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HomeMy WebLinkAbout1997-04-18 Response Comments DEF SUB hDLL �N10 2 t Y r, e•Lat'�:�6 : i'7 l L� FACSIl41LE COVER SHEET To; Kathleeja C alwell Compainy: Town of North Andover Phone: (508) 688-9535 Fax: (S08)68mks From: John Chessia campway_ coler& colantoni a,171c. Phone: (617) 92-5443 Pax: (617) 982.-5490 DaW: December 16, 19rl6 Vag e—�including this �} cover page: 5 �Y b C,uo icy { , C �� Comments. gb a ks�, ReiervnF(7td �Gnte: S, te 0(� [j-V-+-ey- copy to Bellio ain r „d id S i. -'LJLEE t-"' GOLAN .-bmo EA,JGIW_.r,�S 6140 8r-C-N'rl3r3 w.,,cmbt; 16, 1996 plan.,)ing Director j 2 \,ILSin tre�t North Andovor,is 01845 GJ `,4K Eovijieeritig Review Old Comer Gave Proposed SuWivisim Dear Ms.Colw0l: In respomv, Lo you re{hest,Cxylerq Colatuonio..luc..)vas Yevimed tbe-srubut ttul pwlagL for the above referemzd site. ]it tiddiajn,Gwe visited the,site on D-xe-tuber 2, 1996 ro obserye field conditions. The project has been rcTAP-wed for co"fimmunce it,flie reqLfiromEmis of lVe"Rules:and Regulations Governing the SubOvision of LHok]" iri Nwli Oukdo -d o wor a-9 wel: as sianlaj ugine,�,riug practice. The nubmitrA pa,*agc include J the g 19 f)efmi(ivoSubdivi-,iojl Ptan"folw hhmi. daft,-d H/6 6, Prepamd by Now England Bmgiw��ing Ytw- "Pre-do�tlopnwtit drai-u4N- an-me- and "Post-developmcnt JraiaagL -Lxk.,o sbeeLs dqtcxl 1.116196, Piepawd by Nv,-V Hugjaod E non�ring SCrVkt4s. Reports Eatitled 4h Semi= lw. The propomd subdivisimt is on the FAq side-of Tolinson Street,North of Sudan fliA 'Road, wid approximawly 1 r4 mimic south of Nfilh Stwul. Tlm Inod ls currently 011en lawn and meadow. The site slopes front tlte.suueitucst to the iti-xibofrit 7 fffa&. Rmioff front(Ile 5jtk ;UPpeRN to floor to tl)e northeast and conwittm,Ws tit att-,Hxzill li, Hong the --astc.r.y'prop u- ty Oomidwy �D 161 kx;wd Park Dow.:3ui-x,One Q T-4;4)2w4CL- ',Re.C.Li*11 C)3,)c.) SeeM,,o test data has not been provided since the sits will be gmed by mimicip,4 smvwer. A test tit shoidd be po-i-formed. in the dewnt:oa basin. 2. See:ion 3. t3.)1)a.)Refer to Drainago)&slizs bolow. I Section 1. C)3.)j.' Aw Erosion Cowrol Plan has hom providcd in fliz"Stat-c-ment of Envirmaritnufl rMpmV. I'lis ilift-li-juation should ho noted or. die plain— A detail of (jq haybal-.s-.'w erosion protection lias be-u pmvided iii 0*1 plan Slet,lt43_w(-,wr,W1 easoment would be,required ova the Rodengues prop -to inst-M the haybalcs. I t Mle Ktail. The repot 110te's —bistalb-.3 alcmig the 4 Suctioji C.) 3)1_.) Tho plar.,;are draw-)at V­30' vei-mis thereqtdred 1"­410'. 5. Svctioli 3. C.) 3.)1..) The Zoning District identiftoA.L)n for the jmrte(sho-Ad include tttQ %'aWvJwd Distri,�t, It is our anderst9adinp that the site is rk--1 n�m.-any -wotlands w' ich would triggerteyiew ttrder the um-misions of t1w Wallewihk;d DiWicl 6 Section 3, C.) 3,)k.)gg-) Tke plan should indicate eefibjrl iiwskitiow_ VC i,-,unclear wh(,iher the properly 6ong the.,Qtaq(erly side of the site should be PwNjdeJ,,,t&i auk e,, by tl&-, iubdivv-ioii. 7 Sixtioij 1.C.3 3.)k.)i.) Additional easenivjtls should be Provi-Acd till 1h.-t exiLsting fiance , If this se-wx-.r required n�phiccmem 4(id ,4w;w'I A (he,lloTfltwest 1a�711_er_11_Tth_0 par—CF-1 if this i:s7To_,,i_at(A e,m-ron6wenl on LOOSIN wntM N An should also be pmvided for the drop inlot.(in Lot 3 8B-, S. Sxfio-)3. C.)3.)1,,.) k,) rho topographic PIM 51101111 johl-son Street. 'Ale xec4_xmer_d that ilic plans indicate Corr mm-� vnral I q and ci itt,wb5 acrkw; the Tohrson.5treet rig T�011va_v 1), Section .4. C.)3.) L) n's Th-- plans-imuld indicate the TOW af Trqa,��trqq atOOL(Ne v,aswrly i4o of flic situ aw! wi-Ach-reps are to be temiovcd. 