Loading...
The URL can be used to link to this page
Your browser does not support the video tag.
Home
My WebLink
About
2020-01-27 Modification Approval - Decision - 137 ANDOVER STREET 6/25/2021
I • I 6/29/2021 Town of North Andover Mail-Fwd:Modification Approval Massachusts r Jean Enright<jen rig ht@northandoverma.gov> Fwd: Modification Approval Amy Maxner<amaxner@northandoverma.gov> Fri, Jun 25, 2021 at 127 PM To: Jean Enright<jenright@northandoverma.gov> FYI ---------- Forwarded message--------- From: Amy Maxner <amaxner@northan dove rma.gov> Date: Fri, Jun 25, 2021 at 1:36 PM Subject: Modification Approval To: Jim 8orrebach <jborrebach@ohiengineering.com>, Josh Hasenfus <jhasenfus@thetrustees.org> Cc: Jaime Phelan <jphelan@northandoverma.gov> Hi Jim and Josh... See attached. Josh, my Assistant Jaime will send the original document out to you early next week. Thanks —Amy Amy R.Maxner Conservation Administrator Town of North.Andover 120 Main Street North Andover, MA 01845 Phone: 978-688-9530 Fax: 978-688-9542 Email: amaxner@northandoverma.gov Web: www.northandoverma.gov Amy R.Maxner Conservation Administrator Town of North Andover 120 Main Street North Andover, MA 01845 Phone: 978-688-9530 Fax: 978-688-9542 Email: amaxner@noilhandoverma.gov Web:www.northandoverma.gov #242-1764-Modification Approval -Stormwater Basin.pdf 699K https://mail.google.com/ma it/u107i Wo2eff6265&view=pt&sea rch=all&permmsgid=msg-fl%W 703561282147261150&simpl=msg-f%3A170356128214... 1/1 h i' f CONSERVATION DEPARTMENT Community Development Division MODIFICATION TO ORDER OF CONDITIONS DEP FILE #242-1764 Stevens Coolidge Place,Trustees of Reservations Chickering Road/Andover Street,North Andover,MA At the June 23,2021 meeting, the North Andover Conservation Commission(NACC) considered a request for modification to the existing Orden of Conditions, DEP File #242-1764 as submitted by Jim Borrebach, PE of OHI Engineering, Inc. on behalf of the applicant, pursuant to the following documents: • Letter prepared and signed by OHI Engineering, Inc. signed by Jim Borrebach, dated June 11,2021, detailing proposed modification to the stormwater basin; • "Grading& Drainage Plan,Site Plan Chickering Road (Route 125),Cl", prepared by OHI Engineering, Inc., signed and stamped by James Borrebach, PE,scale 1"=40', dated June 11,2021. • Table 1,Stormwater Peak Rate Summary; Routing Diagram for Post- Development Basin Modifications printed May 25, 2021; HydroCad Stormwater Calculations printed May 25, 2021; • Stormwater Operations &Maintenance Plan Stevens-Coolidge Place - prepared by OHI Engineering, Inc. dated June 21, 2021. For the following modifications: The applicant proposes to: Install a sediment foxebay at the inlet of the basin to remove TSS. Regrade the bottom of the basin up to elevation 206,1. Core a 4-inch diameter outlet hole into the face of the outflow structure at elevation 206.1 - this will avoid significant/permanent standing water in the basin. Increase the perimeter basin berm to elevation 209 to increase freeboard above the 100-year flood elevation. Install a stone lined emergency overflow/spillway on the westerly side of the basin, Install a rip-rap lined swale and level spreader off of the existing rip-rap outlet to direct water to the west and avoid flows going to neighbor's backyards on Old Village Lane, This work will remain outside the 25' No Disturb Zone. After due discussion and consideration, the NACC unanimously voted to approve the modification as presented,subject to continued compliance with the Special Conditions issued with the Order. 120 Moln Street,Norlh Andover,Mussucliuselts 01845 Plione 970.608.9530 Fox 978.688.9542 Web www.nortliundovermo.0ov CONSERVATION DEPARTMENT fommunity Devolopment Division Modification to Order of Conditions --Modifications to Storrnwater Basin The NORTH ANDOVER CONSERVATION COMMISSION voted to approve a Modification to the Order of Conditions for; Applicant: The Trustees of Reservations Project Location: 137 Andover Street/0 Clricicerirrg Road,--„Stevens,Coolidge Place.,,_ DEP File #: 242-1764 Issued by the NORTH ANDOVER CONSERVATION COMMISSION. Signed by Amy R. Maxner, Conservation Administrator as authorized by the North Andover Conservatio Commission—See E.R.D. Book: 16327 Page: 22 Amy R. Maxner, Vonse�vatton-LAdmijiVratfart�' Albert Manzi,Jr. Sears McDonough Louis Napoli Jack Mabon Tony Capachietti Date Issued: June 23, 2020 120 Multi Street,Borth Antlover,Mussuchusotts 01045 Phono 978.668.9530 Fax 978.688.9542 Web www.northantioverma.0ov 12/2/2020 Town of North Andover Mail-Modification Request NORTH ANOOVER MaSsachusl�ts Jean Enright<jenright@northandoverma.gov> Modification Request Jean Enright <jenright@northandoverma.gov> Wed, Dec 2, 2020 at 7:31 AM To: Josh Hasenfus <jasenfus@thetrustees.org> Hi Josh, Reconstruction of the existing swale was conditioned in the approval. Redirecting discharge to the newly constructed riprap apron at outlet structure limits disturbance that would otherwise be required in the wooded area and is considered an insubstantial change. I also consider excavation of soil and import of crushed,washed stone in order to resolve slow infiltration rates an insubstantial change. This proposed change does not require a submission to the Planning Board. Jean [Quoted text hidden] I Sincerely, Jean Enright Planning Director Town of North Andover 120 Main Street North Andover, MA 01845 Phone 978.688.9533 Fax 978.688.9542 Email: jenright@northandoverma.gov Web: www.NorthAndoverMA.gov id:imageOO1,jpg@010EOF52.F68A5980 i https://mail.google.com/maillu/0?ik=7c2eff6265&view=pt&search=all&permmsgid=msg-a%3Ar728795181450254015&simpiansg-a%3Ar72879518145... 1/1 1 12f2I2020 Town of North Andover Mail-Modification Request .. 7.7 NORTRAN0,0VER lassachuse;ts Jean Enright<jen rig ht@northandoverma.gov> Modification Request Josh Hasenfus <jhasenfus@thetrustees.org> Tue, Dec 1, 2020 at 8:04 PM To: Jean Enright<jenright@northandoverma.gov> Hi Jean: We are on-track for this to go before the Conservation Commission on the 91h. I tried to be as detailed as possible in hopes that we can close in one meeting. i I wanted to make sure that we do not need to provide the Planning Board with any submission, can you please confirm? Thanks! Josh [Quoted text hidden] Nn Drainage Modification Request_SCP.pdf 2154 K https:llmal l.googio.com/mall/u/0?ik=7c2eff6265&view=pt&search-all&permmsgid=msg-f%3A1684926458004694654&simpl=msg-f%3A'I68492645800... 