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HomeMy WebLinkAbout2005-07-22 Engineering Review �0 En47tneertng Associates, Inc. 236 Pleasant Street, Methuen, MA 01844 PHONE: (978) 689-7272 FAX (978) 689-8181 E-MAIL; CAQEAOAOL..COM June 7, 2005 Timothy B. McIntosh, PE RECEIVED Vanasse Hagen Brustlin i��N Z �J 101 Walnut Street Watertown, MA 02472 NORTH ANDOVER PLANNING DEPARTMENT Re; Map 25 Parcel 4 Willow Street—N. Andover, MA Dear Tim, A set of responses has been submitted to you for review, for the above referenced site. Based on my discussions with Lincoln Daly, additional information was requested regarding the culvert and its sizing. To that we submit the following; 8. Has a culvert analysis been done for the proposed box culvert at the driveway? Will the capacity of the existing drainage ditch be affected by the proposed culvert? As per section 6.14.2 of the Town of North Andover Rules and Regulations,culverts must be designed for 100-year storms. The Applicant should provide calculations shpwing that the culvert can accommodate the lWyear peak flows without causing flooding Opstresm. Pep 4+fMo j, h- n fl tt t c� ► h (i h , try rrt t tl llgv J 11rc +tln a�#���� +��,ftr�tl " ��1�'�" ''��el� it , �1"1►��" ` 1�,��'; "�' `�itgl �lvitre�'. From the enclosed section of the Willow Street design drawings,the existing lopvgraphy indicated a high point in front of the proposed site,draining both ways.As the road was constructed a barrier was created by the elevation of the pavement,and the ditch was constructed to relieve the drainage. The existing ditch has little to no directional gradient, thus acting as a connection between wetlands on both sides. We looked at the maximum potential contributing watershed,per enclosed VSCS map, and assumed that all its drainage will flow through the proposed box culvert(total area�8,26 acres). The en,clo.sedcalculations review this condition and the impact on the culvert. 1�r the 100 year event the culvert would reach 1.22 feet in depth. From field observations the level of the water in the ditch, in high flow limes has never exceeded 6-9 inches, and due to existing Ippography excessive flows will follow the path of least resistance which is toward the west dnd into the flood plain area. I or these reasons we feet the box culvert exceeds any design criteria. Thank you for your attention on this matter. Should you have any questions, please contact this office. Sincerely, CAQtgineering Associates, Inc. Carlos A Quintal, PE c:) n /4e +,c_., ..,.r r'•."' "'�.-✓,,„r'.ter" d:..e'.'�, us/:>• ..:a+;'�.. ���� ail Z ♦ Q� Nf11/ f RIP-OQAP q•` `\ (E! War = 2,1o.71J 1^ \ +s Emei9�Y Canted ��� Sw �2 e' : h✓. (Q HW-JO-RCP) - 2J2.8 2 14 m RCP) - 23-EJ7 Executive Center Limited Partnership (CIO Channel Building Co.) 39' Of 15-RCP a 5 -D.O0T3'J' k f St SAS 11 11+! '.55 (UO \ R7im - 2M97 � hv(n Seth 12) - 2J.L74 41t +� \ hr. (rkrJ -2JS42 1 1 fa 21*J7 •+ \ \ l em =235tS1 � a+ , -� v. = 2J152 a►' m. 1 CSCS Sta-22+46 i% 1 rSS' Of 12-RCP Sta 3o+8J S= -- AOO74'J' (L ItJ lei.,J= 2Jd94 :: \ 1 Drain -242G6 by - 2JS7riJ-- Easement 47K tj2. 2Mrf J3• Of 12-RCP D 1 CS 2� (LfLJ hv(712376 j- - c: CB Rr» 2J798 J Sta 24+16 hv(h 23;68 3T' Of 12-RCP L'J Mv. (Out) =2J4=65 am - 2Jti r9 ��1 o s= -o.Ors •/' �� hv. = 2J4.B4_� - , Dra in \ Easement Cav�a•cte / ��i Jr Of 12-RGp saw s6s •S- -aoowr . Ca hFl r. (12) -2.3ri 0 3 r 1 ad Cancreta Ran = 2J192 / ia.�� Apran 5rv(ky =2MJ2 ��? JI' Of 12-RCP Ryf'30 1 h 2J627 f4. i a S - QOO77'/' •(� Sta-24+49 �\� ; SBS i _. O well.. Rim ; 2.&66 25 �• i ktv. a.2Jz61 �, aa� �� \ f �+ -��"d-• 0027'' 5�f/ f11� bap \`�� �...�._,.�•c`•�-'=��"29 ------- .°..._ ��--- s 2B �� ----- - ----------------- - St 5"3 -- ....-+yam 4 8+0 R �. 