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38-050 (31) W. = The Berkshire Design f Group, Inc. 2005 To: Doug McDonald_ Northampton DPW From: Jeff Squire Re: Village at Hospital Hill Date: July 13, 2005 Doug - The following information is being submitted to comply with the additional stormwater management information requested in the Application Decision for the Village at Hospital Hill —Phase I Site. I. A Stormwater Operation, Maintenance, and Inspection Agreement for the detention basins was prepared as part of the SWPPP for the Phase I-Definitive Subdivision Plans submitted by Beals and Thomas. 2. Stamped calculations documenting the existing and proposed site development andthe expected flows from these areas are attached. 3. Documentation demonstrating the capacity of the proposed 24" drain line to Detention ;Basin 4 is attached. The reason that the two 24" drain lines cannot be combined is because there would be insufficient cover over a drain line with a larger diameter. The costs associated with combining the two drain lines were far greater than providing separate lines. Additionally, it was verbally expressed by the DPW, Landscape Architecture among others, that the structures required to accommodate a larger diameter drain line and the several inlet pipes in what is being referred Civil Engineering to as Olander Drive was undesirable creating additional concerns. Planning Based on these issues, it was determined that two 24"drain lines would be installed. Urban Design Environmental Services Please feel free to contact me with any questions, comments or concerns. 77 Jeffrey Squire Ce: Northampton Planning Office Building Department 4AIlen Place Northampton,Massachusetts 01060 Telephone(413)582-7000 Facsimile(413)582-7005 F-mail bd_C(�herkshircdc�i�n.a�;r -- The Landscape Architecture JOB //o s/-i Ta< L//t,L Berkshire Civil Engineering SHEET NUMBER OF 9 Design CALCULATED BY /—/.T T DATE Planning - Group,Inc. CHECKED BY DATE Urban Design SCALE 4 Allen Place Environmental Services Northampton, Massachusetts 01060 -5 g- t />EF/-/!T/Ve- �v/3/�iv �s�u i Catcr x/'S 7- C- : To T.A L '4'e E.4 Z�Mi E.E'✓/0 al c �� DIY Ac .4'eCA �s,eAS5 I(CAC i I �D Yee (Y. t o ZS- Y,e (S-..moo ) /a o Y,e �o o y c< s 6<S /Z tGs j i I i Phase I Subdivision 7-8-05 Type Ill 24-hr Rainfall=3.20°(2 YEAR STORM) Prepared by The Berkshire Design Group Page 2 HydroCADO 6.00 s/n 000752 © 1986-2001 Applied Microcomputer Systems 7/12/2005 Time span=0.00-24.00 hrs, dt=0.05 hrs, 481 points Runoff by SCS TR-20 method, UH--,SCS, Type III 24-hr Rainfall=3.20" Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment EXIST: Existing Phase I Area Tc=6.0 min CN=83 Area=1.910 ac Runoff=3.53 cfs 0.256 of Subcatchment PROP: Proposed Phase I Area Tc=6.0 rein CN=87 Area=1.910 ac Runoff=4.20 cfs 0.305 of Runoff Area=3.;820 ac Volume= 0.560 of Average Depth = 1.76" I I I I Phase I Subdivision 7-8-05 Type 111 24-hr Rainfall=3.20"(2 YEAR STORM) Prepared by The Berkshire Design Group Page 3 HydroCADO 6.00 s/n 000752 © 1986-2001 Applied Microcomputer Systems 7/12/2005 Subcatchment EXIST: Existing Phase I Area Runoff = 3.53 cfs @ 12.09 hrs, Volume= 0.256 of Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Type III 24-hr Rainfall=3.20" Area (ac) CN Description 0.180 98 Existing Pavement 0.260 98 Existing Roofs 1.470 79 50-75% Grass cover, Fair, HSG C 1.910 83 Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Flow Into Existing CB's Subcatchment PROP: Proposed Phase I Area Runoff = 4.20 cfs @ 12.09 hrs, Volume= " 0.305 of Runoff by SCS TR-20 method, UH=SCS, Time Span=0.00-24.00 hrs, dt= 0.05 hrs Type III 24-hr Rainfall=3.20" Area ac CN Description 0.810 98 Proposed Pavement Areas 0.260 98 Proposed Roof Areas 0.840 74 >75% Grass cover, Good, HSG 1.910 87 Weighted Average i Tc Length Slope Velocity Capacity Description min feet ft/ft ft/sec cfs 1 6.0 Dire Entry, Flow Into B&T's 24" Pipe Phase I Subdivision 7-8-05 Type ///24-hr Rainfall=4.80"(10 YR STORM) Prepared by The Berkshire Design Group Page 4 HydroCADO 6.00 s/n 000752 © 1986-2001 Applied Microcomputer Systems 