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HomeMy WebLinkAbout2017-04-18 Peer Review & Response SPR Horsley Witten Group Sustainable Environmental Solutions 294 Washington Strest--Wte 801•866t6n,MA02108 857-263-8163 hoisleyvAtteh=M April 4, 2017 Mr. Robert Douglas, Director RE-0EIVED Andover Conservation Commission Town Office APR 04 2017 36 Bartlett Street CON VAT QNUIVISIOM Andover, Massachusetts 01810 L GER M Ref Merrimack College, Athletic District Improvements 315 Turnpike Street, North Andover, MA J MassDEP File#090-1287 Dear Mr. Douglas and Commission Members: The Horsley Witten Group, Inc. (HW) Is pleased to provide the Andover Conservation Commission with this letter report summarizing our Initial review of the Stormwater Report for the Athletic District Improvements at Merrimack College, The plans were prepared for Merrimack College(Applicant) by Vanasse Hangen Brustlin, Inc. (VHB). The project Includes a synthetic turf field and running track, viewing bleachers, a field house, and associated hardscape and landscaping. The project also Includes modifications to the existing baseball field and existing multi-use synthetic field as well as a new boardwalk through a wetland resource area. The Andover/North Andover town line bisects the project site, The stormwater management from the proposed development located primarily In North Andover will be directed towiFCsifi"e Fit zCiInT6cat6c1FffAnUover, The stormwater management design for the Athletic Improvements Includes one.propl!gta water_qMa(itydevice LStor!ncqpfor arnd a subsurface Infiltration/detetention system located feoqRt(IhIehe IeliT h esgn vat eexsng h6i"01p616- he e " actives asoTedfihe Master`" Dainag StuIyad Analysis performed by Sasaki Associates, Inc. dated April 2 6, 1999, which include utIlizIn the peak credits provided as part of the Stormwater Master Plan. The following documents and plans were received by HW: 0 VHB provided HW with three figures to clarify the watershed delineation of subcatchment 3.1 as defined on Figure 2a, dated March 4, 2017. Additional figures Included: * Grading, Drainage and Utilities Plan, 02-1, dated June 22, 1998; * Overall Drainage Plan, Figure A, dated December 2011; and * Utility Plan, Volpe Athletic Center Expriasion, C-5, dated May 2, 2013. 0 Stormwater Management Report, prepared for Merrimack College, prepared by VHB, dated March 7, 2017, revised March 10, 2017; 0 Site Plans for the Athletic District improvements, Merrimack College, Andover, MA, prepared by Huntress Associates, Inc. and VHB, dated March 2, 2017, revised March 7, 2017,which Includes: Mr. Robert Douglas April 4, 2017 Page 2 of 5 o Cover Sheet o Existing Conditions Plan of Land Sv-1 o Existing Conditions Plan of Land Sv-2 o Legend and Notes C-1.0 o Erosion and Sedimentation Control Plan C-2.1 revised 3/10/17 o Erosion and Sedimentation Control Plan C-2.2 revised 3/10/17 o Site Utilities Plan C-3.1 revised 3/10/17 o Site Utilities Plan C-3.2 revised 3/10/17 o Civil Details C-4.1 o Civil Details C-4.2 o Layout& Materials L-1 o Grading and Drainage L-2 o Visitor Area Enlargement Plan L-3 o Construction Details L-4 o Construction Details L-5 o Construction Details L-6 o Construction Details L-7 o Construction Details L-8 o Grandstand Layout L-g o Fleldhouse Plan L10 o Layout& Materials L11 o Layout& Materials L12 a Infield Enlargement L13 o Dugout Details L14 o Softball Filed Details L15 o Boardwalk Details L16 Stormwater Review HW conducted a site visit on March 21, 2017 and has reviewed the documents listed above. HW offers the following comments concerning the stormwater management design as per the standards of the Massachusetts Department of Environmental Protection (MassDEP)Wetlands Protection Act(CMR 310 10.00), the Massachusetts Stormwater Handbook (MSH) dated February 2008, the Town of Andover Stormwater Management and Erosion Control Regulations, and the Town of Andover Wetlands Protection By-Law. The project Is required to comply with the MassDEP Stormwater Management Standards. Per the MassDEP Stormwater Management Standards, this project Is considered a new development. Below are comments relating to the standards as presented in the MSH. 1. Standard 1 states that no new stormwater conveyances may cause erosion In wetlands of the Commonwealth. a) The existin