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HomeMy WebLinkAbout2013-02-19 Planning Board Supplemental Materials (38) Eggleston Environmental 32 Old Framingham Rd Unit 29 Sudbury MA 01776 tel 508.259.1137 fax 866.820.7840 January 29, 2013 North Andover Planning Board 1600 Osgood Street North Andover, MA 01845 Attn: Judy Tymon, Town Planner RE: Regency Place PRD, 464 Appleton St. Stormwater Management Review Dear Ms. Tymon and Board Members: Per your request, I have conducted a technical peer review of the January 18, 2013 Definitive Planned Residential Development (PRD) Subdivision for the proposed “Regency Place” project at 464 Appleton St, with respect to stormwater management. Specifically, the materials I have received and reviewed to date include the following: § Definitive P.R.D. Subdivision Plan for “Regency Place” in North Andover, 12 sheets, prepared by Christiansen & Sergi, Inc. for North Andover Realty Corp and dated January 10, 2013. § Stormwater Management Report for the Definitive P.R.D. Subdivision Plan for “Regency Place” in North Andover prepared by Christiansen & Sergi, Inc. for North Andover Realty Corp and dated January 10, 2013. As requested, the focus of my review is on the overall stormwater management approach and design concepts used in the project, as well as its compliance with the Rules and Regulations Governing the Subdivision of Land in Town of North Andover, the Massachusetts Wetlands Protection Act Regulations (310 CMR 10.0), and the North Andover Wetlands Protection Bylaw (Ch. 178) and Regulations, specifically with respect to stormwater. It is my understanding that a Notice of Intent (NOI) application for the project has been or will be filed with the Conservation Commission. My review is aimed at assisting both the Planning Board and the Conservation Commission in their respective reviews of the project. The project site is an aggregation of three parcels totaling 22.2 acres in area located on Appleton Street. It is currently occupied by an existing single family house with a gravel driveway and several outbuildings. The remainder of the site is undeveloped and mostly wooded. There are two isolated vegetated wetlands in the central portion of the property, and bordering vegetated wetlands associated with Mosquito Brook along much of the eastern boundary. Drainage on the site is overland, mostly toward the isolated wetlands and/or Mosquito Brook. A portion of the site drains in a southwesterly direction, toward the abandoned railroad right of way. 464 Appleton St, Stormwater Review 2 January 29, 2013 The proposed project is a planned residential development of six single-family house lots, clustered on approximately 5.7 acres of the site along a 600-ft long roadway. As proposed, runoff from most of the roadway will drain to roadside drainage swales and into two infiltration basins designed to capture and infiltrate all but the largest (100-yr) storm volumes. The lower part of the roadway in the Riverfront Area will be curbed and runoff conveyed through a closed drainage system with deep sump catchbasins and a Stormceptor 900 treatment unit before being discharged through an existing catchbasin and outfall in Blue Ridge Road. My comments are summarized below: 1. In general, the proposed plan uses a low impact drainage design that largely maintains existing drainage patterns and takes advantage of the site’s permeable soils to treat and infiltrate runoff onsite. I support the requested waivers regarding pavement width and curbing on the proposed roadway, as they are consistent with the project’s size and low impact development approach. 2. Pending confirmation of soil suitability, the proposed plan also provides adequate recharge and attenuation of peak runoff rates. Impacts to the runoff volume are not addressed in the Stormwater Report, but I do note that the volume of flow to the two isolated wetlands on the site, while small, would be approximately doubled under post-development conditions. This increase should be evaluated in the context of the total flow to the wetlands to determine whether it would have any impact on the hydrologic regime. 3. The two test pits conducted on the site to date appear to verify the presence of loamy sands (HSG A) suitable for infiltration in the areas proposed for infiltration basins “A” and “C”, however they also indicate a relatively shallow depth to groundwater, with the estimated seasonal high groundwater elevation (ESHGW) approximately 3 to 4 feet below grade. (Both basins do provide the two feet of separation required). Per the DEP and Wetlands Bylaw regulations, both of which require soil testing in each area proposed for stormwater infiltration, additional tests are needed in the locations of Basins “B” and “D”. I am particularly concerned about the suitability of the soils in the vicinity of Basin “B”, as the NRCS soils map shows it to be in close proximity to an area of less permeable HSG C silt loam, and the elevation of the adjacent wetland suggests that the groundwater table may be within two feet of the bottom of the proposed basin. I also note that there are several large rock outcrops on the north side of the proposed roadway that may be indicative of shallow bedrock in the area. 4. Confirmatory soil testing for the roof infiltration systems can probably be deferred until the time of system installation. The plan calls for a single drywell for each house. It should be confirmed based on building architecture that all of the roof runoff can be directed to a single location. 