11 appears that most o( Nes7tmes will_b,,womoved to accosilmodZe'g)-adinF, V, Section 3. C.)3.)k.",p.) 'Fhe OTORIC Sh(-)Ldjfl i3k(UU111.the CrOSS, 9L.CfirAl of Johnson Stree-.at the enuanc,:-, dire prolile.irtdioaWs a wilical c.itrx.t tit Aw irW.m.O.ior wifli 1011jkStV1 St�-.�et� KO I�.-IIA Ofi 11-A.,curve has K­-m providcd. Jt,is ow!ie.w. that%o The watcr --nml should be in6icaicd on the.plan I ScClion T D.)Sidt.walksart:not kdi4:,itLd on the plan. It i,uncfoar if sidevva'Jks me fe'�Llrcd ior Ellis_size,,�Wndtxds�taii �� ,'coioji S) Propose-d St_-ttot tree shoutc l?o iwflcnfind on ate.pka I)& 13- Section 1. 14..)1.)k',�]Qlx,eammient is required along the easterly silo orthe road 4xheve the g I(I P V.C..-,-'reds 4-1. 14 Scojov 7.N)4.) bxsh)n. nianholearfmigm-amt should be u;ed raher*mn lijildiig all the catch bosim. to atkfitioij,it dcWjl of Ahe crop ic-letsbouk; i c proAded, CY) Deirtik ofll-e Leadviall should he proMed. ,6 SmJimn 7,N.) 5.) Nrjilafl swzle wx-3 o-)servc-d on our site visit along the eust;ixiy us property bomiy,n Vve that ti , le he i(denti fied and that LIC &,w-hargc kwould miaimixe ji-OFICTS 10 Twin.-Prope"t, 17 Wc rocoinmend that pucinew radii be in dicaied on Ili e plan F(111C i7)1tT'SVC-1i13r1 %J 1.11 '1t4mg(m, Sirm oTic. -it the cul de sac. IR Sp.,itgindes oraddiljonM lopoguapIlLy ih--)tjld lac.tr-Ouacd (f)dfu-ju-mijuiv lit,;( roadv.►% --w-i flkm iiito the drik,eway oiTot.18A. 0 Subarca rian-s.-Could imlicare the ofbilc area upgrlidietit of the-siw. vulijOl ,,611 ci nin'buiv. flow to 6e LIAL,116ovl b&sii)and Su"Im Sever -Ywem. J.111PE.'rjI IhQ flood ele"'atiou"Ind '111erafilin oc 014 de-t-'-sition -rmiill. VU-11011 C111vt-- wxd ive oillisep"aliYt ITI Sanx(.Lust"s. "T"lis msOS In a.latgr1 ion b)qir) than may 1?z;nt--cenvry, include sdleet flow 'cagos orkwu 100 t�O, Muml[',00imccs,Conc;r--ivv(iix SejLVj('e lelig-ill or. o (0 100 foot is Lypical inilew Lugl= , 'N':modi-lt:Aioll w-uld rtt':;rt'l Ig? so-me.-o-h-il Mgtvn-pmk runoff niu,. 11. C<Jtvujafirw, 1111�dc.l dl,dvAention basin oukta3 an onCim'Alt o,P x( .4- jtdd be LY141JUlk-d OS a udvorL or :he dx1it-p-, tjvYJifbd to Nilcetan on1kc condition, In adTi—ti�,,inlhc�csigpi s�xould firm,—Ck—A The de.wntion ba.�:a demi I-jadic-aieN a L)E-n.�At4 I�{ixtee Z,�fkdwrali ie-1-11�11111 I 5i 11�10 11 in tomo,nwws. Wo,rccomim-nd that ddention Nsit, jikcs h(,, jt�,:jigncii c4jrj,,,rN(mi v":1-, in ASUI.,. M is 31-Ij RUIVOTIS Of Pmck ,'K(). 77-D"igi) acKJ OmEtruclion A Urban Sturiuk-Nwer qjilhwuy Shoild be-,iml u Pn.�S a 100 ycilr ooril., with th'! 111-AMU11 AAJ(tdt r.Wg Od- (4) C[Clmslistr,ItLl this f-arm.uify :hnuld we ZpprQ-6-3LIC tie r-ppoillivi(v to a"i-I tho P ARF1111 . R vr ( jl,MI.; fn�jv,�.i lupv 0 11 ru QT tbt del3jg-ki"'T IV,I Ill-tst 1( L:119� t h I I)MWO at VOW'C On Veni.MCC. if you h a ve an P.4°.L c dc"not.Uz,l aic t.., ..I,. STi I A I'ON rO I Lil ILI r ^ I 0!1 ® 1 ENGINEERS AN[] SCIENTISTSi- I January 21, 1997 Ms, Kathleen Colwell Planning Director 120 Main Street North Andover, MA 01845 RE: Review/Response Robert M. Gill letter Old Center Lane Proposed Subdivision Dear Ms. Colwell: In response to your request, Coler& Colantonio, Inc. has reviewed the letter dated January 6, 1997, written by Mr. Robert M. Gill, P.E, P.L.S. The letter was prepared by Mr. Gill on behalf of the Roderiques' abutters to the proposed Old Center Lane subdivision. The issues raised by Mr. Gill with our assessment of the issue are as follows: I. Cut de sac grade. The proposed cul de sac would be at a six percent grade. We agree that the earthwork proposed is significant, especially for a cul de sac of this size. The proposed design does comply with the Rules and Regulations. The side slope of 2:1 will be a nuisance to maintain and in fact will probably be left to grow since, the homeowner is unlikely to maintain the slope. 