subcatchment labeled 3.2 has an outfall to a wetland resource area which is h draulical) connected to the Football 1=€eld Detent€on Basin. e App cansiau�d verify the current lscharge rom the ex sting 30=nch p pe and confirm that the proposed HAProjects120IN7030 Andover117030C Merrimack Colle$c Athictie-Wep02131170403_1st peer rcvicw Nlerrimtick College rtilletic [mprovemems.dacx i I Mr. Robert Douglas April 4, 2017 Page 3 of 5 discharge will not cause erosion within the bordering vegetated wetland. The Applicant has provided a Closed-Drainage System Hydraulic Analysis which Indicates a velocity j discharge of 8.54 feet per second (fps) at the outfall. A number of the pipe segments have not been included, such as(CB 124, DMH 106, DMH 107, DMH 118, and AD 117) HW recommends that the Applicant update the spreadsheet to Include all proposed Structures and corresponding flows and recalculate the proposed velocity of the 30-Inch pipe at the outfall. 2. Standard 2 requires that post-development runoff does not exceed pre-development runoff off-site. a) The Applicant has provided the HydroCAD calculations to verify that the proposed development is within the parameters of the originally approved Merrimack College Master Plan (Master Plan). The Applicant is requesting_ to subtract an additional 120 —_.. per s c d (cf.).carom the 670ft-�t appear�an a pp can—fTi in cubic feet second cfs from the available compliance with Standard 2. b) The Applicant has utilized the Football Detention Area as the comparison point between exis#ing and ?roposed conditionsiis anaysspa�inappears appropria a given location of this phase of" evelopmelt. However, HW recommends that the Applicant provided a table Illustrating the existing discharge from the football detention area towards Rock Ridge Road, the allowable discharge under the Master Plan, and the proposed discharge with this phase of development. 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a) The Applicant has noted that due to the site being composed of C and D soils as Weil as the shallow depth to seasonal high groundwater the Applicant Is meeting Standard 3 to the maximum extent practicable. T e Ap 1p scant is ro osin to infiltrate stormwater beneath the proposed synthetic turf held The Applicant appears to oe"Cn compliance with Standard 3. pW J 4. Standard 4 requires that the stormwater system be designed to remove 60% Total Suspended Solids(TSS) and to treat 0.5-inch of volume from the Impervious area for water quality. a) The Applicant has provided the water quality calculations and TSS removal calculations in accordance with the Massachusetts Stormwater Handbook. The Applicant appears to be In compliance with Standard 4. 5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads (LUHPPL). a) Standard 5 Is not applicable to this site. 6. Standard 61s 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) Standard 6 Is not applicable to this site. 7. Standard 7 Is related to projects considered Redevelopment. A redevelopment project is required to meet the following Storm water Management Standards only to the maximum H;1Projcctsl2017117030 Alidovel'117030C:Merrimack College Athled6l1eporIA170403_I st peer review_NIMImad'College_Wildic Improvemenis.dasx Mr. Robert Douglas April 4, 2017 Page 4of5 extent practicable: Standard 2, Standard 3, and the pretreatment and structural best management practice requirements of Standards 4, 5, and 6. Existing stormwater discharges shall comply with Standard I only to the maximum extent practicable. A redevelopment project shall also comply with all other requirements of the Stormwater Management Standards and Improve existing conditions. a) The proposed protect is considered a mix of new development and redevelopment. Due to the site being composed of C and D soils as well as the shallow depth to seasonal high groundwater the Applicant Is meeting Standard 3 to the maximum extent practicable. The Applicant appears to be in compliance with Standard 7. 