111 I ' Stevens-Coolidge Place 113 Andover Street North Andover, MA 01845 November 30, 2020 Dear Commissioners: I am writing for formal an approval for a minor modification to our exisiting Order of Conditions issued on December 23rd, 2019 for the Stevens- Coolidge Place Chickering Road Entrance Project. The scope of this modification request ' relates to the drainage improvements that were conditioned by the Planning Board. During the site plan review process, abutters on Old Village lane raised concerns about stormwater run-off entering their property from the Stevens-Coolidge Place property entering their property. As a result of these Conditions, the Planning Board conditioned the re-construction of an existing Swale at the Old Village Lane property line and the need to work with MassDOT to improve the drainage function of existing structures at under Chickering Road. In an effort to improve conditions for our abutters,we evaluated the exisiting conditions during multiple site visits with Jean Enright,John Borgesi, Curtis Johnson and Amy Maxner to review an expanded scope that includes the following areas: 11 Re-construct drainage structure at edge of Chickering Road to correct structure failure. 2. Excavate sediment blocking pipe outlet at shared property line with Heritage Green Condominiums. This outlet pipe conveys stormwater under Chickering Road. 3. Create improved infiltration conditions in newly constructed infiltration basin. 4. Re-construction of drainage swale from field edge, through the wooded buffer along Old Village Lane with discharge at exisiting infiltration basin outlet. The scope will be explained in greater detail on the following pages, I look forward to discussing this in greater detail with the Commission on the December 9th meeting. We feel these project components will greatly benefit our neighbors and the Town of North Andover. Sincerely, Josh Hasenfus Landscape Construction Specialist 339-203-8237 cell Jasenfus@thetrustees.org CC: Jean Enright, Town of North Andover John Borges!,Town of North Andover Curtis Johnson, Town of North Andover Scope of Proposed Work: 1. Re-construct drainage structure at edge of Chickering Road to correct structure failure. Need: Upon drainage structure survey with MassDOT,a 24" manhole casting was discovered. This structure contains pipe inverts from the adjacent piping and contains the RCP that conveys stormwater under Chickering Road. The upper portion of concrete under the iron casting has failed and the surrounding soil is settling. MassDOT has determined that this structure is outside their right-of-way. This repair need was requested by John Borges and Trustees agreed to repair. Location to Wetland Resource: This structure is located just outside the 25' No Disturb in the wetland buffer parallel to Chickering Road, Methodology: The Trustees will access this structure from Chickering Road with a small machine to excavate the area immediately around the manhole. A few saplings will need to be removed to facilitate machine access. The exisiting casting will be removed and the concrete will be prepared for repair. Concrete will be formed and poured. A new drain grate casting will be installed in place of the solid cover. Site walk with Town staff identified this need to receive flows from the proposed swale. Following the grate installation, a narrow apron of rip-rap will be installed T-4'from the grate to prevent clogging by leaves. All spoils and concrete waste will be removed from the area. Resource Protection: 1. Install limit of work stakes and yellow poly roping for approval by Conservation Staff before work begins 2. Install 12" Filtrexx sock to surround work area 3. Following completion of work, apply New England Wetland Plants Wet Mix seed as a dormant seeding. 4. Mulch disturbed area with clean straw or salt hay North Andover L•mna. 3�Vfe IYSn;b'ld67•£C[ C6;rS,7?C2?.�•t 17f�yf ••IjCPr' '::17ACi x G IFj..hFt3yr^r-<<Sx 469 stmf.S6;4-v Ap 'toi ation of ma F [e oi TAW jjj rFf Y „ /e(f �` "� � '•� 9�k#t IMP^ I�i,� ,.A f,..� J " 4 a , r e 2, Excavate sediment blocking pipe outlet at shared property line with Heritage Green Condominiums. This outlet pipe conveys stormwater under Chickering Road, Need: During site visit with MassDOT, it was confirmed that the 12" RCP under Chickering Road had been water jetted by their maintenance crew. This was completed following a request for maintenance by The Trustees. MassDOT indicated that the RCP was in functional condition and clear, but the outlet end was partially obstructed from sediment and blocking flow. MassDOT indicated that this was the greatest need, but pipe outlet was outside of their right-of-way. Location of Wetland Resource: This area is located across the Chickering Road from the flagged wetland. It is assumed that the resource area is the bank of the Swale at pipe outlet, The gradient is very steep, and the bank is well defined, Methodology: Condominium management gave Trustees staff verbal permission to access the site with a small machine and dump truck. Sediment will be removed at the outlet with machine and by hand. Swale in the immediate outlet area will be graded back to correct near vertical slope which will continually erode without re-grading. Rip-rap will be placed on slope and at outfall. All spoils will be removed from the site. Resource Protection: 1. Limit of work stakes will be installed for review by Conservation Staff 2. Seed and mulch any disturbed areas adjacent to swale. k �f -;��, set North n clover- 125 at h4�1 8.2•Stevens Coolidge 5 • p i;, , "..,,i: k wF . B k }. 4T x, Mm, rA �, wr � r try R1K''`',i%. �,� �7 +F • t � �k' �'- r 'y7•' y� y uvs P� ZJ -, 1 F 3. Create improved infiltration conditions in recently constructed infiltration basin Need. Stormwater in the recently completed infiltration basin has been slow to infiltrate. In consultation with two independent engineers, it is believed the high silt content in exisiting soils were compacted during construction and preventing timely infiltration. Location to Wetiand Resource: This area is located within the previously permitted site plan and work is within the buffer zone of BVW. Methodology: Vegetation in the basin is established and the site has stabilized well. Proposed plan is to excavate 60-80 yards of soils from lower area of basin and import 1-1/2"crushed/washed stone to create an area of rapid infiltration. All excavated material will be removed from the site. Resource Protection: I. Erosion controls at the outlet structure remain in place from construction. 2. Excavation will take place with frozen ground to prevent disturbance. 