2. Detention Basin. We agree that guard rails should be provided at the cul de sac and along the entire length of the 2.1 slope. The proposed outlet is a potential erosion problem at the elevation proposed. The design should accommodate erosion protection at the outlet. Additional information to demonstrate protection from erosion at the outlet should be provided. 3. Runoff. The proposed design will alter runoff patterns adjacent to the Roderiques property. Based on our site walk, it is unlikely that surface runoff is significant along the upper limits of the Roderiques property. We did observe a small swale at the rear of the lot which did discharge to the Roderiques property. Our review letter recommended that this swale be located on the plans and that the design be modified to discharge to this point. It is unlikely that the site could be designed to exactly match existing conditions. Directing runoff from the detention basin into the existing swale would minimize impact to the abutting property. There is potential for soil 101 Accord Park Drive, Suite One 617-982-5400 Norwell, MA 02061-1685 Fax: 617-982-5490 1 y + r - 3 erosion to occur if the construction is performed in a careful manrier,which would impact the Roderiques property. E 4. Creation of Wetlands. We recommended that a test pit be excavated in the proposed detention basin location to determine the seasonal groundwater table. It is not known at this time whether the detention basin would become vegetated with wetlands species, however, a four foot cut is proposed at the bottom of the basin which may intercept the seasonal water table. Detention basins do not necessarily become wetlands. In this case there is insufficient information to determine if it is likely to become a wetland. We recommend that the basin be constructed above the seasonal water table if it is critical to prevent wetland vegetation form becoming established. If the basin intercepts the groundwater table the flow offsite would likely be constant through the high groundwater season, which could result in the creation of wetlands on the abutting parcel. The Planning Board should request that the applicant address the issues raised by Mr. Gill. In areas where the plans conform to the Planning Board regulations, it would be at the applicant's discretion to implement the requested change. The stormwater system design may require modifications to comply with our recommendations as well as Mr. Gill's concerns. The suitability of the site for infiltration of runoff should be determined, since this would likely result in the design closely conforming to existing conditions. We appreciate the opportunity to assist the Planning Board on this project and hope that this information is sufficient for your needs. We would be pleased to meet with the Board or the design engineer to discuss this project at your convenience. If you have any questions please do not hesitate to contact us. Very truly yours, COLER & COLANTONIO, INC. IJW,IinXl.' Chessia, P.E. 1 Olc� Csd1\er Lr i COLANTONIOZ ENGINEERS AN"SCIENTISTS - - i February 13, 1997 Ms. Kathleen Colwell Planning Director 120 Main Street North Andover,MA 01845 RE; Engineering Review Old Center Lane Proposed Subdivision Dear Ms, Colwell: In response to your request, Coler&Colantonio, Inc. has reviewed the revised submittal package and response letter for the above referenced site. The submittal package included the following information: Plans Entitled: s "Old Center Lane,Definitive Subdivision Plan"four sheets dated 11/6/96,Prepared by New