8. Standard 8 requires a plan to control construction related Impacts Including erosion, sedimentation or other pollutant sources. a) ']eAppli�eq0thps Qv]Aed an erosion control flan as required to be in compliance with Standard 8. The majority of the site work is within North Andover, HlW,recommends tha ` ]Art-0 VPr-PnO 111)Ans ova.. QPQ!sery t1.4t peQLPLgQ04lctls rAW Ing-thataliV_Qr p,Ws,WJO ted.,czuts de the 0-foot S offer, tha ua dewatering �f plan.,�e�prQvided forappraval and that the SWPPP prepared in accordance with the .PPANi?DHS<��Q�s�r��It�nGe��ral Permit be,pprovidedto the.Town� __ b) HW recommends that the Andover Conservation Commission Include a special condition to Insure that the cr_actor mini_ iz�se use of heavy equipment withir>I the.area which' is utilized as st age`Football. ieid-©_ . e basin". A small portion of the detention area is proposed to be regraded to adjust the layout of the existing synthetic molt]-use field. The Applicant should provide clear direction on the site plan, specifically regarding the bottom of the basin at elevation 227. c) HW recommends that tale Applicant note the number and diameters of trees being remoued_and..any,, ltig to iort Y,I-;easures,to limn the amount of tre'es-beinq rem v6d. HW also recommends that thppllcant provide the number and diameters of _rees proposed to to planted within the buffer zone of the adi ent wetland resource areas. 9. Standard 9 requires a Long Term Operation and Maintenance (0 & M) Plan to be provided. a) The Applicant has provided an O&M Plan in Appendix D of the Stormwater Management Report. The O&M Plan references cleaning the subsurface Infiltration system in accordance with the StormTech Inspection and Maintenance manual. However, it does not appear that the proposed project Includes a StormTech system. HW recommends that the_Appji�a. revise the O&M Plan to reference the proposed stormwater features, 1pcluding the under-drain system the trench drains,and tbg Wgg drains. HW further recommendt the Applicant pr, vle.. h_In te ., M:Pia.-lstrate the s tha location of the various stormwater practices to be maintained. b) FiW on_reco _d..s 1ha_th.E,Applipant igfta e pot ►t a-t catisart tb—sna torage on-tile 0&elan. Fencing or markers could be installed so that dur€ng the snow se ]owing contractor will not be allowed to place snow in the wetland resource H:\]1rgJmts1200\l7030 AndoveA17030C ltierrimack Collop At€iletioUt3epor1s1170403, lst peerrevicw—Nienimock Cal 1e_gc AI11k!6e Improvements.dcwx A Mr. Robert Douglas April 4, 2017 Page 5of5 10. Standard 10 requires an Illicit Discharge Compliance Statement to be provided. 0 a) HW recommends that the propel#owner confirm that_there are no Illicit discharges to a j watland,,.rstormwater ms_"a e ntA 11, Based on the information provided in the 2001 Order of Conditions,the Football Field and the Elm Street detention basins are intended to provide mitigation via a credit system for total Increases in post-development peak rate of runoff with respect to existing conditions under the Master Plan. The Master Plan provided an additional 62 cfs of stormwater flow that could be mitigated by one of the basins as the college continued to expand over a 20 year period. As of February 2017, 18.53 cfs remains available as peak flow mitigation credit for a 100-year storm event. The Applicant has noted that the proposed development results in a net increase of 1.20 cfs for the 100-year storm event resulting In a credit adjustment to 17,23 cfs. 12. In accordance with the original 2001 Order of Conditions, under 5,4,2 Protocol for Administrating the Peak flow Accounting System; It states, "Upon completion of each authorized phase of construction, the College shall have their engineering consultant evaluate the effectiveness and function of the drainage Improvements. The englneerlffl consultant shall prepare„and submit a_report_to the Commission_together. Ith any recommendations for Improvement or modifications of the drainage system to maintain the systerrl`s pperformance." HW recommends that the Applicant provide the required documentation to the Conservation Commission for previous phases that have been completed. HW further recommends that the Applicant confirm that.any.