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Home My WebLink About1996-10-07 Engineer Review SPR k COL R & / � COLNT1 7 �--Nr--ONEEP5 AI•J[') Septen1ber 10, 1996 Ms, Kathleen Colwell Town Planner 120 Main Street North Andover, MA 01845 RF; Engineering Review Ahport 1•langers Dear Ms. Colwell; At your request, Coler& Colantonio, Inc, l,.as visited the site and reviewed the plans and calculations for the above rufcrenced project. Our review specifically addressed the drainage design and general plan information, This correspondence is a result of the above review and includes our comntent.s on the submittal package. The following documents were reviewed, • A flan entitled"Site Development Plan of Land in North Andover, MA Proposed Aircraft Hangers"prepared for Kingsberry building Teclvlologies, Inc.,prepared by Merrimack Engineering Services dated July 17, 1996, • A report entitled"Drainage Report",prepared for Kingsberry Building Tecltitologies, Inc,,prepared by MeiTimack Engineering Services dated August 2% 1996 We offer the following core monts; I. Tire site is located on the north side of Sutton Street, The parcel is currently developed with an existing airport facility. It is proposed to construct four new aire aft hangers, together with associated paving and utilities. Municipal water and sewer are available. to the site. It is proposed to mitigate for increased runoff from impervious areas by constructing a detention basin, The outlet from the detention basin is proposed to connect to the Town drainage system in Sutton Street, 2, No existing conditions plan or existing conditions subarea plant was provided, A post-dev, drainage area map was .included with the Drainage Report. The Subarea used to develop the drainage analysis indicated in the postwdev. drainage area map is arbitrary and not consistent with subarea limits based on contours in the area. Based on existing contours it appears that runoff'from the site flows north, east and west further into airport property. It appears that very little runoff from the site 101 Acoot-d Park Drive, 3010 0110 617-982.5400 k y ) [13/'tCI F I I:07 I•IU.FGG, pGt_, currently flows to Sutton Street. The analysis represents runoff from the study limits without addressing actual flow directions. An existing catch basin is indicated in access drive to the airport, however, piping from this catch basin is not indicated. The plan should identify where flow from this catch Basin discharges. The drainage area plan should indicate realistic subareas based on topography and indicate runoff flow paths used in development of Times of Concentration (Tc). 3. The calculations indicate that the To is unchanged between pre and post development. We disagree with this assumption. No data was provided to substantiate the assumptions for times of concentration. Typically, pavement and storm sewer piping increase runoff velocities and decrease the Tc which would impact pear runoff rates. In this case the mininium To was used for all cases. It is likely that pre development Tc's are longer, 4. As noted above it is proposed to connect to (he Town storm sewer system in Scatfon Street, Calculations to demonz tratte that the existing street systow has adequate capacity to handle this additional flow should be provided. It appears that virtually no runoff from the site currently enters the street system, therefore, to unfelt pear rates in this dircction wotild be difficult. The ultimate discharge point of the street drainage system should be identified. If the street system discharges to Lake C'ochiuhewick we would recommend not Approving this con ectioin, 5. No test pit data has been provided with the"Drainage Report". This inforinaatioli is ttseft" to compare field a.latiil-l'taition with Soil Conservation.Service(SCS)mapping of the area. In addition, a test pit should bo excavated in the proposed detention basin, Without test pit data it is not known if the proposed detention basins will be in groundwater. The detention basin is indicated as a six foot deep excavation with 2:1 side slopes. Groundwater infiltration in this basin could impact the stability of the side slopes and complicate maintenance of the basin. The test pit in the proposed detention basin should be performed by.9 certified soil evaluator and include information on estimated maxiln.um groundwater elevations in tho area. 6. No detail information was provided on the outlet structure (i.c., orifice and