England Engineering Services,,Inc.,revised 1/30/97. + "Pre-development drainage areas"and"Post-development drainage areas",two sheets dated 9/20/9G, Prepared by New England Engineering Services,Inc. Reports Entitled • "Stormwater Management Report",Prepared by Hayashi Corporation, dated 1/28/97. This correspondence follows the numbering sequence used in our initial review of the Definitive Plan and responds to the letter submitted by New England Engineering Services dated Jan. 30, 1997: 1. Section 3. C.)3.)c. Reportedly a test pit bas been excavated in the detention basin. The test pit location should be indicated on the plan and the test pit log included within the information provided. The groundwater depth is indicated as 22 inches below grade. It is likely that seepage will be a problem at the south end of the basin where a six foot cut is proposed. The design should address this concern. We also note that wetland vegetation will likely develop in the basin which is a concern for an abutter and has been a concern of the DPW on previous submittals. 2. Section 3, C.)3.)d.) Refer to drainage issues below. 3. Section 3. C.)3.)k.) An unlabeled line,which appears to represent the erosion control measures, is indicated on the plan. This line should be labeled. A detail of haybales for erosion protection has been provided in the plan set, however, an easement would be required on the Roderigues property to install the haybales consistent with the detail. 101 Accord Park Drive, Suite One 617-982-5400 Norwell, MA 02061-1685 Fax:617-982-5490 4. We recommend the Planning Board address this issue. We have no difficulty with the proposed scale. 5. Section 3. C.)3,)k,)b. Satisfactory. 6. Section 3. C.)3,)k,)g. Satisfactory regarding stationing. We recommend the Planning Board address the issue of a through connection. 7. Section 3. C.)3.)k.)i. Satisfactory. 8. Section 3. C.)3.)k.)k. Part of the requested information has been added. 9. Section 3. C.)3.)k.)n. Spruce trees are indicated on the plan. Grading as indicated would impact most of these trees except the last eight at the south end of the site. 10. Section 3. C.)3.)k.)p. The profile should indicate the cross section of Johnson Street at the entrance. The profile indicates a vertical curve at the intersection with Johnson Street. The data on this curve is insufficient. Information should include PVI station and elevation, grade into the vertical curve, K value to evaluate stopping distances as well as the data for the leveling area, It is unclear if a waiver from the requirements was requested for the profile of the water main, The plan does not appear to comply with section 7. 3, b. Note that the grade in Johnson Street is just over 6% at the intersection. 11. Section 7.D.) Planning Board to address the sidewalk issue. 12. Section 7.E,)S. Proposed street trees as shown on plans appear to interfere with the sewer force main. A detail should be included showing offsets from the sewer force main and the location of the trees. A tree staking detail should be included in the plans. 13, Section 7, H.)3,) Satisfactory. 14. Section 7.N,)4,) Satisfactory regarding layout. A detail should be provided showing a drop inlet. It does not appear that this inlet will function as intended. Based on the topographic plan, runoff is not directed to the drop inlet, The easement does not appear to allow adequate space for future repairs 15. Section 7,N.)5.) Headwall detail does not adequately describe dimensions, 16. Section 7.N.)S.) Swale at outlet is not clearly indicated. The letter states the addition of this existing swale but it is not shown on the plans. 17, Satisfactory. 