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Home My WebLink About2021-03-16 4th Stormwater Peer Review Horsley Witten Group ' r, � � Sustainable Environmental Solutions 112 Water Street-611 Floor•Boston,MA 02109 857-263.8193•horsleywitten.com g� June 24, 2021 Ms. Jean Enright, Planning Director Planning Department Town of North Andover 120 Main Street North Andover, Massachusetts 01845 Ref: Fourth Stormwater Peer Review 419 & 435 Andover 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 fourth review of the Stormwater Management Report and Site Plans for the proposed development at 419 & 435 Andover Street, North Andover, MA. The plans were prepared for Crosspoint Associates (Applicant) by Bohler Engineering. The project proposes the redevelopment of a portion of the 2,68-acre parcel that currently consists of two existing buildings and two parking areas. HW understands that the Applicant conducted soil testing during the initial site clearing, and it was determined that the seasonal high ground water was higher than expected. The Applicant redesigned a portion of the stormwater system to provide the required 2 feet of separation from the bottom of the stormwater practice to the estimated seasonal high groundwater (ESHGW) elevation. The following additional documents and plans were received electronically by HW associated with the modified stormwater system: • Supplemental Drainage Package for Proposed Commercial Redevelopment, prepared by Bohler Engineering, dated June 10, 2021 (56 pages), and • Proposed Site Plan Documents for Crosspoint, 419 & 435 Andover Street, North Andover, Massachusetts, prepared by Bohler Engineering, dated October 22, 2020, revised June 10, 2021, which include: o General Notes Sheet C-102 o Demolition Plan C-201 o Site Layout Plan C-301 o Grading and Drainage Plan C-401 o Utility Plan C-501 o Soil Erosion & Sediment Control Plan C-601 o Erosion and Sediment Control Notes and Details C-602 o Landscape and Materials Plan L-100 o Landscape Notes & Details L-101 o Lighting Plan L-200 Hors leyWitten.com (4?HorsleyWilienGroup Horsley Witten Group, Inc. Town of North Andover June 24, 2021 Page 2 of 4 o Irrigation Plan L-300 o Detail Sheet C-901 o Detail Sheet C-902 o Detail Sheet C-903 a Detail Sheet C-904 o Detail Sheet C-905 o Detail Sheet C-906 o Boundary & Topographic Survey (Control Point Associates, Inc., 10-22-20) Modified Stormwater.Design Peer Review The Applicant has reconfigured the subsurface infiltration system located in the northern corner of the parcel. The approved plan dated December 2020 included one StormTech SC-740 chamber system consisting of 56 chambers with the bottom of stone elevation set at 199.60. The subsurface system discharged to a level spreader f infiltration trench located adjacent to the north property boundary with the top of stone elevation set at 201.0 as well as a secondary overflow to a riprap spillway at the north corner of the parcel set at elevation 206.5. The revised design dated June 2021 includes two subsurface infiltration systems. Cultec System-01 is in a similar location as the approved system, consisting of 99 Cultec R-150XLD chambers. The bottom of stone is set at 202.75, the ESHGW elevation is at 200.75. The modified subsurface system discharges in the same manner as the approved design, to a level spreader 1 infiltration trench located adjacent to the north property boundary with the top of stone elevation set at 201.0 as well as a secondary overflow to a riprap spillway at the north corner of the parcel set at elevation 206.5. Cultec System-02 is located closer to the western property boundary, consisting of 65 Cultec R-150XLD chambers. The bottom of stone elevation is 203.25 and the ESHGW is at 201.25. Cultec System-02 discharges through an outlet control structure into Cultec System-01. The discharge rates of the modified design are reduced slightly from the approved design. The difference between the peak elevations of the approved design during the 100-year storm event compared to the modified design are negligible. During this peer review process, HW questioned the elevations listed on the outlet control structure details provided on Sheet C-904. In discussion with Bohler Engineering it was determined that there were a few mislabeled elevations. The correct elevations are provided below. HW has reviewed the Plan set and the HydroCAD model and agrees that the modified design will provide equivalent stormwater management for the proposed development. HW recommends that Sheet C-904 is corrected with a revision date to avoid confusion during construction. K:111roleets12O13118065 N Andover On-Cal[II8065T 4l9 Andover St\Repor6210624_4th Peer Rcview 4l9 Andover Street.docx t Town of North Andover June 24, 2021 Page 3 of 4 F IEC'a6°.,T A�kh�iC4L 4{�t�fl.ETFr1Trt�"�Y•_ I t,1AWLCJJTLLTT"r'E '" / t.�JTLFr'At 0WT,,L, R.'MF1FV.=tiTI$ t _ G low(xi3 Hk1E•'Vl — \ �� 55fT2Y�hta SrRLVUAr_T v6Fi"iOva, __,��~, —�i"t l�,Y T�P�I�I NALLlr,rk Co 2t yS'ATr kT� 4i CtA'\�TI��'S hTJ<�.klS ;. I�A'cmv t$I ri. .a't�, - !i'P i T[fir 1GE F FIOM SYSTf,= ) 'li'�.FL Vi jQVTy,;W/ . i OUTLET" CONTROL STRUCTURE (OCS-1) H T.5 1(:\Pro.jects1201311 n0G5 N Aiidover On-Ciil ll18065'1'419 Andover Stlltepott121 OG24 411i i'eer ltevie�%,419 Atidciver Street.docx Town of North Andover June 24, 2021 Page 4 of 4 $y rcfr."UT FIST r �c>�firetal:wt�c+t 13'ONCQJTL€111;i c}UFLIT1SE tYe F rt- ..................... Y��;t vr�tl �C1J�� _T4i'ErEY.�i�7570-- IE,`!_ZLEY.IC�E---- ��____. �r r-- -- _ 1�`G4�F1„E4�5E�itYflll OURETMI11WAAA A"Cl :R --------------------- -------------- WAt L TZ.VRRVTO rpgT91iyra S1A11r:T Ar XMMQV" MtAl-mlCM1,( E,hS � Ltiy,f4Ev.{nli4t4iIS All+p�tS — -- - --------------- �i FYAF��4 OMET CONTROL STRUCTURE (OCS-2) Conclusions HW agrees that the proposed stormwater design is equivalent to the approved design. Please contact Janet Bernardo at 508-833-6600 or at jernardo@horsleywitten.com if you have any questions regarding these comments. Sincerely, HORSLEY WITTEN GROUP, INC. Janet Carter Bernardo, P.E. Associate Principal KAl1rojects120l M l8065 N Andover On-Ca11118065'l'419 Andover Stlltelro!t1210624.4tti Peer Review 419 Anddover Streel.docx