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HomeMy WebLinkAbout2003-08-19 Engineer Review SPR I Transportation Land Development Environmental � • S e r v i c e s � r113arftt7attrrn�tulnuvatrrrn r2rtewcpy Creating results for ow.clicrrrts;7rid benefils for oily cotntr7urbtties August 19,2003 Ref: 06716.76 i Mr.Justin Woods,Town Planner 11 .W *m rb I ,w Community Development&Services Town of North Andover 27 Charles Street AUG 2 North Andover,MA 01845 f� llhflvJItCt ttGr�r,i� l".,�; i Re: Brooks School Athletic Facility 3lr, �- Site Plan Review North Andover,MA I Dear Clay: Vanasse Hangen Brustlin,Inc. (VHB)has received Rist-Frost Shumway's written response memorandum(dated August 1,2003) to our Engineering Review for the above referenced project. It appears that all of VHB's comments have been adequately addressed and VHB's concerns in this matter have been satisfied. No further engineering review is required at this time. If you have any questions or concerns,please call me at your convenience. Very truly yours, VANASSE HANGEN BRUSTLIN,INC. Timothy B.MZosh,P.E. Project Manager—Highway&Municipal Engineering 101 Walfrout Street Post office Box 9151 Watertown, Massachusetts 02471-9154 \\Mewatr\te\0671676\does\letters\let-brooks-approv-08-20-03.doe 61Z924,1770 a FAX 61%,924,2286 email: infoGvhb.com www.vhb.com TOWN OF NORTH ANDOVER PLANNING BOARD ENGINEERING REVIEW OF SITE PLAN AND WATERSHED SPECIAL PERMIT FOR CONFORMANCE,BYLAW O E R ZONING AND STANDARD ENGINEERING PRACTICE' Site Plan Title: Br•oolo School—New Athletic Facility VHB Na.: 06716.76 Location: 1160 Great Pond Road Owner: Brook School, 1160 Great Pond Road,North Andoyer,MA 01845 Applicant: Brook School, 1160 Great Pond Road,North Andover,MA 01845 Applicant's Engineer: Rist-Frost-Shumway Engineering,P.C.,I Water St,Laconia NH 03246 May 29 20fl3 Review Date: July 1,2003 Plan Date: Y , Review Date: July 17,2003 Revised Date: July 14,2003 Jul 24,2003 Review Date: July 30,2003 Revised Date: Y Vanasse Hangen Brustlin,Inc. (VHB)is providing a third engineering review of the Site Plan I Special Permit School--New Athletic Facility. This review is conducted in accordance with the Town of Submission for the Brooks ment of Environmental Protection(DEP)Stormwater North Andover Zoning Bylaw,Massachusetts Depart Management Policy and standard engineering practice. VHB has received the following drawings and documents for review: : • Site Plans(15 sheets)dated May 29, 2003--Revised July14,2003--Revised July 24,2003 . Drainage Calculations.Volumes I&II dated May 29,2003—Revised July 14,2003 . Watershed Protection District Map The following comments note non-conformance with specific sections,constructability issues and questionsleomments on the proposed design. comments from our previous letters;however, a few items ressed the Comm p ' eer has add , En :n ezal the Applicant's g s previous Site In Gen have not been satisfactorily resolved. The responses fisted belowloelelon RFS ezes oases ara hrased in italics. Plan review reports,with corresponding Rist-Frost-Shumway Eng g•( ) p p p Our most recent comment or concurrence on RFS's responses are noted at the end of each section. VHB comments that were previously resolved have been remove ty. Section 7:Dimensional Requirements 7.4 Buildin Hei fits In table 2 of the Zoning Bylaws,the maximum building height is 35 feet. On the application for Site Plan Special Permit submitted by the applicant,the proposed building height is listed at 42'=6 /a"• The Applicant should request a waiver or revise the building height. RFS Response: The height listed in the Application was incorrect. The height listed was the vertical distance fi oln first floor to the TOOT peak. By Mass. Building Code collvelttlon, height is measured as the distance between average round the perimeter and the mid point of the pitched roof. Thus the height is 33'-8", which is ground elevation a 1 C:\wlridowsNTEMP\13YOOkSdlnol-review-3.doc less than the alloived 35'. A variance is not therefore required. This would explain why the project received a Building Permit in 2001 and no height issue was raised at the tune. VHB Response: The North And Zoning Bylaws(Sectio " n 2 Definitions) states that the"building height"is the vertical distance as measured from the average finished grade level adjoining the building at all exterior walls to the highest roof surface, but shall not include chimneys,etc..."The Applicant's Engineer should review the building height. It appears that a waiver may be required. RFS Response: The projectA,rchitects have discussed the height issue with the Town Building Corninissioner, who has detennined that neither a waiver nor a variance is required We not e further that the roofpeak will be several feet lower than inlhe 2001 design,for which a Building Permit was issued VHB Response: The Applicant's Engineer has addressed this comment. General Comments: 3. Rim and invert information for the new sewerline was not shown on the plans. A detail was provided for the sewer forcemain but there is not detail for the gravity sewerline. VHB suggests that the AppIicant's Engineer to provide this information. RFS Response: Sewer elevations have been added. The typical trench detail oil C502 applies to gravity sewers. VHB Response: VHB has reviewed the invert information provided for the gravity sewer. It appears.that the slope of the gravity sewer pipe connecting SM114 to the existing SMH on Service Road is negative. VHB recommends the Applicant review the sewer elevations, RFS Response: In computing the invert elevation of the existing sewer line in Manhole 4, ive made an interpolation error. The correct invert elevation at Maiihole 4 is 183.16. The elevations of the other pipes in the inanhole have beeia adjusted to niatch. This existing line has been functioning for some tine and is of coarse pitched in the downstream direction. VHB Response: The plans have been revised and VHB is satisfied with this response Drainage Comments: 11. The Applicant's Engineer has proposed a closed drainage system with catch basins in series (catch basin to catch basin)which is not considered good engineering practice. Area drains in landscaped areas may be inline, however,VHB recommends that catch basins with deep sumps be offline. If the applicant wishes to keep the catch basin to catch basin connections,they can not claim a 25%TSS removal rate unless they provide additional back-up information showing that flow through velocities will not re-suspend settled solids. RFS Response: RFS feels that requiring all catch basins to flow into drain nanholes should result in an excessive number of underground structures on a small site, at veiy little benefit to the storinwater system. The Town has allowed linked catch basins on similar previous projects on the campus. We do acknowledge the 25%TSS removal for deep-linked catch basins does not apply when they are linked. The TSS calculations have been revised to dispense ivith this element. VHB Response: Since the size of a site is generally proportional to the number of catch basins on it, this is not a valid argument. The applicant has proposed two(2)catch basins within a vehicular area. These CB's can be taken offline with the addition of one drainage manhole. The remainder of the proposed CB's and area drains collect runoff from sidewalks and landscaped areas which,per our•original continent, d6 not require an offline connection. Although it is VHB's opinion that a 25%reduction in TSS removal from a parking area is a significant benefit to the drainage system and the wetland to which it drains, VHB is satisfied with the proposed design if the applicant can achieve the required 80%TSS removal by other means. MwindowATEMMrook School-review-Moc 2 RFS Response: Drain.manholes 50 and 51 have been added to unlink catch basins 19 and 20 from the rrrain line of the network. Hydraulically this is a negligible change, so we did not feel it necessary to revise and re-run the HydroCAD program. VHB Response: VHB is satisfied with this response. 12. The bottom of pond elevation shown on the plans is 0.2 feet below the lowest invert elevation on the outlet structure. Will the pond have 0.2 feet of standing water? If there will be standing water in the proposed basin for an extended period of time,VHB recommends that a fence with a lockable gate be provided around the perimeter of the pond. RFS Response: The pond bottom and lowest outlet are intended to match so there is no standing water;the mismatched elevations have been corrected. VHB Response: The detail and drainage calculations still show a 0.2' standing water depth for Pond 1. The pond bottom is 173.3 and the lowest outlet elevation is 173.5. Please revise. RFS Response: The elevation of the lowest set of openings in the outlet riser to pond#1 has been changed on drawing C303 to match the pond bottom of 173.3. Our apologies for•llot following through oil this correction in our first response. VHB Response: VHB is satisfied with this response. 