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HomeMy WebLinkAbout210311 Stormwater_Response_Eng01_rev0 - - 25 Beechwood Drive Civil Engineers Structu�a.1 E��me ems Tralfic Eng,[r i,eer*s � � ��������� L n Landscape At-chitects Scientists, March 11, 2021 Ms.Jean Enright, Planning Director Planning Department Town of North Andover 120 Mein Street North Andover, MassachusettsOlO4S Ref: Initial Stormvvater Peer Review C|imate'Contro||edSe|f'Storage 8eechvvood Drive North Andover, Massachusetts Dear Ms. Enright: TFMoran Inc. is pleased to provide the North Andover Planning Board with this letter report summarizing our responses to The Horsley Witten Group comments dated February 25, 2021. The following is a summary of our response to these comments with the format of this letter following that of the review letter, with our responses underlined in red pen. Stormmmvster Management Design Peer Review HW offers the following overall comments concerning the stormwater management design as per the Massachusetts Stormvvater Handbook(MSH) dated February 2008,the North AndoverStornnwater Management and Erosion Control Regulations (Stormvvater Regulations) adopted February lS, 2011, and the North AndoverStormvvater Management and Erosion Control Bylaw(Bylaw). The comments below correlate with the MSH standards and where the more stringent Town requirements are applicable additional comments are noted. l.Standard 1 states that no new stonnm/oterconveyances(e.g. outfu&d may discharge untreated stonnm/oterdirectiv to or cause erosion/n wetlands or waters of the Commonwealth. a.There appears to be a discrepancy on the number ofoutfa||s proposed, the Grading& Drainage Plan indicates two outfa||s and the Post-Development Drainage Plan indicates three outfa||s. HVV recommends that the Applicant verify that the number ofoutfa||s are consistent between the design plans and the Post-Development Drainage Plan. b. HVV recommends that the Applicant provide riprap apron sizing calculations for all riprap at proposed outts||sto confirm no erosion will occur. 48 Constitution Drive Bedford, NHO311O Phone(SO3)472~4488 Fax(GU3)472'S747 III IIII a rt 191 2,("Y")1 IIII e s ��III �'' �.t �Ilf°� f'.....'III���III"III��..� a��III'III °i�III t� III�� �2�"�.� 6 III � , 2.Standard 2 requires that stormwater management systems shall be designed so that post- development peak discharge rates do not exceed pre-development peak discharge rates. a. In accordance with the North Andover Stormwater Management and Erosion Control bylaw, Chapter 240, Section 27 the following amendments are recommended: i. Addition of a summary table including peak discharge rates and total volume of discharge for all modelled storm events to easily evaluate the pre-and post- development values. TFM ha ation. ii. Amendment of the rainfall data for all modelled storm events to match the values provided in Section B (a). TFM has amended the rainfalls r the above noted condition. iii. Amendment of the Time of Concentrations to include no more than 50 feet of sheet flow for both pre-and post-development conditions as stated in Section B (11). TFM has amended the Tc valuesr b.There appears to be a discrepancy on the number of infiltration chambers for Stormtech System #1 between the HydroCAD model and the design plans,Sheet C-19. HW recommends that the Applicant verify the number of chambers and update the plans or calculations accordingly. TFM has corrected the above noted i c. HW recommends that the Applicant verify the chosen flow path for Drainage Area (DA) 2 in the pre-development conditions as the flow path for DA 201 in the post-development conditions appears to be longer and is within the same area as Pre-development DA 2. flow athsto be consitstent. d. Catch Basin Nodes 214 and 215 in the HydroCAD model do not appear to exist in the design plans. HW recommends that the Applicant verify where these two catch basins are proposed and update the plans or calculations accordingly. TFM haIsubcatchments e. HW recommends that the Applicant confirm the upper boundary of the catchment area and that the property to the west is not flowing onto the site. TFM ha tion of the lawn from the easterlyabuttin . f. For documentation purposes of the Post-Development Drainage Plan HW recommends that the area of DA 212 match the area modelled in HydroCAD as well as specifying the location of Pond Node 1. TFM ha he location �e: e h w(.')