7/12/2005 Time span=0.00-24.00 hrs, dt=0.05 hrs, 481 points Runoff by SCS TR-20 method, UH=SCS, Type III 24-hr Rainfall=4.80" Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment EXIST: Existing Phase I Area Tc=6.0 min CN=83 Area=1.910 ac Runoff= 6.54 cfs 0.476 of Subcatchment PROP: Proposed Phase I Area Tc=6.0 min CN=87 Area=1.910 ac Runoff=7.28 cfs 0.537 of Runoff Area=3.820 ac Volume= 1.014 of Average Depth =3.18" i i i Phase I Subdivision 7-8-05 Type ///24-hr Rainfall=4.80"(10 YR STORM) Prepared by The Berkshire Design Group Page 5 HydroCAD®6.00 s/n 000752 © 1986-2001 Applied Microcomputer Systems 7/12/2005 Subcatchment EXIST: Existing Phase I Area Runoff = 6.54 cfs @ 12.09 hrs, Volume= 0.476 of Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Type III 24-hr Rainfall=4.80" Area (ac) CN Description 0.180 98 Existing Pavement 0.260 98 Existing Roofs 1.470 79 50-75% Grass cover, Fair HSG C 1.910 83 Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Flow Into Existing CB's I Subcatchment PROP: Proposed Phase I Area Runoff = 7.28 cfs @ 12.09 hrs, Volume= 0.537 of Runoff by SCS TR-20 method, UH=SCS, Time Span= 00-24.00 hrs, dt= 0.05 hrs Type III 24-hr Rainfall=4.80" Area ac CN Description 0.810 98 Proposed Pavement Areas 0.260 98 Proposed Roof Areas 0.840 74 >75% Grass cover, Good, HSG 1.910 87 Weighted Average i Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Flow Into B&T's 24" Pipe Phase I Subdivision 7-8-05 Type 111 24-hr Rainfall=5.50"(25 YEAR STORM) Prepared by The Berkshire Design Group Page 6 HydroCADO 6.00 s/n 000752 © 1986-2001 Applied Microcomputer Systems 7/12/2005 Time span=0.00-24.00 hrs;, dt=0.05 hrs, 481 points Runoff by SCS TR-20 method, UH=SCS, Type III 24-hr Rainfall=5.50" Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment EXIST: Existing Phase I Area Tc=6.0 min CN=83 Area=1.910 ac Runoff=7.89 cfs 0.577 of Subcatchment PROP: Proposed Phase I Area Tc=6.0 min CN=87 Area=1.910 ac Runoff=8.64 cfs 0.643 of Runoff Area=3.620 ac Volume= 1.220 of Average Depth =3.83" Phase I Subdivision 7-8-05 Type 111 24-hr Rainfall=5.50"(25 YEAR STORM) Prepared by The Berkshire Design Group Page 7 HydroCADO 6.00 s/n 000752 © 1986-2001 Applied Micrpcomputer Systems 7/12/2005 Subcatchment EXIST: ;Existing Phase I Area Runoff = 7.89 cfs @ 12.09 hrs, Volume= 0.577 of Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Type III 24-hr Rainfall=5.50" Area (ac) CN Description 0.180 98 Existing Pavement 0.260 98 Existing Roofs 1.470 79 50-75% Grass cover, Fair, HSG C 1.910 83 Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Flow Into Existing CB's i Subcatchment PROP: F roposed Phase I Area Runoff = 8.64 cfs @ 12.09 hrs, Volume= 0.643 of Runoff by SCS TR-20 method, UH=SCS, Time Span= 6.00-24.00 hrs, dt= 0.05 hrs Type III 24-hr Rainfall=5.50" i Area (ac) CN Description 0.810 98 Proposed Pavement Areas 0.260 98 Proposed Roof Areas 0.840 74 >75% Grass cover, Good, HSG C 1.910 87 Weighted Average Tc Length Slope Velocity Capacity Desctiption (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Flow Into B&T's 24" Pipe i Phase I Subdivision 7-8-05 type 111 24-hr Rainfall=7.00"(100 YEAR STORM) Prepared by The Berkshire Design Group Page 8 H droCAD®6.00 s/n 000752 © 1986-2001 Applied Microicomputer Systems 7/12/2005 Time span=0.00-24.00 hrs dt=0.05 hrs, 481 points Runoff by SCS TR-20 method, UH=SCS, Type III 24-hr Rainfall=7.00" Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment EXIST: Existing Phase I Area Tc=6.0 min CN=83 Area=1.910 ac Runoff= 10.80 cfs 0.800 of Subcatchment PROP: Proposed Phase I Area Tc=6.0 min CN=87 Area=1.910 ac Runoff= 11.54 cfs 0.872 of Runoff Area=3.820 ac Volume= 1.671 of Average Depth =5.25" Phase I Subdivision 7-8-05 Type ///24-hr Rainfall=7.00"(100 YEAR STORM) Prepared by The Berkshire Design Group Page 9 HydroCADO 6.00 s/n 000752 © 1986-2001 Applied Microcomputer Systems 7/12/2005 Subcatchment EXIST: Existing Phase I Area Runoff = 10.80 cfs @ 12.09 hrs, Volume= 0.800 of Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Type III 24-hr Rainfall=7.00" Area (ac) CN Description 0.180 98 Existing