3. Dormant seed with New England Wetland Plants Wet Mix, 4. Mulch any disturbed soils with clean stray or salt marsh hay. 4. Re-construction of drainage Swale from field edge, through the wooded buffer along Old Village Lane with discharge at exisiting infiltration basin outlet. Need: To mitigate off-site stormwater flow to abutting properties and to satisfy the Planning Board Conditions, the exisiting swale along Old Village Lane requires re-construction. It is our understanding that this swale was constructed during the building of Old Village Lane, but little maintenance has been completed. The approved site plan includes a grading plan for only a portion of this swale. Upon a site walk with town staff, it was determined best to re-construct the Swale in its entirety adjacent to Old Village Lane abutters. In doing so, we can assure we are not directing stormwater into any neighboring properties. Location of Wetland Resources: The majority of this Swale is located outside of the 100' buffer. Lower portion of swale and discharge are within the 50' buffer,of previously permitted BVW. Methodology. The exisiting swale is within the wooded buffer and is still somewhat visible. Swale will be staked using rotary laser to find Swale centerline. Due to the need to preserve as much vegetation as possible, swale will be carefully laid out to avoid significant tree impacts, Following layout, stakes will be reviewed by John Borges!and/or Curtis Johnson before any work begins. Centerline of Swale and elevations to be determined based on field layout to account for tree impacts. Site walk with town staff indicated that swale discharge would best located at the existing rip-rap apron at the infiltration basin outlet structure. This discharge location is preferred as it is within the previously impacted buffer area and avoids any additional BVW impacts. Proposed swale discharge will be within the existing rip-rap apron, any additional rip-rap needed will be installed. Swale will be re-constructed with a small excavator. All vegetation needed to be removed will be cut and placed within the buffer area. Excavated soils will be re-disturbed to build Swale. There is much woodland duff that exists throughout this area. Due to the dense shade, seeding is not practical, duff material will be re-distributed to mulch exposed soils. Seeding and mulching will be completed discharge area. Resource Protection: I. Erosion control surrounding rip-rap apron remains in place from construction- this will be remain in place and replaced as needed until swale stabilizes. 2, Install 12" Filtrexx Sock at downslope limit of swale. 3. Seed and mulch swales areas outside of deep shade a • i )En it 'a r i M h } Imm J/) uisiting rile-rail apron kit outlet structure, Discharge sw alo into rip rap. Intsali 12" Filtrexx sock / / � , eaovosw wnEr car+ s�uc n� 1 �. - JJJ �/ ......-. k540 CAL PRECASF tE3f TNI •� �' WOpritU f lYi Y-NOi kDH A. V� .s � �• 1� �-1. \ \ � „�Y� Y-NOTC+I M+CRi 0 Q.�0 208.6' sL� 1 � / f/! rnorosw CONSI rueCM OASN 0Fr..._.,..`,i)% \ \ ur rtwx•rrr • :. � / OF 709.0' - \`.\;t _ S pArtt[iNDI @\k� �Ti'�gyp•( �'1 \� L�•p - '{!i \r\ s' < s Exisitng Swale witk pose 1,41ill titi'g ... %1 r� fa��rS �3.r r canstriciot r11CF c lGF1us Tor 0 rlurnr; 210.E0 i$frioauc h21 t Milk RORD t t »v // in, .r y• � �� lit is 1 Material Information: NEW ENGLAND WETLAND PLANTS. IN $20 WEST STREETr AM"ERST,MA 01002 PHONE:413-548.8000 FAk 4i3.549.4000 EMAIL:INFO@NEWP.C$M WEB'ADDRESS:WWW.NEWP.COM New England Wetm x(Wetland Seed Niix Botanical Name Co'*art Name indfcator, C dhw 11ilphloi(ka Fax Sedge 08L C:aaw xCOA111(i Blunt Broom Sedge ' FACW (::ores tr+rlcfir Lurid Sedge 08L Citrxs'hiP1141110, Flop Sedge .OSL 1'im fair Jrsifis Fowl Bluegrass FACW Uiileh.s frnriil'xsri Beggar Ticks FACW 41111us atroVifpty dteeit Bulrush OBI. fsclelJias.rttruruutu. Swamp Milkweed 08L C.irrx;t rrlrNrn FringedSiWge M 1 errrqulp rl+is0pnivep-0 New York tromveed FACW} hrheiii e/Jiesr+ Soft Rush FACW t l(Afec ltltu41411-7+.s(,SVrinhjviirlrGr+nr 10141ftirr+nl7 5tarvedJCellco Aster FACW frls r'ei:slcnlor. Blue Flag 08L (7tircl'nt 9rtrlrrfiz American Mannagrass OBI Jl.finiulirs jtngcns Square S.ternmed Monkey Flower 08L- !:'upntrrJi+rrJE n6irnfdnuir 1AWfi-achhun maciJllfl+m) Spatted)"PJ L Weed 081. ..PRICE RICE PER LB` $135,00 MIN.QUAN fV 1 Las, TOT4. $115,00 APPLY;18 U35/ACRC;2500 sq fttlb The Mew England Wetmix{Wetland Seed Mix)contafns a wide,variety of.natiVe seeds that are suitable for mst Wetland restaratlon sites that are ndt permanently f landed,All specles are hest suited to midst ground as,found In imast%yet meadows,scrub Shrub,or foretted wetland restoration areas. a MIX is well suited for detention basfh bardets and the bottam df detention.ttasins nofgenefally under `standing water.The seeds will not germinate under inundated conditions.if ptanted d4ring the fall months the seed mix will geiniinate Ehe following spring.During the flrst season o(Sfm,4Ih several spediis will produce seeds whlie other sp"Fes wIll produce seeds.after the setond gfoWirig teasan..Not all spectes will grow In all well snd situations,This Mix is comprised of the wetland sPetles inapt Ilkety to grow in treated/restisreel%+vthnds and should produce mare than 75%ground cover In tvp full grbyAng Seasons. The wetland seeds In this mix can be sown by hand,with a hand-held Spreader,or hydro-seeded oi►large or hard to reach sites.Lightly rake to insure good seed to so11 contact.Seeding can take place on frozen soil,as the freezing and th4wIng wPalherof Iafe.fall and late Wint+sr grill work the sped into.the soil.if toting tondl(lons are drier(han usual watering inay be required.if somng during the surpnier months st}pplemental%viteiing WIN likely be.required until germinatlpn.A light mulch of clean,weed free straw is recommended. ' E • E PRODUCT INFORMATION&APPLICATION USE s HEADrIJIDTHSVOODE`.STAGES Flllraxxg S11ISoxx'"Ipre-filled}Is a c rnpasi filter sack corhprlsed t�f a.ri aLAcSO la ON cEa'TER tl'HEADu,{DTrr rR 5:SILTSOXX� TREiCCEPTABLE ower luesh a4"Iiiig ruatelial,And fillrrd with t wI!fit'rl('ornpwtrilterMeiI1 `. ) SillSoxx is desiomd to filter�Pdiment and is asu error alternative to silt f'Pnce rY,W,i;% 4 12 TYPI t1 (S';&',9'.oZ 1�`TYPlCAL1 and straw Wattles.It is used In coDstructlon applications of penmelef control, &slel prott�ctlan,chuck darns;slo sr;Inteifiuillion,Cannata washool,And runoff AREA O pe vROTECTk0 C11V�fSIArl.l�c�f6tfOttl(1NIijltRltJpf)f,Geiriar,desr�rispeci�Tc�rlonsForappll�gtian. VIORKAREA design,installation,maintenancg,andremovaldocrrmenta'don, This submitial form is to be used for f iltrexx S.iltsoxx prodLrcts only(pre-filled). Include the corresponding application drawing&installation document if needled, SIItSoxx'"are In compliance with most state and federal agencies SECnon VIEW Including USEPA,AASHTO,USDA NRCS and US AM i fAat4rl+l3ype HATUMLORIGIHAL HANRALPLU3 