINES CULTEC Minor Maintenance Monthly in first year Check inlets and outlets for clogging and remove any debris, as required. Notes ❑ Month 1 Date: • Month 2 Date: ❑ Month 3 Date: r.-j Month 4 Date ❑ Month 5 Date: i-i Month 6 Date: E) Month 7 Date: * Month 8 Date: * Month 9 Date: r._i Month 10 Date: ❑ Month 11 Date: F-j Month 12 Date: Spring and Fall Check inlets and outlets for clogging and remove any debris, as required. N otes i..j Spring Date: o Fall Date: ❑ Spring Date: ❑ Fall Date: ❑ Spring Date: ❑ Fall Date: ❑ Spring Date: ❑ Fall Date: ❑ Spring Date: ❑ Fall Date: 1.-j Spring Date: ❑ Fall Date: One year after commissioning Check inlets and outlets for clogging and remove any debris, as required. and every third year following Notes (i Year 1 Date: ❑Year 4 Date: •Year 7 Date: ❑Year 10 Date: F..i Year 13 Date: ❑Year 16 Date: ❑Year 19 Date: [..j Year 22 Date: 10 For more information, contact CULTEC at (203) 775-4416 or visit www.cultec.com. @ CULTEC,Inc.CLT057 01-20 CHAMBERS CULTEC Major Maintenance Every 3 years Obtain documentation that the inlets, outlets and vents have been cleaned and will function as intended. Notes r.:)Year 1 Date: •Year 4 Date: ❑Year 7 Date: •Year 10 Date: ❑Year 13 Date: •Year 16 Date: 4 47 E)Year 19 Date: ra Year 22 Date: O Spring and Fall Check inlet and outlets for clogging and remove any C debris, as required. M w J Notes C o Spring Date: w n Fall Date: ❑ Spring Date: ri Fall Date: Ei Spring Date: ci Fall Date: o Spring Date: ra Fall Date: o Spring Date: o Fall Date: o Spring Date: o Fall Date: (A 2 years after commissioning ❑ Inspect the interior of the stormwater management L7 chambers through inspection port for deficiencies using CCTV or comparable technique. Mcn Obtain documentation that the stormwater manage- ment chambers and feed connectors will function as anticipated. Notes ❑Year 2 Date: E L. O U) U W J U „N For more information, contact CU�TEC at(203) 775-444 6 or visitwww ucultec.com. ©CULTEC,Inc.CLT057 01-20 OPERATIONS AND MAINTENANCE GUIDELINES CULTEC Major Maintenance 9 years after commissioning o Clean stormwater management chambers and feed every 9 years following connectors of any debris. o Inspect the interior of the stormwater management structures for deficiencies using CCTV or comparable technique, o Obtain documentation that the stormwater man- agement chambers and feed connectors have been cleaned and will function as intended. Notes o Year 9 Date: o Year 18 Date: o Year 27 Date: o Year 36 Date: CJ M 45 years after commissioning o Clean stormwater management chambers and feed .0 connectors of any debris. U o Determine the remaining life expectancy of the stormwater management chambers and recommended M schedule and actions to rehabilitate the stormwater management chambers as required. E L. 0 o Inspect the interior of the stormwater management V) chambers for deficiencies using CCTV or comparable U technique. UJ F_ i..i Replace or restore the stormwater management chambers in accordance with the schedule determined at the 45-year inspection. • Attain the appropriate approvals as required, • Establish a new operation and maintenance sched- ule. Notes Ej Year 45 Date: 12 ...................................... ......................... For more information, contact CULTEC at (203) 775-4416 or visit www.cultec.com. Oc CULTEC,Inc.CLT057 01-20 CULTEC ■ r CHAMBERS [!T WO CULTEC Major Maintenance Monthly in istyear ❑ Check for depressions in areas over and surrounding the stormwater management system. Notes ❑ Month 1 Date: r.:j Month 2 Date: ❑ Month 3 Date: r.:j Month 4 Date: ❑ Month 5 Date: ❑ Month 6 Date: r.:i Month 7 Date: ❑ Month 8 Date: ❑ Month 9 Date: ❑ Month 10 Date: ❑ Month 11 Date: ❑ Month 12 Date: Spring and Fall ❑ Check for depressions in areas over and surrounding the stormwater management system. Q Notes (A r...i Spring Date: Im S ❑ Fall Date: .a C o Spring Date: 4 ❑ Fall Date: L i_: Spring Date: ❑ Fall Date: ❑ Spring Date: ❑ Fall Date: ❑ Spring Date: ❑ Fall Date: r:i Spring Date: ❑ Fall Date: Yearly r.:, Confirm that no unauthorized modifications have been performed to the site. Notes ❑Year 1 Date: ❑Year 2 Date: r_j Year 3 Date: ❑Year 4 Date: ❑Year 5 Date: ❑Year 6 Date: ii Year 7 Date: For more information, contact CULTEC at (243) 775-4416 or visit www.cultec.com. ©CULTEC,Inc.CLT057 01-20 RETENTION � DETENTION INFILTRATION u WATER QUALITY Cc)CULTEC,Inc.CLT057 O1-20 Horsley Wiffen Group Sustainable Environmental Solutions 112 Water Street•V Floor•Boston,MA 02109 857-263-6193-horsleywitten.com February 20, 2023 Ms. Jean Enright, Planning Director North Andover Planning Board 120 Main Street North Andover, Massachusetts 01845 Ref: Third Stormwater Peer Review Extra Space Storage Building 1701 Osgood Street North Andover, Massachusetts Dear Ms. Enright and Board Members: The Horsley Witten Group, Inc. (HW) is pleased to provide the North Andover Planning Board with this letter report summarizing our third review of the Drainage Analysis and Site Plans for the proposed Extra Space Storage Building at 1701 Osgood Street, North Andover, MA. The plans and stormwater report were prepared by Allen Engineering & Associates, Inc. on behalf of Extra Space Properties 104 LP (Applicant). The project proposes the construction of a 47,244 square foot (sf) three-story storage building, along with associated parking, utilities, stormwater management, and landscaping on a previously developed 3.02-acre parcel containing an existing building. The stormwater management for the proposed storage building includes a grass swale, a catch basin, manholes, and a subsurface infiltration system (SIS). A small portion of the site is located within the 100-foot buffer zone of a wetland resource area located across Osgood Street. The proposed work will remain outside of the buffer zone. The following additional documents and plans were received by HW in response to our second review dated January 12, 2023: • Response to Stormwater Peer Review Comments (2nd review) letter for Extra Space Storage at 1701 Osgood Street, North Andover, prepared by Allen Engineering & Associates, Inc., dated February 17, 2023 (8 pages). • Drainage Analysis for Extra Space Storage at 1701 Osgood Street, North Andover, MA, prepared by Allen Engineering & Associates, Inc., revised February 17, 2023 (318 pages). 4 Stormwater Long-Term Operation & Maintenance Plan, 1701 Osgood Street, North Andover, MA, revised February 17, 2023 (18 pages). • Architectural drawings, Proposed Self Storage facility, 1701 Osgood Street, North Andover, MA, prepared by BL Companies, revisions thru December 20, 2022 (6 sheets). ® Site Plans for Extra Space Storage, 1701 Osgood Street (Route 125), North Andover, Massachusetts, prepared by Allen Engineering & Associates, Inc., revised thru February 17, 2023, including: o Cover Sheet C-1 a Existing Conditions Plan C-2 Hors luyW itt n.com 91 @Horsl yVWitturbGroup IM Horsley Witten Group, Inc. Town of North Andover February 20, 2023 Page 2 of 8 o Layout & Materials Plan C-3 o Grading & Drainage Plan C-4 o Landscape & Lighting Plan C-5 o Fire Truck Swept Path C-6 o Construction Details C-7 o Construction Details C-8 o Erosion & Sediment Control Plan C-9 Stormwater Management Design Peer Review In accordance with the North Andover Zoning Bylaw §195-8.14. E. (8) A Stormwater management plan is required for all site plan review applications. The stormwater management plan shall be prepared in accordance with the latest version of the Massachusetts Stormwater Handbook (MSH) and demonstrate full compliance with the Massachusetts Stormwater Standards and the North Andover Stormwater Management and Erosion Control Regulations. HW offers the following comments concerning the stormwater management design. We have used the MSH as the basis for organizing our comments. However, in instances where the additional criteria established in Chapter 250 of the North Andover Code requires further recommendations; we have referenced these as well. The following comments correlate to our January 12, 2023 second peer review letter. Follow up comments are provided in bold underlined font as needed. 1. Standard 1: No new stormwater conveyances (e.g., outfalls) may discharge untreated stormwater directly to or cause erosion in wetlands or waters of the Commonwealth. a. It appears that the southeastern portion of subcatchment 1 S is captured by the proposed grass swale which directs runoff to a proposed catch basin that conveys stormwater into the 18-inch drain line that discharges directly into the wetland to the west of Osgood Street. HW recommends that the Applicant verify that the new discharge velocity at the outfall will not cause erosion in the wetland. January 12, 2023: The Applicant has added a subcatchment area for the southeastern portion of subcatchment 1S. It has stated that the additional runoff of 0.4 CFS that would outfall to the 36" pipe would be negligible in relation to the outfall during the 100 year storm event. HW agrees that the 0.4 cfs is likely negligible to the 36" pipe outfall. However, HW recommends that the Applicant confirm that the existing outfall is not currently causing erosion to the wetland. February 20, 2023: The Applicant provided a photo of the 30" outfall. It does not appear that the outfall causes erosion to the wetland. HW has no further comment. b. Most of the site runoff will be captured by the stormwater basin located at the western end of the site. It appears that an existing outlet control structure conveys stormwater into the wetland to the west of Osgood Street. HW recommends that the Applicant confirm that the existing discharge does not cause erosion in the wetland. January 12, 2023: The Applicant has stated based on the proposed infrastructure the wetland would receive a decrease in runoff in all storms and therefore there would be no significant erosion.It is unclear how this determination was made. HW recommends that the Applicant document how and where the existing outlet K:\Projects\2021\21020 Town of North Andover\21020K 1701 Osgood\Reports\230220_3rd_SWPeerReview 1701 Osgood.docx Town of North Andover February 20, 2023 Page 3of8 control structures discharges and as requested above confirm that the existing discharge does not currently cause erosion in the wetland. Furthermore, HW agrees that by installing the proposed subsurface chamber system for the proposed roof runoff the site is likely reducing the runoff to the existing stormwater basin. However, the Applicant has not demonstrated this. HW recommends that the Applicant provide the HydroCAD model for the entire existing site evaluating the outlet control structure discharge as the design point and compare the entire proposed site at this same location. February 20, 2023: The Applicant has revised the HydroCAD model to include the existing site conditions on the west side of the site. In comparing the catchment area to reach 3R and 6R under existing conditions to EV-1 and EV-2 under proposed conditions the Applicant has documented the reduction in flow and volume to the onsite basin under proposed conditions. HW had also requested that the Applicant evaluate the outlet control structure from the onsite infiltration basin to confirm the velocity in the 30" pipe that outfalls into the wetland. It appears that the HydroCAD model is not consistent with the Existing Conditions Plan. The outlet control device model includes a weir that is not evident on the plan set and does not include the top inlet at elevation 46.02. The HydroCAD model also includes storage below elevations 42, 44, and 46. However, the existing conditions plan does not include a surface elevation of 42. The Applicant has confirmed via a visual inspection that the existing 30" pipe is not causing erosion in the wetland. HW agrees that the proposed design will not negatively impact the wetland resource area. c. January 12, 2023: It appears the area for subcatchment 2S on the Proposed Drainage Plan (9,217 sf) does not match the modeled area in HydroCAD (3,564 sf). HW recommends that the Applicant review the Drainage Plan and the HydroCAD model and revise the model as needed. February 20, 2023: The Applicant has adjusted the HydroCAD model as requested. HW has no further comment. 