464 Appleton St, Stormwater Review 3 January 29, 2013 5. Since the proposed project calls for the infiltration BMPs to attenuate large storm flows (10-yr and larger) and the separation to seasonal high groundwater beneath the systems is less than 4 feet, the DEP Stormwater Standards require that a mounding analysis be performed to demonstrate that the systems will be fully dewatered within 72 hours. 6. The proposed infiltration basins should be treated as impervious areas in the HydroCAD analysis in order to avoid double-counting of the infiltration capacity. 7. Per DEP criteria, the infiltration basins should be designed to have a minimum of one foot of freeboard during the 100-yr storm modeled. 8. As proposed, runoff from the proposed roadway would undergo minimal pretreatment in the grassed drainage channels prior to being discharged to the infiltration basins. Since the basins are in HSG A soils with a rapid infiltration rate (hydraulic conductivity >2.4 in/hr), the DEP regulations call for pretreatment to remove 44% of the TSS load prior to infiltration. I suggest that at a minimum check dams be added to the steeper portions of the drainage channels to reduce flow velocities and allow filtering and/or settling of coarser solids. Sediment forebays should be added to the two infiltration basins to preserve their infiltration capacity over the long term. It may also be possible to incorporate sediment sumps in the ponding areas of the channels upgradient of each driveway culvert to provide additional pretreatment. 9. The proposed stormwater BMPs are designed for a ½-inch water quality volume. The North Andover Subdivision regulations call for stormwater BMPs to be designed for a 1-inch water quality volume, as do the DEP standards for infiltration in soils with a rapid infiltration rate. It does appear that the proposed infiltration structures have ample capacity to capture and infiltrate the larger water quality volume. The Stormceptor unit should be sized for the 1-inch water quality volume on an equivalent flow basis. 10. It is not clear that Infiltration Basins “C” and “D” on Lots 2 and 3 are really needed, as they only receive flow from the driveways and vegetated lawn areas on each lot. Would it be possible to achieve the same level of flow attenuation with a landscape berm or vegetated swale to capture and infiltrate the runoff, rather than concentrating the flow at a single location? Alternatively, could the basins be designed as rain gardens in order to better integrate them into the landscape and ensure their ongoing maintenance? 11. The TSS removal calculations for the runoff from the lower portion of the proposed roadway assume 80% TSS removal by the proposed Stormceptor unit, citing as the basis for the removal rate a Technology Assessment Report done for the Massachusetts STEP Program in 1998. Per the attached notice, that report was recalled by DEP on January 1, 2011, as part of its transition to a stormwater performance rating system using the Technology Acceptance Reciprocity 464 Appleton St, Stormwater Review 4 January 29, 2013 Partnership (TARP) protocol. Since Mass DEP has yet to formally assign TSS removal efficiencies to any hydrodynamic separators under this program, the Stormwater Handbook (V.2, Ch.4) calls for Conservation Commissions to consider other performance evaluations conducted using TARP protocol. New Jersey is the only state currently reviewing and certifying technologies under the TARP protocol, through the New Jersey Department of Environmental Protection (NJDEP) and the New Jersey Corporation for Advanced Technology (NJCAT). The Stormceptor units are currently certified through that program at a TSS removal rate of 50%. http://www.nj.gov/dep/stormwater/treatment.html 12. If possible, the existing catchbasin on Blue Ridge Road through which the proposed Stormceptor would discharge should be taken offline to prevent accumulated solids in the catchbasin from being resuspended by the discharge. 13. I recommend against the use of filter fabric on the bottom of the proposed roof infiltration systems as it can be prone to clogging. 14. The spillway elevations listed in the table of Infiltration Basin Elevations on Sheet 12 are not consistent with the Table on Sheet 7, or with the HydroCAD analysis. Is it the design intent to raise the spillway elevations to fully contain the 100-yr storm? 15. As is indicated in the Stormwater Checklist, the proposed project entails the disturbance of more than one acre and will therefore require a Construction Stormwater Pollution Prevention Plan (SWPPP) filed under the EPA Construction 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/or Planning Board have the opportunity to provide input prior to the plan being filed. 16. The Erosion and Sediment Control Plan on Sheet 9 is listed as providing guidance (versus requirements) for control measures to be implemented. The plan should reference the fact that the project is subject to the requirements of the Construction General Permit and must be implemented in accordance with the SWPPP. 