9 . -kw �.2M19 , " r1"RGa - �- -Sf26+50 s- :2 %� Holbrook Realty must - --_ U Anna-I.cr tseri�. i LL,Lt; cc �1)d REMM4 TOWN OF NORTH ANDOVER PLANNING BOARD JWA 1 4 ENGINEERING REVIEW OF SITE PLAN N0R11 /AiNt=XZK FOR CONFORMANCE WITH THE p�,pi�jlNIIi TOWN OF NORTH ANDOVER ZONING BYLAW I Site Plan Title: Willow Street--Map 25,Parcel 4 V1113 No.: 06716.98 Site Plan Location: Willow Street Applicant: Dr.Sudarshan Chatterjec,55 South Bedford Street,North Andover,MA Applicant's Engineer. CAQ Engineering Associates,Inc.,236 Pleasant Street,Methuen,MA Plan Date: September 24,2004,Rev Nov 8,2004 Original Review Date: 12-16-04 Revised Plan Date: January 27,2005 2 A Review Date: 02-10-2005 Revised Plan Date: February 15,2005 3rd Review Date: 03-15-2005 Revised Plan Date: April 25,2005 4th Review Date: 06-09-2005 The plan was reviewed for conformance to the 1972 Town of North Andover;honing Bylaw(last amended December 2002),the North Andover Wetlands Protection Regulations(NAWPR)and standard engineering practice. The Applicant has submitted the following information for VHB's fourth review: • Technical Supplement to Site Plan Application Notice of Intent revised May 20,2005, • Letter and information from Applicant's Engineer regarding proposed box culvert dated June 7,2005, • Site Development Plans revised April 25,2005, • Response to comments letter dated April 27,2005 VHB's original comments are shown-below in normal font,unaddressed follow-up comments are shown in italics. VHB's fourth round of comments is shown in bold font immediately following the original/unaddressed comment/comments. Drainage Comments 1. The System Design Overview section of the NOI Technical Supplement states that a Drainage Swale,Detention Basin and a Constructed Wetland are used to mitigate impacts,however only a vegetated wet pond with a sediment rorebay,as defined by the DEP Stormwater Management Handbook,is used, Not Addressed. This section was not changed, Not Addressed. This section, located in the Storttisvater Mattagentettt section of the Applicant's technical supplement,should be updated to include the Stortnceptor, the detention basin(sediment trap)and the deep sump catch basin. Not Addressed. In the Stormwater Management section of the Applicant's report,there Is a section entitled System Design Overview. Toward the bottom of this page,the Applicant lists the different BMPs(Best Management Practices)used on the site. The list incorrectly states that Drainage Swales,a Detenetion Basin and a Constructed Wetland are used. These should be replaced with Deep Sump Catch Basins and a Slormceptor,as shown on the current set of pluns. 1 T.ti n,.y i R w•,,,-��...q,..r.�,nark Fae i,•.i�,. .c,�n.�,..�.,.i ncnsnc�,,; r , 3. Does the runoff from the proposed driveway flow to the existing drainage system on Willow Street'? If so,the Applicant should verify that the existing drainage system on Willow Street has enough capacity to accommodate the added Flow. Addressed. However has the Applicant verified that the swale has the capacity to take fire additional J1ou-front the driveway? Partially Addressed. Vie Applicant is Crow proposing a deep sump catch basin at fire driveway entrance. VHB has thefnllowing comments: • It does trot appear that tire catch basin cart be constructed as proposed. As per lire Applicant's detail, there Creeds to be a mirtinurtrr 40"between rint and invert(16"-top caste,8"typ-depth of the frante, 2"-clearance over the outlet pipe, 2" pipe thickness, 12"—pipe size). Tire plans show Rim-invert= 18". • The outlet pipe,flared end section, along with lengths,pipe sizes and inverts should be shown on the plaits. Partially Addressed. The Applicant has added the requested information to the plans and has revised the catch basin detail to have a flat top. The Applicant should note that two different inverts are shown in the insert. In addition,the catch basin wilt remain unconstructible if the 99.84'invert is used. The Applicant should verify that the correct invert is shown on the plan,that the catch basin is constructible using this invert with a 12"reinforced concrete pipe and that the proposed FES has an invert elevation that will permit the water to now out of the catch basin into the ditch. B. Has a culvert analysis been done for the proposed box culvert at the driveway? Will the capacity of the existing drainage ditch be affected by