2. Standard 2: Stormwater management systems shall be designed so that post-development peak discharge rates do not exceed pre-development peak discharge rates. a. The Applicant has drawn the existing and proposed watershed maps to include a portion of the upgradient area northeast of the site. A large upgradient area to the east flows towards the riprap drainage channel and into the 18-inch pipe at the headwall. It appears that some of this upgradient area may flow onto the southeast corner of the site. HW recommends that the'Applicant explain the drainage pattern of the large area to the east that flows onto the site. January 12, 2023: The Applicant has clarified the drainage pattern of the upgradient area northeast of the site. HW has no further comment. b. The Applicant has provided two design points: EV-1 (catch basins at the proposed northern sawcut line) and EV-2 (catch basins at the proposed southern sawcut line). These catch basins convey stormwater to the existing stormwater basin at the western KAProjects\2021\21020 Town of North Andover\21020K 1701 Osgood\Reports\230220_3rd_SWPeerReview 1701 Osgood.docx Town of North Andover February 20, 2023 Page 4of8 end of the site, which appears to overflow via an outlet control structure into the wetland to the west of Osgood Street. HW recommends that the Applicant expand the HydroCAD model to include the stormwater basin as a pond, the existing portion of the site and building that flows into the basin as subcatchments and evaluate the outlet control structure and the wetland as additional design points. January 12, 2023: The Applicant has revised its HydroCAD model to show a reduction in flow and volume will be entering the existing drainage basin starting at the existing on site catch basins. As noted above HW agrees that it is likely that the proposed design reduces the peak discharge rate and volume from the existing stormwater basin. However, HW recommends that the Applicant provide the documentation to confirm this. February 20, 2023: The Applicant has revised the HydroCAD model as noted above. c. It appears that the southeastern portion of subcatchment 1 S is captured by a proposed grass swale which directs runoff to a proposed catch basin that conveys stormwater into the 18-inch drain line that discharges directly into the wetland to the west of Osgood Street. HW recommends that the Applicant verify that the conveyance system is properly sized to handle the additional flow as well as the runoff coming from the east. January 12, 2023: The Applicant has stated in its response to comment 1.a that the additional flow is negligible and should accommodate the flow. HW's agrees that the increase flow to the 18" pipe is negligible. However, we recommend that the Applicant provide conveyance calculations for the sizing of the swale. February 20, 2023: The Applicant has provided calculations to confirm that the swale is adequately sized. HW has no further comment. d. There appears to be a typographical error listed in Table 1: Summary of Peak Rates of Stormwater Runoff for Evaluation Point 1 during the 25-year storm under proposed conditions. HW recommends that the Applicant confirm the rate and adjust the table as needed. January 12, 2023: The Applicant has revised the table in the Drainage Analysis Report. HW has no further comment. e. The Applicant has modeled the primary outlet for the SIS as having an invert of 61.75 in the HydroCAD model under proposed conditions. The detail on Sheet C-7 lists the invert at 61.65. HW recommends that the Applicant verify the invert of the 6-inch pipe and confirm it is constructable. January 12, 2023: The Applicant has revised the detail and the HydroCAD model, both reflect the invert 61.65. HW has no further comment. f. HW recommends that the Applicant confirm if the proposed building will require a sanitary sewer pipe and if applicable show the connection on the plan set. January 12, 2023: The Applicant has confirmed the proposed building does not require a sewer line. g. The drain manhole (DMH) at the northeast corner of the existing building receives flow KAProjects\2021\21020 Town of North Andover\21020K 1701 Osgood\Reports\230220_3rd SWPeerReview 1701 Osgood.docx Town of North Andover February 20, 2023 Page 5 of 8 from two catch basins (CB) under existing conditions. Under proposed conditions, a new connection will be added to the DMH from the subsurface infiltration system (SIS). The Plan says to "match inverts" for this connection. However, the points where the SIS pipe and the CB pipe enter the DMH appear to be very close. HW recommends that the Applicant verify that the DMH will maintain structural stability after this new connection. January 12, 2023: The Applicant has added a note on the plans stating the structure is to be replaced if it cannot accommodate the new pipe connection. However, it is pointing to the wrong structure. HW recommends adding the same note to the DMH receiving the connection from the subsurface infiltration system. February 20, 2023: The Applicant has revised the plan as requested. HW has no further comment. h. HW recommends that the Applicant provide an elevation view detail for the grassed swale or provide spot grades along the centerline. January 12, 2023: The Applicant has provided a detail on Sheet C-7 of the plan set and high point and low point information on the plans. HW has no further comment. i. HW recommends that the Applicant callout the invert elevations for the 8-inch PVC pipes conveying roof runoff to the SIS. January 12, 2023: The Applicant has added inverts to the plans. HW has no further comment. j. The Applicant is proposing the installation of a new headwall for the existing riprap drainage channel. HW recommends that the Applicant provide the bottom wall (BW) elevation for the new headwall on the Plans. HW also recommends that the Applicant include the 18-inch drainpipe in the detail for the Headwall. January 12, 2023: The Applicant has updated the wall detail and provided bottom of wall elevations on the plan. HW has no further comment. 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a. It appears that the subsurface infiltration system has greater than 2 feet of separation to Estimated Seasonal High Groundwater (ESHGW) but less than 4 feet. HW recommends that the Applicant provide a mounding analysis per the MSH Volume 3, Chapter 1, Page 28. January 12, 2023: The Applicant has provided a mounding analysis and recharge calculations. HW has no further comment. b. HW recommends that the Applicant provide required recharge volume and drawdown time calculations per the MSH Volume 3, Chapter 1, Pages 15 and 25. January 12, 2023: The Applicant has provided recharge volume and drawdown calculations. It is unclear how the subsurface basin volume has been calculated for recharge. HW recommends that the Applicant provide the stage-storage volume table for the subsurface system to confirm the volume below the invert. K:\Projects\2021\21020 Town of North Andover\21020K 1701 Osgood\Reports\230220_3rd_SWPeerReview 1701 Osgood.docx Town of North Andover February 20, 2023 Page 6 of 8 February 20, 2023: The Applicant has not responded to this comment. HW was not able to confirm the subsurface infiltration system provides the volume represented by the Applicant. However, HW was able to confirm that the proposed infiltration system provides adequate recharge volume to comply with Standard 3. No further comment. 4. Standard 4 requires that the stormwater system be designed to remove 80% Total Suspended Solids (TSS) and to treat 1-inch of volume from the impervious area for water quality. a. The Applicant has provided a TSS work sheet claiming 80% TSS removal for an infiltration basin. HW assumes this is referring to the existing stormwater basin. HW recommends that the Applicant clarify that the existing stormwater basin has infiltration characteristics. January 12, 2023: The Applicant has clarified that the TSS removal rate noted is for the roof runoff only. It has assumed since the runoff and volume for the 1" event going to the existing system has been decreased, the existing system will be adequate. HW agrees that the impervious area from catchment areas 1S and 2S has been reduced by approximately 50% and the existing treatment which includes the existing stormwater basin should be sufficient. HW notes that the proposed roof runoff to the proposed infiltration chamber system is considered clean and no additional pretreatment is required. 5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads (LUHPPL). a. The site is not considered a LUHPPL. Therefore, Standard 5 is not applicable. January 12, 2023: No further comment needed. 6. Standard 6 is related to projects with stormwater discharging into a critical area, a Zone 11, or an Interim Wellhead Protection Area of a public water supply. a. The proposed development is not discharging near or into a critical area, Zone II or an IWPA area. Therefore, Standard 6 is not applicable. January 12, 2023: No further comment needed. 7. Standard 7 is related to projects considered Redevelopment. a. The proposed project is a mix of new development and redevelopment. The area consisting of the existing parking lot behind the existing building up to the existing retaining wall may be considered redevelopment. In this redevelopment area, a decrease in paved area is proposed and being converting to roof top which is considered an improvement. The proposed roof runoff is being managed by the subsurface infiltration system as new development. HW recommends that the Applicant respond to the other comments in this review letter to confirm it has adequately incorporated Standard 7. January 12, 2023: Once the Applicant has adequately addressed the remaining items in this letter, HW believes that it will have improved existing conditions and complies with Standard 7. K:\Projects\2021\21020 Town of North Andover\21020K 1701 Osgood\Reports\230220_3rd_SWPeerReview 1701 Osgood.docx Town of North Andover February 20, 2023 Page 7of8 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a. The proposed project requires land disturbance of just under 1 acre. Therefore, a Stormwater Pollution Prevention Plan (SWPPP) per the EPA NPDES Construction General Permit will not be required. January 12, 2023: No response required. b. The Applicant has provided a Grading & Drainage Plan (Sheet C-4) which also includes erosion and sediment control measures. HW recommends that the Applicant provide a separate Erosion & Sediment Control Plan clearly illustrating the erosion controls, the limit of work, as well as areas for proposed tree protections. HW recommends including erosion control notes on the Erosion & Sediment Control Plan as well as construction sequencing notes. January 12, 2023: The Applicant has provided an Erosion & Sediment Control (ESC) Plan showing the limit of work and erosion controls. HW has no further comment. c. HW recommends that the Applicant explain how the site will be accessed during construction and if a stabilized construction entrance is necessary. The catch basins at the northeast corner of the existing building may need protection in addition to the proposed silt sacks. HW recommends that the Applicant explain how these catch basins will be protected from sediment. January 12, 2023: The Applicant has stated that the primary construction access will be gained from the north side of the existing building. A temporary rip-rap construction access has been added to the plans which will remain throughout the earthwork operation and until such time that it conflicts with other sitework. The existing catch basins will be protected via silt sacks and straw bales or wattles. Details are included in the Erosion & Sediment Control Plan. HW has no further comment. d. HW recommends that the Applicant provide a detail for the inlet protection. January 12, 2023: The Applicant has provided an inlet protection detail as part of the ESC Plan. HW has no further comment. e. It appears that the storage building is proposed within an existing tree line. HW recommends that the Applicant locate any trees within the limit of disturbance with a diameter greater than 10 inches per§250-23. A. (7). HW recommends that the Applicant confirm whether the critical root zones (CRZs) of any large trees will be impacted by the proposed development; construction activity over CRZs will potentially damage the root systems of trees and cause long-term degradation of the tree's health. HW further recommends that any trees at the edge of the limit of work proposed to be protected are clearly marked in the field and a tree protection detail is added to the plan set. January 12, 2023: The Applicant has stated that the area of work does not contain any trees over 10 inches in diameter due to the previous clearing of the site and revegetation. HW has no further comment. K:\Projects\2021\21020 Town of North Andover\21020K 1701 Osgood\Reports\230220_3rd_SWPeerReview 1701Osgood.docx Town of North Andover February 20, 2023 Page 8 of 8 9. Standard 9 requires a Long-Term Operation and Maintenance (0 & M) Plan to be provided. a. Per MSH Volume 1 Chapter 1 Page 23, HW recommends that the Applicant provide a Long-Term Operation & Maintenance Plan as a standalone document to be signed by the property owner prior to occupancy, that includes the following: i. Stormwater management system owners; ii. Parties responsible for operation and maintenance; iii. Routine and non-routine maintenance tasks to be undertaken after construction is complete and a schedule for implementing those tasks; iv. A simple plan that is drawn to scale and shows the location of all stormwater practices within the parcel requiring inspections and long-term maintenance; and v. An estimated operations and maintenance budget. January 12, 2023: The Applicant has provided a standalone Long-Term Operation & Maintenance Plan. It appears that the Applicant has not addressed a.ii or a.v from the comment above. HW recommends that the Applicant review and revise the O&M Plan as needed. HW also recommends that the Applicant provide a contact for the storm system owners within the O&M Plan and a table listing the routine maintenance for each item in the O&M Plan. February 20, 2023: The Applicant has provided the requested information. HW has no further comment. b. HW recommends that the Applicant provide the O&M guidelines for the CULTEC Chambers. January 12, 2023: The Applicant has provided the O&M guidelines for the CULTEC Chambers. HW has no further comment. 