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HomeMy Public PortalAboutDrainage Report i i DRAINAGE CALCULATIONS AND STORMWATER MANAGEMENT PLAN For: PROPOSED SITE DEVELOPMENT WATERTOWN, MA Located: 80 ELM STREET (PARCEL ID No.: 1238-3-0) WATERTOWN, MASSACHUSETTS Submitted to: TOWN OF WATERTOWN Prepared For: 80 ELM STREET, LLC 26 ELM STREET QUINCY, MASSACHUSETTS 02169 JULY 9, 2018 11 McKenzie Engineering Group , Inc . 150 Longwater Drive, Suite 10 1 , Norwell, Massachusetts 020G I P: (78 I) 792-3900 F: (78 1) 792-0333 M C K E N Z I E www.mckenq.com ENGINEERING GROUP Site Development Plan 80 Elm Street Watertown, Massachusetts Introduction The purpose of this stormwater report is to provide a detailed analysis of the stormwater drainage system proposed for the redevelopment of an approximate 0.82- acre area located at 80 Elm Street in Watertown, Massachusetts. This report contains stormwater runoff calculations for the pre-development and post-development conditions and includes the sizing of the proposed stormwater best management practices (BMPs). The proposed plans are illustrated on the project site plans entitled "Site Development Plan, 80 Elm Street (Assessor's Parcel I.D 1238-3-0), Watertown, Massachusetts, prepared by McKenzie Engineering Group, Inc. dated May 8, 2018. Proiect Summary The project proponent, Landmark Real Estate, proposes to redevelop an approximate 0.82-acre area parcel with frontage along Elm Street in Watertown, Massachusetts. The proposed site redevelopment will consist of the construction of a four story mixed use facility, construction of a parking lot and associated infrastructure, site re-grading, and the installation of a subsurface drainage facility to manage and reduce the stormwater runoff from the proposed parking lot. The site has frontage on Elm Street to the east and is surrounded by commercial/industrial properties. The site is listed as Watertown Assessor's Parcel I.D. 1238-3-0. The site is located within the Industrial-1 Zoning District,See Figure 4—Zoning Map, attached. Industrial-1 zoned property abuts the site to the north and east, The Watertown Mall abuts directly to the south and west of the property and is zoned as Regional Mixed Use (RMUD). The proposed project is considered a redevelopment project under the MA DEP Stormwater Management Standards and is required to meet the Stormwater Management Standards only to the maximum extent practicable. Refer to Figure 1- USGS Locus Map for the location of the parcel. Pre-Development Condition The majority of the approximate 0.82-acre development area consists of the remnants of a one story concrete block building foundation, and deteriorated asphalt and gravel parking areas towards the northeast of the parcel. The majority of the site is now becoming vegetated with small shrubs as the existing structures have been razed. Previously, the site consisted of approximately 75% impervious surfaces, which has been demoplished. The site is somewhat mounded and has a high point through the center of the lot. The back portion of the property slopes steeply downward as you approach the abandon railroad tracks and Watertown Mall parking lot. The front portion of the site slopes gently towards Elm Street and becomes somewhat elevated above the p g Y sidewalk grade at the southern part of the lot frontage. From review of record plans and recent site inspections it has been determined that no existing drain system is present i i Refer to site plans for the drainage system design. The post development condition also includes measures to minimize erosion and sedimentation. All BMPs shall be supported by the comprehensive Construction Phase Pollution Prevention and Erosion Control Plan and Post-Development BMP Operation and Maintenance Plan. Stormwater Best Management Practices (BMP's) Treatment stream for the interim development shall consist of deep sump hooded catch basins and proprietary treatment units as pretreatment, and subsurface infiltration chamber system which will overflow to an infiltration basin to achieve the required removal of at least 80%of the total suspended solids (TSS) and mitigate the anticipated pollutant loading. Refer to the TSS Removal Worksheets in Appendix C for TSS removal rates. Erosion and Sedimentation Controls A silt sock or other suitable erosion control barrier will be placed along the down gradient limit of work and as shown on the Site Plans prior to the commencement of any clearing, earth removal or construction activity. The integrity of the erosion control barrier will be maintained by periodic inspection and replacement as necessary. The erosion control barrier will remain in place until the first course of pavement has been placed, gravel areas established and all landscape areas have been loamed and seeded or planted such that vegetation has been established. Refer to the Erosion and Sedimentation Control Plan in the Site Plans for proposed erosion control measures to be employed for the project. Operations and maintenance plans for the construction phase and long-term operation of the site shall be provided. Compliance with Stormwater Management Standards Standard 1— No New Untreated Discharges The proposed redevelopment will not introduce any new untreated discharges to a wetland area or waters of the Commonwealth of Massachusetts. All discharges from the site will be treated through proposed stormwater quality controls such as deep sump hooded catch basins, pre-treatment structures and a subsurface infiltration chamber system including the establishment of proper maintenance procedures. Standard 2— Peak Rate Attenuation In the pre-development and post-development stormwater analysis, the watershed area analyzed was approximately 0.84 acres consisting of the subject parcel to be developed and all offsite tributary areas to the north of the parcel. Refer to Pre-Development Subcatchment Plan for a delineation of drainage subareas for the pre-development design condition and refer to Post-Development Subcatchment Plan for a delineation of drainage subareas for the post-development design condition. 