Mixed-Use Development Site Plan. for. 131 Eliot Street Milton, Massachusetts

Transcription

1 Mixed-Use Development Site Plan for 131 Eliot Street Milton, Massachusetts August 25, 2010 Prepared for: Carrick Realty Trust c/o Jeremiah Connelly, Trustee 1858 Dorchester Avenue Dorchester, MA Prepared by: DeCelle-Burke & Associates, Inc. 149 Independence Avenue Quincy, MA PH: FX:

2 Table of Contents Section 1 Project Narrative Offsite Flow Summary Section 2 Supplemental Information USGS Map Assessors Map Soils Map FEMA Panel Section 3 Stormwater Management Supporting Data Hydrologic/Hydraulic Stormwater Models Existing Conditions, (2, 10, 25 & 100 Year) Proposed Conditions, (2, 10, 25 & 100 Year) Pipe Sizing Calculations; Rational Method Infiltration System Design TSS Removal Calculation Sheet Operation & Maintenance plan DeCelle-Burke & Associates, Inc. 149 Independence Avenue Quincy, MA PH: FX:

3 Existing Conditions SECTION 1 - PROJECT NARRATIVE The property is located on the corner of Eliot Street and Central Avenue in Milton, Massachusetts with a mailing address of 131 Eliot Street. The site is currently improved with a two story brick warehouse with loading docks, surface parking and underground parking. Utilities servicing the building consist of public water, public sewer and gas, as well as overhead and underground power and communication lines. The site is predominantly impervious with small trees and other vegetation protruding through poorly maintained bituminous concrete parking surfaces. A small section of landscaping located at the corner of Eliot Street and Central Avenue provides a minimal amount of green space for the industrial building s entrance. The intersection of Central Avenue and Eliot Street, formerly known as Central Square, is currently known as Edward T. O Neil Square is located in the Central Avenue Business District. The square provides small business service to the neighborhood including an automobile service station, a dry cleaners, a liquor store, a coffee shop, a pizza parlor and several other small business s. The square also has single family and multi-family residential uses adjacent to the businesses. The locus property is abutted directly to the west and across Eliot Street by a single and multi-family homes. The site also directly abuts the MBTA trolley line that connects Mattapan Square and Ashmont Station. A trolley stop abuts this property. Elevations onsite range from a high of 39 on the westerly side of the lot to a low of 23 located at the entrance of the underground garage along Central Avenue and adjacent to the MBTA trolley tracks. The elevations are based on a local site datum used on the most recent existing conditions plan by Anderson Surveys, Inc. The conversion for the local datum to the National Geodetic Vertical Datum of 1929 (NGVD-29) is adding 5.65 feet and the conversion to the Town of Milton datum is adding Stormwater generated on site follows the contours discussed above; generally west to east. The westerly runoff flows to Eliot Street and the easterly portion of the lot to Central Avenue. There are several catch basins located on Eliot Street and Central Avenue which capture the majority of stormwater generated on the site. A single on-site catch basin located within the existing parking structure captures a small portion of the site runoff and conveys it to the public drainage system. The public drain conveys the stormwater to the Neponset River. Existing site soils were mapped by the Natural Resource Conservation Service (NRCS) and were determined to be Urban Land. The abutting soils were mapped as Charlton-Hollis Rock Complex and Woodbridge. The Urban Land is typical of an industrialized site in that the soils are disturbed and have indeterminate characteristics. However, the abutting soils have defined characteristics that ledge may be present or a tight silty till material. Given the unpredictable nature of the soils, this office has used a Hydrologic Group C for hydrologic models. DeCelle-Burke & Associates, Inc. 149 Independence Avenue Quincy, MA PH: FX:

4 The site is located near two perennial streams which make the property subject to the Massachusetts Rivers Protection Act. The Neponset River is located to the north of the parcel directly abutting the trolley track and Pine Tree Brook is located to the east behind the dry cleaners and service station. The entire site is located within the 200-foot Riverfront Area but the property does not abut the actual riverbank of either perennial stream. Any proposed work for this site will require a filing with the Milton Conservation Commission. Proposed Conditions The proposed Mixed-Use Development includes the construction of a new four-story residential/commercial building consisting of approximately four thousand square feet of commercial space on the ground level and 38 residential units on the upper levels. The commercial space shall enhance the current business uses located in the Square while the residential units will provide a new influx of neighborhood patrons that will use the dry cleaners, the pizza parlor and the trolley. The existing building will be demolished along with the surface and structural parking areas. The existing utilities servicing the building will be cut, capped and abandoned in place. Erosion and construction control measures shall be implemented to prevent off-site sediment transport, minimize fugitive dust and provide public safety while the site preparation and actual construction proceeds. Once the existing building is razed and the demolition debris removed from the site and disposed of in a legal manner, the proposed building construction will begin. The same erosion and construction control measures will continue. The building s foundation will be constructed and then multiple stories framed and weatherproofed. Proposed utilities servicing the new building will include a 6 D.I. fire pipe and a 4 D.I. domestic water service. The two services will be tapped from an existing 12 water main in Eliot Street. An 8 CI sewer service is proposed to connect to the existing 15 sewer main in Central Avenue. An oil/water separator for the parking garage will connect to the proposed sewer service within the building envelope. A gas service will connect to the gas main in Central Avenue. Power and communications will be provided by rerouting an existing underground line that currently services the site. These services will be connected as the building proceeds to be vertically constructed. The proposed stormwater management for the project includes reducing the overall impervious nature of the site and recharging a portion of the site runoff. The site s calculated existing conditions hydrologic curve number (CN) is 97 while the proposed conditions hydrologic curve number (CN) is 91. This translates into an overall reduction in off-site stormwater runoff without introducing any stormwater controls. DeCelle-Burke & Associates, Inc. 149 Independence Avenue Quincy, MA PH: FX:

5 We have proposed the installation of a water quality structure and recharge structure that will improve stormwater quality and further reduce the stormwater flow and volume. The proposed surface parking lot has two proposed catch basins that will connect to the water quality manhole near the entrance to the parking lot. This manhole connects to two 6-foot diameter leaching pits that will have a 12 RCP overflow connecting to a new drain manhole on the property. The overflow will connect to the existing Town drainage system near the Central Avenue and Eliot Street intersection. The stormwater management calculations along with a signed Stormwater Management Form are included in this report. A stormwater flow summary is attached after this narrative for review. Parking lot construction and landscaping will occur toward the end of the project as this provides the property s finished look at the ground surface. The 32-space parking lot located to the west of the proposed building is proposed to be used as shared parking during the day and then revert back to resident only parking during the night. The additional 66 underground spaces, located on two-levels, totaling 98 site spaces (9 handicap spaces) provides the necessary parking volume for the proposed use. The required spaces according to local zoning was calculated to be 86. Landscaping includes stone walls, a pergola, surface lighting and several plants, shrubs and trees as outlined in the plan prepared by William Fleming Associates. DeCelle-Burke & Associates, Inc. 149 Independence Avenue Quincy, MA PH: FX:

6 Offsite Flow Summary 2-Year Storm (3.2 ) Existing Conditions (ec) Proposed Conditions (pc) Area Description Flow (CFS) Area Description Flow (CFS) Total Flow 3.09 Total Flow Year Storm (4.7 ) Existing Conditions (ec) Proposed Conditions (pc) Area Description Flow (CFS) Area Description Flow (CFS) Total Flow 4.60 Total Flow 4.15 Existing Conditions (ec) 25-Year Storm (5.6 ) Proposed Conditions (pc) Area Description Flow (CFS) Area Description Flow (CFS) Total Flow 5.50 Total Flow Year Storm (7.0 ) Existing Conditions (ec) Proposed Conditions (pc) Area Description Flow (CFS) Area Description Flow (CFS) Total Flow 6.90 Total Flow 6.53 DeCelle-Burke & Associates, Inc. 149 Independence Avenue Quincy, MA PH: FX:

7 Section 1 Project Narrative Drainage Methodology & Summary DeCelle-Burke & Associates, Inc. 149 Independence Avenue Quincy, MA PH: FX:

8 Section 2 Supplemental Information USGS Map Assessors Map Soils Map FEMA Panel DeCelle-Burke & Associates, Inc. 149 Independence Avenue Quincy, MA PH: FX:

9 Section 3 Stormwater Management Supporting Data Hydrologic/Hydraulic Stormwater Models Existing Conditions, (2, 10, 25 & 100 Year) Proposed Conditions, (2, 10, 25 & 100 Year) Pipe Sizing Calculations; Rational Method Infiltration System Design TSS Removal Calculation Sheet Operation & Maintenance plan DeCelle-Burke & Associates, Inc. 149 Independence Avenue Quincy, MA PH: FX:

10 DATE: TITLE: SCALE: MARCH 10, 2010 USGS MAP NOT TO SCALE PREPARED FOR: Carrick Realty Trust 1858 Dorchester Avenue Dorchester, MA PROJECT TITLE: Mixed Use Development 131 Eliot Street Milton, MA 149 Independence Avenue Quincy, MA (617) (O) (617) (F)

11 Soil Map Legend DATE: TITLE: SCALE: MARCH 10, 2010 Map Unit Symbol Map Unit Name 1 Water 52 Freetown muck, 0 to 1 percent slopes 103B Charlton-Hollis-Rock outcrop complex, 3 to 8 percent slopes 103C Charlton-Hollis-Rock outcrop complex, 8 to 15 percent slopes 104C Hollis-Rock outcrop-charlton complex, 3 to 15 percent slopes 254B Merrimac fine sandy loam, 3 to 8 percent slopes 260B Sudbury fine sandy loam, 2 to 8 percent slopes 305B Paxton fine sandy loam, 3 to 8 percent slopes 305C Paxton fine sandy loam, 8 to 15 percent slopes 305D Paxton fine sandy loam, 15 to 25 percent slopes 310B Woodbridge fine sandy loam, 3 to 8 percent slopes 602 Urban land, 0 to 15 percent slopes 626B Merrimac-Urban land complex, 0 to 8 percent slopes 653 Udorthents, sandy SOILS MAP NOT TO SCALE PREPARED FOR: Carrick Realty Trust 1858 Dorchester Avenue Dorchester, MA PROJECT TITLE: Mixed Use Development 131 Eliot Street Milton, MA 149 Independence Avenue Quincy, MA (617) (O) (617) (F)

12 DATE: TITLE: SCALE: MARCH 10, 2010 ASSESSOR S MAP NOT TO SCALE PREPARED FOR: Carrick Realty Trust 1858 Dorchester Avenue Dorchester, MA PROJECT TITLE: Mixed Use Development 131 Eliot Street Milton, MA 149 Independence Avenue Quincy, MA (617) (O) (617) (F)

13 DATE: TITLE: MARCH 10, 2010 PREPARED FOR: SCALE: FEMA FLOOD MAP NOT TO SCALE PROJECT TITLE: Carrick Realty Trust 1858 Dorchester Avenue Dorchester, MA Mixed Use Development 131 Eliot Street Milton, MA 149 Independence Avenue Quincy, MA (617) (O) (617) (F)

14 EC DRAINAGE Type III 24-hr Rainfall=3.20" Prepared by {enter your company name here} Page 1 HydroCAD 6.00 s/n Applied Microcomputer Systems 8/25/2010 Subcatchment 1S: Existing Site Runoff = hrs, Volume= af Runoff by SCS TR-20 method, UH=SCS, Time Span= hrs, dt= 0.05 hrs Type III 24-hr Rainfall=3.20" Area (sf) CN Description 28, Paved parking & roofs 12, Paved parking & roofs 2, % Grass cover, Fair, HSG C 43, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry,