10. Standard 10 requires an Illicit Discharge Compliance Statement be provided. a. HW recommends that the Planning Board include a condition of approval requiring an Illicit Discharge Compliance Statement signed by the property owner prior to land disturbance. January 12, 2023: The Applicant is amenable to this condition. Conclusions The Applicant has adequately responded to HW's comments. Please contact Janet Bernardo at 508-833-6600 or at jbernardo@horsleywitten.com if you have any questions regarding these comments. Sincerely, HORSLEY WITTEN GROUP, INC. Janet Carter Bernardo, P.E. Associate Principal KAProjectsQ021\21020 Town of North Andover\21020K 1701 Osgood\Reports\230220-3rd—SWPeerReview-1 701 Osgood.docx a g e February 17, 2023 Town of North Andover Planning Board C/o Ms. Jena Enright, Planning Director 120 Main Street North Andover, MA 01845 Re: Response to Stormwater Peer Review Comments(2 n' review) Extra Space Storage 1701 Osgood Street ALLEN ENGINEERING North Andover,MA &AssocIATES, INC. Dear Chairman Goldberg and Members of the Board: Ct\0 Engineers,Sui\oots& Allen Engineering&Associates, Inc. is in receipt of written comments from the Land Dnelopment Consultants Board's peer review consultant, Horsley Witten Group, dated January 12,2023. On behalf of the Applicant, Extra Space Properties 104 LP, we offer the following responses to the comments. Each comment is restated (italicized). AEA's latest esponse follows in bold text. HW q1fers the following comments concerning the stormwater management design. We have used the MSH as the baviv,fbr organizing our comments. However, in instances where the additional criteria established in Chapter 250 of'the North Andover Code ADDRESS requires further recommendations; we have referenced these as well. 140 Hartford Avenue East 1. Standard k No new stormwater conveyances (e.g., outfalls) may discharge untreated Hopedale,MA 01747 stormwater directly to or cause erosion in wetlands, or waters of'the Commonwealth. a. It appears that the southeastern portion of'subcatchment IS is captured by the proposed grass swale which directs runoff to a proposed catch basin that conveys stormwater into the 18-inch drain line that discharges directly into the PHONE wetland to the west of Osgood Street. HW recommends,that the Applicant verify (508)381-3212 that the new discharge velocity at the outfall will not cause erosion in the wetland AEA I" Response: The small portion of subcatchment IS that is captured by the swale is approximately 0.13 acres of wooded area. This minor increase in flow WEB SITE (approximately 0.4 CFS in the 100 year storm) is not anticipated to create erosion at www.allen-ea.com the existing outfall. The discharge pipe to the wetland is a 36-inch diameter concrete pipe that receives flow from a portion of Osgood Street as well as the flow from this site. It is AEA's opinion that the small amount of velocity will be negligible at the discharge pipe. AEA has added subcatchment 45 to the Hyrdocad model to show this flow. January 12, 2023: The Applicant has added a subcatchment area for the southeastern portion ofsubcatchment IS. It has stated that the additional runoff of 0.4 CFS that would out/all to the 36"pipe would be negligible in relation to the outfall during the 100 year storm event. HW agrees that the 0.4 cfs is likely negligible to the 36"pipe out/all. However, HW recommends that the Applicant confirm that the existing outfall is not currently causing erosion to the wetland AEA Response: As previously noted,the outfall is shared infrastructure from the subject site and from Osgood Street drainage (DOT Jurisdictional). The outfall is located at the edge of the right-of-way on the opposite side of Osgood Street. AEA was able to observe it without trespassing. There is no erosion at the outfall, however there is some sediment that had accumulated(see photo provided). Any future removal of sediment would be the responsibility of MassDOT. o I �,� g� e 12 b. Most of'the site runofj'vvill be captured by the stormwater basin located at the western end ql'the site. It appears that an existing outlet control structure conveys stormwater into the wetland to the west of Osgood Street. HW recommends that the Applicant confirm that the existing discharge does not cause erosion in the wetland AEA I"Response: AEA has shown a net decrease in flow to the existing basin along Osgood Street. The result will be a decrease in velocity to the 36-inch pipe from the basin. Therefore it is AEA's opinion that the erosion will not occur. January 12, 2023: The Applicant has stated based on the proposed infrastructure the wetland would receive a decrease in runof.1'in all storms and therefore there would be no signif icant ficant erosion. It is unclear how this determination was made. HW recommends that the Applicant document how and where the existing outlet control structures discharges and as requested above confirm that the existing discharge does not currently cause erosion in the wetland. Furthermore, HW agrees that by installing the proposed subsurface chamber system for the proposed roof' runoff the site is likely reducing the runoff to the existing stormwater basin. However, the Applicant has not demonstrated this. HW recommends that the Applicant provide,the HydroCAD model.fbr the entire existing site evaluating the outlet control structure discharge as the design point and compare the entire proposed site at this same location. AEA Response: See response above and photo attached regarding the existing outfall. AEA continues to assert that modeling the entire site is not a necessary exercise. Notwithstanding,we have obtained additional topographic survey, obtained all of the site's drainage inverts and modeled the entire existing condition. The results can be found in Section I of the attached revised drainage report. Page iii also shows a summary of the velocities for each storm in Table 3. AEA's calculations,for the ESS property only,shows that the velocity(2-3 ft/sec)of the water is below the limits that would cause scouring of the soil at the culvert exit(Evaluation Point 4). Also,AEA witnessed no scour to the soil during the site inspection. c. January 12, 2023:It appears the area far subcatchment 2S on the Proposed Drainage Plan (9,217 sfi does not match the modeled area in HydroCAD(3,564 sfi. HW recommends that the Applicant review the Drainage Plan and the HydroCAD model and revise the model as needed AEA Response: AEA has revised the HydroCAD model as mentioned above. 2. Standard 2: Stormwater management systems shall be designed so that post-development peak discharge rates do not exceed pre-development peak discharge rates. a. The Applicant has drawn the existing and proposed watershed maps to include a portion of'the upgradient area northeast of'the site. A large upgradient area to the east flows towards the riprap drainage channel and into the 18-inch pipe at the headwall. It appears that some oj'lhis upgradient area may flow onto the southeast corner of the site. HW recommends that the Applicant explain the drainage Pattern of'the large area to the east that flows onto the site. AEA I"Response: The drainage area flows into the 18-inch rip-rap channel and by-pass pipe per the original site design. The bypass line was not evaluated for its capacity as the overall flow to this pipe will not change or will have a negligible increase as mentioned above. AEA has called for a new 18-inch pipe to carry the flow around the new building and re-connect on site. January 12, 2023: The Applicant has clarified the drainage pattern of'the upgradient area northeast of'the site. HW has no further comment. b. The Applicant has provided two design points: EV-1 (catch basins at the proposed northern sawcut line) and EV-2 (catch basins at the proposed southern sawcut line). These catch basins convey stormwater to the existing stormwater basin at the western end of'the site, which appears to overflow via an outlet control structure into the wetland to the west Qj'Osgood Street. HW recommends that the Applicant expand the ONE CHARLESVIEw ROAD,SUITE 2 HOPEDALE, MASSACHUSE-T7SO1747 (508) 381-321 2 WWW,ALLEN-EA.COM P a g (, 13 HydroCAD model to include the stormwater basin as a pond, the existing portion of'the site and building that flows into the basin as subcatchments and evaluate the outlet control structure and the wetland as additional design points. AEA I st Response: AEA has shown that a reduction in flow and volume will be entering the existing drainage basin starting at the 2 evaluation points. For this reason,AEA is of the opinion that there is no need to evaluate the existing basin. January 12, 2023: The Applicant has revised its HydroCAD model to show a reduction inflow and volume will be entering the existing drainage basin starting at the existing on site catch basins. As noted above HW agrees that it is likely that the proposed design reduces the peak discharge rate and volume from the existing stormwater basin. However, HW recommends that the Applicant provide the documentation to confirm this. AEA Response: See response above regarding the revised model for the enter site. c. It appears that the southeastern portion of'subcatchment IS is captured by a proposed grass swale which directs runoff to a proposed catch basin that conveys stormwater into the 18-inch drain line that discharges directly into the wetland to the west ql'Osgood Street. HW recommends that the Applicant verify that the conveyance system is properly sized to handle the additional flow as well as the runoff coming fi-om the east. AEA I" Response:As stated in the response to comment I a,the increase in flow is minor(0.4 CFS in the I 00-year storm) It is AEA's opinion that the 18"pipes which are set at very steep slopes will have more than enough capacity to handle this small amount of additional stormwater. January 12, 2023: The Applicant has stated in its response to comment ].a that the additional flaw is negligible and should accommodate the flow. HWs agrees that the increase flow to the 18"pipe is negligible. However, we recommend that the Applicant provide conveyance calculations for the sizing of the swale. AEA Response: The revised post condition drainage analysis includes a reach (4R)which represents the swale. The calculations show that the swale will have more than enough capacity to handle the runoff. d. There appears to be a typographical error listed in Table I.