13. Manholes should be located at atl bends within the drainage system. RFS Response: A manhole has been added to the downspout leader pipe on the northwest corner. VHB Response: There are still three(3)bends without structures. VHB suggests that the applicant either revise the pipe layout to eliminate these bends or add structures. RFS Response: Cleanouts to grade have been added to roof leaders 41 and 45, and for infiltrator outlet 40. These lines will be carrying clean roof runoff and are unlikely to clog. The interiorplirlrrbilrg for the roof drains will incotporate cleanouts, so this should suffice for the underground portion also. A cleanout detail is shown oil C502 0 j VHB Response: VHB is satisfied with this solution. ' 15. VHB questions the long-term reliability of the proposed detention basin outlet control structure. VHB o recommends that this structure be inspected routinely for damage to the plastic riser section and for sediment build-up within the 6"stone. RFS Response: The riser has been changed to a precast concrete barrel section with flat top incorporating a fluslr gate. VHB Response: VHB is satisfied that this modification will improve the structural characteristics of the outlet g structure. Please add additional information to the detail depicting the structural material required below the unit to prevent settlement. > > " rete base sections", not barrel sections. We RFS Response: Ira our first response, 3l e meant to sad precast conc have f tither•clarified the details on C303 to show this intent. VHB Response: It is clear to VHB that this structure is essentially a catch basin. VHB is satisfied with this response as long as RFS instructs the contractor to"over-excavate below the structure and backfill with 12"of crushed stone" per the typical catch basin detail provided on sheet C502. i 17. The groundwater recharge calculations in Volume I show that the proposed intittrator recharge units do not have a large enough tributary area per the DEP Stormwater management policy. A note on the calculations reads, "Very close. Surely some recharge is happening in the drip trenches at the Maintenance Building." The proposed project has sufficient roof area to meet this requirement. VHB recommends that the Applicant's 3 C:\windows\TEMMBrook School-review-3.dac Engineer either quantify the Maintenance Building roof area tributary to, as well as the amount of void space in (assume 30%of total trench volume)the drip trenches or redirect additional roof area to the proposed units and increase the capacity proportionally. RFS Response: The recharge calculations have been revised due to a new information revealed by the soils investigation. The revised design incorporate sufficient roof area to compensate for the entire Maintenance Building. VHB Response: Based on the supplemental information provided, specifically the Norse Environmental Services Soil Test information stating that the onsite soil permeability is less than 0.2 inches per hour,VHB recommends that the applicant does not provide infiltration for this project. VHS is satisfied that the onsite soils are hydrologic group D and therefore exempt from the infiltration requirement of the MA DEP Stormwater Management Policy. RFS Response: This project is also being reviewed by the Conservation Commission for an cnnendtnent to the DEP permit. Their consultant, Eggleston Environmental, has agreed witty the proposed design concept in our 7110103 memo. As this rrratter seems closer to the mandate of the Conservation Commission than to that of the Planning Board, we respectfully propose to keep the infiltrators in the project runless directed otherwise by the Conservation Commission. VHB Response: VHB is satisfied with this response as long as the overflow pipe is increased in size to a 12" diameter pipe,the same size as the pipe into the recharge system. 18. A"Test pit log for detention pond"was included in the drainage calculations. The log included in the calculations references a sketch that is not provided. The Applicant's Engineer should provide this sketch as it is needed to determine the location of the test pit. In addition, the Applicant's Engineer should provide a plan showing the boring locations. RFS Response: The location of the test pit is shown on C301 and the boring locations are shown on both C201 and C301 VHB Response:Drawing C301 shows a test pit was excavated at elevation 176.0 within the limits of the proposed detention basin. The seasonal high ground water elevation for this test pit was observed to be 18"below existing grade,which places the groundwater at elevation 174.5. The proposed bottom of basin elevation is 172.0. Based on this information,there will be as much as 2.5 feet of standing water in the proposed basin. This has major implications on the proposed drainage system design. First, we recommend that RFS move the bottom of basin elevation above 174.5 or see Comment 12. Second,we recommend that RFS does not model any storage volume below elevation 174.5,since this storage volume will be wet for part of the year. Third, the Down Stream Defender is completely submerged at this elevation. Many stormwater quality devices do not work under submerged conditions. Please provide backup information the shows the following: a. That this is an acceptable condition that will not re-suspend previously captured solids. b. That the TSS removal rates provided are applicable for a submerged condition. RFS Response: Detention pond#2 is a dry pond, with outlet invert elevation equal to the bottom of the pond(see response to#12 above). Any groundwater which enters the pond will flow immediately out the outlet pipe. Thus the pond is normally empty, and its entire volume is available as active storage. Lowering the local water table at the pond will not tend to dry out the wetland, as the pond bottom is well above the level of the wetland. The water table under the adjacent hockey rink has been lowered by its undercdrain system ever since its construction, as will the water table ruiner•the proposed Athletic Facility. There is nothing unusual about lowering a local water table to prevent water problems inside structures, nor is it unusual to construct a dry detention pond. The same issue was raised in.2001 by the Conservation Commission, which is satisfied with this response. The Downstream Defender w411 be surcharged briefly during major storm events. Operation of the writs and their removal efficiencies are unaffected by submergence. Attached is a corfrr-rnator),rraerrro from H.I.L. Technologies, 4 C:\windows\-FE\4P\Brook School-review-3.doc rnl.atttfacttrrers of the Downstream Defender. Furthermore, the treatment standard is to remove 80%or-more of the total annual TSS load, not necessarily 80%of the TSS in every single event. Most of the annual TSS load occurs during events of ordinary intensity. VHB Response: Based on the letter from Hydro International,VHB is satisfied with this response in regards to the downstream defender. In reference to the groundwater elevation and it's interaction with Detention Pond#2,VHB requests that underdrain is placed below the pond to insure the proper functioning of Pond 2. 21.Please provide sizing calculations for tine"Down Stream Defender"water quality unit. These calculations should show a 6' diameter on-line unit is capable of achieving the required T.S.S.removal rate for the proposed tributary area. for Do+vnstrean included in Drainage Calculations. RFS Response: Sizing calculations i VHB Response:These calculations are acceptable for north basin. Please confirm that the TSS removal rates provided are applicable for a submerged condition. RFS Response: See merino from.H.I.L. Technologies. VHB Response: VHB is satisfied with this response. 