15 EC DRAINAGE Type III 24-hr Rainfall=4.70" Prepared by {enter your company name here} Page 1 HydroCAD 6.00 s/n Applied Microcomputer Systems 8/25/2010 Subcatchment 1S: Existing Site Runoff = hrs, Volume= af Runoff by SCS TR-20 method, UH=SCS, Time Span= hrs, dt= 0.05 hrs Type III 24-hr Rainfall=4.70" Area (sf) CN Description 28, Paved parking & roofs 12, Paved parking & roofs 2, % Grass cover, Fair, HSG C 43, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry,

16 EC DRAINAGE Type III 24-hr Rainfall=5.60" Prepared by {enter your company name here} Page 1 HydroCAD 6.00 s/n Applied Microcomputer Systems 8/25/2010 Subcatchment 1S: Existing Site Runoff = hrs, Volume= af Runoff by SCS TR-20 method, UH=SCS, Time Span= hrs, dt= 0.05 hrs Type III 24-hr Rainfall=5.60" Area (sf) CN Description 28, Paved parking & roofs 12, Paved parking & roofs 2, % Grass cover, Fair, HSG C 43, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry,

17 EC DRAINAGE Type III 24-hr Rainfall=7.00" Prepared by {enter your company name here} Page 1 HydroCAD 6.00 s/n Applied Microcomputer Systems 8/25/2010 Subcatchment 1S: Existing Site Runoff = hrs, Volume= af Runoff by SCS TR-20 method, UH=SCS, Time Span= hrs, dt= 0.05 hrs Type III 24-hr Rainfall=7.00" Area (sf) CN Description 28, Paved parking & roofs 12, Paved parking & roofs 2, % Grass cover, Fair, HSG C 43, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry,

18 PC DRAINAGE-rev Type III 24-hr Rainfall=3.20" Prepared by {enter your company name here} Page 1 HydroCAD 6.00 s/n Applied Microcomputer Systems 8/25/2010 Subcatchment P-Lot: Exterior Parking Lot Runoff = hrs, Volume= af Runoff by SCS TR-20 method, UH=SCS, Time Span= hrs, dt= 0.05 hrs Type III 24-hr Rainfall=3.20" Area (sf) CN Description 10, Paved parking & roofs 2, >75% Grass cover, Good, HSG C 13, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Subcatchment Rem. Site: P-Bldg & Rem. Area Runoff = hrs, Volume= af Runoff by SCS TR-20 method, UH=SCS, Time Span= hrs, dt= 0.05 hrs Type III 24-hr Rainfall=3.20" Area (sf) CN Description 10, >75% Grass cover, Good, HSG C 17, Prop. Roof 2, Impervious Area 30, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Reach 1R: (new node) Inflow = hrs, Volume= af Outflow = hrs, Volume= af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind+Trans method, Time Span= hrs, dt= 0.05 hrs Max. Velocity= 20.3 fps, Min. Travel Time= 0.0 min Avg. Velocity = 16.6 fps, Avg. Travel Time= 0.0 min Peak Depth= 0.10' Capacity at bank full= 10, cfs Inlet Invert= 3.00', Outlet Invert= 2.00' 100.0" Diameter Pipe n= Length= 1.0' Slope= '/' Pond 1P: (new node) Inflow = hrs, Volume= af Outflow = hrs, Volume= af, Atten= 0%, Lag= 0.6 min Discarded = hrs, Volume= af Primary = hrs, Volume= af