18. Not addressed, Drainage Issues: 19. Revised subarea plans were not provided with the latest submission. 20. Satisfactory. 21. Satisfactory, 22. More information should be submitted for the trash grate. Specifically opening size, bar size, etc. We recommend trash grates be sloped to minimize clogging, 23. The width of the maintenance drive around the detention pond as shown on the plans is not consistent with the details in the report. The plans should be modified to reflect the details in the report. Access from Old Center Lane to the maintenance drive should be shown on the plans. 24. Not addressed. 25. Section 7.N.) 11. The velocity in reach 5 exceeds 10 fps. Other Concerns: 1. A guard rail is now shown adjacent to the detention basin. The guard rail should be extended to station 1+00 on Old Center Lane. This guard rail should be clearly labeled on the plans and a detail should be added to the plans, 2. Calculations for the size of rip-rap should be submitted. 3. Grading is incomplete at the level lip spreader. All grading should be shown to assure the level lip spreader will be constructed within the proposed subdivision property line. Drainage Report: 1. The drainage structure summary table should be updated to reflect catch basin to manhole configuration. 2. Time of concentration data table: The description for shallow concentrated flow in subcatchment area 3 should have the same description as subarea 5. We appreciate the opportunity to assist the Planning Board on this project and hope that this information is sufficient for your needs. We would be pleased to meet with the Board or the design engineer to discuss this project at your convenience. If you have any questions please do not hesitate to contact us, Very truly yours, COLER&COLANTONIO, INC. a John C, Chessia, P.E. cc: Benjamin C. Osgood, Jr.,President 03i 1 o/97 16:47 h f]. 1 1 D 2 COLPR COL/ NTON10 z ENJGhVEEFIS AN U-1 eCIElVT:sTs March 18, 1997 Ms. Kathleen Colwell Planning Director 120 Maid Street North Andover, MA 01845 RE,, Engineering Review Old Center Lane Proposed Subdivision Dear Ms. Colwell; In response to your request, Coler & Colantonio, hie. has reviewed the revised submittal packuge and response letter Cor the above referenced site. The submittal package included the following information; Plans Eliti-rled: • "Old Center Lane, Definitive Subdivision Plan" three sheets dated 1116/96. Prepared by New England Engineering Services. Inc., revised 31*97, • 'Yre.development drainage areas' yid"Post-development drainage;areas", two sheets dated 2126/97, prepared by New England Engineering Services, Inc, Deports Entitled "Stormwater Maziagement Report", Prepared by Hayashi Corporation, dated 2/26/97. 'Phis new set tii'plans has been revised itorn the original concept of how the lots will he accessed. We reference New Fngland Engineering Services, Inc., letter dated March 8, 1997 which describes the proposed 20' wide private access drive and all waivers ],tieing rearrested. Our review will concentrate on issues other than tho reC Uested waivers, It is our understanding that the Planning Board will review the requested waivers. 1. Section 3, C.) A test pit has been excavated in the area of the proposed detention basin. The test pit location is shown on the plans and the test pit log has been included with the March 8, 1997 letter. The groundwater depth is indicated as 22 inches below grade. It is likely that groundwater will discharge; into the lowest elevations of the basin due to the proposed 2.8' cut. We do not tziitieipate slope 03/120/9? 