22. Spot elevations are needed at building corners to clarify surface drainage patterns. RFS Response: Spot elevations at building corners and more cot.totrr rrtrrrtbers added to plans. VHB Response: Drawing C301 shows the west side of the proposed athletic facility at elevation 190. The CB rim elevations on this side of the building are at 190.5. As currently shown on the drawings,stormwater drains to the building. The west elevation an sheet A301shows the grade at this part of the building at 190.5. Please clarify. RFS Response: Finished grade along the west exterior wall is 191.0, as shown on dra+ving L201. Catch basin rin.s are set 6 inches lower at 190.5. Fromi there, the finished grade slopes up+nand to the grade along tJre road. Tlne .at the very corners of the building, where the grade drops around the north and spot grades on A301 are shown south ends. If one carefully observes the grade line along the base of the building shown on the West Elevation vie+v oil A301, it agrees with L201. Obviously, the intent is to slope grade a+vay from the building into the drainage System to avoid ponded water against the building. VHB Response: VHB is satisfied that plan L201 shows this grading correctly. For clarity, it would make sense to show this information on sheet C301,the Grading and Drainage Plan.. 28. The rip-rap for outfalls 10, 13 and 40 are not shown graphically on Sheet C301 of the drawings. RFS Response: Apron far outfall 10 shown;outfalls 13 and 40 go to a level spreader VHB Response: VHB is concerned that there may be erosion at outfalls 13 and 14. How are erosive forces minimized at FES inside the level spreader? RFS Response: We have extended the riprap of the secondary outlet 14 by]Oft. to create an apron 15 and have moved the outlet pipe so it discharges onto the apron. The riprap sizing nomograph yields a d50 of 0.4 ft., so 6" stone is used. d with this response in regards to outlet 14. Please provide outlet protection at the VHB Response: VHB is satisfie outlet to Detention Pond 1 as well. 32. Drain manhole 37 is not constructible as currently designed(rim to invert= 1.8% 18"outlet pipe). m has been raised and surrounding ground surface mounded slightly. RFS Response: This manhole ri VHB Response:VHB suggests that RFS show this grading on the drawings. 5 C:\windows\VMP\Brook School-review-Mac RFS Response: Finished grade contoitrs have beery added ai orntd DMH 37. VHB Response: VHB is satisfied with this response. 33. As currently designed,several of the proposed 12"drain lines are flowing full for the 1-year design storm and water is ponding on the surface at catch basins 19 and 20 for the 25-year design storm. The grading plan shows the area in the vicinity of CB's 19 and 20 to be relatively flat and near a handicap accessible route. It is likely that the surface ponding will spread across this accessible route. Therefore,VHB recommends increasing the capacity of the drain line where necessary to eliminate the surface ponding in this area. A bypass has been added around the downstream Defender to divert high flows around the unit into the detention pond. This bypass precludes any surcharging of catch basins 19 and 20. The basins have been moved slightly to coordinate their location with curb tip-downs. VHB Response: It is unclear how the RFS response addresses this comment. The Downstream defender will be completely submerged for a 25-year storm, including the bypass, and therefore it is unclear why the bypass is needed. Please explain? RFS Response: The bypass ivas added to eliminate ponding in the 25-year storm at basins 19 and 20. It becomes active whenever flow depth exceeds 12" in the pipe to the Downstream Defender, and diverts some of the flow around the Defender, thus avoiding enough head loss to prevent upstream ponding. Though this pipe is surcharged during the height of the 25-year storm, it is passing a high volume of water(4.08 cfs)and is effective at avoiding ponding, which is its propose. This is confirmed by HydroCAD. VHB Response: VHB is satisfied that the additional 12"pipe added by RFS provides sufficient capacity to the closed drainage system to prevent ponding in the parking lot for the 25 year design storm for the previous submission. Due to the fact that the HydroCAD calculations have not been resubmitted per the Comment 34 revisions, VHB cannot confirm that this is still the case. VHB asks RFS to check the revised calculations to ensure that no ponding occurs at catch basins 19 and 20 for the 25-year storm. 34. In both the existing and proposed hydrologic analysis of the site, the Applicant's Engineer consistently uses times-of-concentrations(te's)of less than 5 minutes. We recommend that the engineer uses a minimum to of 5 minutes. RFS Response: We understand that VHB prefers to limit times of concentration to a minimum of 5 minutes,for pipe sizing proposes. This is a very conservative approach, as it theoretically forces more flow thru certain pipes, as all the peaks occur at once. RFS feels this is unnecessarily conservative. Our design.shows that the system can handle the 25-year stor-m and is required by[lie town DPW. VHB Response: RFS has used the computer program HydroCAD to develop the hydrologic model for the site. This program uses U.S. S.C.S.Urban Hydrology for Small Watersheds Technical Release 55 (TR-55)methodology for calculating times of concentrations. TR-55 models complex forces of nature by making several assumptions and simplifications about some parameters. Page 1-4 of The U.S. S.C.S. Urban Hydrology for Small Watersheds Technical Release 55 handbook reads, "To ensure(fiat the degree of error is tolerable,specific limitations are given in Chapters 2-6. " One of the limitations listed is that a minimum time of concentration of 0.1 hours(6 minutes)is used, Do to the limitations of the hydrologic model,and to ensure that the degree of error is within reason, we suggest that RFS does not use a time of concentration of less than 5 minutes, which is still less than that recommended by the S.C.S. RFS Response: Please note that the revised HydroCAD model of 7111103 has a dt of 0.01 horns(or 0.6 minutes), whereas otrr•original model of 5129103 used 0.1 horns. Seepage I or each storm analysis. This allows for an. accurate modeling of drainage areas with times of concentration less than 5 minutes. VHB Response: VHB is satisfied with this response however;we have not received or reviewed the revised model. Please see VHB's response to the previous comment. 6 C:\windows\TE41P\E3rook School-review-3.dac It is recommended that the applicant address the comments outlined above. If RFS is agreeable to the above recommendations,then VHB is satisfied with the proposed design and recommends that no further engineering review is needed at this time. If RFS would like to discuss any of the above outlined comments further,RFS should provide written responses to VHB. Reviewed by: Dates Christopher Nowak,P.E. Drainage Review Reviewed by: Date• Tracie Lenhardt Civil Review Checked by: Date: Tim McIntosh,P.E. Project Manager—Highway and Municipal Engineering s 7 CAwindows\TFMP\Brook School-review-ldoc pE ENO pT b qHp Town of North Andover Office of the Planning Department * c a Community Development and Services Division 27 Charles Street SSACHUSF North Andover,Massachusetts 01845 Planning Director: http F://www.townofnorthandover.com (978) 688-9535 J.Justin Woods jwoods@townofnorthandover.com (978} 688-9542 To: John Scott From: J. Justin Woods Fax: 603-528-7653 Pages: 8,including coversheet Phone: 603-524-4647 Date: July 31,2003 Re: Brooks School Athletic Facility CC: °o u a ❑Urgent Q For Review ❑Please Comment C!Please Reply 21 Please Recycle fi g Comments: Attached please find the Planning Board's outside engineer's third review of your application. The public hearing on this application has been continued to the Planning Board's regularly scheduled meeting on August 5, 2003. It is recommended that the applicant be prepared to address outstanding issues in this report. Please note that if RFS is agreeable to the attached recommendations, then VHB is satisfied with the proposed design and recommends that no further engineering review is needed at this time. It is further ents recommended that the applicant prepare PLAN REVISIONS in compliance with the comm €' contained in VHB's third review in anticipation of the hearing remaining open and being continued I' to August 19, 2003. The deadline for submission of revised plans for the August 19, 2003 meeting is August 11, 2003 at 12:00 noon. If the changes are limited to and include all of the VHB's recommendations, then the responses and revisions only have to be submitted to the Planning Department. Si V�j f in THE DOCUMENTS INCLUDED IN THIS TRANSMISSION ARE INTENDED FOR THE RECIPIENT TO WHOM IT IS ADDRESSED. IT MAY BE PRIVILIGED AND CONFIDENTIAL OR PROTECTED AS AN ATTORNEY CLIENT COMMUICATION. IF