ORIGIRAt WRtlriE (Cotton ) (ill Weber) f9dil-filammlPd>Iyproplien MFPP) (MuW-AlamentPnl)propyiefre&1fPP) A1awalawactefm Bwe9fadaMe Biodegradable Photodegradahle Plwtudegfadable Design Diameters 51ri,8412[n 5W,819,1116 5 IA,8K12 In,is in,Ain 8 In,12In Mes 00ming 1181il f3mm) 118iri(3mm) Its in(3mm) 1116 ki(13mm) TemileRregih(ATfM5D3S-0 44pst(3.09.kghm2) 14pst(5.341gkm2) 242psi(16.44kg1[Tar) Undeftevtew 75flr19Ena151rengihfrantKMiolet lip lip 1lIR3t>a1111wht 1t1I%Atl*hr Ex'powre(Aii1r1 G-155t frarirgrxtalintgeviiy?Piv)rrlDuralkrn uptallrnrdlno' uplol4irwntlrs'" .:vptaiyr . Ides001 Brkac Ufb1YId1r GirerdBlark;larr GrLr�s+Blacli;Drarxtr Innr0001lDngekhyQ090 reeotlmat(ISOnry_5itespedflc myMo111ns r firanll slrnrterorlogerlimtptri* 44 Wood Avenue Engineering, Inc. Mansfield,MA o2048 I Tel(508)339-3929 Fn0ineers&Fnvironniental Scientists Fax(508)339-3140 www.ohiengineering.com June 11, 2021 Amy Maxner Conservation Administrator Town of Borth Andover 120 Main Street North Andover, MA 01845 Re: Request for Minor Change Approval 0 Chickering Road MassDEP File#242-1764 Dear Amy, OHI Engineering, Inc. (OHI) has prepared the attached supplemental information on behalf of The Trustees of Reservations regarding the stormwater control system at Stevens- Coolidge Place in North Andover, MA. The stormwater control system was shown on drawings entitled "Permit Plan Set, Chickering Road, Route 125, North Andover, MA" prepared by Hancock Associates (Hancock), latest revision dated 12/10/19. Operational issues with the infiltration Basin installed in the northwesterly corner of the property were encountered shortly after construction. According to the stormwater calculations prepared by Hancock, the infiltration basin was designed based on Class B soils with an infiltration rate of 1.02 inches per hour. The basin was expected to dewater within approximately eight (8) hours of the cessation of rainfall event. However, the basin did not dewater; standing water was present in the basin over a long time period. Issues were also identified with discharge from the outlet structure flowing onto an abutting property to the north. OHI conducted a site reconnaissance and reviewed the calculations prepared by Hancock. Soil types were identified in the SCS soil map as Class C/D. The infiltration rate for these types of soil ranges from zero to 0.27 inches per hour. Based on the long-term standing water in the basin, there is effectively no infiltration, The stormwater calculations for the post-development condition were re-run using SCS TR20 and the HydroCAD stormwater modelling software, assuming no infiltration from the basin, Post-development stormwater flow rate was calculated to be less than the pre- development rate under the 2-year, 10-year, 25-year and 100-year storm events even assuming no infiltration from the basin. The HydroCAD calculations are attached. Mansfield, MA Amherst, MA Chester, VT 2 In order to address operational issues, the following modifications are proposed: 1) Install a sediment forebay prior to the stormwater basin for removal of total suspended solids; 2) Core a four-inch diameter in the outflow structure at elevation 206.1 and regrade the bottom of the basin to elevation 206.1, in order to avoid significant permanent standing water in the basin; 3) Install a rip-rap lined swale and level spreader directing basin outflow towards on- Site wetland area and away from the abutting property while avoiding work in the 25-foot no build zone; and, 4) Increase the basin embankment to elevation 209 to increase freeboard above the 100-year flood elevation and install emergency overflow. The Site Plan showing the proposed modifications and associated details is attached. In our opinion,these modifications are minor, are generally within the work areas already included in prior permitting with the Town of North Andover Conservation Commission, and should be approved as a minor modification. We request Minor Project Change approval for the modifications described above in accordance with Condition #40 of the Order of Conditions. It is our understanding that this request will be on the docket at the Commission's June 23, 2021, public hearing. Representatives of OHI and The Trustees of Reservations will be in attendance. Please contact me should you have questions or comments regarding this matter or if you require further information. Sincerely, OHI ENGINEERING, INC. James R. Borrebach, P.E., L.S.P. President Cc: Josh Hasenfus—The Trustees of Reservations Request for Minor Change Approval The Trustees of Reservations MassDEP File#242-1764 0 Chickering Road June 11,2021 North Andover, MA I i Table I Starmwater Peak Rate Suanmm PEAK DISCHARGE RATE OF FLOW OFF-SITE Pre-Development(cfs) Analysis Point 2-YR 10-YR 25-YR 100-YR AP 1 3.17 7.69 1 L51 20A 1 Post-Development cfs Pre-Development vs.Developed(cfs) Analysis Point 2-YR 10-YR 25-YR 100-YR AP 1 -1.76 .1.69 -1.10 -3.00 i i PR1 PR . ... Post Upper Watershed Post Lower Watershed 4P - 1 P DP1 Forebay Basin Subcat Reach Otljl�k Routing Diagram for Post-Development-Basin Modifications Prepared by OHI Engineering, Inc., Printed 5/25/2021 HydroCADO 10,10-4a sh 11276 ©2020 HydroCAD Software Solutions LLC i Post-Development-Basin Modifications Type Ill 24-hr 2-Year Rainfall=3.20" Prepared by OHI Engineering, Inc. Printed 5/25/2021 H droCAD®10.10-4a s/n 11276 ©2020 H droCAD Software Solutions LLC Pacie 2 Summary for Subcatchment PR1: Post Upper Watershed Runoff = 4.91 cfs @ 12.41 hrs, Volume= 24,782 of, Depth> 0.89" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 2-Year Rainfall=3.20" _ Area (sf) _ CN Description 296,460 71 Meadow, non-grazed, HSG C 2,550 98 Unconnected roofs, HSG C 33,920 89 Gravel roads, HSG C 2,880 80 Decomposed Granite Walk 335,810 73 Weighted Average 333,260 99.24% Pervious Area 2,550 0.76% Impervious Area 2,550 100.00% Unconnected To Length Slope Velocity Capacity Description min feet ft/ft ftlsec cfs 26.9 800 0.0147 0.49 Lag/CN Method, Summary for Subcatchment PR2: Post Lower Watershed Runoff _ 0.10 cfs @ 12.35 hrs, Volume= 448 cf, Depth> 1.10" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 2-Year Rainfall=3.20" Area (sf) CN Description -- 3,225 71 Meadow, non-grazed, HSG C 1,640 89 Gravel roads, HSG C 4,865 77 Weighted Average 4,865 100.00% Pervious Area To Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 24.0 800 0.0147 0.56 Lag/CN Method, Summary for Pond 1 P: Basin Inflow Area = 335,810 sf, 0.76% Impervious, Inflow Depth > 0.87" for 2-Year event Inflow - 4.96 cfs @ 12.41 hrs, Volume= 24,266 cf Outflow - 1.38 cfs @ 13.16 hrs, Volume= 17,958 of, Atten= 72%, Lag= 45.3 min Primary - 1.38 cfs @ 13.16 