- Summary ofPeak Rates qf Stormwater Runofffbr Evaluation Point I during the 25-year storm under proposed conditions. HW recommends that the Applicant confirm the rate and adjust the table as needed. AEA I"Response: AEA has edited the typo and the new table is in the revised Drainage Analysis Report ,January 12, 2023: The Applicant has revised the table in the Drainage Analysis Report. HW has no further comment. e. The Applicant has modeled the primary outlet for the SIS as having an invert of 61.75 in the HydroCAD model under proposed conditions. The detail on Sheet C-7 lists the invert at 61.65. HW recommends that the Applicant verify the invert of the 6-inch pipe and confirm it is constructible. AEA I't Response: AEA has changed the Hydrocad model to match the plan detail. Both are now shown at 61.65 January 12, 2023: The Applicant has revised the detail and the HydroCAD model, both reflect the invert 61.65. HW has no further comment. f HW recommends that the Applicant confirm if the proposed building will require a sanitary sewer pipe and if applicable show the connection on the plan set. AEA I" Response: The proposed building does not require sewer. January 12, 2023: The Applicant has confirmed the proposed building does not require a sewer line. g. The drain manhole(DMH) at the northeast corner of the existing building receives flow from two catch basins (CB) under existing conditions. Under proposed conditions, a new connection will be added to the DMH from ONE CHARLESVIEw ROAD,SUITE 2 HOPEDALE, MASSACHUSETTS 01747 - (508)381-321 2 WWW.ALLEN-EA.COM Pa 14 the subsurface infiltration system (SIS). The Plan says to "match inverts"for this connection. However,the points where the SIS pipe and the CB pipe enter the DMH appear to be very close. HW recommends that the Applicant verify that the DMH will maintain structural stability after this new connection. AEA 1st Response: A note has been added to the plan to upgrade the existing structure to a new 6-foot diameter manhole if needed to accommodate the new pipe connection. January 12, 2023: The Applicant has added a note on the plans stating the structure is to be replaced if it cannot accommodate the new pipe connection. However, it is pointing to the wrong structure. HW recommends adding the same note to the DMH receiving the connection from the subsurface infiltration system. AEA Response: The plan has been revised to address the appropriate structure. h. HW recommends that the Applicant provide an elevation view detail for the grassed swale or provide spot grades along the centerline. AEA I"Response: A detail is provided on Sheet C-7 of the plan set and spot elevations are provided on the plan. The swale will be constructed with a constant pitch from the high point elevation indicated,to the rim of the proposed catch basin. January 12, 2023: The Applicant has provided a detail on Sheet C-7 of the plan set and high point and low point information on the plans. HW has no further comment. i. HW recommends that the Applicant callout the invert elevations for the 8-inch PVC pipes conveying roof runoff to the SIS. AEA I"Response: Inverts have been added to the plan as recommended. January 12, 2023: The Applicant has added inverts to the plans. HW has no./urther comment. j.. The Applicant is proposing the installation of a new headwall for the existing riprap drainage channel. HW recommends that the Applicant provide the bottom wall (BW)elevation for the new headwall on the Plans. HW also recommends that the Applicant include the 18-inch drainpipe in the detail for the Headwall. AEA I"Response: Bottom of wall elevations have been added to the plan. The 18-inch drain pipe has been indicated on the typical headwall detail as recommended. January 12, 2023: The Applicant has updated the wall detail and provided bottom of wall elevations on the plan. HW has no further comment. 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a. It appears that the subsurface infiltration system has greater than 2./eet of'separation to Estimated,5easonal High Groundwater (EWGW) but less than 4jeet, HW recommends that the Applicant provide a mounding analysis per the MSH Volume 3, Chapter 1, Page 28. AEA I"Response: AEA has performed the hydraulic mounding calculations and the results are shown in the revised Drainage Analysis Report. ,January 12, 2023: The Applicant has provided a mounding analysis and recharge calculations. HW has no further comment. b. HW recommends that the Applicant provide required recharge volume and drawdown time calculations per the MSH Volume 3, Chapter 1, Pages 15 and 25. AEA I"Response: AEA has added these calculations to the Revised Drainage Analysis Report(see Section 3) January 12, 2023: The Applicant has provided a mounding analysis and recharge calculations. HW has no further comment. AEA Response: N/A ONE CHARLESVIEw ROAD,SUITE 2 HOPEDALE, MASSACHUSETTS 01747 - (508) 381-321 2 WWW.ALLEN-EA.COM P a g e, 15 4. Standard 4 requires that the stormwater system be designed to remove 80% Total Suspended Solids (TSS) and to treat]-inch of'voluineftom the impervious area,fbr water quality. a. The Applicant has provided a TSS work sheet claiming 80% TSS removal,for an it basin. HW assumes this is referring to the existing stormwater basin. HW recommends that the Applicant clarify that the existing stormwater basin has infiltration characteristics. AEA I"Response: AEA has provided the TSS Calculations for the proposed roof infiltration system(Cultec). The proposed project will not impact the existing basin or its functionality. As previously noted,the flow to the existing basin is decreased. January 12, 2023: The Applicant has clarified that the TSS removal rate noted is for the roof runoff It has assumed since the runoff and volume for the I"event going to the existing system has been decreased, the existing system will be adequate. HW agrees that the impervious area from catchment areas IS and 2S has been reduced by approximately 50%and the existing treatment which includes the existing stormwater basin should be sufficient. HW notes that the proposed roof runoff to the proposed infiltration chamber system is considered clean and no additional pretreatment is,required 5. Standard 5 is related to projects with a Land Use qf'Higher Potential Pollutant Loads (L UHPPL). a. The site is not considered a LUI-IPPL. Therefore, Standard 5 is not applicable. AEA V Response: No response required. January 12, 2023:No further comment needed 6. Standard 6 is related to pr(#ects with stormwater discharging into a critical area, a Zone 11, or an Interim Wellhead Protection Area of a public water supply. a. The proposed development is not discharging near or into a critical area, Zone II or an IWPA area. Therefore, Standard 6 is not applicable. AEA I"No response required. January 12, 2023: No./urther comment needed. 7. Standard 7 is related to projects considered Redevelopment. a. The proposed project is a mix of'new development and redevelopment. The area consisting of the existing parking lot behind the existing building tip to the existing retaining wall maybe considered redevelopment. In this redevelopment area, a decrease in paved area is proposed and being converting to roof top which is considered an improvement. The proposed roo/'run(?f,fis being managed by the subsurface infiltration system as new development. HW recommends that the Applicant respond to the other comments, in this review letter to confirm it has adequately incorporated Standard 7. AEA I"Response: AEA recognizes the project to be both new and redevelopment. All of the responses and revised report incorporate this status. Page 2 of the checklist has also been edited accordingly. January 12, 2023: Once the Applicant has adequately addressed the remining items in this letter, HW believes that it will have improved existing conditions and complied with Standard 7. 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a. The proposed project requires land disturbance of just under I acre. Therefore, a Stormwater Pollution Prevention Plan (SWPPp)per the EPA NPDES Construction General Permit will not be required AEA I"No response required. January 12, 2023: No response required b. The Applicant has provided a Grading& Drainage Plan (Sheet C-4) which also includes erosion and sediment control measures. HW recommends that the Applicant provide a separate Erosion & ONE CHARLESVIEw ROAD,SUITE 2 ~ HOPEDALE, MASSACHUSETTS 01747 (508) 381-321 2 WWW.ALLEN-EA.COM F1 a � (,-i 16 Sediment Control Plan clearly illustrating the erosion controls, the limit oj'work, as well as areas for proposed tree protections. HW recommends including erosion control notes on the Erosion & Sediment Control Plan as well(is construction sequencing notes. AEA I"Response: A separate Erosion& Sediment Control Plan has been added along with notes and construction sequencing as recommended. January 12, 2023: The Applicant has provided an Erosion &Sediment Control(ESC)Plan showing the limit of work and erosion controls. HW has no further comment. c. HW recommends that the Applicant explain how the site will be accessed during construction and if a stabilized construction entrance is necessary. The catch basins at the northeast corner of'the existing building may need protection in addition to the proposed silt sacks. HW recommends that the Applicant explain how these catch basins will be protected fromsediment. AEA I"Response: Primary construction access will be gained from the north side of the existing building. A temporary rip-rap construction access has been added to the plans which will remain throughout the earthwork operation and until such time that it is in conflict with other sitework. Existing catch basins will be protected via silt sacks and straw bales or wattles. Details are included on the Erosion& Sediment Control Plan. January 12, 2023: The Applicant has stated that the primary construction access will be gained from the north side of the existing building.A temporary rip-rap construction access has been added to the plans which will remain throughout the earthwork operation and until such time that it col?flicts with other silework. The existing catch basins will be protected via silt sacks and straw bales or wattles. Details are included in the Erosion& Sediment Control Plan. HW has no further comment. d HW recommends that the Applicant provide,a detail for the inlet protection. AEA Is'Response: Inlet protection details have been provided on the new Erosion& Sediment Control Plan. January 12, 2023: The Applicant has provided an inlet protection detail as part of the ESC Plan. HW has no further comment. e. It appears that the storage building is proposed within an existing tree line. HW recommends that the Applicant locate any trees within the limit of disturbance with a diameter greater than 10 inches per§250-23. A. (7). HW recommends that the Applicant confirm whether the critical root zones (CRZs) of any large trees will be impacted by the proposed development,, construction activity over(.RZs will potentially damage the root systems o,l'trees and cause long-term degradation of'the tree's health. HW further recommends that any trees at the edge of the limit of work proposed to be protected are clearly marked in the field and a tree protection detail is added to the plan set. AEA I"Response: The wooded area was cleared several years ago and has become revegetated primarily with Young, colonizing tree species such as Quaking Aspen and Birch species, and Pine. There are no trees within or immediately adjacent to the work that that exceed 10 inches. January 12, 2023: The Applicant has stated that the area of'work does not contain any trees over 10 inches in diameter clue to the previous clearing oj'the site and revegetation. HW has,no further comment. 9. Standard 9 requires a Long-Term Operation and Maintenance (0&M)Plan to be provided a. Per MSH Volume I Chapter I Page 23, HW recommends that the Applicant provide a Long-Term Operation &Maintenance Plan as a standalone document to be signed by the property owner prior to occupancy, that includes the fallowing: i. Stormwater management system owners; ii. Parties responsible for operation and maintenance; iii. Routine and non-routine maintenance tasks to be undertaken after construction is complete and a schedule for implementing those tasks,, iv.A simple plan that is drawn to scale and shows the location qf'all stormwater practices within the parcel requiring inspections and long-term maintenance; and ONE CHARLESVIEw ROAD,SUITE 2 - HOPEDALE, MASSACHUSETTS01747 (508)381-321 2 WWW.ALLEN-EA.COM f I f,7, e 17 v.An estimated operations and maintenance budget. AEA I" Response: A stand-alone O&M plan has been prepared with the items suggested. January 12, 2023: The Applicant has provided a standalone Long-Term Operation &Maintenance Plan. It appears that the Applicant has not addressed a,ii or a.v from the comment above. HW recommends that the Applicant review and revise the O&M Plan as needed. HW also recommends that the Applicant provide a contact for the storm system owners within the O&M Plan and a table listing the routine maintenance,for each item in the O&MPlan. AEA Response: AEA has highlighted the responsible parties previously noted in red and has added the estimated budged as suggested. b. HW recommends that the Applicant provide the O&Mguidelinesfor the CULTEC Chambers. AEA I" Response: Information for Cultec Chamber Maintenance has been provided in the 0& M plan. January 12, 2023: The Applicant has provided the O&AIguidelines.fbr the CULTEC Chambers. HW has no further comment. 10. Standard 10 requires an Illicit Discharge Compliance Statement be provided a. HW recommends that the Planning Board include a condition oJ'approval requiring an Illicit Discharge Compliance Statement signed by the property owner prior to land disturbance. AEA Is' Response: The applicant has no objection to this condition. ,January 12, 2023: The Applicant is amenable to this condition. Please feel free to contact me at(508)381-3212 with any questions regarding this correspondence. Sincerely, ALLEN ENGINEERING &AssoCIATES, INC. ............. 