19 PC DRAINAGE-rev Type III 24-hr Rainfall=3.20" Prepared by {enter your company name here} Page 2 HydroCAD 6.00 s/n Applied Microcomputer Systems 8/25/2010 Routing by Stor-Ind method, Time Span= hrs, dt= 0.05 hrs Peak Elev= 29.71' Storage= 174 cf Plug-Flow detention time= 29.5 min calculated for af (96% of inflow) Elevation Cum.Store (feet) (cubic-feet) Discarded OutFlow (Free Discharge) 2=Exfiltration Primary OutFlow (Free Discharge) 1=Culvert 3=Orifice/Grate # Routing Invert Outlet Devices 1 Primary 29.30' 12.0" x 172.0' long Culvert RCP, groove end projecting, Ke= Outlet Invert= 24.00' S= '/' n= Cc= Discarded 0.00' 0.02 cfs Exfiltration at all elevations 3 Primary 33.00' 24.0" Horiz. Orifice/Grate X 2.00 Limited to weir flow C= 0.600

20 PC DRAINAGE-rev Type III 24-hr Rainfall=4.70" Prepared by {enter your company name here} Page 1 HydroCAD 6.00 s/n Applied Microcomputer Systems 8/25/2010 Subcatchment P-Lot: Exterior Parking Lot Runoff = hrs, Volume= af Runoff by SCS TR-20 method, UH=SCS, Time Span= hrs, dt= 0.05 hrs Type III 24-hr Rainfall=4.70" Area (sf) CN Description 10, Paved parking & roofs 2, >75% Grass cover, Good, HSG C 13, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Subcatchment Rem. Site: P-Bldg & Rem. Area Runoff = hrs, Volume= af Runoff by SCS TR-20 method, UH=SCS, Time Span= hrs, dt= 0.05 hrs Type III 24-hr Rainfall=4.70" Area (sf) CN Description 10, >75% Grass cover, Good, HSG C 17, Prop. Roof 2, Impervious Area 30, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Reach 1R: (new node) Inflow = hrs, Volume= af Outflow = hrs, Volume= af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind+Trans method, Time Span= hrs, dt= 0.05 hrs Max. Velocity= 23.5 fps, Min. Travel Time= 0.0 min Avg. Velocity = 16.7 fps, Avg. Travel Time= 0.0 min Peak Depth= 0.12' Capacity at bank full= 10, cfs Inlet Invert= 3.00', Outlet Invert= 2.00' 100.0" Diameter Pipe n= Length= 1.0' Slope= '/' Pond 1P: (new node) Inflow = hrs, Volume= af Outflow = hrs, Volume= af, Atten= 1%, Lag= 0.5 min Discarded = hrs, Volume= af Primary = hrs, Volume= af

21 PC DRAINAGE-rev Type III 24-hr Rainfall=4.70" Prepared by {enter your company name here} Page 2 HydroCAD 6.00 s/n Applied Microcomputer Systems 8/25/2010 Routing by Stor-Ind method, Time Span= hrs, dt= 0.05 hrs Peak Elev= 29.83' Storage= 183 cf Plug-Flow detention time= 22.0 min calculated for af (97% of inflow) Elevation Cum.Store (feet) (cubic-feet) Discarded OutFlow (Free Discharge) 2=Exfiltration Primary OutFlow (Free Discharge) 1=Culvert 3=Orifice/Grate # Routing Invert Outlet Devices 1 Primary 29.30' 12.0" x 172.0' long Culvert RCP, groove end projecting, Ke= Outlet Invert= 24.00' S= '/' n= Cc= Discarded 0.00' 0.02 cfs Exfiltration at all elevations 3 Primary 33.00' 24.0" Horiz. Orifice/Grate X 2.00 Limited to weir flow C= 0.600