hrs, Volume= 17,958 of Secondary= 0.00 cfs @ 5.00 hrs, Volume= 0 of Routing by Dyn-Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 206.80'@ 13.16 hrs Surf.Area= 15,101 sf Storage= 10,131 of Flood Elev= 209.00' Surf.Area= 20,434 sf Storage= 48,481 of Post-Development-Basin Modifications Type 11l 24-hr 2-Year Rainfall=3.20" Prepared by OHI Engineering, Inc. Printed 5/25/2021 HydroCADO 10.10-4a s/n 11276 0 2020 HydroCAD Software Solutions LLC Page 3 Plug-Flow detention time= 137.0 min calculated for 17,898 cf(74% of inflow) Center-of-Mass det, time=74.6 min ( 914.1 - 839.5 ) Volume Invert Avail.Stora e Storage Descri tion #1 206.10' 48,481 cf Custom Stage Data (irregular)Listed below(Recalc) Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft) 206.10 14,146 483.0 0 0 14,146 206.50 14,599 495.0 5,749 5,749 15,100 207.00 15,464 510.0 7,512 13,261 16,326 208.00 17,306 550.0 16,371 29,632 19,741 209.00 20,434 630.0 18,848 48,481 27,277 Device Routing Invert Outlet Devices #1 Primary 206.10' 18.0" Round Culvert X 2.00 L= 30.0' CPP, projecting, no headwall, Ke= 0.900 Inlet/Outlet Invert= 206.10'/205.70' S= 0.0133 T Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 1.77 sf #2 Device 1 206.50' 30.0 deg x 2.0' long x 2.00' rise Sharp-Crested VeelTrap Weir Cv= 2.61 (C= 3.26) #3 Device 1 208.50' 120.0" x 60.0" Horiz. Orifice/Grate C= 0.600 Limited to weir flow at low heads #4 Device 1 206.10' 4.0" Vert. OrificelGrate C= 0.600 Limited to weir flow at low heads #5 Secondary 208.50' 10.0' long x 8.5' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 Coef. (English) 2.45 2.54 2.70 2.69 2.68 2.68 2.66 2.64 2.64 2.64 2.65 2.65 2.65 2.66 2.67 2.69 2.71 Primary OutFlow Max=1.38 cfs @ 13.16 hrs HW=206.80' TW=0,00' (Dynamic Tailwater) t-- =Culvert (Passes 1.38 cfs of 3.59 cfs potential flow) 2=Sharp-Crested Vee/Trap Weir(Weir Controls 1.08 cfs @ 1.76 fps) 3=OrificelGrate ( Controls 0.00 cfs) 4=Orifice/Grate (Orifice Controls 0.31 cfs @ 3.50 fps) Secondary OutFlow Max=0.00 cfs @ 5.00 hrs HW=206.10' TW=0.00' (Dynamic Tailwater) 5=Broad-Crested Rectangular Weir( Controls 0.00 cfs) Summary for Pond 4P: Forebay Inflow Area 335,810 sf, 0.76% Impervious, Inflow Depth > 0.89" for 2-Year event Inflow - 4.91 cfs @ 12.41 hrs, Volume= 24,782 cf Outflow = 4.96 cfs @ 12.41 hrs, Volume= 24,266 cf, Atten= 0%, Lag= 0.0 min Primary = 4.96 cfs @ 12.41 hrs, Volume= 24,266 of Routing by Dyn-Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Peals Elev= 207.63'@ 12.41 hrs Surf.Area= 516 sf Storage= 572 cf Flood Elev= 205.50' Storage= 0 cf Plug-Flow detention time= 10.3 min calculated for 24,266 cf(98% of inflow) E I Post-Development-Basin Modifications Type i1124-hr 2-Year Rainfall=3.20" Prepared by OHI Engineering, Inc. Printed 5/25/2021 H droCADO 10.10-4a sln 11276 O 2020 H droCAD Software Solutions LLC Page 4 Center-of-Mass det. tune=3.0 min ( 839.5 - 836.5 ) 1 Volume Invert Avail.Stora a Storage Description #1 206.00' 1,201 cf Custom Stage Data (lrregular)isted below(Recalc) Elevation Surf.Area Perim. Voids Inc.Store Cum.Store Wet.Area _feet) (sq-ft) (feet) (%) (cubic-feet) (cubic-feet) (sq-ft) 206.00 220 58.0 0.0 0 0 220 206.50 280 65.0 100.0 125 125 295 207.00 386 76.0 100.0 166 290 423 208.00 603 98.0 100.0 490 781 740 208.50 1,104 153.0 100.0 420 1,201 1,841 Device Routing Invert Outlet Devices #1 Primary 207.50' 45.0' long x 3.0' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.50 3.00 3.50 4.00 4.50 Coef. (English) 2.44 2.58 2A8 2,67 2.65 2.64 2.64 2.68 2.68 2.72 2.81 2.92 2.97 3.07 3.32 Primary OUtFlow Max=4.93 cfs @ 12.41 hrs HW=207.63' TW=206.42' (Dynamic Tailwater) L1=Broad-Crested Rectangular Weir(Weir Controls 4,93 cfs @ 0.87 fps) Summary for Link DP1: Inflow Area = 340,675 sf, 0.75% Impervious, Inflow Depth > 0.65" for 2-Year event Inflow - 1,41 cfs @ 13.15 hrs, Volume= 18,406 cf Primary - 1.41 cfs @ 13.15 hrs, Volume= 18,406 cf, Atten= 0%, Lag= 0,0 min Primary outflow = Inflow, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Post-Development-Basin Modifications Typo 11124-hr 10-Year Rainfall=4.80" Prepared by OHI Engineering, Inc. Printed 5/25/2021 HydroCADO 10.10-4a sln 11276 ©2020 HydroCAD Software Solutions LLC Page 5 Summary for Subcatchment PR1: Post Upper Watershed Runoff = 11.23 cfs @ 12.39 hrs, Volume= 54,499 cf, Depths 1.95" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 10-Year Rainfall=4.80" Area (sf) CN Description 296,460 71 Meadow, non-grazed, HSG C 2,550 98 Unconnected roofs, HSG C 33,920 89 Gravel roads, HSG C * 2,880 80 Decomposed Granite Walk 335,810 73 Weighted Average 333,260 99.24% Pervious Area 2,550 0.76% Impervious Area 2,550 100.00% Unconnected Tc Length Slope Velocity Capacity Description min feet ftlft ftlsec cfs 26.9 800 0.0147 0.49 Lag/CN Method, Summary for Subcatchment PR2: Post Lower Watershed Runoff — 0.20 cfs @ 12.34 hrs, Volume= 920 of, Depths 2.27" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 10-Year Rainfall=4.80" Area (sf) CN Description 3,225 71 Meadow, non-grazed, HSG C 1,640 89 Gravel roads HSG C 4,865 77 Weighted Average 4,865 100.00% Pervious Area Tc Length Slope Velocity Capacity Description min feet ftlft ftlsec cfs 24.0 800 0.0147 0.56 Lag/CN Method, Summary for Pond 1 P: Basin Inflow Area = 335,810 sf, 0.76% Impervious, Inflow Depth > 1.93" for 10-Year event Inflow - 11.24 cfs @ 12.39 hrs, Volume 53,979 cf Outflow 5.91 cfs @ 12.78 hrs, Volume= 46,759 cf, Atten= 47%, Lag= 23.2 min Primary = 5.91 cfs @ 12.78 hrs, Volume= 46,759 cf Secondary= 0.00 cfs @ 5.00 hrs, Volume= 0 cf Routing by Dyn-Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Peals Elev= 207.34'@ 12.78 hrs Surf.Area= 16,072 sf Storage= 18,622 cf Flood Elev= 209.00' Surf.Area= 20,434 sf Storage=48,481 cf i Post-Development-Basin Modifications Type 11124-hr 90-Year Rainfall=4.80" Prepared by ON Engineering, Inc. Printed 5/25/2021 H droCADO 10,10-4a s/n 11276 O 2020 H droCAD Software Solutions LLC Pa e 6 j Plug-Flow detention time=86.8 min calculated for 46,759 cf(87% of inflow) Center-of-Mass det. time=48.1 min ( 869.4 - 821.4 ) 1 Volume Invert Avail.Stora e Storage Description #1 206.10' 48,481 cf Custom Stage Data (Irregular)Listed below(Recalc) Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft) 206.10 14,146 483.0 0 0 14,146 206.50 14,599 495.0 5,749 5,749 15,100 207.00 15,454 510.0 7,512 13,261 16,326 208.00 17,306 550.0 16,371 29,632 19,741 209.00 20,434 630.0 18,848 48,481 27,277 Device_ Routing Invert Outlet Devices #1 Primary 206.10' 18.0" Round Culvert X 2.00 L= 30.0' CPP, projecting, no headwall, Ke= 0.900 Inlet/ Outlet Invert= 206,10'/205.70' S= 0.0133 T Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 1.77 sf #2 Device 1 206.50' 