Pavement 0.260 98 Existing Roofs 1.470 79 50-75% Grass cover, Fair, HSG C 1.910 83 Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Flow Into Existing CB's Subcatchment PROP: Proposed Phase I Area Runoff = 11.54 cfs @ 12.09 hrs, Volume= 0.872 of i Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Type III 24-hr Rainfall=7.00" Area (ac) CN Description 0.810 98 Proposed Pavement Areas 0.260 98 Proposed Roof Areas 0.840 74 >75% Grass cover, Good HSG C 1.910 87 Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Flow Into B&T's 24" Pipe The Landscape Architecture JOB Alo-5 Berkshire Civil Engineering SHEET NUMBER / OF Design DATE -.z_o,- Planning j CALCULATED BY ��T Group,Inc. CHECKED BY DATE Urban Design ' SCALE 4 Allen Place Environmental Services Northampton,Massachusetts 01060 <s4:-C TV f; Asi y SM�. ,C!,e E o �v�G E"L 7 E/� /-�! �.ea i-•..�A 6^� SYS rE M Ac LoT �Zx� �/Gir ♦rsN a O. 60 q c Z/0 Y4 12- /00 Z/Oo I i S SifOwN o� l�f�- {FoLL owivG- PAG£ /`'1i+X 93 c ,�s > 1 cFS Y 24" Pipe to Proposed Basin 4 Manning Pipe Calculator Given Input Data: shape . . . . . . . . . . . . . . . . . . . . . . . . . . . Circular solving for . . . . . . . . . . . . . . . . . . . . . Flowrate Diameter . . . . . . . . . . . . . . . . . . . . . . . . 24.0000 in Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . 24.0000 in slope . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.0070 ft/ft manning's n . . . . . . . . . . . . . . . . . . . . . 0.0130 Computed Results: Flowrate . . . . . . . . . . . . . . . . . . . . . . . . 18.9273 cfs Area . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1416 ft2 wetted Area . . . . . . . . . . . . . . . . . . . . . 3.1416 ft2 wetted Perimeter . . . . . . . . . . . . . . . . 75.3982 in Perimeter . . . . . . . . . . . . . . . . . . . . . . . 75.3982 in velocity . . . . . . . . . . . . . . . . . . . . . . . . 6.0,247 fps Hydraulic Radius . . . . . . . . . . . . . . . . 6.0000 in Percent Full . . . . . . . . . . . . . . . . . . . . 100!.0000 Full flow Flowrate . . . . . . . . . . . . . . 18.'9273 cfs 1 Full flow velocity . . . . . . . . . . . . . . 6.0247 fps Page 2 P O REAR NWG 199x0 L Z ." 199.0 -TTQ- a . .226 \ 22` 7H l 1 22z. Po i { LP 7, 1? .10 ti '� � • ,t.. . . . . . ` ._.. Q 210 oA ♦x•r yes a y; 1 The Imp. Areas Flowing into Basin#4 Berkshire Design Village at Hospital Hill Group,IRC. Northampton,MA PM I 4 Alen Pi— NortFgmpton,MassocNwus 01060 (413)582-7000 FAX(413) 582-7005 SCALE: 1x=100' DATE: July 12, 2005 w THE VILLAGE AT HOSPITAL HILL NORTHAMPTON,MASSACHUSETTS OPERATION AND MAINTENANCE PLAN The following 0 & M Plan has been developed to comply with DEP's Stormwater Management Policy. The responsibilities outlined in the 0 &M Plan run with ownership of the property. Responsible Party: Owner/Operator: Hospital Hill Development, LLC. c/o Mass Development 1441 Maim Street Springfield,MA 01103 Hospital Hill Development, LLC., or their successors shall maintain ownership of the on- site stormwater management system as well as the responsibility for operation and routine maintenance during the post-development stages of the project. This O &M Plan outlines the various Best Management Practices (BMPs) associated with the proposed project and identifies the relevant maintenance tasks to be undertaken as well as a corresponding schedule for inspection and maintenance activity. Infiltration Basin Maintenance Ensure proper function in initial months of operation: • Observe at several intervals during and after small and large rain storms to ensure that the basin is functioning as intended. Note how long water remains standing in basin after storm events and how well the water infiltrates over a period of 48 to 72 hours. Repair items such as upland sediment erosion, excessive compaction of soils and low spots which may cause clogging. Semi-annually inspect the basins for proper functioning: Look for: • Subsidence, erosion, cracking or tree growth on embankment; • Accumulation of sediment within the basin; • Condition of riprap; and • Health of the turf Semi-annually: • Mow the side slopes of the embankment; and • Remove trash and debris As necessary: • Remove sediment from the basin at least once every ten years; i R • Dispose and transport accumulated sediment off-site in accordance with local, state and federal guidelines and regulations; • Re-seed during the growing season; • Any required modifications to the detention basin or the contributing watershed shall be reported to the Conservation Commission as the issuing authority. Deep Sump and Hooded Catch Basins and Water Quality Inlets Semi-annually: • Remove accumulated sediment and hydrocarbons during the late winter/early spring and late spring/early summer; and. • Dispose and transport. accumulated sediment off-site in accordance with applicable local,state, and federal guidelines and regulations. As necessary: • Remove accumulated debris Subsurface Infiltration System Maintenance(StormTech Units) Ensure proper function in initial months of operation: • Observe at several intervals during and after small and large rain storms to ensure that the infiltration system is functioning as intended. Note how long water remains standing in basin after storm events and how well the water infiltrates over a period of 48 to 72 hours. Repair items such as upland sediment erosion, excessive compaction of soils and low spots which may cause clogging. Annually: • Inspect infiltration system 24 and 48 hours after an approximate 1"storm event to be sure that the system is functioning properly. Semi-annually inspect the units for proper functioning: Look for: • Accumulation of sediment within all infiltrator components. • Proper infiltrations of stormwater. Semi-annually: • Remove trash and debris • Remove accumulated sediment and hydrocarbons from water quality inlets, header pipes and outlet control weirs during the late winter/early spring and late spring/early summer; and • Dispose and transport accumulated sediment off-site in accordance with applicable local, state, and federal guidelines and regulations. As necessary: • Remove sediment from at least once every ten years; • Dispose and transport accumulated sediment off-site in accordance with local, state and federal guidelines and regulations. Detention Basin/Water Quality Swale Inspect at least once a year to ensure that the basins and swales are operating as intended: • observe at several intervals during and after small and large rain storms to ensure that the basin is functioning as intended. Proper function shall include discharge through the outlet device during runoff occurrence, temporary retention after runoff ceases and infiltration within the anticipated time period. • inspect outlet control structure for evidence of clogging Look for: • subsidence, erosion, cracking or tree growth on embankment • accumulation of sediment within the basin • adequacy of the inlet/outlet channel erosion control measures • condition of the inlet channel and drainage Swale • erosion within basin and banks of swale Semi-annually: • mowing of the side slopes and embankment to a height of 4 inches • removal of trash and debris As necessary: • removal of sediment from the basins and swales as necessary and at least once every ten years • disposal of accumulated sediment will be transported off-site in accordance with local, state and federal guidelines and regulations • re-seed during the growing season • repairs will be made immediately any required modifications to the detention basin or the contributing watershed shall be reported to the Conservation Commission as the issuing authority Parking Lot Sweeping Sweeping of paved areas will take place two times during the year. • Sweep access driveways and parking lots. • Accumulated sediment will be transported and disposed off-site in accordance with applicable local, state and federal guidelines and regulations. Snow and Snowmelt Management The use of salt on the proposed parking lot shall no time exceed state or local specifications. Snow removal and storage: J. +y • Place plowed snow outside wetland resource areas; and • Remove accumulated sediments from snow storage areas every spring, 170009OT002