22 PC DRAINAGE-rev Type III 24-hr Rainfall=5.60" Prepared by {enter your company name here} Page 1 HydroCAD 6.00 s/n Applied Microcomputer Systems 8/25/2010 Subcatchment P-Lot: Exterior Parking Lot Runoff = hrs, Volume= af Runoff by SCS TR-20 method, UH=SCS, Time Span= hrs, dt= 0.05 hrs Type III 24-hr Rainfall=5.60" Area (sf) CN Description 10, Paved parking & roofs 2, >75% Grass cover, Good, HSG C 13, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Subcatchment Rem. Site: P-Bldg & Rem. Area Runoff = hrs, Volume= af Runoff by SCS TR-20 method, UH=SCS, Time Span= hrs, dt= 0.05 hrs Type III 24-hr Rainfall=5.60" Area (sf) CN Description 10, >75% Grass cover, Good, HSG C 17, Prop. Roof 2, Impervious Area 30, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Reach 1R: (new node) Inflow = hrs, Volume= af Outflow = hrs, Volume= af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind+Trans method, Time Span= hrs, dt= 0.05 hrs Max. Velocity= 24.6 fps, Min. Travel Time= 0.0 min Avg. Velocity = 16.7 fps, Avg. Travel Time= 0.0 min Peak Depth= 0.14' Capacity at bank full= 10, cfs Inlet Invert= 3.00', Outlet Invert= 2.00' 100.0" Diameter Pipe n= Length= 1.0' Slope= '/' Pond 1P: (new node) Inflow = hrs, Volume= af Outflow = hrs, Volume= af, Atten= 1%, Lag= 0.5 min Discarded = hrs, Volume= af Primary = hrs, Volume= af

23 PC DRAINAGE-rev Type III 24-hr Rainfall=5.60" Prepared by {enter your company name here} Page 2 HydroCAD 6.00 s/n Applied Microcomputer Systems 8/25/2010 Routing by Stor-Ind method, Time Span= hrs, dt= 0.05 hrs Peak Elev= 29.89' Storage= 188 cf Plug-Flow detention time= 19.1 min calculated for af (97% of inflow) Elevation Cum.Store (feet) (cubic-feet) Discarded OutFlow (Free Discharge) 2=Exfiltration Primary OutFlow (Free Discharge) 1=Culvert 3=Orifice/Grate # Routing Invert Outlet Devices 1 Primary 29.30' 12.0" x 172.0' long Culvert RCP, groove end projecting, Ke= Outlet Invert= 24.00' S= '/' n= Cc= Discarded 0.00' 0.02 cfs Exfiltration at all elevations 3 Primary 33.00' 24.0" Horiz. Orifice/Grate X 2.00 Limited to weir flow C= 0.600

24 PC DRAINAGE-rev Type III 24-hr Rainfall=7.00" Prepared by {enter your company name here} Page 1 HydroCAD 6.00 s/n Applied Microcomputer Systems 8/25/2010 Subcatchment P-Lot: Exterior Parking Lot Runoff = hrs, Volume= af Runoff by SCS TR-20 method, UH=SCS, Time Span= hrs, dt= 0.05 hrs Type III 24-hr Rainfall=7.00" Area (sf) CN Description 10, Paved parking & roofs 2, >75% Grass cover, Good, HSG C 13, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Subcatchment Rem. Site: P-Bldg & Rem. Area Runoff = hrs, Volume= af Runoff by SCS TR-20 method, UH=SCS, Time Span= hrs, dt= 0.05 hrs Type III 24-hr Rainfall=7.00" Area (sf) CN Description 10, >75% Grass cover, Good, HSG C 17, Prop. Roof 2, Impervious Area 30, Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Reach 1R: (new node) Inflow = hrs, Volume= af Outflow = hrs, Volume= af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind+Trans method, Time Span= hrs, dt= 0.05 hrs Max. Velocity= 25.9 fps, Min. Travel Time= 0.0 min Avg. Velocity = 16.8 fps, Avg. Travel Time= 0.0 min Peak Depth= 0.16' Capacity at bank full= 10, cfs Inlet Invert= 3.00', Outlet Invert= 2.00' 100.0" Diameter Pipe n= Length= 1.0' Slope= '/' Pond 1P: (new node) Inflow = hrs, Volume= af Outflow = hrs, Volume= af, Atten= 1%, Lag= 0.4 min Discarded = hrs, Volume= af Primary = hrs, Volume= af