09:40 NO, 164 002 stability problems since the groundwater level is close to the bottatn elevation of the basin, We also note that wetland vegetation will likely develop in tl e basin which is a concern for aal abtttter and has been a concern of the L)I'W on previous submittals, 2. Section 3. d.) Refer to drainage issues below, 3, Section 3. k.)g. Stationing has not been provided on the plans 4. Section 3. k.)p. A proiile of the proposed street has not been included in the plans, 5. Section 7, E,)5. A detail should be included for street trees showing offscts from the sewer force plain. A tree staking detail should be included in the {Mans, 6, We recommend that pavement radii be iodicated on the plane at the Inters, cfaion with Johnson Street and along other roadway curves. 7. Erosion control nAeasures should be shown around the catch basins. Drainage Issues: 1, Section 7.N,)4,) We recommend a catch basin to nlauliole configuration which connects to C,D.91 in-lieu of the rip-rap s%vale which directs runoff tiiom Olt! Center Lane to the detention basin, 2. T.liere appears to be a typographical error dcscrlbitlg the invert outlet for the 6" DIY, y. A catch basin detail should be included in the plans. 4. The drainage casement should be shown to include the detention pond and all access roads. The drainage eitsemen.t bowidary should be adjusted and run from the existing point adjacent to the stone wall to a point located on the wastcrly most point on the lot 33A driveway. A proposed .street tree adjacent to the lot 38A driveway should be removed for access to the outlet, The grading north of Old Center Lanc between. contour 268 and 266 shoLdd be revised to show an access way to the detention basin outlet, 5. Section 7. N,)5.) The outlet from the detention pond is currently Shown as a pipe coming out of the side slope of the basin., We recommend a headwall be provided with a trash grate over the outlet, We also recommend that the mattltole be located a l'ew feet south with a catch basin grate in-lieu ol'the solid cover and a rim clevation of 259.0. 6. Calculations for the size of rip-rap should be submitted. �7, The drainage report should be stamped and signed by a P.E, R The drainage calc-ulations for the detention basin have been modeled incorrectly. The model assume an orifice control at the detention basin although it is actually a pipe culvert. In addition, the model uses reach routing from the "orifice" to lull-1#4. These assumptions are repeated from MH#4 to the level lip spreader. Reach rooting in HydroC:ad, the model used, is limited by using Manning's equation which does not r 11*3/12/97 16:49 Flo. 151 904 i account for surcharge, Outflow is limited to the nianning's pipe capacity in this model. For a pipe culvert outlet the Flow entering the pipe and the flow exiting the pipe would be essentially the sarne, especially 101- the short pipe lengths i i this system. The calculations indicate that the eight (8") ooItlet pipe from the detention pond has an inflow of 3.6 cfs during the 100 year storm and an outlet flow of 1.9 cFs. This would not be the case for this system. This 1-low reduction also occurs in the six inch pipe. We would assume flow continuity thrOUghnut the pipe or an increase in water elevation. Roach routing in HydroCad does not accommodate an increase in the;flood elevation in the detention pond due to a flow restriction in the pipe. The design also includes a smaller pipe leaving the manhole, i.e. 6" diameter that the eight inch pipe leaving the detention}pond. based on the design, we would assume the Six (6) inch pipe would control the flow out or the detention basin. The model does not reflect this condition. We appreciate the opportunity to assist the Planning Board on this project and Dope that this information is sufficient for your needs, We would be pleased to meet with (13e