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HomeMy WebLinkAboutStormwater Report - 234 DALE STREET 12/5/2017 1 A N MEMORANDUM i To: Town of North Andover:honing Board of Appeals Applicant/Owner: David Cronin Property: 234 Dale Street Date: December 5, 2017 The Applicant,David Cronin,is requesting dimensional variances to allow for a proposed addition to an existing dwelling at 234 Dale Street to include relief from side yard setbacks and to allow for expansion of gross floor area in excess of 50°% of existing I gross floor area for existing structures under 2,500 SF within the watershed district. The details of the Applicant's variance requests were set forth in the application as previously submitted by the Applicant to the Board. The hearings for the Variances were opened at the Board's October,2017 meeting. The Board heard testimony from the Applicant in support of the applications as well as testimony from abutters speaking in support to the Variance requests at the initial hearing.The matter was continued at the conclusion of the prior hearing,and subsequently further continued until the December 12,2017 meeting,with a number of issues to be addressed by the Applicant in response to specific inquiries of the Board to j the extent feasible. The purpose of this memo is to respond and provide background with respect to the issues raised by the Board at the initial hearing,which have been addressed in turn as follows: 1. Variance Plan. A revised variance plan has been submitted to address issues raised at the prior hearing including to correct typographical errors and to add I reference to the applicable watershed and wetland zones. 2. Drainage. Stormwater runoff control or stormwater treatment is not required for a project of this size pursuant to applicable regulations,but given the Board's J i (00t13110;v1) Ea,st Mill,21 High S(re .t, Suite 301,North Atidover, MA 01845 " 7W.SM0LA VACJ(:aE-1AN,x:01' Memo to North Andover ZBA Re:234 Dale Street December 5,2017 concerns and in light of the fact that the property is located within the watershed district,the Applicant's engineer has proposed a stormwater control system for an increase in impervious area of 972 square feet. Stormwater calculations have been provided by the engineer for a 9 inch rain storm which exceeds the 100 year storm for this area, Two StormTech 740 chambers in series are proposed which the engineer believes are more than adequate to ensure that there wont be any increase in runoff from the property. A revised watershed special permit plan (including a specification sheet for the stormwater detention chambers) along with the stormwater calculations have been submitted with this application. 3. Special Permit Plan. For expense and feasibility reasons,the Applicant has elected not to proceed with a simultaneous filing with the Planning Board as the Planning Board Special Permit filing will be contingent upon the ability to first obtain this Variance as an initial permit/approval matter. For this reason,the Applicant,rather than include additional endorsement of the Zoning Board on the Watershed Special Permit Plan,would propose that the Variance be approved subject to a condition in the decision substantially as follows: This Variance is granted subject to the Grant of a Watershed Special Permit by the Town of North Andover Planning Board and the project being completed to include the proposed improvements as shown on the Watershed Special Permit Plan for 234 Dale Street,North Andover, MA prepared for David Cronin,by Christiansen&Sergi,Inc. and originally dated 7/27/17 and last revised 12/4/17,consisting of 2 sheets,as submitted with this application,together with any modifications to said plan or proposed improvements as may be approved or required by the Town of North Andover Planning Board to be evidenced by reference to the final approved plan in the Final Watershed Special Permit Decision of the Town of North Andover Planning Board. Further, the Final Watershed Special Permit Plan shall include a notation and reference to this Variance Decision and Condition on its face to evidence compliance herewith. Respectfully submitted, David Cronin By his at ey, Brian G.)ta K hon,Esq. SMOLA AUGHAN LLP 21 High Street,Suite 301 North Andover,Massachusetts 01845 (001 13116;vl 2 r i ' 1 i ol C I (new ubcat) N7 2P . (new Pond ) OSUbCat [Reach' ren L nk Prepared b (enter youracom Diagram nname here to '...,__.