3 for all storm events up to and including the 100-yr design storm condition. In addition, all of the runoff that emanates from the site will comply with the Department of Environmental Protection's Stormwater Management Regulations pertaining to renovation. Standard 3—Groundwater Recharge Runoff generated from the parking lot will be infiltrated by a subsurface infiltration chamber system, and the roof runoff will be infiltrated by an infiltration basin, both methods will the meet the Stormwater Guidelines for infiltration: • Infiltration structures will be a minimum of four feet above seasonal high groundwater. • Utilize the "Simple Dynamic" method for sizing the storage volume, which takes into account the fact that stormwater is exfiltrating from the infiltration basin at the same time that the basin is filling. • Hydraulic conductivity are based on soil data from the Geotechnical Report and values developed from Rawls, Brakensiek and Saxton, 1982, Estimation of Soil Water Properties, Transactions of the American Society of Agricultural Engineers, vol.25, no. 5. • Refer to Appendix C for infiltration and drawdown calculations and Appendix E for soil data. Groundwater Recharge Volume Total Provided Infiltration Soil Target Depth Impervious Required Recharge Recharge Basin Type Factor(F) (in) Area (ac) Volume (cf)l Volume (cf)Z A 0.60 0.38 828 Subsurface Infiltration 4,777 A 0.60 0.16 344 Infiltration Basin 7,502 A 0.60 0.01 26 Infiltration 212 (1a) Gardens I 401 (1b) I) 1,198 12,892 [Simple le p 1. Required Recharge Volume =Target Depth Factor x Impervious Area/ dynamic (d+Kt) method] (Refer to supplemental calculations in Appendix C) 2. Provided Recharge Volume =Volume Provided from Bottom of Basin to lowest outlet invert. 5 Removal Worksheets for TSS removal rates and sizing calculations for treatment unit water quality flow rates in Appendix C. Standard 5 — Land Use with Higher Potential Pollutant Loads (LUHPPL) The proposed project is not considered a land use with higher potential pollutant loads. Not applicable. Standard 6—Critical Areas The proposed project does not lie within a critical resource area. Not applicable. Standard 7 - Redevelopments and Other Proiects Subiect to the Standards onlv to the maximum extent practicable The proposed project is considered a redevelopment project and as such meets the Stormwater Management Standards to the maximum extent practicable. Standard 8—Construction Period Pollution Prevention and Erosion and Sedimentation Control A detailed Erosion and Sedimentation Control Plan is included in the plan set. The project will require a NPDES Construction General Permit and the Stormwater Pollution Prevention Plan (SWPPP) will be prepared prior to commencement of construction activities that will result in the disturbance of one acre of land or more. A Construction Phase BMP Operation and Maintenance Plan has been provided as a basis for the SWPPP. Refer to Appendix D. Standard 9—Operation and Maintenance Plan The Long-Term Operation and Maintenance Plan is provided in Appendix D. 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ARSENAL STREET Town•�of _ :� �P�° a�tertown v� ZONE X ZONE AE 0 2502�2<3 �oJG�e I r ZONE AE o��� Clan•es lti�e C1ltirles R;�,e LINE /� FIGURE — L Asslnippl Office Park 150 Longwater Drive,Suite 101 Norwell,MA 02061 781.792.3900 M C K E N Z I E www.mckeng.com ENGINEERING GROUP 0 500' 1000, 12501 FEMA FLOOD MAP COMMUNITY PANEL NO: 25017C0556E 80 ELM STREET EFFECTIVE DATE: JUNE 4, 2010 MAP 1 PARCEL 3 WATERTOWN, MASSACHUSETTS © MCKENZIE ENGINEERING GROUP,INC. DATE: JANUARY 30, 2018 w �V O T �¢O O FIPARK LO PARK MI x X X E6ER ,A „ x ZONING DISTRICTS OVER--kY DISTRICTS -CENTRAL BUSINESS -REGIONAL MIXED USE�RMUD! CLUSTER RESIDENTIAL O HISTORIC OVERLAY DISTRICT LIMITED BUSINESS -Pleasant Street Corridor-1 IPSCO.1) -SINGLE FAI iILY j3-101 ASSISTED LIVING QYERLAN _NEIGHBORHOOD BUSINESS -Pleasant Street Comdor-2 IPSCD•21 SINGLE FAMILY IS-R! .-q ARSENAL OVERLAY DEVELOPMENT DISTRICT INDUSTRIAL-I Pleasant Street Comdor-3 kPSCLL?1 SINGLE FAMILN CONVERSION _ t DESIGN OFERLAIr DISTRICT INDUSTRIAL-2 RESIDENTIAL.7o TWO FAMILN ' RELIGIOUS.-SCHOOL BUILDING OVERLAY INDUSTRIAL-3 -RESIDENTIAL 1.2 OPEN rr'I L-AITE==E=E iE--T[---FI•-T C'F=L :IcTF-.- FIGURE - 4 Asslnlppl Office Park 150 Longwater Drive,Suite 101 Norwell, MA 02061 781.792.3900 M C K E N Z I E www.mckeng.com ENGINEERING GROUP 0 500, 1000, 1250' ZONING MAP TOWN OF WATERTOWN 80 ELM STREET MAP 1238, PARCEL 3 ZONING MAP WATERTOWN, MASSACHUSETTS Q MCKENZIE ENGINEERING GROUP, INC. DATE:JANUARY 30. 2018