Board or the design engineer to discuss this project at your convenience. If you have ally questions please do not hesitate to contact us. Very truly }tours, f'l?l TR &. (`nT.ANTtINK), / John C Chessla, Fx. cc: Renjmnin C. Osgood, X, President NO. 151 [?02 L)dc U b,2 -A, 5 1-40q Pi e-OA)cre�rkf dv- 0161-i-e C.eAlrew &APC e,dy Planning Director e0K4,"4++5>t6N,ed, 0Aj4-*Lkz 120 Main Street North Andover, MA 01845 OL66 RE: Engineerbl,$, Review Sob Ch vtsmv Old Center Lane proposed Subdivision Dear Ms. Colwel); In response to your request, Coley & C01antOniO, Inc:, hats reviewed the revised submittal package and response letter Jbr the above referenced site. The submittal package included the following information: Plans Entitled: • "Old Center Lane, Definitive Subdivision Plan" three sheets dated 11/6/96, Prepared by New England Engineering Services, Inc., revised 3/4/97, • kYre-development drainage areas' and "Yost-development drainage areas' , two sheets dated 2/26/97, Prepared by New England Engineering Services, Tile, Repotis Entitlod ;'S(ormwater Nimagement Report", Prepared by Hayashi Corporation, dated 2/26/97, '111is new set ol'plans has been revised Itom the original concept of how Tile lots will he accessed. We reference New Frigland Engineering Services, Inc,, letter dated Match 8, 1997 which describes the, proposed 20' wide private access drive and all Nvaivers being requested. Our review will colicenuUte 011 issues other than the reqUeSted waivers. It is our understanding that the Planning Board will review the requested waivers. 1, Section 3. C.) A test pit has been excavated in the area of the proposed detention basin. 'I'lle test pit location is shown on the plans and the test Pit leg has been included,,vith the Miuch 8, 1997 letter. The groundwater depth is indicated as. 22 inches below grade. it is likely that groundwater will discharge into the lowest elevations of the basin due to the proposed 2X cut. We do not anticipate slope 03/210/97 09:40 NO. 164 P02 stability problems since the groundwater level is close to tlxe bouotn e;lcvation cat the basin. We also note that wetland vegetation will likely develop in the basin which is a Witcern for wi abutter and has been a concern of the L PIM On previous subminaals, 2. Section 3, d.) Exeter to drainage issues below. 3. Section 3. k.)g. Stationing has not been provided can (lie plans 4. Section 3. k.)p. A profile; of the proposed street has not been included in the plans, 5, Section 7, E.)5. A detail should be included fur street trees showing offsets front the sewer force main, jl tree stacking detail should he included in the plans. 6. We recommend that pavement radii be indicated on the plans at the: intersection with Johnson Street and along; gather roadway curves. 7, Erosion control measures should be shown arotuid the catch basins. Drainage Issues; 1, Section 7. N.)4,) We reccamtjje:nd a catch basin to manbole configuration which connects to C.B.91 in-lieu of tfte rip-rap swale which directs runoff From {old Center Lane to the detention basin. 2. There appears to be a typographical error describing the; invert outlet for the 6" DIP, 3. A catch basis, detail should be included in the plans, 4, Tlie drainage easement Should be shown to include the detention pond and al access roads. The drainage omeme:nt boundary should be adjusted and run from the existing point adjacent to the ,,,tone Wall to a point located on. the 4vestcrly most Point an the lot 38A driveway. A proposed street tree adjacent to the lot 38A driveway should be removed for access to the outlet, The grading north of Old Center Lcuic between contour 268 and �266 should be revised to show an access way to the