Loading...
HomeMy WebLinkAbout2011-11-01 Planning Board Supplemental Materials (9) Transportation Land Development Environmental Services ° j ,magmatton innovation energy Creating results for our clients and benefits for out communities October 18,2011 yGd72Glsse—.. Ia12_g n BY Win Inc,__ Mr.John Simons,Chairman North Andover Planning Board 1600 Osgood St.-Bldg 20-Suite 2-36 North Andover,Ma 01845 North Andover,Massachusetts Mr. Louis Napoli,Chairman North Andover Conservation Commission 1600 Osgood Street,Suite 2-36 North Andover,MA 01845 Re: Response to Stormwater Peer Review Comments DEP File#:242-1531 Volpe Athletic Center Expansion—Merrimack College North Andover,Massachusetts Dear Chairmen Board members and Commissioners, On behalf of Merrimack College,VHB provides the following information in response to the peer review comment letter prepared by Eggleston Environmental and dated September 28,2011. The responses also reflect input from a coordination meeting with Eggleston Environmental and the Town of North Andover on October 13,2011. The site plans have been revised to reflect these comments as well as the previously discussed concepts to pull the proposed building expansion out of the"50-foot"No-Build Zone". The Eggleston Environmental comments are listed below,followed by the response in italics. Comment: 1. The proposed project is considered a mix of new development and redevelopment under Standard 7 of the DEP Stormwater Management Standards,since the site is previously developed by a net increase in impervious area is proposed. All new impervious areas on the site are fully subject to the requirements of the ten state standards,and existing stormwater discharges on the site are subject to Standards 1,7,8,9,and 10 fully,and Standards 2 through 6 to the"maximum extent practicable",i.e.reasonable effort must be made to comply fully with these standards and the project should be implementing the highest practicable level of 101 Walnut Street Post Office Box 9151 Watertown, Massachusetts 02471-9151 617.924.1770 a FAX 617.924.2286 L:\11625.00\docs\letters\StormwaterRTCdoc email: info@vhb.com www.vhb.com Stormwater Response to Comments Project No.: 11625.00 October 18,2011 Page 2 stormwater management. A redevelopment project must also improve existing conditions. While the proposed project is aimed at complying with the DEP standards for the expanded building and new parking area,nothing is currently being proposed to bring existing stormwater discharges into compliance or to improve existing conditions. Response:The project design has been modified to include stormwater quality improvements along Cullen Avenue and portions of the lobby parking lot. This includes the addition of a water quality structure and new eatchbasins with deep sumps and hoods. Additional outlet protection is also proposed at existing roof drain outlets adjacent to Wetland 2, Comment: 2. The Applicant makes the case that drainage from the project site is covered under a Stormwater Master Plan,for which the Andover Conservation Commission issued an Order of Conditions in October,2001,and that the detention basins were ever constructed and,if so whether they were built in accordance with the approved design and maintained accordingly. In addition,it appears from this material that the"wetland/football field basin" is actually a berm designated to detain flow within the naturally occurring wetland system to the south and west of the football field. The current DEP stormwater regulations prohibit the use of wetland resources for this purpose;all of the stormwater standards including peak rate attenuation need to be met prior to discharge to a wetland source. Response: The improvements detailed in the Stormwater Master Plan were constructed in 2001-2002 and modifications were made in 2005 to the football field basin. Certificates of Compliance were issued for the initial construction and the 2005 modifications. The stormwater improvements projects were constructed to not only address future growth of the campus, but also to address existing downstream flooding issues partially caused by upstream areas flowing through the Merrimack campus. Merrimack is filing far an Amended Order of Conditions with the Town of Andover Conservation Commission to update the Stormwater Master Plan to reflect the Volpe Center Expansion project. This submittal will reflect the modifications presented in this letter. Comment: 3. Subcatchment M-113-1 discharges to the wetland to the northeast of the building(Wetland 2) through what appears to be two roof drain outlets,as well as in the form of overland flow in area to the east of the building,including the tennis courts. In order to more accurately assess 0 L:\11625,00\docs\letters\Stormwater RTC.doc Stormwater Response to Comments Project No.: 11625.00 October 18,2011 Page 3 impacts on that wetland,these areas should be modeled individually and the wetland treated as a separate design point. Response: The stormwater model has been revised to break out the areas draining to wetland 2.And these have been modeled as separate areas. The wetland is treated as a separate design point. The design intent is not to modify the existing internal plumbing associated with the roof drain systems. Comment: 4. The building extension in the southeast corner of the existing building has roof drains along the eastern wall and looks like it should be included in the Existing Conditions Subarea M- IB-1,not in M-1B-3A which discharges to the south. Response:Agreed. The model has been adjusted to reflect this as well as additional feedback on the plumbing system. Comment: 5. Additional information on the proposed modifications and additions to the building are needed in order for me to better understand the roof drainage areas modeled. The plans merely show the footprint of the building,but it appears that a