� ... Pr Y� company }. Printed'1214/2017 `" ti'ydroCAt@ 9.00 stn 01057 @ 2009 HydroCAO Software Solutions LLC cronin cronin Prepared by (enter your company name here) Printed 12/4/2017 H droCAD0 9.00 s/n 01057 012009 H droCAD Software Solutions LLC P Area Listing (ail nodes) Area CN Description f (acres) (subcatchment-numbers) 0.022 98 Paved parking, HSG A (1 S) 0.022 TOTAL AREA Cronin Cronin Prepared by{enter your company name here} Printed 12!4!2017 H droCADD 9.00 s/n 01057 U 2009 H droCAD Software Solutions LLC Page Soil Listing (all nodes) Area Soil Subcatchment (acres) Goup Numbers 0.022 HSG A 1S 0.000 HSG B 0.000 HSG C 0.000 HSG D 0.000 Other 0.022 TOTAL AREA i i i i i I cron1n eronin Type 111 24-hr 9 Rainfall=9,00" Prepared by(enter your company name here) Printed 12/412017 H droCAD®9.00 sin 01057 ©2009 H droCAD Software Solutions LLC a e 4 E Time span=5.00-20,00 hrs, dt=0.05 hrs, 301 points Runoff by SCS TR-20 method, UH=SCS Reach routing by Stor-Ind*Trans method - Pond routing by Stor-Ind method Subcatchment 1S. (new Subcat) Runoff Area=972 sf 100.00% Impervious Runoff Depth>8,05" Tc=2.0 min CN=98 Runoff=0.21 ofs 0,015 of Pond 2P: (new Pond) Peak Eiev=101.89' Storage=0.003 of Inflow--0.21 cfs 0.015 of Outflow--0.06 cfs 0.015 of Total Runoff Area=0.022 ac Runoff Volume=0.015 of Average Runoff Depth =B4O6" 0.00%Pervious=0.000 ac 100,00%Impervious=0.022 ac I i i i 3 cronin cronin Type 1N 24-hr 9 Rainfafl=9.00" Prepared by (enter your company name here) Printed 12/412017 -Hydr-oCAD@9.00 sin 01057 020 —Pane 5 Summary for Subcatchment IS: (new Subcat) Runoff 0.21 cfs @ 12.03 hrs, Volume= 0.015 af, Depth> 8.05" Runoff by SCS TR-20 method, UH=SCS, Time Span= 5,00-20.00 hrs, dt= 0,05 hrs Type III 24-hr 9 Rainfafl=9.00" Area (sf) CN Description 972 98 972 100.00% Impervious Area Tc Length Slope Velocity Capacity Description rain (feet 2.0 Direct Entry, Subcatchment IS: (new Subcat) Hydrograph, 0.2 0.22'�'-, Type III 24-hr 9 0.2:i Rainfall=9.010" 0.18 Runoff Area=972 of 0.16 ,' RunoffVolume=0.015 of 0.14 Runoff Depth>8.05" 0.112" Tc=2.0 min OA CN=98 o.08-,: 0.06" 0.04" OM-- 0 5 6 7 B 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) cronin cronin Type 11124-hr 9 Rainfall=9.00" Prepared by{enter your company name here) Printed 12/4/2017 H droCADO 9.00 On 01057 O 2009 H droCAD Software Solutions LLC Page 6 Summary for Pond 2P: (new Pond) I Inflow Area = 0.022 ac,100.00% Impervious, Inflow Depth > 8.05" for 9 event Inflow = 0.21 cfs @ 12.03 hrs, Volume= 0.015 of Outflow = 0.06 cfs @ 12.35 hrs, Volume= 0.015 af, Atten= 74%, Lag= 19.2 min Discarded = 0.06 cfs @ 12.35 hrs, Volume= 0.015 of Routing by Stor--Ind method,Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Peak Eiev= 101.89' @ 12,35 hrs Surf.Area= 0.006 ac Storage= 0.003 of Plug-Flow detention time= 17.8 min calculated for 0.015 of(100%of inflow) Center-of-Mass dot. time= 17.5 min ( 747.3-729,8 ) Volume Invert Avail.Stora a Stora a Description #1A 100.00' 0.005 of 6.25'W x 16.241 x 3.50'H Field A Z=1.0 0.016 of Overall -0.002 of Embedded =0.014 of x 40.0% Volds #2A 100.50' 0.002 of StormTech SC-740 x 2 Inside#1 Effective Size=44.6"W x 30.0"H=> 6,45 sf x 7.121 =45.9 cf Overall Size=51.0"W x 30.0"H x 7,561 with 0.44' Overla 0.008 of Total Available Storage Storage Group A created with Chamber Wizard Device Routing Invert Outlet Devices #1 Discarded 100.00' 10.000 inlhr Extiltration over Wetted area Qiscarded OutFlow Max=0.06 cfs @ 12.35 hrs HW=101.89' (Free Discharge) 1=Exfiltratlon (Exfiltration Controls 0.06 cfs) E i i I i i i cronin, cronin Type ///24-hr 9 Rain/611=9.00" Prepared by{enter your company name here) Printed 12/4/2017 H droCA� x.00 sln 01057 t 2009 H draCAC Software Solutions LLC Pa 7 Pond 2P: (new Pond) - Chamber Wizard Field A Chamber Model =StormTech SC-740 Effective Size= 44.6"W x 30.0"'H => 6.45 sf x 7.1121= 45.9 cf Overall Size= 51.0""W x 30.0"H x 7.561 with 0.44' Overlap 51.0" Wide + 0.0" Spacing = 51.0" C-C 2 Chambers/Row x 7,12' Lang = 14.24' + 12.0" End Stone x 2 = 16,24' Base Length 1 Rows x 51.0" Wide + 12.0" Side Stone x 2 = 6.25' Base Width 6.0" Base + 30.0" Chamber Height+6.0" Cover= 3.50' Field Height 1.0 '/' Side-Z x Height= 42.0" Flare/Side Base Length + Flare x 2= 23,24'Top Length Base Width + Flare x 2 = 13.25' Top Length 2 Chambers x 45.9 cf= 91.9 cf Chamber Storage 687.9 cf Field - 91.9 of Chambers = 596.0 cf Stone x 40.0% Voids =238.4 cf Stone Storage Stone + Chamber Storage = 330.3 cf= 0.008 of 2 Chambers 25,5 cy Field 22.1 cy Stone Y b crvnin croniin Type !!/24-lar 9 Rainfall=9.00" Prepared by(enter your company name here) Printed 12/412017 H droCADO 9.00 s/n 01057 0 20,05 H droCAD Software Solutions LLC Page 8 i Pond 2P: (new Pond) Hydrograph 0. r IN Inflow M Discarded U2 Inflow res=0.022 ac 0.2 oak Ie1 01®09' 0.18 for =0.003 of 0.16 0.12,::r 0.1 0.08' 0.06 Cfs 0.06 0.04 t 0.02 6 6 7 8 9 10 11 12 18 14 18 16 17 18 19 20 dime (hours) i