the proposed culvert? Partially addressed. The Applicant should provide the calculations in the Technical Supplement. Partially addressed. The Applicant has provided a sketch comparing existing grotrrtd and proposed culvert sections. VHB offers tlne following cornrttents: • No scale was provided for fire sketch. • A limited nunsber of spot elevations are shown our rite plan. The Applicant should clarify how the existing ground line wa,s drawn based on these existing spot elevations. • The sketch, which shows the existing ground narrower than the culvert, seems to contradict the sewer profile section, in which the existing ground is wider than the proposed culvert. The Applicant should clarify. • As per section 6,14.2 of fire Town of North Andover Rules arid Regulations,culverts must be designed for 100-year storms. The Applicant should provide calculations showing that the culvert can accommodate tire 100-year peak flows without causing flooding upstream. VHB agrees with the Applicant's responses and reasoning. The Applicant has adequately addressed VHB's comments regarding the culvert. 11. Length and size of proposed drainage pipes should be shown on the Layout and Utilities Plan. Not addressed, Lengths were trot added. Not addressed. Lengths were not added. Addressed. 2 .. 12. The Applicant should provide capacity calculations to demonstrate that the 12"RCP outlet pipe is adequately sized. Partially addressed. Although the 12"pipe will only handle the flow through the 4"and S" orifices, the Applicant should provide a complete set of pipe capacity calculations in the technical supplement. Tit is would also include the 6"PVC pipe from the curb itrlet. Partial!v addresser!. The Applicarat has provided pipe capacity calcidations with the latest revision of ilie technical stipplenrent. VHB offers the folloit,ing eoninrenis: • The Applicant should jtistify the rainfall intensity used. The Iritensity-bra'aliorr-pregiiericy curves should be provided!it the Technical Supplement, • If all times of concentration are the same(S min), the rainfall intensity should be consistent for all pipe calculations. • As stated ill the Applicant's previous response, the detention basin outlet pipe only needs to accommodate the flow through the orifices of the outlet structure. Therefore Qfiill(4,40 cfs) .shotdd be compared directly to the calculated outflow of fire delentiorr basin(0.88 cfs for 10 year, higher for 25 vear stone). • The pipe size and Manning's coefficient used to calculate the capacity of the pipe going fi-oru the curb inlet to the Stormceptar(8", 12CP)are not consistent with the size and material shown in the curb inlet detail(6", PVC). • The Applicant should include caleitlations for the pipe at the catch basin at the driveway entrance. • It does not appear that the Sronnceptor cart be constructed as proposed. As per the Applicant's detail, there needs to be a minitnurn 18"between rim and invert(5"-cover and grate, 8" -depth of concrete slab, 6" -pipe size). The plans show hint-invert= 13". Partially Addressed. The Applicant has made revisions to the pipe calculations and has provided some rainfall intensity data. VHB offers the following notes: • The Applicant has added rainfall intensity data for the SCS method of calculating slormwater runoff, The Applicant uses the Rational method for his pipe calculations and therefore should have included Intensity-Duration-Frequency curves for the Town of North Andover or relative area. By using the City of Boston I-D-F curve,VHB finds the 25-yr intensity to be 6 inches per hour. By using a 6 inch per hour intensity,VHB finds that the 8 inch PVC pipe from the curb Inlet to the Stormceptor falls. All other pipes appear to have the proper capacity. The Applicant should revise his calculations or justify the use of 4.5 infhr intensity. • As stated in previous comunents,the pipe from the Outlet Control Structure to the FES only needs to handle to outflow of the detention basin. This pipe currently has a capacity of 3.86 cfs and therefore can handle the 100-yr