number of existing roof drains are being redirected. Response:The plumbing and roof drain system have not been designed for the building. The proposed stormwater design delineates areas that the plumber and architect will need to incorporate into their designs. We would suggest a condition of approval would be for the plumbing plans to be submitted for record prior to construction. Comment: 6. The hydrologic calculations should include the 1-year storm,in accordance with the North Andover Wetlands Bylaw. In addition,impacts to both the rate and the volume of discharge need to be quantified for each wetland resource,and flow paths and control points should be shown on the pre-development and post-development watershed maps. Response:The 1-yr storm has been modeled and rates and volumes provided for each resource. Flow paths have been added to the drainage figures. AMNk L:\1162.00\docs\letters\StOT'mwatetRTC.doc Stormwater Response to Comments Project No.: 11625.00 October 18,2011 Page 4 Comment: 7. The three pipes exiting the existing building at the concrete headwall n the south side of the building are unlabelled;what is the source of this discharge? Response:The three pipes are part of the under drain/perma-frost system under the rink. They are not part of the roof drain system. These pipes will be re-routed under the new foundation and directed to the storm drain system. This will be included on the plumbing plans. Comment: 8. Appendix A contains rip rap sizing calculations for three outfalls;FES-1,FES-Roof-north and FES-Roof-South. However,only two outfalls are shown on the design plans and both are unlabeled and on the north side of the building. In addition,it is unclear what the basis for the discharge rates used in the calculations is;they do not correspond to the HydroCAD calculations. Response:The outlets have been adjusted based on the proposed design modifications and labels added. Outlet protection sizing has been performed based on discharge rates for the 25-year storm for FES-Roof- North and FES-Roof-South. The outlet protection was sized based on the full flow capacity of the proposed 30"drain, Comment: 9. The design plans call for replacing the existing drain line that extends south from DMH-2 in Cullen Ave. A significant portion of the flow from the proposed project will be discharged to the 15-inch drain from CB-1 and not the drain from DMH-2;has it been determined that this drain had adequate capacity to accommodate the increased flow? Response:The proposed project design will not result in increased rates or volumes of stormwater to the 15"pipe. Merrimack Facilities reports that there have not been surcharge issues with this system. Comment: 10. The proposed plan makes an effort to offset lost recharge on the site,on the basis that the soils are poor(HSG C and D)and the groundwater table is high,and that it is consistent with L:\11625.00\docs\letters\Stormwater RTC.doc Stormwater Response to Comments Project No.: 11625.00 October 18,2011 Page 5 the Stormwater Master Plan Approval by the Andover Conservation Commission. The Andover OOC does not provide any such waiver of recharge requirements,expect for the projects entailing<2,000 sf net impervious area within the Town of Andover,and I do not believe it has any bearing on wetlands permitting by the Town of North Andover. Stormwater Management Standard 3 does require that sites comprised solely of C and D soils comply with the recharge requirement"to the maximum extent practicable:,e.g.the applicant must make all reasonable efforts to meet the Standard,including evaluating alternatives that minimize impervious surfaces. The Geotechnical study conducted by McPhail Associates indicated that groundwater levels in the areas studied(to the south and west of the building)range from 2 to 4 ft below grade,suggesting that there should be some opportunity for infiltration on the site. Alternatively,I would suggest that the college might be able to provide compensatory recharge elsewhere on the campus. Response: The proposed project will attempt to provide recharge to the maximum extent practicable through the construction of rain garden systems to promote infiltration. Additional testing will be done, but initial indications are that the DEP guidelines for separation from groundwater will not be attainable. Modifications to the plan have reduced impervious area. Comment: 11. I am aware that Merrimack College and VHB recently submitted two conceptual design alternatives outlined in a letter to the Conservation Commission dated September 21,2011. The plans include several design modifications aimed at minimizing buffer zone incursion, shrinking and relocating the new parking lot and providing LID elements in the form of a rain garden. Based on the configuration and proposed grading it does not appear that any of the paved areas on the site would drain to the rain garden,therefore I presume that is purpose would be to capture and recharge roof runoff only. While this may address the requirement to provide groundwater recharge to the maximum extent practicable on the site, additional detail in the soils in that area and projected recharge volume would be needed. Response:Additional soil testing will be done,but based on record information we are not confident that there are areas on site that provide the 2'of separation from groundwater required by DEP. Comment: 12. The treatment train for the proposed new parking lot is comprised if deep sum catch basins and an in-line Stormceptor 450i treatment unit. The calculations use a 75%TSS removal L:\11625 00\docs\1etters\Sto=vater RTC.doc Stormwater Response to Comments Project No.: 11625.00 October 18,2011 Page 6 credit for the Stormceptor unit based on the NJCAT evaluation cited on the M<ASTEP website. The JJCAT evaluation did corroborate a 75%TSS removal rate for the unit in laboratory