25 PC DRAINAGE-rev Type III 24-hr Rainfall=7.00" Prepared by {enter your company name here} Page 2 HydroCAD 6.00 s/n Applied Microcomputer Systems 8/25/2010 Routing by Stor-Ind method, Time Span= hrs, dt= 0.05 hrs Peak Elev= 29.98' Storage= 195 cf Plug-Flow detention time= 16.4 min calculated for af (97% of inflow) Elevation Cum.Store (feet) (cubic-feet) Discarded OutFlow (Free Discharge) 2=Exfiltration Primary OutFlow (Free Discharge) 1=Culvert 3=Orifice/Grate # Routing Invert Outlet Devices 1 Primary 29.30' 12.0" x 172.0' long Culvert RCP, groove end projecting, Ke= Outlet Invert= 24.00' S= '/' n= Cc= Discarded 0.00' 0.02 cfs Exfiltration at all elevations 3 Primary 33.00' 24.0" Horiz. Orifice/Grate X 2.00 Limited to weir flow C= 0.600

26 P-Lot Rem. Site 1P 1R Subcat Reach Pond Link Drainage Diagram for PC DRAINAGE-rev Prepared by {enter your company name here} 8/25/2010 HydroCAD 6.00 s/n Applied Microcomputer Systems

27 Project: 131 Eliot Street Prepared by: DeCelle-Burke & Associates Milton, MA 149 Independence Avenue Client: Carrick Realty Trust Quincy, MA Date: 8/25/10 DRAINAGE CALCULATIONS FOR A 25-YEAR STORM, CHEZY-MANNING'S FORMULA, N=0.013, REINFORCED CONC. PIPE STRUCTURE DESC. AREA "C" CA (min.) I Q L S DIA. QFULL VFULL Q/ V/ V D/V RIM INVERTINVERT from to (acres) (acres) PIPE Tc (in/hr) (cfs) (ft) (ft/ft) (in.) (cfs) (ft/s) QFULL VFULL (ft/s) (min.) IN OUT DA 1 CB1&2 PAVE GRASS CB1&2 WQ

28 Infiltration System Design Client: Carrick Realty Trust Project Name: Mixed-Use Development Project Location: 131 Eliot St. Milton, MA Job Number: Date: 8/25/2010 STORAGE VOLUME Number of Drywells = 2 Depth (Stone, Below Drywell) = 1.00 Radius (Drywell, Inside) = 3.00 Depth (Stone, Side Drywell) = 1.00 Drywell Wall Width = 0.5 Percent Voids in Stone = 30.00% Depth (Drywell, Below Invert) = 3 Total Impervious Area On-Site= n/a s.f. Excavation Width= 9 Excavation Length= 18 Volume of Drywell= Volume in Drywell = Volume of Stone Below Drywells = Volume of Stone Surrounding Drywells = Volume of Drywells= Total Drywell System Volume Provided= Bottom Leaching Area = Sidewall Leaching Area = Total Leaching Area = 115 c.f. 85 c.f. 49 c.f. 77 c.f. 231 c.f. 356 c.f. 162 s.f. 162 s.f. 324 s.f. RECHARGE RATE Leaching Area Assumed Infiltration Rate Calculated Recharge Rate 324 s.f. 20 mpi 0.02 cfs DeCelle-Burke Associates, Inc. 149 Independence Avenue Quincy, MA PH: FX:

29 Project: Mixed-Use Development Location: 131 Eliot Street Milton, MA Date: 8/25/2010 Total Suspended Solids Removal Calculations BMP TSS Start Amount Total Remaining Removal Load Removed Removed Load 4' Deep Sump Catch Basins 25% 100% 25% 25% 75% 4' Deep Sump Water Quality MH 25% 75% 19% 44% 56% Remaining Load 44% DeCelle-Burke Associates, Inc. 149 Independence Avenue Quincy, MA PH FX