21"'57 .......... Michael J. Dryden, RLA Mark E. Allen, PE Senior Project Manager President Cc: Greg Susko,Applicant ONE CHARLESVIEw ROAD,SUITE 2 HOPEDALE, MASSACHUSETTS 01747 (508) 381-321 2 WWW.ALLEN-EA.COM `J t ry r, r I I � d�ua r Y / c I 4., i� Horsley Witten Croup Sustainable Environnvrital Solutions 1121Nater Street•V Floor-Boston,MA 02109 857-263-8193-horsleywitten.com January 12, 2023 Ms. Jean Enright, Planning Director North Andover Planning Board 120 Main Street North Andover, Massachusetts 01845 Ref: Second Stormwater Peer Review Extra Space Storage Building 1701 Osgood Street North Andover, Massachusetts Dear Ms. Enright and Board Members: The Horsley Witten Group, Inc. (HW) is pleased to provide the North Andover Planning Board with this letter report summarizing our second review of the Drainage Analysis and Site Plans for the proposed Extra Space Storage Building at 1701 Osgood Street, North Andover, MA. The plans and stormwater report were prepared by Allen Engineering & Associates, Inc. on behalf of Extra Space Properties 104 LP (Applicant). The project proposes the construction of a 47,244 square foot (sf) three-story storage building, along with associated parking, utilities, stormwater management, and landscaping on a previously developed 3.02-acre parcel containing an existing building. The stormwater management for the proposed storage building includes a grass swale, a catch basin, manholes, and a subsurface infiltration system (SIS). A small portion of the site is located within the 100-foot buffer zone of a wetland resource area located across Osgood Street. The proposed work will remain outside of the buffer zone. The following additional documents and plans were received by HW: • Response to Stormwater Peer Review letter for Extra Space Storage at 1701 Osgood Street, North Andover, prepared by Allen Engineering &Associates, Inc., dated December 28, 2022 (5 pages). • Drainage Analysis for Extra Space Storage at 1701 Osgood Street, North Andover, MA, prepared by Allen Engineering & Associates, Inc., revised December 28, 2022 (117 pages). m Stormwater Long-Term Operation and Maintenance Plan for Extra Space Storage at 1701 Osgood Street, North Andover, MA, prepared by Allen Engineering & Associates, Inc., dated December 28, 2022 (17 pages). • Architectural drawings, Proposed Self Storage facility, 1701 Osgood Street, North Andover, MA, prepared by BL Companies, revisions thru December 20, 2022 (6 sheets). ® Site Plans for Extra Space Storage, 1701 Osgood Street (Route 125), North Andover, Massachusetts, prepared by Allen Engineering & Associates, Inc., revised December 28, 2022, including: o Cover Sheet C-1 a Existing Conditions Plan C-2 He,rs:ey`7Jitten.rmCXTI M @ Hors lley ittenGrol.P IM Hors ey Wiften Group, Inc. Town of North Andover January 12, 2023 Page 2 of 8 o Layout & Materials Plan C-3 o Grading & Drainage Plan C-4 o Landscape & Lighting Plan C-5 o Fire Truck Swept Path C-6 o Construction Details C-7 o Construction Details C-8 o Erosion & Sediment Control Plan C-9 Stormwater Management Design Peer Review In accordance with the North Andover Zoning Bylaw §195-8.14. E. (8)A Stormwater management plan is required for all site plan review applications. The stormwater management plan shall be prepared in accordance with the latest version of the Massachusetts Stormwater Handbook (MSH) and demonstrate full compliance with the Massachusetts Stormwater Standards and the North Andover Stormwater Management and Erosion Control Regulations. HW offers the following comments concerning the stormwater management design. We have used the MSH as the basis for organizing our comments. However, in instances where the additional criteria established in Chapter 250 of the North Andover Code requires further recommendations; we have referenced these as well. The following comments correlate to our November 16, 2022 initial peer review letter. Follow up comments are provided in bold font. 1. Standard 1: No new stormwater conveyances (e.g., outfalls) may discharge untreated stormwater directly to or cause erosion in wetlands or waters of the Commonwealth. a. It appears that the southeastern portion of subcatchment 1 S is captured by the proposed grass swale which directs runoff to a proposed catch basin that conveys stormwater into the 18-inch drain line that discharges directly into the wetland to the west of Osgood Street. HW recommends that the Applicant verify that the new discharge velocity at the outfall will not cause erosion in the wetland. January 12, 2023: The Applicant has added a subcatchment area for the southeastern portion of subcatchment 1S. It has stated that the additional runoff of 0.4 US that would outfall to the 36" pipe would be negligible in relation to the outfall during the 100 year storm event. HW agrees that the 0.4 cfs is likely negligible to the 36" pipe outfall. However, HW recommends that the Applicant confirm that the existing outfall is not currently causing erosion to the wetland. b. Most of the site runoff will be captured by the stormwater basin located at the western end of the site. It appears that an existing outlet control structure conveys stormwater into the wetland to the west of Osgood Street. HW recommends that the Applicant confirm that the existing discharge does not cause erosion in the wetland. January 12, 2023: The Applicant has stated based on the proposed infrastructure the wetland would receive a decrease in runoff in all storms and therefore there would be no significant erosion. It is unclear how this determination was made. HW recommends that the Applicant document how and where the existing outlet control structures discharges and as requested above confirm that the existing discharge does not currently cause erosion in the wetland. K:AProjects\2021\21020 Town of North Andover\21020K 1701 Osgood\Pepoils\230112_2nd_SWPeer-Review_1701Oscgood.docr. Town of North Andover January 12, 2023 Page 3 of 8 Furthermore, HW agrees that by installing the proposed subsurface chamber system for the proposed roof runoff the site is likely reducing the runoff to the existing stormwater basin. However, the Applicant has not demonstrated this. HW recommends that the Applicant provide the HydroCAD model for the entire existing site evaluating the outlet control structure discharge as the design point and compare the entire proposed site at this same location. c. January 12, 2023: It appears the area for subcatchment 2S on the Proposed Drainage Plan (9,217 sf) does not match the modeled area in HydroCAD (3,564 sf). HW recommends that the Applicant review the Drainage Plan and the HydroCAD model and revise the model as needed 2. Standard 2: Stormwater management systems shall be designed so that post-development peak discharge rates do not exceed pre-development peak discharge rates. a. The Applicant has drawn the existing and proposed watershed maps to include a portion of the upgradient area northeast of the site. A large upgradient area to the east flows towards the riprap drainage channel and into the 18-inch pipe at the headwall. It appears that some of this upgradient area may flow onto the southeast corner of the site. HW recommends that the Applicant explain the drainage pattern of the large area to the east that flows onto the site. January 12, 2023: The Applicant has clarified the drainage pattern of the upgradient area northeast of the site. HW has no further comment. b. The Applicant has provided two design points: EV-1 (catch basins at the proposed northern sawcut line) and EV-2 (catch basins at the proposed southern sawcut line). These catch basins convey stormwater to the existing stormwater basin at the western end of the site, which appears to overflow via an outlet control structure into the wetland to the west of Osgood Street. HW recommends that the Applicant expand the HydroCAD model to include the stormwater basin as a pond, the existing portion of the site and building that flows into the basin as subcatchments and evaluate the outlet control structure and the wetland as additional design points. January 12, 2023: The Applicant has revised its HydroCAD model to show a reduction in flow and volume will be entering the existing drainage basin starting at the existing on site catch basins. As noted above HW agrees that it is likely that the proposed design reduces the peak discharge rate and volume from the existing stormwater basin. However, HW recommends that the Applicant provide the documentation to confirm this. c. It appears that the southeastern portion of subcatchment 1 S is captured by a proposed grass swale which directs runoff to a proposed catch basin that conveys stormwater into the 18-inch drain line that discharges directly into the wetland to the west of Osgood Street. HW recommends that the Applicant verify that the conveyance system is properly sized to handle the additional flow as well as the runoff coming from the east. January 12, 2023: The Applicant has stated in its response to comment 1.a that the additional flow is negligible and should accommodate the flow. HW's agrees that the increase flow to the 18" pipe is negligible. However. we recommend that the Applicant provide conveyance calculations for the sizing of the swale. KAProjects\2021\21020 Town of North Andover\21020K 1701 Osgood\Reports\230112_2nd_SVVPeerReview 1701Osgood.docx Town of North Andover January 12, 2023 Page 4 of 8 d. There appears to be a typographical error listed in Table 1: Summary of Peak Rates of Stormwater Runoff for Evaluation Point 1 during the 25-year storm under proposed conditions. HW recommends that the Applicant confirm the rate and adjust the table as needed. January 12, 2023: The Applicant has revised the table in the Drainage Analysis Report. HW has no further comment. e. The Applicant has modeled the primary outlet for the SIS as having an invert of 61.75 in the HydroCAD model under proposed conditions. The detail on Sheet C-7 lists the invert at 61.65. HW recommends that the Applicant verify the invert of the 6-inch pipe and confirm it is constructible. January 12, 2023: The Applicant has revised the detail and the HydroCAD model, both reflect the invert 61.65. HW has no further comment. f. HW recommends that the Applicant confirm if the proposed building will require a sanitary sewer pipe and if applicable show the connection on the plan set. January 12, 2023: The Applicant has confirmed the proposed building does not require a sewer line. g. The drain manhole (DMH) at the northeast corner of the existing building receives flow from two catch basins (CB) under existing conditions. Under proposed conditions, a new connection will be added to the DMH from the subsurface infiltration system (SIS). The Plan says to "match inverts" for this connection. However, the points where the SIS pipe and the CB pipe enter the DMH appear to be very close. HW recommends that the Applicant verify that the DMH will maintain structural stability after this new connection. January 12, 2023: The Applicant has added a note on the plans stating the structure is to be replaced if it cannot accommodate the new pipe connection. However, it is pointing to the wrong structure. HW recommends adding the same note to the DMH receiving the connection from the subsurface infiltration system. h.. HW recommends that the Applicant provide an elevation view detail for the grassed swale or provide spot grades along the centerline. January 12, 2023: The Applicant has provided a detail on Sheet C-7 of the plan set and high point and low point information on the plans. HW has no further comment. i. HW recommends that the Applicant callout the invert elevations for the 8-inch PVC pipes conveying roof runoff to the SIS. January 12, 2023: The Applicant has added inverts to the plans. HW has no further comment. j. The Applicant is proposing the installation of a new headwall for the existing riprap drainage channel. HW recommends that the Applicant provide the bottom wall (BW) elevation for the new headwall on the Plans. HW also recommends that the Applicant include the 18-inch drainpipe in the detail for the Headwall. January 12, 2023: The Applicant has updated the wall detail and provided bottom of wall elevations on the plan. HW has no further comment. K:AProjects\2021\21020 Town of North Andover\21020K 1701 Casgood\Ropoi-is\230112_2rid_SWPoerRp-view 17010sgood.docx Town of North Andover January 12, 2023 Page 5 of 8 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a. It appears that the subsurface infiltration system has greater than 2 feet of separation to Estimated Seasonal High Groundwater(ESHGW) but less than 4 feet. HW recommends that the Applicant provide a mounding analysis per the MSH Volume 3, Chapter 1, Page 28. January 12, 2023: The Applicant has provided a mounding analysis and recharge calculations. HW has no further comment. b. HW recommends that the Applicant provide required recharge volume and drawdown time calculations per the MSH Volume 3, Chapter 1, Pages 15 and 25. January 12, 2023: The Applicant has provided recharge volume and drawdown calculations. It is unclear how the subsurface basin volume has been calculated for recharge. HW recommends that the Applicant provide the stage-storage volume table for the subsurface system to confirm the volume below the invert. 