(,.,)ci a rt h 191 2,("Y")1 e s o nseto Carr�urr i e n ts 01 ���)age 3 of 6 g.To verify that the paved area within DA 212 is draining toward C13 5, HW recommends that the Applicant provide spot grades at the end of the turnaround area in the southeastern drivevvay. TFM has added h. For construction purposes, HW recommends that the Applicant list the following items on the plan set for each of the subsurface infiltration systems: • System # • Size and number ofchambers • Proposed surface elevation (minimum) • Top of stone elevation ~ Top of chambers elevation ~ Bottom of chambers elevation • Bottom of stone elevation • ESHGVV TFM has gpdated the Ian details to include thisinformation.. 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a.The Applicant has provided a Test Pit Report dated December 5, 2020.Test pits 1 and 2 were conducted within the vicinity ofthe proposed subsurface infiltration systems.The saturated hydraulic conductivity rate (Ksat)was determined using an Amoozemeter test at Test Pit 1,which is an acceptable method. In accordance with Volume 3, Chapter 1, page 13 of the MSH, "When the "Dynamic Field" Method is used,the exfiltration rate for design purposes must be assumed to be no more than 5096 of the in-situ saturated hydraulic conductivity rate at the actual location on site where infiltration is proposed." HW recommends that the Applicant revisit the exfiltration rate used in the HydroCAD modeling calculations to be 50%of the lowest Ksat rate determined in the field. TFM has west Ksat rate determined in the field for each system. b. In accordance with the MSH,Volume 3, Chapter 1, page 28, a mounding analysis is required when the vertical separation from the bottom of an exfi|tration system to seasonal high groundwater is less than four (4)feet and the recharge system is proposed to attenuate the peak discharge from a 10-year 24-hour storm or greater. HW recommends that the Applicant determine if the infiltration chamber designs require a mounding analysis and provide the same as necessary. TFM has u dated the drqiDg�elans to show the location of the seasonal ides 4.2 fee des 5.5 feet qf separation to the Lgg_�Li red. 4.Standard 4 requires that the stormwater system be designed to remove f0% Total Suspended Solids III IIII a rt 191 2,("Y")1 IIII e s ��III se.t �Ilf.� f"°°III���III"III��;..� u��III'°urr'm�IInt III;�� ° �4�"�.� 6 III � , a.The Applicant has provided water quality volume calculations in the Stormwater Management Report. It appears that the Applicant will meet this criteria however it is not clear how the Applicant calculated the Provided Water Quality Volume.The volume utilized must be the total volume in the infiltration chambers below the outlet elevation. For documentation purposes HW recommends that the Applicant revisit the provided water quality volume and clarify how the values listed were determined. TFM has o indicate I the lowest invert l i i i i I b.The Applicant has included 5%of TSS removal for street sweeping. HW recommends that the Applicant confirm that the street sweeping schedule will be in accordance with the Table provided in Volume 2, Chapter 1, page 9 of the MSH. Furthermore, HW recommends that the Applicant update the Inspection & Maintenance Manual to include the applicable street sweeping schedule. TFM haside thejpplicable swggpjnz_���� c.The Applicant has proposed a stormwater management system with deep sump catch basins and two subsurface infiltration systems with isolator rows for pretreatment of the parking lot runoff. HW recommends that the closed drainage system be revised to eliminate the catch basin to catch basin configuration. According to the MSH, Volume 2, Chapter 2, page 3 to provide TSS removal the catch basins must be placed offline. Providing manholes between connections is standard engineering practice in Massachusetts. TFM has e. 5.Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads(LUHPPL). a.The proposed development is not considered a LUHPPL and therefore, Standard 5 is not applicable to this project. 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 within a critical area, Zone II or an IWPA area and therefore, Standard 6 is not applicable. 