YOU ARE NOT THE INTENDED RECIPIENT, PLEASE NOTIFY(978)688-9535 AND DESTROY THE DOCUMENTS YOU RECEIVED 1N ERROR. TOWN OF NORTH ANDOVER PLANNING BOARD ENGINEERING REVIEW OF SITE PLAN AND WATERSHED SPECIAL PERMIT FOR CONFORMANCE WITH THE TOWN OF NORTH ANDOVER ZONING BYLAW AND STANDARD ENGINEERING PRACTICE Site Plan Title: Brooks School--New Athletic Facility VHB No.:06716.76 Location: 1160 Great Pond Road Owner: Brook School, 1160 Great Pond Road,North Andover,MA 01845 Applicant: Brook School, 1160 Great Pond Road,North Andover,MA 01845 u Applicant's Engineer: Rist-Frost-Shumway Engineering,P.C.,71 Water St,Laconia NH 03246 9 4 Plan Date: May 29,2003 Review Date: July I,2003 J Revised Date: July 14,2003 Review Date: July 17,2003 l R Vanasse Hangen Brustiin,Inc. (VHS)is providing a second engineering review of the Site Plan/Special Permit Submission for the Brooks School—New Athletic Facility. This review is conducted in accordance with the Town of North Andover Zoning Bylaw,Massachusetts Department of Environmental Protection(DEP)Stormwater Management Policy and standard engineering practice. VHB has received the following drawings and documents for review: I: • Site Plans(15 sheets)dated May 29,2003 Revised]u1y14,2003 a Drainage Calculations Volumes I&II dated May 29,2003—Revised July 14,2003 • Watershed Protection District Map The following comments note non-conformance with specific sections,constructability issues and questions/comments on the proposed design. In General the Applicant's Engineer has addressed several of the comments from our previous letter;however,a few items still need to be addressed.The responses listed below follow the general outline of VHB's July 1,2003 Site Plan review letter,with corresponding Rist-Frost-Shumway Engineering.(RFS)responses paraphrased in italics. Our concurrence/comment on RFS's responses are noted at the end of each section. Section 4: Building and Uses Permitted Section 4.136 Watershed Protection District A plan showing the Watershed Protection District boundaries for the Brooks School property was provided in this submission. The Applicant's Engineer has concluded that because the Athletic Facility project drains into the northerly wetland,which does not connect to Lake Cochichewick,the project is outside the Watershed Protection District. VHB has reviewed the plans and agrees with the Applicant's Engineer's finding. RFS Response: No Response needed. Section 5:Earth Materials Removal Please verify that all requirements have been met under the Earth Removal By-Law. 1 TAD671676\dots\reports\Drook School-review.doc RFS Response: The Operations Standards of Section 5.7 of the bylaw will be incorporated verbatim into the Earthwork specifications in the construction documents. VHB Response: VHB is satisfied with this response. Section 6:Signs and Sign Lighting Regulations It is unclear from the drawings submitted if any signs are proposed for this site. If there is a proposed sign,please provide details of the sign. RFS Response: The will be no signs associated with the project. VHB Response: VHB is satisfied with this response. Section 7:Dimensional Requirements 7.1 Lot.Area An existing boundary plan was not submitted and the Applicant has requested a waiver. Although VHB could not review this section for compliance,it appears that all requirements pertaining to this section have been fulfilled and a waiver could be considered. RFS Response: No Response needed. 7.4 Building Heiizhts Y In table 2 of the Zoning Bylaws,the maximum building height is 35 feet. On the application for Site Plan Special Permit submitted by the applicant,the proposed building height is listed at 42'-6 3/a". The Applicant should request a waiver or revise the building height. RFS Response: The height listed in the Application was incorrect. The height listed was the vertical distance from first floor to the roof peak. By Mass.Building Code convention, height is measured as the distance between average ground elevation around the perimeter and the mid-point of the pitched roof. Thus the height is 33'-8", which is less than the allowed 35'. A variance is not therefore required. This would explain why the project received a Building Permit in 2001 and no height issue was raised at the time. VHB Response: The North Andover Zoning Bylaws(Section 2 Definitions)states that the"building height"is the "vertical distance as measured from the average finished grade level adjoining the building at all exterior walls to the " view the building Applica nt's Engineer should re etc.., The A g highest roof surface,but shall not Include chimneys, pp g height. It appears that a waiver may be required. Section 8:Supplementary Regulations Section 8.1 Off Street Parkin 1, A Traffic Study of the site was not been provided. On the Site Plan Special Permit Application,the Applicant's Engineer has stated that a Campus Parking Report was submitted to the Town in August of 1999. The application seems to indicate that the existing and future parking is"sufficient." VHB could not review this section for compliance. 2. The North Andover Zoning Bylaws state that for an athletic field there should be 1 parking space per 4 persons (based on design). The Applicant's Engineer has not provided the capacity of the athletic facility,so this requirement could not be reviewed. VHB recommends that the Applicant address this issue. 3. Parking stalls should not be less that 9' x 18'based on the Zoning Bylaws. No detail or dimensions of the parking stalls have been shown on the plans. VHB recommends that the Applicant provide a detail of the parking stalls. 4. See General Comments No.4 for Handicap Accessible parking comments. 2 T.\p671676\dms\reports\13rook School-review.doc RFS Response: IVe stand by our comments in the Narrative, and refer to the 1999 parking report which was well received by the Planning Board at the time. This facility will not be opera to the general public. Most of the users of the facility will be boarding students who will come and go on fool. All of the functions in the Facility which draw a crowd are already occurring in the existing gym, so there is no need to increase parking. This is not the same type of facility as that covered by rite bylaw. VHB Response: The Applicant's Engineer appears to have provided a reasonable response to our original comment. Section 8.3 Site Plan Review 8.3-5Tnfortnation Required c) General: The landscape and architectural plans have not been signed and stamped by certified architects. e-i) North Arrow/Location Map: Although a locus map was provided with the Site Plan Special Permit Application,it would be helpful for the map to be added to the drawings. e-ii) Survey of Lot/Parcel:The applicant is requesting a waiver for the boundary survey. c-iv) Easements/Legal Conditions: A boundary survey was not provided. VHB could not review this u requirement. VHB recommends that the Applicant verify that there are no easements or legal conditions that affect the proposed development. e-v) Topography: The proposed grading plans submitted were illegible. The Applicant's Engineer should provide clearer grading plans. a-xii) Location of Walls/Signs: The Materials Plan indicated that there is a proposed seatwatl. Please provide more detail of the proposed wall. No signs are indicated on the plans(see General Comments Nos.9& 10). e-xiii) Location of Roadways/Drives: The plans do not show the dimensions of the proposed driveway or the parking area nor do the plans indicate the location(s)of the proposed curbing. See General I Comments No.b. e-xviii) Drainage Basin Study:See Drainage Comments. e-xix) Traffic Impact Study:The Applicant has not provided a traffic study. This section could not be reviewed for compliance. The Applicant is requesting a wavier from submitting a traffic study impact. See Comments for Section 8.1 Off Street Parking. e-xx) Commonwealth Review:Since the project is located within the 100' wetland buffer zone,VHB assumes that the Applicant has notified North Andover Conservation Commission. e-xxi)Utilities:See General and Drainage Comments VHB Response: The Applicant's Engineer has addressed all of these continents. VHS is satisfied with these responses. General Comments: 1. Although erosion control measures are proposed on the plans,VHB assumes that the Conservation Commission will review the plans for compliance to their regulations. RFS Response: This is correct. 