30.0 deg x 2.0' long x 2.00' rise Sharp-Crested VeelTrap Weir Cv= 2.61 (C= 3.26) #3 Device 1 208.50' 120.0" x 60.0" Horiz. Orifice/Grate C= 0,600 Limited to weir flow at low heads #4 Device 1 206.10' 4.0" Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #5 Secondary 208.50' 10.0' long x 8.5' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.50 3.00 3.50 4.00 4,50 5.00 5.50 Coef. (English) 2.45 2.54 2.70 2.69 2.68 2.68 2.66 2.64 2.64 2.64 2.65 2.65 2.65 2.66 2.67 2.69 2.71 Primary OutFlow Max=5.90 cfs @ 12.78 hrs HW=207.34' TW=0.00' (Dynamic Tailwater) t =Culvert (Passes 5.90 cfs of 9.34 cfs potential flow) 2=Sharp-Crested VeelTrap Weir(Weir Controls 5.47 cfs @ 2.93 fps) 3=Orifice/Grate ( Controls 0.00 cfs) =Orifice/Grate (Orifice Controls 0.44 cfs @ 4.99 fps) Secondary OutFlow Max=0.00 cfs @ 5.00 hrs HW=206.10' TW=0.00' (Dynamic Tailwater) 5=Broad-Crested Rectangular Weir( Controls 0.00 cfs) Summary for Pond 4P: Forebay Inflow Area = 335,810 sf, 0.76% Impervious, Inflow Depth > 1.95" for 10-Year event Inflow - 11,23 cfs @ 12.39 hrs, Volume= 54,499 cf Outflow - 11,24 cfs @ 12.39 hrs, Volume= 53,979 cf, Atten= 0%, Lag= 0.1 min Primary 11.24 cfs @ 12.39 hrs, Volume= 53,979 cf Routing by Dyn-Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 207.72' @ 12.39 hrs Surf.Area= 537 sf Storage= 620 cf Flood Elev= 205.50' Storage= 0 cf Plug-Flow detention time=5.5 min calculated for 53,800 cf(99% of inflow) i Post-Development-Basin Modifications Type I1124-hr 10-Year Rainfal1=4.80" Prepared by OHI Engineering, Inc. Printed 5/25/2021 H droCAD® 10.10-4a sin 11276 ©2020 H droCAD Software Solutions LLC Page 7 Center-of-Mass det. time=2.0 min ( 821.4 - 819.3 ) Volume Invert Avail.Storage Storage Description #1 206.00 1,201 cf Custom Stage Data (irregular)Listed. ..... ' g below(Recalc) Elevation Surf.Area Perim. Voids Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (%) (cubic-feet) (cubic-feet) (sq-ft) 206.00 220 58.0 0.0 0 0 220 206.50 280 65.0 100.0 125 125 295 207.00 386 76.0 100.0 166 290 423 208.00 603 98.0 100.0 490 781 740 208.50 1,104 153.0 100.0 420 1,201 1,841 Device Routing Invert Outlet Devices #1 Primary 207.50' 45.0' long x 3.0' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2,50 3.00 3.50 4.00 4.50 Coef. (English) 2.44 2.58 2.68 2.67 2.65 2.64 2.64 2.68 2.68 2.72 2.81 2.92 2.97 3.07 3.32 Primary OutF[ow Max=11.20 cfs @ 12.39 hrs HW=207.72' TW=206.98' (Dynamic Tailwater) L1=Broad-Crested Rectangular Weir(Weir Controls 11.20 cfs @ I.14 fps) Summary for Link DP1: Inflow Area = 340,675 sf, 0.75% Impervious, Inflow Depth > 1.68" for 10-Year event Inflow 6.00 cfs @ 12.77 hrs, Volume= 47,679 of Primary - 6.00 cfs @ 12.77 hrs, Volume= 47,679 cf, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs 6 Post-Development-Basin Modifications Type !I! 24-hr 25-Year Rainfall=6.00" Prepared by OHI Engineering, Inc. Printed 5/2512021 HydroCADO 10.10-4a sin 11276 ©2020 HydroCAD Software Solutions LLC Page 8 Summary for Subcatchment PR1: Post Upper Watershed j Runoff - 16.50 cfs @ 12.38 hrs, Volume= 79,761 cf, Depth> 2,85" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 25-Year Rainfall=6.00" Area (sf) CN Description 296,460 71 Meadow, non-grazed, HSG C 2,550 98 Unconnected roofs, HSG C 33,920 89 Gravel roads, HSG C 2,880 80 Decomposed Granite Walk 335,810 73 Weighted Average 333,260 99,24% Pervious Area 2,550 0.76% Impervious Area 2,550 100.00% Unconnected Tc Length Slope Velocity Capacity Description min feet ft/ft ftlsec cfs 26.9 800 0.0147 0.49 Lag/CN Method, Summary for Subcatchment PR2: Post Lower Watershed Runoff - 0.28 cfs @ 12,33 hrs, Volume= 1,310 cf, Depth> 3.23" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 25-Year Rainfall=6.00" Area (sf) CN Description 3,225 71 Meadow, non-grazed, HSG C 1,640 89 Gravel roads, HSG C 4,865 77 Weighted Average 4,865 100.00% Pervious Area Tc Length Slope Velocity Capacity Description min feet ft/ft ftlsec cfs 24.0 800 0.0147 0.56 Lag/CN Method, Summary for Pond 1 P: Basin Inflow Area = 335,810 sf, 0.76% Impervious, Inflow Depth > 2.83" for 25-Year event Inflow = 16.50 cfs @ 12.38 hrs, Volume= 79,239 cf Outflow - 10.27 cfs @ 12.69 hrs, Volume= 71,465 cf, Atten= 38%, Lag= 18.7 min Primary - 10.27 cfs @ 12.69 hrs, Volume= 71,465 cf Secondary= 0.00 cfs @ 5.00 hrs, Volume= 0 cf Routing by Dyn-Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 207.71'@ 12.69 hrs Surf.Area= 16,751 sf Storage= 24,630 cf Flood Elev= 209.00' Surf.Area= 20,434 sf Storage=48,481 cf Post-Development-Basin Modifications Type W 24-hr 25-Year Rainfall=6.00" Prepared by OHI Engineering, Inc. Printed 5/25/2021 H droCADO 10.10-4a sln 11276 ©2020 H droCAD Software Solutions LLC Pa e 9 Plug-Flow detention time=72.0 min calculated for 71,465 cf(90% of inflow) Center-of-Mass det. time=41.5 min ( 854.1 - 812.7 ) Volume Invert Avail.Storage Storage Description #1 206.10' 48,481 cf Custom Stage Data (Irregular)Listed below(Recalc)� Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft) 206.10 14,146 483.0 0 0 14,146 206.50 14,599 495.0 5,749 5,749 15,100 207.00 15,454 510.0 7,512 13,261 16,326 208.00 17,306 550.0 16,371 29,632 19,741 209.00 20,434 630.0 18,848 48,481 27,277 Device Routing Invert Outlet Devices #1 Primary 206.10' 18.0" Round Culvert X 2.00 L= 30.0' CPP, projecting, no headwall, Ke= 0.900 Inlet/Outlet Invert 206.10'1205.70' S= 0.0133 '1' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 1.77 sf #2 Device 1 206.50' 30.0 deg x 2.0' long x 2.00' rise Sharp-Crested VeelTrap Weir Cv= 2.61 (C= 3.26) #3 Device 1 208.50' 120.0" x 60.0" Horiz. Orifice/Grate C= 0.600 Limited to weir flow at low heads #4 Device 1 206.10' 4.0" Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #5 Secondary 208.50' 10.0' long x 8.5' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 Coef. (English) 2.45 2.54 2.70 2.69 2.68 2.68 2.66 2.64 2.64 2.64 2.65 2.65 2.65 2.66 2.67 2.69 2.71 Primary OutFlow Max=10.26 cfs @ 12.69 hrs HW=207.71' TW=0.00' (Dynamic Tailwater) t =Culvert (Passes 10.26 cfs of 12.43 cfs potential flow) 2=Sharp-Crested VeelTrap Weir(Weir Controls 9.75 cfs @ 3.48 fps) 3=OrificelGrate ( Controls 0.00 cfs) 4=Orifice/Grate (Orifice Controls 0.50 cfs @ 5.78 fps) Secondary OutFlow Max=0.00 cfs @ 5.00 hrs HW=206.10' TW=0.00' (Dynamic Tailwater) S=B road-Crested Rectangular Weir( Controls 0.00 cfs) Summary for Pond 4P: Forebay Inflow Area = 335,810 sf, 0.76% Impervious, Inflow Depth > 2.85" for 25-Year event Inflow - 16.50 cfs @ 12.38 hrs, Volume= 79,761 cf Outflow = 16.50 cfs @ 12.38 hrs, Volume= 79,239 cf, Atten= 0%, Lag= 0.1 min Primary - 16.50 cfs @ 12.38 hrs, Volume= 79,239 of Routing by Dyn-Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 