7.Standard 7 is related to projects considered Redevelopment. a.The proposed development is not considered redevelopment and therefore, Standard 7 is not applicable 8.Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a.The Applicant has provided a Site Preparation Plan. Silt Fence is proposed along the down gradient limit of work. HW recommends that the Applicant add a compost sock, in addition to the siltation fence, where the limit of work is within the 50-foot wetland buffer. TFM hasI i ik. �R e e h w ci �A,irrh 1912,(�� e s o nseto Carr�urr i e n ts 01 ���)age 5 of 6 b. HW recommends that the Applicant include Catch Basin Protection on all existing catch basins within lOO feet of the construction entrance. TFM has ion. c. HVV recommends that the Applicant review the required contents and controls of the Erosion and Sediment Control Plan listed in Article VIII, 250-29 and 250-30 of the North Andover 5tormvvater Regulations and verify all items have been addressed. se truction exits. For these reasonsall items contained in Arti water RfEglafions have been addressed. d.The property will be disturbing more than 1 acre of land and will therefore be required to develop a Stormwater Pollution Prevention Plan (SWPPP) in accordance with the Environmental Protection Agency(ER4) National Pollutant Discharge Elimination System (NPDES) Stormvvater Program. HW recommends that the Applicant provide the Town of North Andover with a copy of its SVVPPP prior to construction. 9.Standard 9 requires a long-term operation and maintenance(O&M)plan shall be developed and implemented to ensure that stomnwotermanagement systems function osdesigned. a.The Applicant has provided an Inspection and Maintenance Manual. HW recommends that the Applicant review the requirements listed in Article IX, 250-32 of the North Andover Stormwater Regulations and verify all items have been addressed including but not limited to the following: e In accordance with the MSH Vol. 2, Ch. 2, the deep sump catch basins frequency of inspection and cleaning should be increased to four times per year and at the end of the foliage and snow-removal seasons. TFM haLgpdated the O&M Plan to include this frequency. e |n accordance with the M5H Vol. l, Ch. l, p. 9, an estimated operations and maintenance budget should be added to the O&M Plan. TFM haLgpdated the O&M Plan to include this bud et. ~ A simple plan that illustrates the location of each of the sLormvvater practices that require inspections should be included.The figure should also include the components of the septic system. TFM haLgpdated the O&M Plan to include this_plan. e Locations for snow storage. TFM haLgpdated the O&M Plan to include these areas. ~ Signatures of property Owners. 11 e-B e"haood Drive �Aw,th I I � es p(D nseto i g e e i n g� a�i n'�i e n ts 01 ���)age 6 of 6 lU.Standard 2Orequires that an Illicit Discharge Compliance Statement be provided. a.The Applicant has not provided an Illicit Discharge Compliance Statement in the Drainage Report signed by the property owner. HW recommends that the Planning Board or Conservation Commission include a condition of approval requiring an Illicit Discharge Compliance Statement be signed by a representative of The Stubblebine Company prior to land disturbance. TFM has added a note to the plans of this.LSheet C-8 note 131 ll.Additional Comments: a.The retaining vva|| along the eastern driveway is over 4 feet high,the design of this vva|| requires a structural engineer. HW recommends that the Applicant verify it has adequately considered the extent nf land disturbance needed tn construct the wall. Thi work associated with wall room to work within the b. HW recommends that the Applicant verify that the 18-inch drainpipe between C131 and C132 has adequate separation from the wastewater pipe it goes under. TFM has added learance. As such there is c. Stormtech System#1 includes DIVIH4 and Inlet 4that do not appear necessary. HVV recommends that the Applicant revisit this structure and verify it is required DMH4i let connection from DMH 4 into the Isolator Row. As such these are each necessgLy. We believe we have adequately addressed the comments provided at this time. Should there beany questions or concerns regarding this submittal or the project in general please do not hesitate to contact the undersigned at(GO3) 472'44Q8or . Sincerely,, 1[FMoran Inc. Jason Hill,P.B.