4. Standard 4 requires that the stormwater system be designed to remove 80% Total Suspended Solids (TSS) and to treat 1-inch of volume from the impervious area for water quality. a. The Applicant has provided a TSS work sheet claiming 80% TSS removal for an infiltration basin. HW assumes this is referring to the existing stormwater basin. HW recommends that the Applicant clarify that the existing stormwater basin has infiltration characteristics. January 12, 2023: The Applicant has clarified that the TSS removal rate noted is for the roof runoff only. It has assumed since the runoff and volume for the 1" event going to the existing system has been decreased, the existing system will be adequate. HW agrees that the impervious area from catchment areas 1S and 2S has been reduced by approximately 50% and the existing treatment which includes the existing stormwater basin should be sufficient. HW notes that the proposed roof runoff to the proposed infiltration chamber system is considered clean and no additional pretreatment is required. 5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads (LUHPPL). a. The site is not considered a LUHPPL. Therefore, Standard 5 is not applicable. January 12, 2023: No further comment needed. 6. Standard 6 is related to projects with stormwater discharging into a critical area, a Zone ll, or an Interim Wellhead Protection Area of a public water supply. a. The proposed development is not discharging near or into a critical area, Zone II or an IWPA area. Therefore, Standard 6 is not applicable. January 12, 2023: No further comment needed. K:\Projects\202 1\21020 Town of North Andover\21020K 1701 Osgood\Reports\230112_2nd_SVVPeerReview_1701 Osgood.docx Town of North Andover January 12, 2023 Page 6 of 8 7. Standard 7 is related to projects considered Redevelopment. a. The proposed project is a mix of new development and redevelopment. The area consisting of the existing parking lot behind the existing building up to the existing retaining wall may be considered redevelopment. In this redevelopment area, a decrease in paved area is proposed and being converting to roof top which is considered an improvement. The proposed roof runoff is being managed by the subsurface infiltration system as new development. HW recommends that the Applicant respond to the other comments in this review letter to confirm it has adequately incorporated Standard 7. January 12, 2023: Once the Applicant has adequately addressed the remining items in this letter, HW believes that it will have improved existing conditions and complied with Standard 7. 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a. The proposed project requires land disturbance of just under 1 acre. Therefore, a Stormwater Pollution Prevention Plan (SWPPP) per the EPA NPDES Construction General Permit will not be required. January 12, 2023: No response required. b. The Applicant has provided a Grading & Drainage Plan (Sheet C-4) which also includes erosion and sediment control measures. HW recommends that the Applicant provide a separate Erosion & Sediment Control Plan clearly illustrating the erosion controls, the limit of work, as well as areas for proposed tree protections. HW recommends including erosion control notes on the Erosion & Sediment Control Plan as well as construction sequencing notes. January 12, 2023: The Applicant has provided an Erosion & Sediment Control (ESC) Plan showing the limit of work and erosion controls. HW has no further comment. c. HW recommends that the Applicant explain how the site will be accessed during construction and if a stabilized construction entrance is necessary. The catch basins at the northeast corner of the existing building may need protection in addition to the proposed silt sacks. HW recommends that the Applicant explain how these catch basins will be protected from sediment. January 12, 2023: The Applicant has stated that the primary construction access will be gained from the north side of the existing building. A temporary rip-rap construction access has been added to the plans which will remain throughout the earthwork operation and until such time that it conflicts with other sitework. The existing catch basins will be protected via silt sacks and straw bales or wattles. Details are included in the Erosion & Sediment Control Plan. HW has no further comment. d. HW recommends that the Applicant provide a detail for the inlet protection. January 12, 2023: The Applicant has provided an inlet protection detail as part of the ESC Plan. HW has no further comment. K.:AProjects\2021\21020 Town of Nor i AndoverA21020K:1701 Osgood\Reports\230112 2nd_SUVPeerPeview 17010sguod-d0cx Town of North Andover January 12, 2023 Page 7 of 8 e. It appears that the storage building is proposed within an existing tree line. HW recommends that the Applicant locate any trees within the limit of disturbance with a diameter greater than 10 inches per§250-23. A. (7). HW recommends that the Applicant confirm whether the critical root zones (CRZs) of any large trees will be impacted by the proposed development; construction activity over CRZs will potentially damage the root systems of trees and cause long-term degradation of the tree's health. HW further recommends that any trees at the edge of the limit of work proposed to be protected are clearly marked in the field and a tree protection detail is added to the plan set. January 12, 2023: The Applicant has stated that the area of work does not contain any trees over 10 inches in diameter due to the previous clearing of the site and revegetation. HW has no further comment. 9. Standard 9 requires a Long-Term Operation and Maintenance (O & M) Plan to be provided. a. Per MSH Volume 1 Chapter 1 Page 23, HW recommends that the Applicant provide a Long-Term Operation & Maintenance Plan as a standalone document to be signed by the property owner prior to occupancy, that includes the following: i. Stormwater management system owners; ii. Parties responsible for operation and maintenance; iii. Routine and non-routine maintenance tasks to be undertaken after construction is complete and a schedule for implementing those tasks; iv. A simple plan that is drawn to scale and shows the location of all stormwater practices within the parcel requiring inspections and long-term maintenance; and v. An estimated operations and maintenance budget. January 12, 2023: The Applicant has provided a standalone Long-Term Operation & Maintenance Plan. It appears that the Applicant has not addressed a.ii or am from the comment above. HW recommends that the Applicant review and revise the O&M Plan as needed. HW also recommends that the Applicant provide a contact for the storm system owners within the O&M Plan and a table listing the routine maintenance for each item in the O&M Plan. b. HW recommends that the Applicant provide the O&M guidelines for the CULTEC Chambers. January 12, 2023: The Applicant has provided the O&M guidelines for the CULTEC Chambers. HW has no further comment. 10. Standard 10 requires an Illicit Discharge Compliance Statement be provided. a. HW recommends that the Planning Board include a condition of approval requiring an Illicit Discharge Compliance Statement signed by the property owner prior to land disturbance. January 12, 2023: The Applicant is amenable to this condition. K:\Projects\2021\21020 Town of[North Andover\21020K 1701 Osgood\Reports\230112_2nd_SVVPeerReview 17010sgood.docx Town Of North Andover January 12' 2U23 Page Dof8 Conclusions HVV recommends that the Planning Board require that the Applicant provide @ written response tO address the remaining comments G0 part Ofthe Board's review process. The Applicant iS advised that provision of these comments does not relieve him/her of the responsibility to comply with all Town of North Andover Codes and By-Laws, CODlnOODVV8@|th of Massachusetts |@VvS' and federal regulations as applicable tothis project. Please contact Janet Bernardo at 5O8-O33-08OOOr8t 'b8[DardO@hO[s|eyVVitteD.CU[Dif you have any questions regarding these cOrDnleD1a. SiDCeF8|y' HC)RSLEYVV|TTEN GROUP, INC. Janet Carter Bernardo, P.E. StevoSLanish. P.E. Associate Principal Senior Engineer K�Pn�eo��O21�(82OTown nfNur�hAndoveh21Uu0K17O1 Ds900d\Rapor�s\230/12_�nU_SVvPa�R�wa�_178|DoQood.dou Page 1 December 28, 2022 Town of North Andover Planning Board C/o Ms. Jena Enright,Planning Director 120 Main Street North Andover, MA 01845 Re: Response to Stormwater Peer Review Comments ALLEN ENGINEERING Re: Space Storage &ASSOCIATES, INC. 1701 Osgood Street Civil Engineers,Surveyors& North Andover,MA Land Development Consultants Dear Chairman Goldberg and Members of the Board: Allen Engineering&Associates, Inc. is in receipt of written comments from the Board's peer review consultant,Horsley Witten Group, dated November 16,2022. On behalf of the Applicant, Extra Space Properties 104 LP,we offer the following responses to the comments. Each comment is restated(italicized), and a response, .follows in bold text. HW offers the following comments concerning the stormwater management design. We ADDRESS have used the MSH as the basis for organizing our comments. However, in instances 14o Hartford Avenue East Hopedale,MA 01747 where the additional criteria established in Chapter 250 of the North Andover Code requires further recommendations; we have referenced these as well. 1. Standard 1:No new stormwater conveyances (e.g., outfalls) may discharge untreated stormwater directly to or cause erosion in wetlands or waters of the Commonwealth. PHONE a. It appears that the southeastern portion of subcatchment IS is captured by the (508)381-3212 proposed grass Swale which directs runoff to a proposed catch basin that conveys stormwater into the I8-inch drain line that discharges directly into the wetland to the west of Osgood Street. HW recommends that the Applicant verify that the new discharge velocity at the outfall will not cause erosion in the wetland. WEB SITE Response: The small portion of subcatchment 1S that is captured by the swale is www.allen-ea.com approximately 0.13 acres of wooded area. This minor increase in flow (approximately 0.4 CFS in the 100 year storm) is not anticipated to create erosion at the existing outfall. The discharge pipe to the wetland is a 36-inch diameter concrete pipe that receives flow from a portion of Osgood Street as well as the flow from this site. It is AEA's opinion that the small amount of velocity will be negligible at the discharge pipe. AEA has added subcatchment #5 to the Hyrdocad model to show this flow. b. Most of the site runoff will be captured by the stormwater basin located at the western end of the site. It appears that an existing outlet control structure conveys stormwater into the wetland to the west of Osgood Street. HW recommends that the Applicant confirm that the existing discharge does not cause erosion in the wetland. Response: AEA has shown a net decrease in flow to the existing basin along Osgood Street. The result will be a decrease in velocity to the 36-inch pipe from the basin. Therefore it is AEA's opinion that the erosion will not occur. Page 12 2. Standard 2: Stormwater management systems shall be designed so that post-development peak discharge rates do not exceed pre-development peak discharge rates. a. The Applicant has drawn the existing and proposed watershed maps to include a portion of the upgradient area northeast of the site. A large upgradient area to the east flows towards the riprap drainage channel and into the 18-inch pipe at the headwall. It appears that some of this upgradient area may flow onto the southeast corner of the site. HW recommends that the Applicant explain the drainage pattern of the large area to the east that flows onto the site. Response: The drainage area flows into the 18-inch rip-rap channel and by-pass pipe per the original site design. The bypass line was not evaluated for its capacity as the overall flow to this pipe will not change or will have a negligible increase as mentioned above. AEA has called for a new 