- drainage-Improvements associated with any previously,approved phase are completed prior to construction be Inning on the Athletic D g g .. _ ._. District improvements 13. HW recommends that the Andover.Conservation Commission consider requesting that the proposed adjusted bottom of the Football Detention Area be marked in the field prior to construction and that_an_as-built plan..of the footl?ail.detentlon area.be provided at the end of construction to verify that the proposed stormwater detention volume has been provided, Conclusions HW recommends that the Commission require that the Applicant address these comments as part of the Board's review process. The Applicant Is advised that provision of these comments does not relieve himiher of the responsibility to comply with all Town of Andover Codes and i3y- Laws, Commonwealth of Massachusetts laws, and federal regulations as applicable to this project. Please contact Janet Bernardo at 867-263-8193 or atjbernardo@horsleywitten.com if you have any questions regarding these comments. Sincerely, HORSLEY WITTEN GROUP, INC Janet Carter Bernardo, P.E., LEED AP Senior Project Manager H:IProjccts12t1171t703O Andmcr1t703OC lferrintack C'ottegc Athictiuli2eiro31s1170403_Ist pear reviem Menimaek College_Athletic improvemenls.docx O to r:e j "Vhboo April 11, 2017 Ref: 1162S.01 Mr. Robert Douglas, Director Andover Conservation Commission Town Office 36 Bartlet Street Andover, MA 01810 Re: Merrimack College Detention Basin Flow Monitoring Dear Mr. Douglas, Merrimack College has been conducting a stormwater monitoring program since 2012 in accordance with the Stormwater Master plan approved by the Andover Conservation Commission in 2001 (DEP #090-075).The program requires outflow monitoring from two detention basins to confirm that they are functioning as designed. The Merrimack College Stormwater Management Plan included predicted peak flow values discharging from each detention basin for various 24-hour storm events,with a 2-year storm (3.4 inches) being the smallest. The peak outflows from the Stormwater basins are expected to be 43.95 cfs for the Elm St Basin and 12,01 cfs for the Football Field under 2020 full-build conditions in a 24- hour, 2-year storm event. To monitor the flow, Merrimack College contracted with EST Associates, Inc,who installed two continuous area velocity flow meters on April 20, 2012; one flow meter is located at the Football Field Detention Basin outlet and the other at the Elm Street Detention Basin outlet. In addition, EST installed a rainfall gauge to record local rainfall depths.VHB regularly reviews the monitoring data and evaluates the detention basins performance following rainfall events. EST provides regular inspection and calibration of the equipment to insure it is functioning properly.On May 12, 2012, the Football Field outlet control structure was modified to function as detailed in the Stormwater Master Plan and the flow gauge was relocated to a point farther downstream in the outfall pipe to avoid turbulence associated with the outlet control structure modifications. Table 1 below summarizes the storm events since 2012 that have had over 0.5 inches of rainfall within a 24-hour period along with the associated peak flows from the Football Field Basin and then Elm Street basins. The peak flows never exceeded the expected flow for the proposed full-build conditions for the 2- year event, It is notable however,that four storm events, December 9tn 2014,August loth 2014,August 101 Walnut Street PO Box 9151 Engineers I Scientists I Planners I Designers Watertown,Massachusetts 02471 P 617,924,1770 51ldAL'JAL011d11 L625.Ulldocdllattrrsl4lU-l75tonm,raleMonitorinp75amm�y.Jox F 617.924.2286 '., Mr,Robert Douglas, Director j� �gpt4 Ref. 11625.01 q;m¢�� April 11,2017 Page 2 22n6 2014 and October 21"2016,show some uncharacteristically high peak flows compared to the amount of precipitation that fell for those storms.These specific events are notable because the vast majority of the rain fell in a short timeframe (less than 9, 3,3, &6 hours respectively) instead of the distribution of rainfall associated with the modeled 24-hour events.The basins are designed for 24 hour events, not short intense storms which would explain the higher peak flow results for those storms. On Oct 22, 2014, a 48-hour rain event occurred resulting in 3.66 inches of rain,just greater than the 2-year, 24-hour storm event rainfall depth.The Elm Street Basin had a peak outflow of approximately 8.0 cfs,which significantly below the 2020 fu[I-build predicted flows of 43.95 cfs from a 2-year storm. The Football Field Basin had a peak outflow of 10.63 cfs,which is also below the 2020 fu[I-build predicted flows of 12.01 cfs,This