storm of(1.15 cfs). No further response is necessary on this issue. • The calculation for the pipe going from the catch basin to the FES at the driveway shows a slope of 13%. This slope should be revised to be 1.3%. Using the revised slope,VHB calculates that the pipe is correctly sized. No further response is Necessary on this issue. • The Applicant has revised the Stormceptor detail, however it remains unconstructible. The detail now shows a 5"frame with a 12"concrete slab. By adding the pipe width and thickness, 12"and 2",a minimum of 31"of clearance are needed between the rim elevation and the invert elevation to construct the Stormceptor. The plan Shows a rim to invert distance of 1.1 feet. „..._.. 3 r 17. It appears that the proposed grades at the bottom of the proposed wet pond are lower than some of the existing spot grades near the site, Hnve any test pits been taken to verify ground water elevation,infiltration rates,etc,,.'? If the proposed wet pond will contain standing water,the Hydrocad model must take this into account. Not addressed. The Applicant should verify ground water elevation to know whether the bottom of the detention basin is above it or not, Partially addressed. Two bore(roles were takers, VHB has the following connrrrelrts: • The results of the bore holes should be provided in the technical supplements. • The Applicant claims that groutdwater was recorded at elevation 97.3% The Applicant should clarify whether this is seasonal high groundwater. The infiltration system and retention pond should be a rninitnrun 2'over seasonal high groundwater, as specified in Appendix V,section 5.c of the Town of North Andover Ruler and Regulations. Addressed. DEP Stormwater Management Standards Standard#3 1. it is unclear how the Applicant calculated the volume to be recharged. The total impervious area of the site is 18,687 SF and the recharge rate for C soils is 0.1 in, for a volume of 156 CF. Partially addressed. The area stated in Appendix C should be 18,687 SP(the driveway area needs to be recharges)as well). Recharge vohone calculations should also be provider)in the technical supplement. A detail of the leaching trench should be provided. Partially Addressed, The Applicant has provided infiltration calculations and a leaching trench eletall. VH8 has the following comments: • Have percolation tests been performed? Partially Addressed, The Applicant states in his response that percolation tests cannot be performed,due to the high groundwater level at the site. Since the Applicant cannot Justify the Infiltration rate used, VHB suggests removing Infiltration from the Hydrocad model. The Applicant should verify that the How out of the in111tration system remains smaller or matches the flow into the system. In this case,the Infiltration system will act as,a detention area while still providing the necessary recharge volume,since the water will eventually seep into the ground. • How was the 0.01 efs infiltration rate which was used in the Hydrocad model determined? See previous, • Conflicting pipe sizes are shown for the PVC roof drain in the leaching trench detail, It is labeled as a 25'-8"PVC, however the inverts are shown as "inv 4"PVC= 101.35". Addressed. • Based on the Hydrocad model, it appears that an overflow pipe is being proposed for the infiltration system(12"vertical orifice @ elevation 101.0). This pipe or orifice does not appear ill the plan, nor the detail. Partially Addressed, As shown on the detail,the outlet should be modeled as a 12" horizontal orifice,not vertical, • h is unclear how the 43 cubic feet of storage in the Hydrocael model was calculated. What is the void ratio used for the leaching trench material and the septic gravel? Partially Addressed. The Applicant has provided an explanation of how the storage volume Is calculated,however the model does not reflect the Applicant's calculation or 185 cubic feet. The Applicant should revise the model to show 185 cubic feet of storage between elevation 100'and elevation 1011. • The leaching trench detail