207.78'@ 12.38 hrs Surf.Area= 551 sf Storage= 653 cf Flood Elev= 205.50' Storage= 0 cf Plug-Flow detention time=4.1 min calculated for 78,975 cf(99% of inflow) i Post-Development-Basin Modifications Type 11124-hr 25-Year Rainfall=6,00" Prepared by OHI Engineering, Inc. Printed 5/25/2021 H droCADO 10.10-4a s/n 11276 ©2020 H droCAD Software Solutions LLC Pacie 10 Center-of-Mass det. time= 1.7 min ( 812.7 - 811.0 Volume Invert Avail.Stora e Storage Description ##1 206.00' 1,201 cf Custom Stage Data (Irregular)Listed below(Recalc) Elevation Surf.Area Perim. Voids Inc.Store Cum.Store Wet.Area (feet) _(sq-ft) (feet) (%) (cubic-feet) (cubic-feet) (sq-ft) 206,00 220 58.0 0,0 0 0 220 j 206.50 280 65.0 100.0 125 125 295 207.00 386 76.0 100.0 166 290 423 208.00 603 98.0 100.0 490 781 740 208,50 1,104 153.0 100.0 420 1,201 1,841 _Device Routine Invert Outlet Devices #1 Primary 207.50' 45.0' long x 3.0' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.50 3.00 3.50 4.00 4.50 Coef. (English) 2.44 2.58 2.68 2.67 2.65 2.64 2.64 2.68 2.68 2.72 2,81 2.92 2.97 3.07 3.32 Primary OutFlow Max=16,43 cfs @ 12,38 hrs HW=207.78' TW=207.37' (Dynamic Tailwater) t1=Broad-Crested Rectangular Weir(Weir Controls 16.43 cfs @ 1.31 fps) Summary for Link DPI: Inflow Area = 340,675 sf, 0.75% Impervious, Inflow Depth > 2.56" for 25-Year event Inflow 10.41 cfs @ 12.69 hrs, Volume= 72,775 cf Primary _ 10.41 cfs @ 12.69 hrs, Volume= 72,775 cf, Atten= 0%, Lague 0.0 min Primary outflow = Inflow, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Post-Development-Basin Modifications Type H/24-hr 100-Year Rainfall=8.60" Prepared by OHI Engineering, Inc. Printed 5/25/2021 HydroCADO 10.10-4a s/n 11276 ©2020 HydroCAD Software Solutions LLC Page 11 Summary for Subcatchment PR1: Post Upper Watershed Runoff = 28.61 cfs @ 12.37 hrs, Volume= 139,206 cf, Depth> 4.97" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 100-Year Rainfall=8.60" Area (sf) CN Description 296,460 71 Meadow, non-grazed, HSG C 2,550 98 Unconnected roofs, HSG C 33,920 89 Gravel roads, HSG C 2,880 80 Decomposed Granite Walk 335,810 73 Weighted Average 333,260 99.24% Pervious Area 2,550 0.76% Impervious Area 2,550 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) feet) (ft/ft) (ft/sec) (cfs) 26.9 800 0.0147 0.49 LaglCN Method, Summary for Subcatchment PR2: Post Lower Watershed Runoff - 0.47 cfs @ 12.33 hrs, Volume= 2,209 cf, Depth> 5.45" Runoff by SCS TR-20 method, UH-SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 100-Year Rainfall=8.60" Area (sf) CN Description 3,225 71 Meadow, non-grazed, HSG C 640 89 Gravel roads HSG C 4,865 77 Weighted Average 4,865 100.00% Pervious Area Tc Length Slope Velocity Capacity Description min feet ftlft ftlsec cfs I 24.0 800 0.0147 0.66 LaglCN Method, i Summary for Pond 1 P: Basin Inflow Area = 335,810 sf, 0.76% Impervious, Inflow Depth > 4.96" for 100-Year event Inflow - 28.34 cfs @ 12.37 hrs, Volume 138,679 cf Outflow = 17.16 cfs @ 12.69 hrs, Volume= 129,891 cf, Atten= 39%, Lag= 19.4 min Primary - 17.16 cfs @ 12.69 hrs, Volume= 129,891 of Secondary= 0.00 cfs @ 5.00 hrs, Volume= 0 cf Routing by Dyn-Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 208.48'@ 12.69 hrs Surf.Area= 18,779 sf Storage= 38,313 cf Flood Elev= 209.00' Surf.Area= 20,434 sf Storage= 48,481 cf i Post-Development-Basin Modifications Type III 24-hr 100-Year Rainfall=8.60" Prepared by OHI Engineering, Inc. Printed 5/25/2021 HydroCAD® 10.10-4a sln 11276 _©_2020 HydroCAD Software Solutions LLC Page 12 Plug-Flow detention time=58.1 min calculated for 129,891 cf(94% of inflow) Center-of-Mass det. time= 36.6 min ( 836.5 - 799,8 ) Volume Invert Avail.Stora e Storage Description #1 206.10' 48,481 cf Custom Stage Data (Irregular)Listed below(Recalc) Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area feet s Tft feet cubic-feet cubic-feet s -ft 206.10 14,146 483.0 0 0 14,146 206.50 14,599 495.0 5,749 5,749 15,100 207.00 15,454 510.0 7,512 13,261 16,326 208.00 17,306 550.0 16,371 29,632 19,741 209.00 20,434 630.0 18,848 48,481 27,277 Device Routing Invert Outlet Devices #1 Primary 206.10' 18.0" Round Culvert X 2.00 L= 30.0' CPP, projecting, no headwall, Ke= 0.900 Inlet/ Outlet Invert= 206.10'/205.70' S= 0.0133 '/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 1.77 sf #2 Device 1 206.50' 30.0 deg x 2.0' long x 2.00' rise Sharp-Crested VeelTrap Weir Cv= 2.61 (C= 3.26) #3 Device 1 208.50' 120.0" x 60.0" Horiz. Orifice/Grate C= 0.600 Limited to weir flow at low heads #4 Device 1 206.10' 4.0" Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #5 Secondary 208.50' 10.0' long x 8.5' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 Coef. (English) 2.45 2.54 2,70 2.69 2,68 2.68 2.66 2.64 2.64 2.64 2.65 2.65 2.65 2.66 2.67 2.69 2.71 Primary OutFlow Max=17,15 cfs @ 12,69 hrs HW=208.48' TW=0.00' (Dynamic Tailwater) t- =Culvert (Inlet Controls 17.15 cfs @ 4.85 fps) 2=Sharp-Crested VeelTrap Weir(Passes < 22.03 cfs potential flow) 3=Orifice/Grate ( Controls 0.00 cfs) =Orifice/Grate (Passes < 0.63 cfs potential flow) §econdary OutFlow Max=0.00 cfs @ 6.00 hrs HW=206.10' TW=0.00' (Dynamic Tailwater) T---S=Broad-Crested Rectangular Weir( Controls 0.00 cfs) Summary for Pond 4P: Forebay Inflow Area = 335,810 sf, 0.76% Impervious, Inflow,Depth > 4.97" for 100-Year event Inflow 28.61 cfs @ 12,37 hrs, Volume= 139,206 cf Outflow = 28.34 cfs @ 12.37 hrs, Volume= 138,679 cf, Atten= 1%, Lag= 0.0 min Primary = 28.34 cfs @ 12.37 hrs, Volume= 138,679 cf Routing by Dyn-Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 208,48' @ 12.74 hrs Surf.Area= 1,086 sf Storage= 1,185 of Flood Elev= 205.50' Storage= 0 cf Plug-Flow detention time=2.8 min calculated for 138,218 cf(99% of inflow) Post-Development-Basin Modifications Type 11124-hr 100-Year Rainfall=8.60" Prepared by OHI Engineering, Inc, Printed 5/25/2021 H droCADO 10.10-4a sin 11276 ©2020 H droCAD Software Solutions LLC Page 13 Center-of-Mass det. time= 1.5 min ( 799.8 - 798.4 ) Volume Invert Avail.Storage Storage Description #1 206.00' 1,201 cf Custom Stage Data (Irregular)Listed below(Recalc) Elevation Surf.Area Perim. Voids Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (%) (cubic-feet) (cubic-feet) (sq-ft) 206.00 220 58.0 0.0 0 0 220 206.50 280 65.0 100.0 125 125 295 207.00 386 76.0 100.0 166 290 423 208.00 603 98.0 100.0 490 781 740 208.50 1,104 153.0 100.0 420 1,201 1,841 Device Routing Invert Outlet Devices #1 Primary 207.50' 45.0' long x 3.0' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.50 3.00 3.50 4.00 4.50 Coef. (English) 2.44 2.58 2.68 2.67 2.65 2.64 2.64 2.68 2.68 2.72 2.81 2.92 2.97 3.07 3.32 Primary OutFlow Max=0.00 cfs @ 12.37 hrs HW=208.00' TW=208.02' (Dynamic