emergeney overflow catch basin). The proposed 4"and G"orifices are likely to be a maintenance problem. Details of bow this structure will be kept clear of debris should be provided. We note than the invert in to the outlet structure is lower than.the invert out which would impact the calculations and result in some :standing writer in the basin, In addition, the caileulations include storage volume below the outlet invert. The calculations should be revised to reflect no storage below the outlet invert, 7. The storni sewer Gaalctilations should be revised to rctlect the impact of water levels in the detention basin on storm sewer capacities, During a 10 ,year storm eveltt the maximuni water elevation is calculated to be El 159.3. All but one of the storm sewer inverts are below this elevation. We also recommend that the minimum Te for storm sewer calculations be S min, rather than 10 min. given the small tributary areas to catch basins, 8, Stonn sewers have been designed in a Catch basin to catch basin arrangement. This design does not settling of sediments in some of the oatch basins, We.recommond that manholes be added to the system to improve sedinlent collection in Catch hmins, 9. A sewer manhole is indicated.near the base ofthe detention basin. This manhole may be subject to inflow duriIlg sigIlificant storm events. We recommend relocating this manhole to the top of or outside basin limits, We appreciate the opportunity to assist the Planning Board on this prgiect and hope (ha[ this iliforiAlat.joli is sufficient for your. heeds, If you have any questions please do not hesitate to contact us, Very truly yours, C'OLER& COLANTONIO, INC:, C.I a�� Johzl C'. C13essia, P.E. xe Merrimack Engineering Services COLER I 2 L ENGINEEHS AND SCIENTISTS October 28, 1996 "77" Ms.Kathleen Colwell Town Planner 120 Main Street North Andover,MA 01845 RE: Engineering Review Airport Hangers Dear Ms.Colwell: At your request,Coler&Colantonio,Inc.has reviewed the new plan for the above referenced project. The previous design,which discharged runoff to the existing street drainage system, was not approved. The plan dated September 25, 1996, indicates a Swale along the south side of the site which discharges on-site west of the proposed buildings. It is our understanding that the September 25, 1996 plan has been approved by the Board subject to certain conditions. The submittal did not include any calculations or narrative on the design. We offer the following comments: 1. A plan indicating the terminus of the Swale should be provided. It is not clear from the plan provided where runoff will ultimately discharge. Reportedly runoff from the site will discharge to the Merrimack River. In addition, it is our understanding that mitigation for increased runoff from proposed impervious areas will not be required on this site. 2. Calculations to demonstrate the capacity of the Swale should be provided. 3. A detail of the proposed Swale construction should be provided. We appreciate the opportunity to assist the Planning Board on this project and hope that this information is sufficient for your needs. If you have any questions please do not hesitate to contact us. Very truly yours, COLER&COLANTONIO,INC. a4-�'�k John C.4Chessia,P.E. xe Merrimack Engineering Services 101 Accord Park Drive,Suite One 617-982-5400 Norwell, MA 02061-1685 Fax:617-982-5490 P C COLER & COLANTON107 Not cnibor 'l, his, Kathleen Colwell Fov'vo Plaimer I M Main street North Andover, NIA 0184: RE: 8uppl( mental Lnginecring Rcvje v Airport I[wigers Dear leis. Colwell: At voiLr request, Coler& Colantonio, file, has pFviewo(f the ncw supplemental information provided for the above referenced project. As you are aware. it is proposed to discharge runoff from the site to a siAale which ultimately discharges to the I'vIerrintack River, It was determined by the Pinning Board that detention cif this runoff would nw be required since the impact would not he significant, Provided the rviioff from the area stays within the limits of the airport property we have no issues with the design. We appreciate the oppoaurtity to assist the Plan.iiing Board on this project and hope tnat this information is ',uffieient for your needs. It you have any questions please, do not Hesitate to contact LIS, Very truly Yours, CMER&. COLANT ONIO, INC. John Ghessia, P1. xe Merrimack Engineehng Services 101 Accord Park Dive,Suile Oiie 61 7-BB2,54UO Nork9pit. MA 02061-i b85 Fax:617-982-5490