3 "r:\0671676\does\repo rts\Brook School•reviemdoc 2. It does not appear that any fire hydrants are proposed. Are there any existing fire hydrants in close proximity to this location? VHB recommends that the North Andover Fire Department review the plans. RFS Response: There is art existing hydrant adjacent to Service Road in the southwest corner of the site. The Fire Department has been consulted on multiple occasions by the project team. VHB Response: VHB is satisfied with this response. 3. Rim and invert information for the new sewerline was not shown on the plans. A detail was provided for the sewer forcemain but there is not detail for the gravity sewerline. VHB suggests that the Applicant's Engineer to provide this information. RFS Response: Seiver elevations have been added. The typical trench detail on C502 applies to gravity sewers. VHB Response: VHB has reviewed the invert information provided for the gravity sewer. It appears that the slope of the gravity sewer pipe connecting SMH4 to the existing SMH on Service Road is negative. VHB recommends the Applicant review the sewer elevations. 4. The number of handicapped accessible parking spaces does not appear to meet Architectural Access Board (AAB)requirements, The plans only indicate two spaces are provided. Based on the number of parking spaces indicated on the plans,the minimum number of accessible spaces should be three;and one of these three spaces should also be a van accessible space. Further the plans do not clearly indicate how these spaces with be differentiated from all the other parking spaces. Will a handicapped symbol be painted in the spaces and/or a sign be provided? VHB recommends that the Applicant provide additional detail. RFS Response: Three handicapped spaces are now shown. A symbol will be painted on the pavement,plus a sign. VHB Response: VHB is satisfied with this response. 5. The plans do not clearly illustrate where wheelchair ramps will be constructed. The wheelchair ramps should be labeled on the plans. The detail on Sheet C502 does not conform to AAB standards. The Applicant's Engineer should review the current AAB standards and revise the detail accordingly. RFS Response: Identification of curb tip-dawns has been added. Detail of tip-down on C502 corrected. VHB Response: VHB is satisfied with this response. 6. The plans do not indicate the proposed geometry for new driveway. VHB recommends that the Applicant's Engineer label the radii,dimensions and any other information pertaining to the driveway and parking area. RFS Response: .Layout data added. VHB Response: VHB has reviewed the proposed geometry and is satisfied with the information provided. 7. it is not clear from the plans how the parking area will drain.The Applicant's Engineer should provide additional grading information. RFS Response: The existing parking area, which will not be re-graded, sheet flows in an easterly direction, across the gradual grassy slope and into the wetland. Contours are shown on file plait and the flow direction is evident. VHB Response: VHB has reviewed the grading and is satisfied with the information provided. 8. The width of the driveway,sidewalks and walkways are not detailed on the plans. The Applicant's Engineer should label the plans. RFS Response: See response to&3-5(e-xiii)above. VHB Response: VHB is satisfied with this response. 9. VHB recommends that the Applicant's Engineer provide details of any proposed walls. 4 TAC671676\does\reports\Brunk School-revlew.doc RFS Response: The wall at the northeast corner of the new building has been eliminated. There are no site walls other than the sealing wall. VHB Response: VHB is satisfied with this response. 10. Proposed signs should be shown on the plans. RFS Response: There will be no signs. VHB Response: VHB is satisfied with this response. Drainage Comments: 11. The Applicant's Engineer has proposed a closed drainage system with catch basins in series(catch basin to catch basin)which is not considered good engineering practice. Area drains in landscaped areas may be inline, however,VHB recommends that catch basins with deep sumps be offline. If the applicant wishes to keep the catch basin to catch basin connections,they can not claim a 25%TSS removal rate unless they provide additional back-up information showing that flow through velocities will not re-suspend settled solids. RFS Response: RFS feels that requiring all catch basins to flow into drain manholes would result in an excessive number of underground structures on a small site,at very little benefit to the stormwater system. The Town has allowed linked catch basins on similar previous projects on the campus. We do acknowledge the 25%TSS removal for deep-linked catch basins does not apply when they are linked. The TSS calculations have been revised to dispense with this element. i oVHB Response: Since the size of a site is generally proportional to the number of catch basins on it,this is not a valid argument. The applicant has proposed two(2)catch basins within a vehicular area. These CB's can be taken offline with the addition of one drainage manhole. The remainder of the proposed CB's and area drains collect runoff from sidewalks and landscaped areas which,per our original comment,do not require an offline connection. Although it is VHB's opinion that a 25%reduction in TSS removal from a parking area is a significant benefit to the j drainage system and the wetland to which it drains,VHB is satisfied with the proposed design if the applicant can achieve the required 80%TSS removal by other means. 12. The bottom of pond elevation shown on the plans is 0.2 feet below the lowest invert elevation on the outlet structure. Will the pond have 0.2 feet of standing water? If there will be standing water in the proposed basin s for an extended period of time,VHB recommends that a fence with a lockable gate be provided around the perimeter of the pond. d RFS Response: The pond bottom and lowest outlet are intended to match so there is no standing water,the mismatched elevations have been corrected. VHB Response: The detail and drainage calculations still show a 0.2'standing water depth for Pond 1. The pond bottom is 173.3 and the lowest outlet elevation is 173.5. Please revise. 13. Manholes should be located at all bends within the drainage system. RFS Response: A manhole has been added to the downspout leader pipe on the northwest corner. VHB Response: 'There are still three(3)bends without structures. VHB suggests that the applicant either revise the pipe layout to eliminate these bends or add structures. 14. Flared end sections should be located at all drainage outfalls to prevent erosion around the pipe. RFS Response: Notes calling for flared end sections at outfalls 40 and 41 have been added. They were left off the unintentionally. VHB Response: VHB is satisfied with this response. 5 T:\6671676\docs\repotts\€3rook School•review.doc 15. VHB questions the long-term reliability of the proposed detention basin outlet control structure. VHB recommends that this structure be inspected routinely for damage to the plastic riser section and for sediment build-up within the 6"stone. RFS Response: The riser has been changed to a precast concrete barrel section with flat top incorporating a flush gate. VHB Response: VHB is satisfied that this modification will improve the structural characteristics of the outlet structure. Please add additional information to the detail depicting the structural material required below the unit to prevent settlement. 16. The Soil Survey Map provided in Volume I of the Drainage Calculations is illegible, The Applicant's Engineer should provide a legible copy for review. RFS Response: Legible copy of SCS Map 23 attached. VHB Response: VHB is satisfied with this response. 