studies;however their approved TSS removal rate for field installations is 50%. This is the removal rate that should be used in the TSS removal calculations. Response:The design has been modified to include STC 900 units. Water quality calculations are included in the Stormwater Report documenting 80% TSS Removal. Comment: 13. The existing catch basins in Cullen Avenue are in-line and in series,one has a broken grate, and in all likelihood they do not have deep sumps or oil/debris hoods. Even if flow attenuation is provided further downstream in the system,the proposed increase in the flow rate discharged through these storm drains has the potential to mobilize sediments accumulated in the catch basins. Consideration should be given to moving the catch basins in Cullen Avenue(particularly C13-1 through which much of the proposed flow is discharged)offline and upgrading them with deep sumps and outlet hoods. Response:The proposed design has been modified to provide new cathchbasins with deep sumps and hoods and to eliminate the catchbasin to catchbasin connections. A Stormceptor unit is also proposed downstream of the Cullen Avenue system. Comment: 14. The proposed plan does not call for any drainage improvements for the existing parking area to the west of the building,even though the parking lot is being reconfigured. It is unclear what condition the existing catch basins serving this lot are in and whether they provide any degree of water quality treatment. Response:The Monican Boulevard Relocation Project in 2004 included the replacement of the existing catchbasins with new catchbasins with deep sumps and hoods. A Stormceptor has also been added downstream of this catchbasin on the easterly side of the lot to treat flows from the lot and Cullen Avenue. Comment: 15. The application does not address the fact that there is an approved Total Maximum Daily Load allocation(TMDL)for bacteria in the Shawsheen River basin,and that the Town is r 0 LA11625.00\docs\letter s\Stoi mwater RTC.doc Stormwater Response to Comments Project No.: 11625.00 October 18,2011 Page 7 required through its Phase 2 NPDES Permit to reduce the discharge of these pollutants. To the maximum extent practicable,the project should employ stormwater BMPs that are effective at addressing these pollutants,e.g.through filtration or infiltration. Response:As noted in Comment 17, the typical source of bacteria is from illicit connections and CSOs. As part of the plumbing design, the existing systems will be confirmed and all existing connections modified appropriately. Recharge is also being attempted on site. Comment: 16. As is indicated in the Stormwater Management Report,the proposed project entails the disturbance of more than once acre and will therefore require a Construction Stormwater Pollution Prevention Plan(SWPPP)filed under the EPA General Permit. I recommend that the Construction SWPPP be prepared by or in conjunction with the contractor selected for project construction,and that the Conservation Commission and Planning Board have adequate time to provide input prior to the plan being filed. Response:Merrimack will submit the SWPPP to the Commission and the Planning Board and address comments provided. The Commission will also have access to the site throughout construction and any concerns identified by the Commission will be addressed by the contractor and included in the active SWPPP maintained on site. Comment: 17. Measures to prevent illicit discharges from the proposed project are addressed in the Long- Term Pollution Prevention Plan. They are,however,somewhat generic and not specific to the sports facility or the nature of the operations. More specific snow storage areas need to be designated,and the use of alternative deicers should be discussed,particularly in wetland buffer areas. An Illicit Discharge Statement is also required under Standard 10 and has not been submitted. Given that the existing building is being rehabbed rather than replaced,that some portion of the interior plumbing(roof drains)appear to discharge directly to the wetland,and that the Shawsheen River has an approved TMDL for elevated levels of bacteria largely attributed to illicit discharges,the existing building should be thoroughly dye-tested to confirm that there are no illicit connections to the storm drain system. Response:As part of the plumbing design for the building,the plumbing engineer will confirm that there are no illicit connections and that all modifications to the system are designed per code. G\11625.00\docs\letters\Stormwater RTC doc Stormwater Response to Comments Project No.: 11625.00 October 18,2011 Page 8 The college provides for snow storage in Austin Field which is adjacent to Rock Ridge Road. They are aware of and don't push any snow towards the isolated wetland adjacent to Volpe. The college also has all roads and parking lots swept of sand three times per year and removes all debris from catch basins yearly. The College uses a sand/salt mix on roads and walkways to prevent slips and falls and limits use of ice melt product primarily to exterior stairs. Merrimack College is appreciative of the input provided on the project and the willingness of the parties to meet to further discuss the project. We look forward to continuing to work with the Commission and Eggleston Environmental to make this a project that we can all be proud of. We look forward to the opportunity to present these updates at the October 26"'Conservation Commission meeting and the November 1"Planning Board meeting. Very truly yours, �f VANNASE HANGEN BRUSTLIN,Inc Christopher M. ov. E,P ,LEED AP Senior Project ager Cc: Lisa Eggleston—Eggleston Environmental Jeff Doggett—Merrimack College—Chief of Staff Robert Coppola—Merrimack College—Director of Facilities Attachments: Site Plans Stormwater Report L:\11625.00\docs\letters\Stormwater RTC.doc