detention basin outlet, 5. Section 7. N,)5.) The outlet from the detention pond is currently 5boN n as a pipe coming out of the side slope of the basin. We recommend a headwall be provided with a trash grate over the outlet, We also recommend that the manhole be located a few feet south with a catch basin grate in-lieu of the solid cover and a rim elevation of 6, Calculations for the size of rip-rap should be submitted, 7. The drainage report should be stamped and signed by a P,E. R. The drainage calculations for the detetitic n basin have been modeled incorrectly, The, y at the detention basin although model, assume all orifice coA�.taY h it is actually a pip l i g culvert. In addition. the model teas reach routing tiom the "orifice" to Ml-i#4. These ,Assumptions are repeated from MH#4 to the level lip spre:adcr, Leach routing in HydroCad, the model used, is limited by using Mannl.ug'S equation which dies not n3/1 s 7 15.49 NO. 151 U04 i I Z10eO«nt for surcharge. Outilow is limited to the manning'.", pipe capacity in this model. For a pipe culvert outlet the flow entering the pipe and the flow exiting the pipe would be essentially the same, especially fir the short pipe lengths in this system. The calculations indicate that the eight(811) cxE(let pipe from the detention pond has an inflow of 3,6 efs during the 100 year storm and Lin outlet flow of 1.9 cks. This would not b6 the case for this system, This flow reduction also occurs in the six inch pipe, We would assume flow continuity thrOLIgIlmut the pipe or an increase in watcr elevation, Reach rooting in HydroCad does not acc(rnmodate an increase ill. the flood elevation in the detention pond due to a flow restriction in the pipe, The design also includes a smaller pipe leaving the manhole, i,e. 6" diameter that the eight inch pipe leaving the detention pond. Fused on the design, we would assume the six {6) Inch pipe would cmltrol the flow out of the detention Basin. The model does not reflect this condition. We appreciate the opportunity Lk) assist the Planning Board on this project and hope that this information is sufficient for your needs. We would be pleased to meet with the Board or the design engineer to discuss this project at your convenience. If you havo any questions please do not hesitate to contact us. Very truly yours, C01,FR & cnT.ANTC_}NIO, INC". / Jolul C., Cllessla, Fx. CC' Benjwnin C. Osgood, in, President i , i i� 1 r r;i 1 1' +)!; ! �`• � � is ,a r .,.. ! , rr". 41 'i!, li�, i11t-- I ,`I I•s l'_, � •. .i ..,, I+..rl: .11..+. i• i,ll ! fr Iyl :i ;11' � !"�'.I,L } r . '�!' , �l _ r. �, 11< u lu LU y 04/16/97 16;4�, . I COLER & ENGINEERS FACSIMILE COVED. SHEET To: Kathleen Colwell Company: 'Town of North Andover Phone: (508) 688-9535 Fax: (508) 688-9542 From: John Chessia Com any: Coler & Colantonio Inc. Phone: (617) 982-5443 Fax: (617) 982-5490 Date: April 16, 1997 Pales including this Cover page: � commebts: Kathleen; T have revjlewed the Old Center Lane file and recommend a 15 inch pipe at tho Sallie slope 21% as proposed for the S inch pipe. This pipe Nvill have the capacity to pass the peak 100 year inflow easily, If they want to route the flow through the outlet manhole to justify a 12 in(;la pile t1lis is also acceptable. I have di8:used Stop and Shop at length with Bob Daley at Merrimack Engineering and t think we are making progress. As we disoussed. he is generating graphs to compare the site outflow with the stream flood lcvols to allow us to come to agreement on a tailwater elevation for the various sterns events. When the, tailwater elevation is agreed upon the calculations can then be generated!to check the peak rates, I'll keep you posted on our progress.