should,Specify dimensions and proposed materials, Addressed. + VIIB suggests a geo-membrmre or filter fabric should be proposed around the leaching trench. Addressed. • The leaching irench detail in not at 20-scale. Addressed. • Appendix C of the NOl has not been revised to sho",the correct impervious area and recharge voliane. Addressed, VHB offers the following notes regarding the infiltration system; • The Applicant should note that,as currently designed and modeled,the infiltration system has a 0.19 efs(0.006 of=260 cf volume)overflow from the 12"orifice during the 1-yr storm. This overflow will run across the parking lot before making its way to the curb inlet and Stormceptor, • As per DEP Standards,roof runoff is considered uncontaminated and does not need to be treated, By designing the system to overflow onto the parking lot surface,the water then Is considered "contaminated"and needs to be treated. • VHB suggests proposing an overflow outlet pipe from the proposed DMH which would outlet toward the adjacent wetland. By constructing a baffle wall inside the manhole,the roof runoff will first flow Into the 2 infiltration trenches. When overflow conditions occur,the water will back up and rise inside the manhole until it flows over the baffle wall and out of the overflow pipe. This would reduce the amount of water to be treated by the Stormceptor. In addition,the recharge volume requirement remains satisfied since the remaining water In the Infiltration system will seep Into the ground, Standard#t4 1. The Applicant is claiming an 80%TSS removal rate.The detention basin/wet pond doesn't have a forebay•Without a forebay, it can't be claimed as a wet pond(70%),only as a sediment trap (25%).As of now,the sediment trap and the pavement sweeping equal a 32.5%TSS removal rate. Not addressed. As stated in VHB's initial comment, the Applicant cxtttrrot c•labn the 701yo TSSremoval ratefor the detention basin unless it has a sediment trap, therefore Appendix Cshottdd be revised to only claim 2S°lo• The Applicant should also provide the manufacturer's sizing chart in the technical supplement, .showing TSS renioi al races for the proposed irripetviotrs area. Partially addressed. VHB offers the following comments,- • A.s stated in previoxs comments, a 70%TSS removal rate cannot be user!for a detention pond runless it has a.sediment forebay. As proposed, the Applicant can only claim credit for Street Sweeping, Deep Sump Catch Basin, and the Stormceptor. Not addressed. VIIB agrees that a Stormceptor has a greater TSS removal rate than a sediment trap,however the Applicant cannot double-count the Stormceptor. As 5 "k`k1r.�li ipi.f..emn•.•...\ry,YkFgO kllilln.•CI.n 9n,in.• j/v�lgq:.{,� designed,and as per DEP Standards,the wet pond has no TSS removal value. It is detaining the water,not treating it. • As per DEP standards, Curless othenvise specified by lire T0wn's DPW, the Applicant is able to claim a 25%TSS removal rate for the deep srunp catch basin. • Taking into accoturt the previous continents, VHB calculates the TSS removal rates as 821k for the parking lot portion, and 33%for the driveway portion. The Applicant should note that the Conservation Commission may not accept the sveighred TSS removal rates as miggested by the Town's DPW. Not Addressed. The Applicant states in his response that the TSS removal rates have been accepted by the North Andover Conservation Commission. VIIB would like to note that the Applicant's NOI Stormwater Management Form(WPA Appendix C,P.3 of 5,standard#4),is still inconsistent with the additional TSS Removal calculations provided. In addition,the Applicant's TSS calculations still claim 70%n for the wet pond and uses a weighted rate,which VHB has previously commented on and disagrees with. It is recommended that the Applicant provide WRITTEN RESPONSES to the issues and comments contained herein. / Reviewed.by: Date: 6 3 -0 Darryl Gallant Civil Engineer—Highway and Municipal Checked by Date: z"u Ci 7 05 Timothy B.Mkntosh,P.E. Project Manager—Highway and Municipal 6