Tailwater) t1=Broad-Crested Rectangular Weir( Controls 0.00 cfs) Summary for Link DP'[: Inflow Area = 340,675 sf, 0.75% Impervious, Inflow Depth > 4.65" for 100-Year event Inflow - 17.41 cfs @ 12.67 hrs, Volume= 132,100 cf Primary - 17.41 cfs @ 12.67 hrs, Volume= 132,100 cf, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 5,00-20,00 hrs, dt= 0,05 hrs i Table 1 Stormwater Pear Rate Summary PEAK DISCHARGE RATE OF 1!LOW OFF-SITE Pre-Development(cfs) Analysis Poi It 2-YR 10-YR 25-YR 100-YR AP 1 3.17 7.69 11.51 20A I Post-Development(cfs) �F Jowls r , Pre-Development vs.Developed(cfs) Analysis Point 2-YR 10-YR 25-YR 100-YR AP 1 -1.76 -1.69 -1.10 -3.00 Forebay Sizing The required forebay volume is based on 0.10-inch over the contributing impervious area. Forebay.Volume Required Subcatelnrient PR1 impervious areas Unconnected roofs 2,550sf Gravel roads 39,920sf Decomposed granite walks 2,880sf Total Impervious Area 39,350sf 0.1 inches x(lft. /12in.)x(39,350) sq. ft. =328 c.f. Volume Provided Forebay 1 —509 cu. ft. (see stage storage table) Post-Development-Basin Modifications Type !!! 24-hr 900-Year Rainfall=8.60" i Prepared by OHI Engineering, Inc. Printed 6/8/2021 H droCAD@ 10.10-4a sln 11276 O 2020 H droCAD Software Solutions LLC Stage-Area-Storage for Pond 4P: Forebay Elevation Surface Storage (feet) (sq-ft) (cubic-feet) 206.00 220 0 I 206.05 226 11 206.10 231 23 206.15 237 34 i 206.20 243 46 206.25 249 59 206.30 255 71 206.35 261 84 206.40 267 97 206.45 274 111 206.50 280 125 206.55 290 139 206.60 300 154 20U5 310 169 206.70 320 185 206.75 331 201 206.80 342 218 206.85 352 235 206.90 363 253 206.95 375 271 207,00 386 290 207.05 396 310 207.10 406 330 207.15 415 351 207.20 426 372 207.25 436 393 207.30 446 415 207.35 456 438 207.40 467 461 207.45 478 484 207.50 488 509 207.55 II I�IIII III IIIIIIIIII III III IIII IIIIII III II II IIIYYIWYIIYW 533 207.60 510 559 207.65 522 584 207.70 533 611 207.75 544 638 207.80 556 665 207.85 567 693 207.90 579 722 207.95 591 751 208.00 603 781 208.05 646 812 208.10 691 846 208.15 738 881 208.20 785 919 208.25 835 960 208.30 886 1,003 208.35 938 1,048 208.40 992 1,097 208.45 1,047 1,148 208.50 1,104 1,201 -- - --------- ------ d"%T-Ti ,r"^' 4NI ENGINEERING.INC. n n `°7r_�-r• r,/1 �;Y»j, __ ��;', ? �j wMannlenglrwenrlg.cem rxou 'u,Ywr`ae • F p'_ xsrur"uoew / } —Mrs.aeauA.:, ' �!� / � aroauniar rom ec nm o�nwu�co� 1 y < o arec �wr,Ir un = f ! l fy/ • X \\\ ••i --- 10�._ vro ac Ton wNon All V�. man r�nc-uun - _:\ •. _ �1 rr(x,,, ,', ti��. �• _ enlvi.w.wy roxe-__..+Nly.dq ___ c bw�Tsmm 1¢riti �WVM�[ — � it .J 1Px 0'' f �acwsc mimicim io`mi r '�'� _ tr _ ? -•.. S\ ?1 � ro �'f� + cunoNlcscl�x -----------_ 1- mm 3 —•••••—J—y...—_— DRAWNG ISSUE'0 FOR, J CCNCVs T Q CCNSMCTICN ■PERMIT Q C C�CiNN p =.:"d�3 1, FK r * ,� a Ne:s1 / ,KSWr numxxyros�o.ao-a�nwr.mm 2 SrAE:N¢PRFATIFR ReN _ �S J h___,�.T � �` �I tiwrs�"n�a ww�ma�r�rv�nv,2�v 94 y sw asp wax eH owir wig owos�mcwic @ ww+�.r m To ae cowmurnx w cuwac,m urs�vr To axm e v[C meva rymoe aw oup'm�wx� �Mm s'.au.iro um mgma 21— ,oxw vuxr maa ro a r ranr.r v.,Nxca GRADING LLM 1PUw1o�T��' � � INWL k waR{ql CAW p S'C eC r I .�`fr �A.�iJ✓Tv"CTRr aL DRAINAGE PLASM S17EPLAN mmaTe wrar tivas CHiCICERINGROAD (ROUTE 125) svuWaY pNor7tt Nss�,aw r w NORT}t ANAQVF.R.ArtP. Tic o mr.,a o THE TROUS TEES RESERVATIONS 299 HIGH S7RF,1;7,47 H FLOOR OTYPICAL EMPANICI MISPILLWAY O CU(CFF'WALL CDNFIGURAMN MAIL O LANDSCAPF CATCH HASN REPAIR BD5TON,N.P.92119 Spill N.TS SGLf MTS. S:NL-MTS 6123/2021 Town of North Andover Mall-TTOR-Chickering Road Entrance,4242-1764-Modification to 000-Basin NORT�,H OVER Jean Enright <jenright@northandoverma.gov> Massachuselis �� „ ,- TTOR - Chickering Road Entrance, #242-1764 - Modification to OOC - Basin Amy Maxner<amaxner@northandoverma.gov> Tue, Jun 22, 2021 at 2:11 PM To: Amy Maxner<amaxner@northandoverma.gov> Bcc:jenright@northandoverma.gov Attached are materials in support of a Modification request to the OOC#242-1764. "The Plan Sheet is the last page in this document" • The Commission issued an OOC in December of 2019 governing construction of a new gravel access driveway off of Chickering Road to serve proposed gravel and grassed overflow parking, with associated stormwater system and plantings (at entrance, along gravel drive and parking and perimeter of work for screening and aesthetics). Work related to Chickering Road curb cut, gravel access drive, stormwater infiltration basin, associated grading and landscaping will take place within the 100-Foot Buffer Zone to Bordering Vegetated Wetland. • The Commission will recall getting reports from Joe Lynch and I on the basin failing to infiltrate in the 8 hours as proposed, Soils within the footprint are not infiltrating, we dare say at all! • TTOR hired a new engineer, James Borrebach with OHI Engineering, who has reviewed Hancock's analysis, has undertaken his own site reconnaissance and survey to evaluate alternatives for making this basin functional. • The OHI has proposed converting the basin from infiltration to detention by making the following modifications to the basin: o Install a sediment forebay at the inlet of the basin to remove TSS o Regrade the bottom of the basin up to elevation 206.1 o Core a 4-inch diameter outlet hole into the face of the outflow structure at elevation 206.1 -this will avoid significant/permanent standing water in the basin o Increase the perimeter basin berm to elevation 209 to increase freeboard above the 100-year flood elevation o Install a stone lined emergency overflow/spillway on the westerly side of the basin o Install a rip-rap lined swale and level spreader off of the existing rip-rap outlet to direct water to the west and avoid flows going to neighbor's backyards on Old Village Lane. This work will remain outside the 25' NDZ • I have requested an updated O&M Plan for these new features - hopefully they can provide this by the meeting • Joe has been part of the discussion on these changes and gave his nod to submitting this as a modification request Recommendation: • These modifications do not require additional land disturbance for storage capacity and therefore are minor in nature considering the goal. • Approve Modification as presented -if necessary require submission of an updated O&M. Amy R.Maxner Conservation Administrator Town of North Andover 120 Main Street North Andover, MA 01845 Phone: 978-688-9530 Fax: g78-688-g542 Email: amaxnor@northandoverma.gov Web:www.northandoverrna.gov MassDEP#242-1764 Modification Request 6-11-2021.pdf 1116K littps://mail.google.com/mar llu/0?ik=7o2eff6265&view=pt&search=all&pe rmm sgid=msg-f%3A i 7O3291643321184508&si mpl=msg-f%3A170329164332... 111