storm event confirms that both detention basins are functioning as designed and that the Elm Street Basin has additional capacity for future flow. Table 1: Merrimack College Detention Basin Monitoring Summary 24-hr rainfall Elm Street Football Field Storm Event (in) peak flaw(cfs) peak flow(cfs) Notes 2-year 24-hour 3,40 43.95 12,01 Modeled Peak Flow design event 4/22/2012 2.08 4.60 20.14 (Flow constriction control installed at football field 5/1/2012 0.56 * 2.82 basin on 5/10/2012-Monitoring equipment relocated 5/10/2012 0.94 0.61 16.71 downstream from outlet control structure on 6/2/2012 135 0,32 3.72 5/12/2012) 10/29/2012 2.33t 0.47 9.75 (Hurricane Sandy) 12/18/2012 0,83 0.37 12/27/2012 1.37 1.38 2/27/2013 0.76 2.07 7.50 6/8/2013 2.04 1.75 8.06 6/13/2013 0.95 0.92 6.27 7/1/2013 135 2,21 9,59 7/23/2013 0.92 1,68 7,01 8/9/2013 0.68 1.05 4.62 9/12/2013 0.93 0.47 3.89 11/27/2013 0.96 0.56 4.58 12/20/2013 0.74 0.19 2.07 12/29/2013 0.78 1.52 5.99 2/20/2014 0,68 0.44 2,04 3/30/2014 1.57 4.55 9.05 4/15/2014 0.55 0.43 3.43 4/30/2014 0,53 US 1.38 ��T.�Al'JAL�11d1E16?SAl�dnrs\letters`d-10-17 Stom.vaterPAon€toiing5umnxry.docx 3 Mr.Robert Douglas, Director ' 0 g �� Ref:11625.01 April 11, 2017 Page 3 ,#�% 7/4/2014 0.96# 0.23 3.85 7/15/2014 0.9 2.70 5.84 7/28/2014 0.68 1.52 3.60 8/13/2014 0.76 0.90 2.67 9/7/2014 0.63 0.23 4.14 10/2/2014 0.56 0.17 10/22/2014 3.66 8.00 10.63 11/17/2014 0.99 0.86 4.58 12/6/2014 1.07 0.96 4.80 12/9/2014 2.2 8.40 11.02 ail precip in a 9-hour period 1/4/2015 0.78 1.52 3.90 4/2012015 0.61 1.50 4.24 5/31/2015 1.59 2.53 5.57 Could be reported as a 2.85"storm in 48 hours or 2.96" 6/1/2015 1.33 3.21 6.57 storm in 50-hour storm 6/21/2015 0.81 1.25 5.13 6/28/2015 0.96 0.96 4.30 8/22/2015 0.82 1.59 3.47 9/30/2015 1.65 5.68 8,10 10/29/2015 0.57 0.89 3.19 11/20/2015 0.56 1.09 3.28 12/24/2015 0.61 2.64 5.15 1/10/2016 0.76 5.87 7.03 2/16/2016 0.56 4.64 5.91 2/24/2016 0.68 3.36 5.22 3/15/2016 0.62 1.33 4.27 3/28/2016 0.5 1.22 3.83 4/7/2016 0.61 3.88 6.67 8/10/2016 0.64 2.88 3.42 all precip In a 3-hour period,0,5"In a 1-hour period 8/22/2016 0.7 4.78 4.27 all precip in a 3-hour period,0.65"in a 1.5-hour period 9/19/2016 0.56 0.59 1.62 9/30/2016 0.73 0,69 0.88 10/8/2016 1.34 0.42 4.36 10/21/2016 1.81 14.67 6.13 1.54"In 6 hours,1,05"in 1 hour,0.76"in 30 mins. 10/28/2016 1.06 2.35 5.30 11/15/2016 0.80 2.39 4.33 11/30/2016 0.81 2.16 5.68 12/30/2016 0.59 4.34 4.67 1/4/2016 0.56 1.87 5.12 1/23/2017 1 1.73 5.87 2/15/2017 0.51 0.13 0.54 pPAAWALL)Ud111625.01�d-sVowe,A4-In,l7_Slour:vaverAionilaring5"minary don; Mr. Robert Douglas, Director ego Ref:11625.01 ���j April 11,2017 ihb Page 4 3/28/2017 0.63 2.02 5.26 Data not available due to technical issues with monitoring equipment t Rainfall from Nashua NH Airport rain gauge overall,the monitoring data has shown that the basins are functioning as designed.The predicted build out for the portion of the college campus that drains to the Football Field Basin is close to complete which will cap the amount of stormwater routed to the basin.The majority of all future plans for the Merrimack College Campus have the stormwater routing to the Elm Street Basin which has capacity when compared to the predicted flows. Sincerely, Vanasse Hangen Brustlin,Inc. Jeff Koetteritz, P.E. Senior Project Engineer jkoetteritz@vhb.com 111dAWALDIId\11625.01\clncs\laltersl4-10-17_5[nnrrnatzrF.4aniro ring5ummary.daa Legend AL6revietlona Hata 1C� Vhb MERRIMACK COLLEGE North A(A.—,M—hm"S 7 Athletic District Legend and Notes Permit Drawings Not for Construclion C-1.0 7 MERR{MACK COLLEGE � ! ! fr ! r! I �- 1� !;i•�i%i ! 't� ��� Athletic District i 1 Permit Drawings( Erosion and Sedimentation Control Plan Not for Construction 1 � 'ice`� -• / �� ,',w`;\��'":.� .t;�.'fil,if \� ��', � .- ....,...:,..�-n_.,, � ".��, c.'. � 1f C'•L..E. 7 1 E I 1 E i I i I I i E I //\`��/ _%�/�-"�a"'t"'���llf �` � �r F! /�j�✓� �autiau�w�.m....o. ' `}} r \ �J ' O � `{O,I I MATCIIUPif I` �.- ,. � .-....... .......... [ l •� �T ! - � .�`•......_._.�R Al /r r•`� ; `—ter--- 7'---e-`" 1a� l L ,aara tM _:,, r H L•y 1 l fl nYe:. 1 MERRiMACK COLLEGE �� t = ' ° _� �. .�: S S y - _ y,••� NormAneo ,Ma cc ktes O -` I! r,t'EF1. �t 1, .. Athletic District !r # t I Perniit Drawings } A Erasion and Sedimentation Control Plan ..-�1 �� \ Not for Construction G ~ tom iay .7 C` .L J I