17. The groundwater recharge calculations in Volume I show that the proposed infiltrator recharge units do not have a large enough tributary area per the DEP Stormwater management policy. A note on the calculations reads, "Very close. Surely some recharge is happening in the drip trenches at the Maintenance Building." The proposed project has sufficient roof area to meet this requirement. VHB recommends that the Applicant's Engineer either quantify the Maintenance Building roof area tributary to,as well as the amount of void space in (assume 30%of total trench volume)the drip trenches or redirect additional roof area to the proposed units and increase the capacity proportionally. RFS Response: The recharge calculations have been revised due to a new information revealed by the soils investigation. The revised design incorporate sufficient roof area to compensate for the entire Maintenance Building. VHB Response: Based on the supplemental information provided,specifically the Norse Environmental Services Soil Test information stating that the onsite soil permeability is less than 0.2 inches per hour,VHB recommends that B: the applicant does not provide infiltration for this project. VHB is satisfied that the onsite soils are hydrologic group D and therefore exempt from the infiltration requirement of the MA DEP Stormwater Management Policy. E' 18. A"Test pit log for detention pond"was included in the drainage calculations. The log included in the calculations references a sketch that is not provided. The Applicant's Engineer should provide this sketch as it is needed to determine the location of the test pit. In addition,the Applicant's Engineer should provide a plan showing the boring locations. RFS Response: The location of the test pit is shown on C301 and the boring locations are shown on both C201 and C301 Drawing C301 shows a test pit was excavated at elevation 176.0 within the limits of the proposed detention basin. The seasonal high ground water elevation for this test pit was observed to be 18"below existing grade,which places the groundwater at elevation 174.5. The proposed bottom of basin elevation is 172.0, Based on this information, there will be as much as 2.5 feet of standing water in the proposed basin. This has major implications on the proposed drainage system design. First,we recommend that RFS move the bottom of basin elevation above 174.5 or see Comment 12. Second,we recommend that RFS does not model any storage volume below elevation 174.5,Since this storage volume will be wet for part of the year. Third,the Down Stream Defender is completely submerged at this elevation. Many Stormwater quality devices do not work under submerged conditions. Please provide backup information the shows the following: a. That this is an acceptable condition that will not re-suspend previously captured solids. b. That the TSS removal rates provided are applicable for a submerged condition. 6 TAi7671676\dots\reports%tlrook 5ehoot-review.dw 19. Percolation test information is not provided for the proposed infiltration location on the south side of the proposed building. An exfiltration rate of 0.004167 ft/min is used in the calculations. How was this number obtained? if it is assumed,the applicant should verify prior to construction. RFS Response: Norse Environmental Services performed test pits and percolation tests on July 3, 2003.Report is attached. Based on the results, it is apparent that the original soil on-site has been removed and othenvise disturbed.See separate memo of July 10,2003 to VHB and Eggleston for discussion of the results and impact on the recharge design. ,Revised drainage calculations are enclosed, which include revised recharge calculations VHB Response: See VHB's response to Comment 17. 20. The infiltration units on the north side of the proposed building are placed in fill. The bottoms of the units are roughly 3 feet above the toe of the fill slope. Have any measures been taken to prevent infiltrated water from bleeding out of this slope? RFS Response: Fill increased in extent and fill slope flattened to minimize breakout. VHB Response: See VHB's response to Comment 17. 21. Please provide sizing calculations for the"Down Stream Defender"water quality unit. These calculations should show a 6'diameter on-line unit is capable of achieving the required T.S.S.removal rate for the proposed ° tributary area. RFS Response: Sizing calculations for the Downstream included in Drainage Calculations. These calculations are acceptable for north basin. Please confirm that the TSS removal rates provided are applicable for a submerged condition. ' 22. Spot elevations are needed at building corners to clarify surface drainage patterns. RFS Response: Spot elevations at building corners and more contour numbers added to plans. VHB Response: Drawing C301 shows the west side of the proposed athletic facility at elevation 190. The CB rim elevations on this side of the building are at 190.5. As currently shown on the drawings,stormwater drains to the building. The west elevation an sheet A301shows the grade at this part of the building at 190.5. Please clarify. 23. Note 4 on sheet C501 of the plans should refer to the"The Massachusetts Erosion and Sediment Control Guidelines for urban and Suburban Areas"not the New Hampshire regulations currently specified. RFS Response: Note 4 corrected VHB Response: VHB is satisfied with this response. 24. Notes 1 through 7 of the"Erosion Control Notes"and"Erosion Control Measures"on sheet C501 are redundant, RFS Response: Redundancy eliminated. VHB Response: VHB is satisfied with this response. 25. Note 3 on sheet C501 should read,"...stockpile outside of the 100 foot wetland buffer."instead of"—stockpile away from wetlands." RFS Response: Wording Clarified VHB Response: VHB is satisfied with this response. 7 TA0671676\do \reports\Brook School-review.doc 26. The inlet protection details on C501 and Note 7 of the"General Civil Notes"on sheet C101 are in conflict. VHB requests that"hale bales"be changed to"inlet protection"and that the notes reference the details. RFS Response: Conflict between notes and details eliminated VHB Response: VHB is satisfied with this response. 27. The sample rip-rap sizing calculation provided in Volume 11 of the Drainage Calculations references a"Figure 3"but did not include it. In addition,all of the sizing calculations,with the exception of outfall 10,do not appear to follow the method from the sample problem. Please explain. RFS Response: Figure 3 included—see reversed riprap sizing calculation included Drainage Calculations. For most of the outfalls, the result is an absurdly small stone, so 6"minus was selected as the mininurn size. VHB Response: VHB is satisfied with this response. 28. The rip-rap for outfalls 10, 13 and 40 are not shown graphically on Sheet C301 of the drawings. RFS Response. Apron for outfall 10 shown;outfalls 13 and 40 go to a level spreader 9 VHB Response: VHB is concerned that there may be erosion at outfalls 13 and 14. How are erosive forces IJ minimized at FES inside the level spreader? 29. Note 16 was not found. Where is this roof drain located and where does it discharge? Does it discharge to Pond ? I (north pond)? 1 RFS Response: This was an errant note left over front the 2001 plans which escaped erasure. We have reused#16 for a new note. VHB Response: VHB is satisfied with this response. 30. The rip-rap sizing calculation for outlets 13, 16,26 and 27 are not provided. PIease submit these calculations. RFS Response. Riprap sizing calculations revised. VHB Response: VHB is satisfied with this response. 31. The dimensions for the rip-rap at outfalls 13, 16,26,27,41 and 42 are not given on the drawings. We recommend that the engineer include this information. RFS Response: Schedule a apron sizes added to plans VHB Response: VHB is satisfied with this response. 32. Drain manhole 37 is not constructible as currently designed(rim to invert 1.8% 18"outlet pipe). RFS Response: This manhole rim has been raised and surrounding ground surface mounded slightly. VHS suggests that RFS show this grading on the drawings. 33. As currently designed,several of the proposed 12"drain lines are flowing full for the 1-year design storm and water is ponding on the surface at catch basins 19 and 20 for the 25-year design storm. The grading plan shows the area in the vicinity of CB's 19 and 20 to be relatively flat and near a handicap accessible route. It is likely that the surface ponding will spread across this accessible route. Therefore,VHB recommends increasing the capacity of the drain line where necessary to eliminate the surface ponding in this area. A bypass has been added around the downstream Defender to divert high flows around the unit into the detention pond. This bypass precludes any surcharging of catch basins 19 and 20. The basins have been moved slightly to coordinate their location with curb tip-downs. 8 TAU671676\dots\reports\brook Scho Weview.doc VHB Response: It is unclear how the RFS response addresses this comment. The,Downstream defender will be completely submerged for a 25-year storm,including the bypass, and therefore it is unclear why the bypass is needed. Please explain? 