30 STORMWATER OPERATION AND MAINTENANCE PLAN 131 Eliot Street, Milton, MA OWNER & RESPONSIBLE PARTY DURING CONSTRUCTION: Carrick Realty Trust 1858 Dorchester Avenue Dorchester, MA RESPONSIBLE PARTY FOLLOWING CONSTRUCTION: PROJECT OVERVIEW: Carrick Realty Trust 1858 Dorchester Avenue Dorchester, MA The project consists of constructing a 16,800 square foot mixed use building footprint and bituminous concrete drive and parking area on the corner of Eliot Street and Central Avenue in Milton, MA. The site improvements include the construction of a parking lot, utilities and stormwater management facilities. The exterior parking area will consist of impervious bituminous concrete with cape cod berm. The stormwater will be conveyed along the curbing to two deep-sump catch basins located in the parking area. The catch basins will capture particulates and suspended solids. The stormwater will then be conveyed to a deep sump water quality structure and then to leaching pits that allow stormwater to be discharged into the ground. The water quality structure will capture additional particulates and suspended solids and the leach pits will recharge groundwater. Overflow from the leach pits will be conveyed to a drain manhole that connects to the existing storm sewer in Eliot Street. The Best Management Practices (BMPs) used in this design were chosen for their effectiveness and ease of maintenance. Providing for maintenance requirements that are practical is essential to achieve the desired result of improved water quality and a reductions in overall off-site stormwater flows. It is intended that the project infrastructure will be privately owned and maintained by the developer. Therefore, the owner of the property will be responsible for maintaining the stormwater system located within the project limits. To ensure proper functioning of the proposed systems, periodic inspection and maintenance is necessary. The following document has been prepared as a stand-alone guide for the responsible party to implement an inspection and maintenance program for the proposed stormwater management facilities. Maintenance of the stormwater management system (i.e. Catch basins, etc.) is the responsibility of the final property management or the landowner. This agreement between the Town of Milton and property management shall be recorded at the Norfolk County Registry of Deeds. Stormwater Operation Eliot Street and Maintenance Plan August 25, 2010

31 NON-STRUCTURAL APPROACHES: STREET SWEEPING Post-construction, street sweeping will be performed biannually during the spring and fall. SNOW MANAGEMENT Proper snow management practices will be implemented to minimize runoff and pollutant loading impacts. Plowed snow will be placed in pervious areas where it can slowly infiltrate. Plowed snow will be placed on to pervious areas that are not subject to excessive shade from buildings or vegetation. This will allow snowmelt to run off onto paved areas, enter the stormwater management facilities and be subjected to the majority of the treatment system. All accumulated sediment from snowmelt shall be removed each spring. STRUCTURAL BEST MANAGEMENT PRACTICES: LEACHING PITS Subsurface infiltration chambers are proposed to recharge the site runoff into the ground. The system shall include manholes to finish grade for annual inspection to determine if any loss of infiltration capacity has occurred. If any large amounts of sediment accumulate in the leaching chambers, they shall be removed by vacuum truck. DEEP-SUMP CATCH BASIN AND WATER QULAITY STRUCTURE Deep-sump catch basins and a water quality strucutre manhole will be installed to remove trash, debris, sediment and a limited amount of grease and oil from stormwater. Oil and grease will float on the surface of the pooled water and be trapped by an inverted elbow. To ensure maximum capacity and efficiency, the sumps will be cleaned when half of the available capacity of the deep sump has been used or at a minimum of once per year. The condominium association shall inspect the units a minimum of twice per year to maintain the units and be able to increase the cleaning of the units if necessary based on the inspections. Cleaning will take place following construction at the completion of the project. Stormwater Operation Eliot Street and Maintenance Plan August 25, 2010