18-inch pipe to carry the flow around the new building and re-connect on site. b. The Applicant has provided two design points:EV-1 (catch basins at the proposed northern sawcut line) and EV-2 (catch basins at the proposed southern sawcut line). These catch basins convey stormwater to the existing stormwater basin at the western end of the site, which appears to overflow via an outlet control structure into the wetland to the west of Osgood Street. HW recommends that the Applicant expand the Hydro CAD model to include the stormwater basin as a pond, the existing portion of the site and building that flows into the basin as subcatchments and evaluate the outlet control structure and the wetland as additional design points. Response: AEA has shown that a reduction in flow and volume will be entering the existing drainage basin starting at the 2 evaluation points. For this reason,AEA is of the opinion that there is no need to evaluate the existing basin. c. It appears that the southeastern portion of subcatchment IS is captured by a proposed grass swale which directs runoff to a proposed catch basin that conveys stormwater into the 18-inch drain line that discharges directly into the wetland to the west of Osgood Street. HW recommends that the Applicant verify that the conveyance system is properly sized to handle the additional flow as well as the runoff coming from the east. Response: As stated in the response to comment la, the increase in flow is minor (0.4 CFS in the 100- year storm) It is AEA's opinion that the 18"pipes which are set at very steep slopes will have more than enough capacity to handle this small amount of additional stormwater. d. There appears to be a typographical error listed in Table 1: Summary of Peak Rates of Stormwater Runoff for Evaluation Point 1 during the 25-year storm under proposed conditions. HW recommends that the Applicant confirm the rate and adjust the table as needed. Response: AEA has edited the typo and the new table is in the revised Drainage Analysis Report e. The Applicant has modeled the primary outlet for the SIS as having an invert of 61.75 in the HydroCAD model under proposed conditions. The detail on Sheet C-7 lists the invert at 61.65. HW recommends that the Applicant verify the invert of the 6-inch pipe and confirm it is constructible. Response: AEA has changed the Hydrocad model to match the plan detail. Both are now shown at 61.65 f. HW recommends that the Applicant confirm if the proposed building will require a sanitary sewer pipe and if applicable show the connection on the plan set. Response: The proposed building does not require sewer. g. The drain manhole (DMH) at the northeast corner of the existing building receives flow from two catch basins (CB)under existing conditions. Under proposed conditions, a new connection will be added to the DMH from the subsurface infiltration system(SIS). The Plan says to "match inverts"for this connection. However, the points where the SIS pipe and the CB pipe enter the DMH appear to be very close. HW recommends that the Applicant verify that the DMH will maintain structural stability after this new connection. Response: A note has been added to the plan to upgrade the existing structure to a new 6-foot diameter manhole if needed to accommodate the new pipe connection. ONE CHARLESVIEw ROAD, SUITE 2 ^ HOPEDALE, MASSACHUSETTS 01747 - (508) 381-321 2 WWW.ALLEN-EA.COM Page 13 h. HW recommends that the Applicant provide an elevation view detail for the grassed swale or provide spot grades along the centerline. Response: A detail is provided on Sheet C-7 of the plan set and spot elevations are provided on the plan. The swale will be constructed with a constant pitch from the high point elevation indicated,to the rim of the proposed catch basin. i. HW recommends that the Applicant callout the invert elevations for the 8-inch PVC pipes conveying roof runoff to the SIS. Response: Inverts have been added to the plan as recommended. j. The Applicant is proposing the installation of a new headwall for the existing riprap drainage channel. HW recommends that the Applicant provide the bottom wall(BW) elevation for the new headwall on the Plans. HW also recommends that the Applicant include the 18-inch drainpipe in the detail for the Headwall. Response: Bottom of wall elevations have been added to the plan. The 18-inch drain pipe has been indicated on the typical headwall detail as recommended. 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a. It appears that the subsurface infiltration system has greater than 2 feet of separation to Estimated Seasonal High Groundwater(ESHGW) but less than 4 feet. HW recommends that the Applicant provide a mounding analysis per the MSH Volume 3, Chapter 1, Page 28. Response: AEA has performed the hydraulic mounding calculations and the results are shown in the revised Drainage Analysis Report. b. HW recommends that the Applicant provide required recharge volume and drawdown time calculations per the MSH Volume 3, Chapter 1, Pages 15 and 25. Response: AEA has added these calculations to the Revised Drainage Analysis Report(see Section 3) 4. Standard 4 requires that the stormwater system be designed to remove 80% Total Suspended Solids (TSS) and to treat 1-inch of volume from the impervious area for water quality. a. The Applicant has provided a TSS work sheet claiming 80%TSS removal for an infiltration basin. HW assumes this is referring to the existing stormwater basin. HW recommends that the Applicant clarify that the existing stormwater basin has infiltration characteristics. Response: AEA has provided the TSS Calculations for the proposed roof infiltration system (Cultec). The proposed project will not impact the existing basin or its functionality.As previously noted,the flow to the existing basin is decreased. 5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads (LUHPPL). a. The site is not considered a LUHPPL. Therefore, Standard 5 is not applicable. No response required. 6. Standard 6 is related to projects with stormwater discharging into a critical area, a Zone II, or an Interim Wellhead Protection Area of a public water supply. a. The proposed development is not discharging near or into a critical area, Zone II or an IWPA area. Therefore, Standard 6 is not applicable. No response required. 7. Standard 7 is related to projects considered Redevelopment. a. The proposed project is a mix of new development and redevelopment. The area consisting of the existing parking lot behind the existing building up to the existing retaining wall may be considered redevelopment. In this redevelopment area, a decrease in paved area is proposed and being converting to roof top which is considered an improvement. The proposed roof runoff is being managed by the subsurface infiltration system ONE CHARLESVIEw ROAD, SUITE 2 - HOPEDALE, MASSACHUSE-rrS 01747 - (508) 381-321 2 WWW.ALLEN-EA.COM zige 14 as new development. HW recommends that the Applicant respond to the other comments in this review letter to confirm it has adequately incorporated Standard 7. Response: AEA recognizes the project to be both new and redevelopment. All of the responses and revised report incorporate this status. Page 2 of the checklist has also been edited accordingly. 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a. The proposed project requires land disturbance of just under 1 acre. Therefore, a Stormwater Pollution Prevention Plan (SWPPP)per the EPA NPDES Construction General Permit will not be required. No response required. a. The Applicant has provided a Grading&Drainage Plan (Sheet C-4) which also includes erosion and sediment control measures. HW recommends that the Applicant provide a separate Erosion &Sediment Control Plan clearly illustrating the erosion controls, the limit of work, as well as areas for proposed tree protections. HW recommends including erosion control notes on the Erosion & Sediment Control Plan as well as construction sequencing notes. Response: A separate Erosion & Sediment Control Plan has been added along with notes and construction sequencing as recommended. b. HW recommends that the Applicant explain how the site will be accessed during construction and if a stabilized construction entrance is necessary. The catch basins at the northeast corner of the existing building may need protection in addition to the proposed silt sacks. HW recommends that the Applicant explain how these catch basins will be protected from sediment. Response: Primary construction access will be gained from the north side of the existing building.A temporary rip-rap construction access has been added to the plans which will remain throughout the earthwork operation and until such time that it is in conflict with other sitework. Existing catch basins at will be protected via silt sacks and straw bales or wattles.Details are included on the Erosion & Sediment Control Plan. c. HW recommends that the Applicant provide a detail for the inlet protection. Response: Inlet protection details have been provided on the new Erosion & Sediment Control Plan. d. It appears that the storage building is proposed within an existing tree line. HW recommends that the Applicant locate any trees within the limit of disturbance with a diameter greater than 10 inches per§250-23. A. (7). HW recommends that the Applicant confirm whether the critical root zones (CRZs) of any large trees will be impacted by the proposed development; construction activity over CRZs willpotentially damage the root systems of trees and cause long-term degradation of the tree's health. HWJurther recommends that any trees at the edge of the limit of work proposed to be protected are clearly marked in the field and a tree protection detail is added to the plan set. Response: The wooded area was cleared several years ago and has become revegetated primarily with young, colonizing tree species such as Quaking Aspen and Birch species, and Pine. There are no trees within or immediately adjacent to the work that that exceed 10 inches. 2. Standard 9 requires a Long-Term Operation and Maintenance (O&M)Plan to be provided. a. Per MSH Volume 1 Chapter 1 Page 23, HW recommends that the Applicant provide a Long-Term Operation &Maintenance Plan as a standalone document to be signed by the property owner prior to occupancy, that includes the following: i. Stormwater management system owners; ii. Parties responsible for operation and maintenance; iii. Routine and non-routine maintenance tasks to be undertaken after construction is complete and a schedule for implementing those tasks; iv.A simple plan that is drawn to scale and shows the location of all stormwater practices within the parcel requiring inspections and long-term maintenance; and ONE CHARLESVIEw ROAD,SUITE 2 - HOPEDALE, MASSACHUSETTS 01747 - (508)381-321 2 WWW.ALLEN-EA.COM Page 15 v. An estimated operations and maintenance budget. Response: A stand-alone O&M plan has been prepared with the items suggested. HW recommends that the Applicantprovide the O&M guidelines for the CULTEC Chambers. Response: Information for Cultec Chamber Maintenance has been provided in the O &M plan. 3. Standard 10 requires an Illicit Discharge Compliance Statement be provided. a. HW recommends that the Planning Board include a condition of approval requiring an Illicit Discharge Compliance Statement signed by the property owner prior to land disturbance. Response: The applicant has no objection to this condition. Please feel free to contact me at(508) 381-3212 with any questions regarding this correspondence. Sincerely, ALLEN ENGINEERING &ASSOCIATES, INC. a j A"a Michael J. Dryden,RLA Mark E. Allen, PE Senior Project Manager President Cc: Greg Susko, Applicant ONE CHARLESVIEw ROAD, SUITE 2 - HOPEDALE, MASSACHUSETTS 01747 (508) 381-321 2 WWW.ALLEN-EA.COM Horsley 'Wiffen GroupSustainable Environmental Solutions 112 Water Street-60 Floor w Boston,MA 02109 857-263-8193•horsleywitten.corn I1tYV�r November 16, 2022 Ms. Jean Enright, Planning Director North Andover Planning Board 120 Main Street North Andover, Massachusetts 01845 Ref: Initial Stormwater Peer Review Extra Space Storage Building 1701 Osgood Street North Andover, Massachusetts Dear Ms. Enright and Board Members: The Horsley Witten Group, Inc. (HW) is pleased to provide the North Andover Planning Board with this letter report summarizing our initial review of the Drainage Analysis and Site Plans for the proposed Extra Space Storage Building at 1701 Osgood Street, North Andover, MA. The plans and stormwater report were prepared by Allen Engineering & Associates, Inc, on behalf of Extra Space Properties 104 LP (Applicant). The project proposes the construction of a 47,244 square foot (sf)three-story storage building, along with associated parking, utilities, stormwater management, and