34. In both the existing and proposed hydrologic analysis of the site,the Applicant's Engineer consistently uses times-of-concentrations(te's)of less than 5 minutes. We recommend that the engineer uses a minimum tc of 5 minutes. We understand that VHB prefers to limit tunes of concentration to a minimum of 5 mintues,for pipe sizing purposes. This is a very conservative approach, as it theoretically forces more flow thru certain pipes, as all the peaks occur at once.RFS feels this is unnecessarily conservative. Our design shows that the system can handle the 25-year storm and is required by the town DPW. VHB Response: RFS has used the computer program HydroCAD to develop the hydrologic model for the site. This program uses U.S.S.C.S.Urban Hydrology for Small Watersheds Technical Release 55(TR-55)methodology for calculating times of concentrations. TR-55 models complex forces of nature by making several assumptions and simplifications about some parameters. Page 1-4 of The U.S.S.C.S.Urban Hydrology for Small Watersheds Technical Release 55 handbook reads,"To ensure that the degree of error is tolerable,specific limitations are given in Chapters 2—6." One of the limitations listed is that a minimum time of concentration of 0.1 hours(6 minutes)is used. Do to the limitations of the hydrologic model,and to ensure that the degree of error is within reason,we suggest that RFS does not use a time of concentration of less than 5 minutes,which is still less than that recommended by the S.C.S. 35. Sumps of catch basins should not be included in the hydrologic model of the site. The volume of the sump is "wet"at the beginning of a storm and therefore no credit for this volume should be taken. The small volume in the sumps has been assumed full in the revised calculations. VHB Response: VHB is satisfied with this response. It is recommended that the applicant provide WRITTEN RESPONSES to the issues and comments contained herein. '`rf Reviewed by: / Date: 7 L3 Christopher Nowak,P.E. Drainage Review ] rrjj II ,' ] �} Reviewed by: `�'u l �f `��(� Y Date:. Tracie Lenhardt Civil Review i Checked by: Date• o 17 Tim McIntosh,P.E. Project Manager—.Highway and Municipal Engineering I i 4 9 T:\0671676\doesNreports\Brook School-review.doc t `r. TOWN OF NORTH ANDOVER PLANNING BOARD ENGINEERING REVIEW OF SITE PLAN AND WATERSHED SPECIAL PERM4(11 3 2003 FOR CONFORMANCE WITH THE TOWN OF NORTH ANDOVER ZONING BYLAW AND STANDARD ENGINEERING PRACTICE f�10f_(CIA ANDC)VF-,A OFPARTME-N-l' Site Plan Title: Brooks School—New Athletic Facility VIIB No.: 06716.76 Location: 1160 Great Pond Road Owner: Brook School, 1160 Great Pond Road,North Andover,MA 01845 Applicant: Brook School, 1160 Great Pond Road,North Andover,MA 01845 Applicant's Engineer: Rist-Frost-Shumway Engineering, P.C.,71 Water St,Laconia NH 03246 Plan Date: May 29,2003 Review Date: July 1,2003 Vanasse Hangen Brustlin,Inc. (VHB)has been retained by the Town of North Andover to provide an engineering review of the Site Plan/Special Permit Submission for the Brooks School—New Athletic Facility. This review is conducted in accordance with the Town of North Andover Zoning Bylaw,Massachusetts Department of Environmental Protection(DEP)Stormwater Management Policy and standard engineering practice. VHB has received the following drawings and documents for review: • Site Plans(15 sheets)dated May 29,2003 • Drainage Calculations Volumes I&II dated May 29,2003 • Watershed Protection District Map The following comments note non-conformance with specific sections,constructability issues and questions/comments on the proposed design. Section 4: Building and Uses Permitted Section 4.136 Watershed Protection District A plan showing the Watershed Protection District boundaries for the Brooks School property was provided in this submission. The Applicant's Engineer has concluded that because the Athletic Facility project drains into the northerly wetland, which does not connect to Lake Cochichewick, the project is outside the Watershed Protection District. VHB has reviewed the plans and agrees with the Applicant's Engineer's finding. Section 5: Earth Materials Removal Please verify that all requirements have been met under the Earth Removal By-Law. Section 6: Signs and Sign Lighting Regulations It is unclear from the drawings submitted if any signs are proposed for this site. If there is a proposed sign, please provide details of the sign. • TA0671676\dm\reports\Brook School-review.doc Section 7:Dimensional Requirements 7.1 Lot Area An existing boundary plan was not submitted and the Applicant has requested a waiver. Although VHB could not review this section for compliance,it appears that all requirements pertaining to this section have been fulfilled and a waiver could be considered. 7.4 Building Heights In table 2 of the 7A)ning Bylaws, the maximum building height is 35 feet. On the application for Site Plan Special Permit submitted by the applicant,the proposed building height is listed at 42'-6 3/4". The Applicant should request a waiver or revise the building height. Section 8: Supplementary Regulations Section 8.1 Off Street Parking 1. A Traffic Study of the site was not been provided. On the Site Plan Special Permit Application,the Applicant's Engineer has stated that a Campus Parking Report was submitted to the Town in August of 1999. The application seems to indicate that the existing and future parking is"sufficient," VHB could not review this section for compliance. 2. The North Andover Zoning Bylaws state that for an athletic field there should be I parking space per 4 persons (based on design). The Applicant's Engineer has not provided the capacity of the athletic facility,so this requirement could not be reviewed. VHB recommends that the Applicant address this issue. 3. Parking stalls should not be less that 9' x 18' based on the Zoning Bylaws, No detail or dimensions of the parking stalls have been shown on the plans. VHB recommends that the Applicant provide a detail of the parking stalls. 4. See General Comments No.4 for Handicap Accessible parking comments. Section 8.3 Site Plan Review 8.3-51riformation Required C) General: The landscape and architectural plans have not been signed and stamped by certified architects. c-i) North Arrow/Location Map: Although a locus map was provided with the Site Plan Special Permit Application,it would be helpful for the map to be added to the drawings. c-ii) Survey of Lot/Parcel:The applicant is requesting a waiver for the boundary survey. e-iv) Easements/Legal Conditions: A boundary survey was not provided. VHB could not review this requirement. VHB recommends that the Applicant verify that there are no easements or legal conditions that affect the proposed development. e-v) Topography: The proposed grading plans submitted were illegible. The Applicant's Engineer should provide clearer grading plans. e-xii) Location of Walls/Signs: The Materials Plan indicated that there is a proposed seatwall. Please provide more detail of the proposed wall. No signs are indicated on the plans(see General Comments Nos.9& 10). e-xiii) Location of Roadways/Drives: The plans do not show the dimensions of the proposed driveway or the parking area nor do the plans indicate the location(s)of the proposed curbing. See General Comments No. 6. e-xviii) Drainage Basin Study: See Drainage Comments. 2 'FA0671676\docs\reports\Drmk Schaal-review.doc e-xix) Traffic Impact Study:The Applicant has not provided a traffic study. This section could not be reviewed for compliance. The Applicant is requesting a wavier from submitting a traffic study impact, See Comments for Section 8.1 Off Street Parking. e-xx) Commonwealth Review: Since the project is located within the 100' wetland buffer zone, VHB assumes that the Applicant has notified North Andover Conservation Commission. e-xxi)Utilities: See General and Drainage Comments General Comments: 1. Although erosion control measures are proposed on the plans,VHB assumes that the Conservation Commission will review the plans for compliance to their regulations. 2. It does not appear that any fire hydrants are proposed. Are there any existing fire hydrants in close proximity to this location? VHB recommends that the North Andover Fire Department review the plans. 3, Rim and invert information for the new sewerline was not shown on the plans. A detail was provided for the sewer forcemain but there is not detail for the gravity sewerline. VHB suggests that the Applicant's Engineer to provide this information. 4. The number of handicapped accessible parking spaces does not appear to meet Architectural Access Board (AAB)requirements. The plans only indicate two spaces are provided. Based on the number of parking spaces indicated on the plans,the minimum number of accessible spaces should be three;and one of these three spaces should also be a van accessible space. Further the plans do not clearly indicate how these spaces with be differentiated from all the other parking spaces. Will a handicapped symbol be painted in the spaces and/or a sign be provided? VHB recommends that the Applicant provide additional detail. 