17. The detail for the proposed construction entrance calls for 1 - 2-inch stone. I recommend a stone size of at least 2-inches to more effectively prevent tracking. 18. The Erosion and Sediment Control Plan or Construction SWPPP should specifically address the protection of proposed infiltration areas during construction. The proposed infiltration basins should not be used as sedimentation basins during construction without full restoration of their infiltration capacity. 19. The O&M Plan indicates that the owners of each lot will be responsible for maintaining the roof infiltration systems and the grassed swale on their lot, and 464 Appleton St, Stormwater Review 5 January 29, 2013 that if and when the Town accepts the roadway and easements the maintenance (including mowing) of the infiltration basins, catchbasins and Stormceptor would be conducted by the Town. Consideration should be given to the establishment of a Homeowners Association to assume responsibility for the maintenance of the swales and any pretreatment structures, infiltration basins and Stormceptor, as these are not drainage system components that the DPW typically maintains. 20. The infiltration basins on Lots 3 and 4 are not included in the proposed drainage easements. Since their function is to limit the rate of runoff to downgradient properties, some sort of deed restriction may be needed to ensure that the basins (or suitable alternatives) remain in place and that their storage and infiltration capacities are maintained by the individual homeowners. I appreciate the opportunity to assist the North Andover Planning Board with the review of this project, and hope that this information is suitable for your needs. Please feel free to contact me if you or the applicants have any questions regarding the issues addressed herein. Sincerely, EGGLESTON ENVIRONMENTAL Lisa D. Eggleston, P.E. C: Jennifer Hughes 1 The Commonwealth of Massachusetts Executive Office of Energy and Environmental Affairs 100 Cambridge Street, Suite 900 Boston, MA 02114 TRANSITIONTOASTORMWATERPERFORMANCE RATINGSYSTEM Background Governmentandindustryeffortstopreventpollutionfromstormwaterhavecomealongwaysince1998when thisExecutiveOfficewasapartnerintheMassachusettsStrategicEnvirotechnologyPartnership(STEP)and STEPissuedindependenttechnologyassessmentreportsontheperformanceofthreeproprietarystormwater controlproducts.Duetofundingcutbacks,STEPnolongerexistsasaprogramtoevaluatenewtechnologiesor toupdateexistingreports.Thiscreatesanunevenplayingfield,withnonewtechnologyvendorabletogo throughaSTEPrevieworobtainanyofthemarketingadvantagesthattheSTEPfactsheetsorassessment reportsoffer.Theexistingreportsarestatic,allowingfornoadditionalmodelstobeevaluatedorforupdated datacollectionprotocolstobeapplied. Also,whiletheSTEPprogramwasuniqueinitsday,commonlyacceptedcriteriaforcollectingdataand evaluatingperformanceinformationhavechangedintenyears.TheCommonwealthpartneredwithotherstates (inaTechnologyAcceptanceandReciprocityPartnershiporTARP)tocreateaperformancedemonstration pathwaythatreliesonacommonmethodology.Thisuniformmethod,theTARPStormwaterfieldtesting protocol,isacontemporary,scientificallycredibleanddefensiblemethodthatistodayrecognizedasthecurrent standardevaluationtoolinthis stateandinothers.OtherprotocolsmaybedeemedequivalentbyMassDEPand astechnologiesdevelopand scienceevolves,TARPmaybereplacedwithanewerevaluationtool. StormwaterPerformanceRatingsinMassachusettsusing TARP WhendatafromtheTARPfieldstudiesbecomeavailable,Massachusetts’staffwillevaluatetheresultsand findingsofotherstatestomakearegulatoryperformancedecisiononhowtheproductmeetsrelevantstate stormwaterstandards.Thestatewillissuearegulatorydeterminationletterbasedoncompletionofadequate fieldstudieswhichcomplywithTARPorequivalenttesting.Thestateisdraftingaregulatoryfindingforone technologythathascompletedtheTARPfieldtesting,andmoreareexpectedthisyear.Thesefindingswillbe postedonMassDEP’swebsite.MassDEP’swrittenregulatoryfindingwillreplaceallSTEPdocumentationas describedbelow. STEPSunset- TransitioningtotheStormwaterPerformanceRatingSystem InordertorecognizethevendorsthatparticipatedinSTEPingoodfaithandtoprovideanorderlytransitionto thefinalperformanceratingsystem,theSTEPfactsheetsandtechnologyassessmentreportswillremainin effectuntileitherthecompletionoftheTARPpathtoafinalstormwaterperformanceratingorthevendor wishestowithdrawitsSTEPfactsheetandreportfindings.Inanycase,thestatewillrecalltheSTEP TechnologyFactSheetson January1,2011. TheSTEPfactsheetsandverificationreportsonlydetermineremovalefficienciesoftotalsuspendedsolids (TSS)andnototherparameterssuchasnutrients,metalsoroilandgrease.AlltechnologiesverifiedbySTEP mustbesizedinaccordancewiththeinformationpublishedintheSTEPassessmentreportandaccompanying fact sheets.A studyisunderwaytoexaminedifferentmethodstoconvertwaterqualityvolumetoanequivalent 2 flowrateasrequiredforadequatesystemsizing.Whenthatstudyiscompleted,MassDEPmaynotifythe publicthatthereneedstobeachangeinthesizingpracticesandthismayaffectthevalidityof someorallofthe STEPreports. Oncethestormwatertechnologyfactsheetsarerecalled,theywillnolongerbereliedonformakingregulatory decisionsatanylevelofgovernment.Thecoverletterstotheassessmentreportsneverhadanyregulatory meaningandshouldneverbeusedasevidenceofperformanceefficiency.TheSTEPTechnologyPerformance AssessmentReportswillremainavailableon www.mastep.net.