landscaping on a previously developed 3.02-acre parcel containing an existing building. The stormwater management for the proposed storage building includes a grass swale, a catch basin, manholes, and a subsurface infiltration system (SIS). A small portion of the site is located within the 100-foot buffer zone of a wetland resource area located across Osgood Street. The proposed work will remain outside of the buffer zone. The following documents and plans were received by HW: • Applications for Site Plan (Amended), CDD3 and Parking Special Permits, 1701 Osgood Street, North Andover, MA, prepared by Smolak &Vaughan, LLP, dated November 3, 2022 (155 pages) including; o Drainage Analysis for Extra Space Storage at 1701 Osgood Street, North Andover, prepared by Allen Engineering & Associates, Inc., dated November 3, 2022. • Site Plans, Extra Space Storage, 1701 Osgood Street (Route 125), North Andover, Massachusetts, prepared by Allen Engineering & Associates, Inc., dated November 3, 2022, including: o Cover Sheet C-1 o Existing Conditions Plan C-2 o Layout & Materials Plan C-3 a Grading & Drainage Plan C-4 o Landscape & Lighting Plan C-5 o Fire Truck Swept Path C-6 a Construction Details C-7 o Construction Details C-8 Horsley` ittren.cWorn 91 @Hors0eyWiftenGroup Hor^sl y Witten Group, Inc. Town of North Andover November 16, 2022 Page 2 of 5 Stormwater Management Design Peer Review In accordance with the North Andover Zoning Bylaw §195-8.14. E. (8) A Stormwater management plan is required for all site plan review applications. The stormwater management plan shall be prepared in accordance with the latest version of the Massachusetts Stormwater Handbook (MSH) and demonstrate full compliance with the Massachusetts Stormwater Standards and the North Andover Stormwater Management and Erosion Control Regulations. HW offers the following comments concerning the stormwater management design. We have used the MSH as the basis for organizing our comments. However, in instances where the additional criteria established in Chapter 250 of the North Andover Code requires further recommendations; we have referenced these as well. 1. Standard 1: No new stormwater conveyances (e.g., outfalls) may discharge untreated stormwater directly to or cause erosion in wetlands or waters of the Commonwealth. a. It appears that the southeastern portion of subcatchment IS is captured by the proposed grass swale which directs runoff to a proposed catch basin that conveys stormwater into the 18-inch drain line that discharges directly into the wetland to the west of Osgood Street. HW recommends that the Applicant verify that the new discharge velocity at the outfall will not cause erosion in the wetland. b. Most of the site runoff will be captured by the stormwater basin located at the western end of the site. It appears that an existing outlet control structure conveys stormwater into the wetland to the west of Osgood Street. HW recommends that the Applicant confirm that the existing discharge does not cause erosion in the wetland. 2. Standard 2: Stormwater management systems shall be designed so that post-development peak discharge rates do not exceed pre-development peak discharge rates. a. The Applicant has drawn the existing and proposed watershed maps to include a portion of the upgradient area northeast of the site. A large upgradient area to the east flows towards the riprap drainage channel and into the 18-inch pipe at the headwall. It appears that some of this upgradient area may flow onto the southeast corner of the site. HW recommends that the Applicant explain the drainage pattern of the large area to the east that flows onto the site. b. The Applicant has provided two design points: EV-1 (catch basins at the proposed northern sawcut line) and EV-2 (catch basins at the proposed southern sawcut line). These catch basins convey stormwater to the existing stormwater basin at the western end of the site, which appears to overflow via an outlet control structure into the wetland to the west of Osgood Street. HW recommends that the Applicant expand the HydroCAD model to include the stormwater basin as a pond, the existing portion of the site and building that flows into the basin as subcatchments and evaluate the outlet control structure and the wetland as additional design points. c. It appears that the southeastern portion of subcatchment 1 S is captured by a proposed grass swale which directs runoff to a proposed catch basin that conveys stormwater into the 18-inch drain line that discharges directly into the wetland to the west of Osgood Street. HW recommends that the Applicant verify that the conveyance system is properly sized to handle the additional flow as well as the runoff coming from the east. KAProjects\2021\21020 Town of North Andover\21020K 1701 Osgood\Reports\221116_SWPeerReview 1701 Osgood.docx Town of North Andover November 16, 2022 Page 3 of 5 d. There appears to be a typographical error listed in Table 1: Summary of Peak Rates of Stormwater Runoff for Evaluation Point 1 during the 25-year storm under proposed conditions. HW recommends that the Applicant confirm the rate and adjust the table as needed. e. The Applicant has modeled the primary outlet for the SIS as having an invert of 61.75 in the HydroCAD model under proposed conditions. The detail on Sheet C-7 lists the invert at 61.65. HW recommends that the Applicant verify the invert of the 6-inch pipe and confirm it is constructable. f. HW recommends that the Applicant confirm if the proposed building will require a sanitary sewer pipe and if applicable show the connection on the plan set. g. The drain manhole (DMH) at the northeast corner of the existing building receives flow from two catch basins (CB) under existing conditions. Under proposed conditions, a new connection will be added to the DMH from the subsurface infiltration system (SIS). The Plan says to "match inverts"for this connection. However, the points where the SIS pipe and the CB pipe enter the DMH appear to be very close. HW recommends that the Applicant verify that the DMH will maintain structural stability after this new connection. h. HW recommends that the Applicant provide an elevation view detail for the grassed swale or provide spot grades along the centerline. i. HW recommends that the Applicant callout the invert elevations for the 8-inch PVC pipes conveying roof runoff to the SIS. j. The Applicant is proposing the installation of a new headwall for the existing riprap drainage channel. HW recommends that the Applicant provide the bottom wall (BW) elevation for the new headwall on the Plans. HW also recommends that the Applicant include the 18-inch drainpipe in the detail for the Headwall. 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a. It appears that the subsurface infiltration system has greater than 2 feet of separation to Estimated Seasonal High Groundwater(ESHGW) but less than 4 feet. HW recommends that the Applicant provide a mounding analysis per the MSH Volume 3, Chapter 1, Page 28. b. HW recommends that the Applicant provide required recharge volume and drawdown time calculations per the MSH Volume 3, Chapter 1, Pages 15 and 25. 4. Standard 4 requires that the stormwater system be designed to remove 80% Total Suspended Solids (TSS) and to treat 1-inch of volume from the impervious area for water quality. a. The Applicant has provided a TSS work sheet claiming 80% TSS removal for an infiltration basin. HW assumes this is referring to the existing stormwater basin. HW recommends that the Applicant clarify that the existing stormwater basin has infiltration characteristics. K:\Projects\2021\21020 Town of North Andover\21020K 1701 Osgood\Reports\221116_SWPeerReview 1701 Osgood.docx Town of North Andover November 16, 2022 Page 4 of 5 5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads (LUHPPL). a. The site is not considered a LUHPPL. Therefore, Standard 5 is not applicable. 6. Standard 6 is related to projects with stormwater discharging into a critical area, a Zone II, or an Interim Wellhead Protection Area of a public water supply. a. The proposed development is not discharging near or into a critical area, Zone II or an IWPA area. Therefore, Standard 6 is not applicable. 7. Standard 7 is related to projects considered Redevelopment. a. The proposed project is a mix of new development and redevelopment. The area consisting of the existing parking lot behind the existing building up to the existing retaining wall may be considered redevelopment. In this redevelopment area, a decrease in paved area is proposed and being converting to roof top which is considered an improvement. The proposed roof runoff is being managed by the subsurface infiltration system as new development. HW recommends that the Applicant respond to the other comments in this review letter to confirm it has adequately incorporated Standard 7. 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a. The proposed project requires land disturbance of just under 1 acre. Therefore, a Stormwater Pollution Prevention Plan (SWPPP) per the EPA NPDES Construction General Permit will not be required. a. The Applicant has provided a Grading & Drainage Plan (Sheet C-4) which also includes erosion and sediment control measures. HW recommends that the Applicant provide a separate Erosion & Sediment Control Plan clearly illustrating the erosion controls, the limit of work, as well as areas for proposed tree protections. HW recommends including erosion control notes on the Erosion & Sediment Control Plan as well as construction sequencing notes. b. HW recommends that the Applicant explain how the site will be accessed during construction and if a stabilized construction entrance is necessary. The catch basins at the northeast corner of the existing building may need protection in addition to the proposed silt sacks. HW recommends that the Applicant explain how these catch basins will be protected from sediment. c. HW recommends that the Applicant provide a detail for the inlet protection. d. It appears that the storage building is proposed within an existing tree line. HW recommends that the Applicant locate any trees within the limit of disturbance with a diameter greater than 10 inches per §250-23. A. (7). HW recommends that the Applicant confirm whether the critical root zones (CRZs) of any large trees will be impacted by the proposed development; construction activity over CRZs will potentially damage the root systems of trees and cause long-term degradation of the tree's health. HW further recommends that any trees at the edge of the limit of work proposed to be protected are clearly marked in the field and a tree protection detail is added to the plan set. KAProjects\2021\21020 Town of North Andover\21020K 1701 Osgood\Reports\221116_SWPeerReview 1701 Osgood.docx Town of North Andover November 16, 2022 Page 5 of 5 2. Standard 9 requires a Long-Term Operation and Maintenance (0 & M) Plan to be provided. a. Per MSH Volume 1 Chapter 1 Page 23, HW recommends that the Applicant provide a Long-Term Operation & Maintenance Plan as a standalone document to be signed by the property owner prior to occupancy, that includes the following: i. Stormwater management system owners; ii. Parties responsible for operation and maintenance; iii. Routine and non-routine maintenance tasks to be undertaken after construction is complete and a schedule for implementing those tasks; iv. A simple plan that is drawn to scale and shows the location of all stormwater practices within the parcel requiring inspections and long-term maintenance; and v. An estimated operations and maintenance budget. b. HW recommends that the Applicant provide the O&M guidelines for the CULTEC Chambers. 3. Standard 10 requires an Illicit Discharge Compliance Statement be provided. a. HW recommends that the Planning Board include a condition of approval requiring an Illicit Discharge Compliance Statement signed by the property owner prior to land disturbance. Conclusions HW recommends that the Planning Board require that the Applicant provide a written response to address these comments as part of the Board's review process. The Applicant is advised that provision of these comments does not relieve him/her of the responsibility to comply with all Town of North Andover Codes and By-Laws, Commonwealth of Massachusetts laws, and federal regulations as applicable to this project. Please contact Janet Bernardo at 508-833-6600 or at jbernardo@horsleywitten.com if you have any questions regarding these comments. Sincerely, HORSLEY WITTEN GROUP, INC. Janet Carter Bernardo, P.E. Veronica Seward-Aponte, E.I.T. Associate Principal Environmental Engineer KAProjects\2021\21020 Town of North Andover\21020K 1701 Osgood\Reports\221116—SWPeerReview-1 701 Osgood.docx