5. The plans do not clearly illustrate where wheelchair ramps will be constructed. The wheelchair ramps should be labeled on the plans. The detail on Sheet C502 does not conform to AAB standards. The Applicant's Engineer should review the current AAB standards and revise the detail accordingly. 6. The plans do not indicate the proposed geometry for new driveway. VIJB recommends that the Applicant's Engineer label the radii,dimensions and any other information pertaining to the driveway and parking area. 7. It is not clear from the plans how the parking area will drain.The Applicant's Engineer should provide additional grading information. S. The width of the driveway,sidewalks and walkways are not detailed on the plans. The Applicant's Engineer should label the plans. 9. VHB recommends that the Applicant's Engineer provide details of any proposed walls, 10. Proposed signs should be shown on the plans. Drainage Comments: VIJB has reviewed the drainage design and calculations provided by RFS. The proposed drainage design collects surface stormwater runoff from the south side of the project area in a series of area drains and catch basins. Tile collected runoff is then transported via a closed drainage system to a"Down Stream Defender"particle separator and then onto one of the two detention basins(tile south basin)associated with the project. The stormwater runoff from the north side of the project site is also collected in a series of area drains and catch basins and transported via a closed drainage system to a"Down Stream Defender"particle separator and then onto the other detention basin(the north basin)associate with the project. This basin is an existing basin that will be enlarged to accommodate the project. Roof runoff is collected in a third system that connects to infiltration chambers with an overflow to the north basin. VHB offers the following comments in regards to the proposed drainage design-, 3 T:\0671676\docs\reports\Brook Schcx)l-review.doc 11. The Applicant's Engineer has proposed a closed drainage system with catch basins in series(catch basin to catch basin)which is not considered good engineering practice. Area drains in landscaped areas may be inline, however, VHB recommends that catch basins with deep sumps be offline. If the applicant wishes to keep the catch basin to catch basin connections,they can not claim a 25%TSS removal rate unless they provide additional back-up information showing that flow through velocities will not re-suspend settled solids. 12. The bottom of pond elevation shown on the plans is 0.2 feet below the lowest invert elevation on the outlet structure. Will the pond have 0.2 feet of standing water? If there will be standing water in the proposed basin for an extended period of time,VHB recommends that a fence with a lockable gate be provided around the perimeter of the pond. 13. Manholes should be located at all bends within the drainage system, 14. Flared end sections should be located at all drainage outfalls to prevent erosion around the pipe. 15. VHB questions the long-term reliability of the proposed detention basin outlet control structure. VHB recommends that this structure be inspected routinely for damage to the plastic riser section and for sediment build-up within the 6"stone. 16. The Soil Survey Map provided in Volume I of the Drainage Calculations is illegible. The Applicant's Engineer should provide a legible copy for review. 17. The groundwater recharge calculations in Volume I show that the proposed infiltrator recharge units do not have a large enough tributary area per the DEP Stormwater management policy. A note on the calculations reads, "Very close. Surely some recharge is happening in the drip trenches at the Maintenance Building." The proposed project has sufficient roof area to meet this requirement. VHB recommends that the Applicant's Engineer either quantify the Maintenance Building roof area tributary to,as well as the amount of void space in (assume 30%of total trench volume)the drip trenches or redirect additional roof area to the proposed units and increase the capacity proportionally. 18. A"rest pit log for detention pond"was included in the drainage calculations. The log included in the calculations references a sketch that is not provided. ']File Applicant's Engineer should provide this sketch as it is needed to determine the location of the test pit. In addition, the Applicant's Engineer should provide a plan showing the boring locations. 19. Percolation test information is not provided for the proposed infiltration location on the south side of the proposed building. An exfiltration rate of 0.004167 ft/min is used in the calculations. How was this number obtained? If it is assumed,the applicant should verify prior to construction. 20. The infiltration units oil the north side of the proposed building are placed in fill. The bottoms of the units are roughly 3 feet above the toe of the fill slope. Have any measures been taken to prevent infiltrated water from bleeding out of this slope? 21. Please provide sizing calculations for the"Down Stream Defender"water quality unit. These calculations should show a 6' diameter on-line unit is capable of achieving the required T.S.S.removal rate for tile proposed tributary area. 22. Spot elevations are needed at building corners to clarify surface drainage patterns, 23. Note 4 on sheet CSOI of the plans should refer to the"File Massachusetts Erosion and Sediment Control Guidelines for urban and Suburban Areas"not the New Hampshire regulations currently specified. 24. Notes I through 7 of the"Erosion Control Notes"and"Erosion Control Measures"on sheet C501 are redundant. 25. Note 3 on sheet C501 should read, "...stockpile outside of the 100 foot wetland buffer,"instead of"...stockpile away from wetlands." 4 T:\0671676\docs\reports\Rrook School-review.doc 26. The inlet protection details on C501 and Note 7 of the"General Civil Notes"on sheet CIO] are in conflict. VHJ3 requests that"hale bales"be changed to"inlct protection"and that the notes reference the details. 27. The sample rip-rap sizing calculation provided in Volume 11 of the Drainage Calculations references a"Figure 3"but did not include it. In addition,all of the sizing calculations,with the exception of outfall 10,do not appear to follow the method from the sample problem. Please explain. 28. The rip-rap for outfalls 10, 13 and 40 are not shown graphically on Shect C301 of the drawings. 29. Note 16 was not found. Where is this roof drain located and where does it discharge? Does it discharge to Pond I (north pond)? 30. The rip-rap sizing calculation for outlets 13, 16,26 and 27 are not provided. Please submit these calculations. 31. The dimensions for the rip-rap at outfalls 13, 16,26,27,41 and 42 are not given on the drawings. We recommend that the engineer include this information. 32. Drain manhole 37 is not constructible as currently designed(rim to invert= 1.8'; 18"outlet pipe). 33. As currently designed,several of the proposed 12"drain lines are flowing fall for the 1-year design storm and water is ponding oil the surface at catch basins 19 and 20 for the 25-year design storm. The grading plan shows the area in the vicinity of CB's 19 and 20 to be relatively flat and near a handicap accessible route. It is likely that the surface ponding will spread across this accessible route. Therefore,VHB recommends increasing the capacity of the drain line where necessary to eliminate the surface ponding in this area. 34. In both the existing and proposed hydrologic analysis of the site, the Applicant's Engineer consistently uses tirnes-of-concentrations(te's)of less than 5 minutes. We recommend that the engineer uses a minimum tc of 5 minutes. 35. Sumps of catch basins should not be included in the hydrologic model of the site. The volume of the sump is "wet"at the beginning of a storm and therefore no credit for this volume should be taken. It is recommended that the applicant provide WRITTEN RESPONSES to the issues and comments contained herein. Reviewed by: Date: L c, Christopher Nowak Drainage Review Reviewed by: Date: Tracie Lenhardt Civil Review Checked by: Date: Tim McIntosh P.E. Project Manager—Highway and Municipal Engineering (D 5 CAcadtemp\Brook School-reviemdoc "1-