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HomeMy WebLinkAboutSP-23-002 - Supplemental - 0200 Market Street 208 Flynn Avenue, Suite 2A, Burlington, VT 05401  Tel: 802-863-6225 85 Mechanic Street, Suite E2-3, Lebanon, NH 03766  Tel: 603-442-9333 414 Union Street, Schenectady, NY 12305  Tel: 518-205-9141 Narrative, Location Map, Soils Map & Soils Report Rick Marcotte Central School, ZEM Classrooms 1. Introduction Engineering Ventures, PC are writing on behalf of the South Burlington School District to apply for a State Stormwater Discharge Permit pursuant to General Permit 3-9050 for the above referenced project. 2. Project Description The ZEM (Zero Energy Modular) Classrooms project involves the placement of pre-constructed modular classrooms at an existing public elementary school, the addition of a hallway to connect the two, and minor site updates. These classrooms are intended to serve the emerging need due to an increase in population and are planned to remain on site for three to eight years. The project requires a permit as the impervious surface expansion is greater than 5,000 square feet resulting in a total impervious area greater than one acre. The campus is also a 3-Acre site which is currently undergoing Engineering Feasibility Analysis by Stone Environmental Inc. through the Green Schools Initiative. The proposed practice is intended to treat and manage all stormwater associated with this project and not encroach on the greater campus. 3. Existing Condition The existing campus is comprised of approximately 11.2 acres and includes a school building, two parking areas, vehicle and pedestrian access to Dorset and Market Streets, and a large area of recreation fields. The existing impervious cover is approximately 4.25 acres, of which 2.29 was covered under permit 8794-INDS.A1. The project area is approximately 0.37 acres located east of the existing building. The mapped soils in the project area are Adams and Windsor loamy sands, 0-5% slopes, hydrologic group A. Soils investigation in October of 2022 confirmed this mapping and yielded infiltration rates associated with this soil type. 4. Existing Stormwater System (remove if not applicable) The project area has a stormwater catchment system consisting of area drains which discharge to the municipal system on Dorset Street. 5. Proposed Stormwater System: a) Description of Impervious Area: Impervious Type Area Required to be Treated Treated Existing Permitted 0.029 ac 0.0 ac 0.024 ac New 0.152 ac 0.152 ac 0.152 ac Total: 0.181 ac 0.152 ac 0.176 ac b) Receiving Body: Potash Brook c) Fish Habitat Designation for Receiving Water: Warm 208 Flynn Avenue, Suite 2A, Burlington, VT 05401  Tel: 802-863-6225 85 Mechanic Street, Suite E2-3, Lebanon, NH 03766  Tel: 603-442-9333 414 Union Street, Schenectady, NY 12305  Tel: 518-205-9141 d) Description of compliance with each of the treatment standards in the 2017 VSMM including the treatment practices or waivers used to meet each of the following standards: i) Post-Construction Soil Depth and Quality Standard: Met through a combination of Options #1 and #3 per §3.2 of the VSMM ii) Groundwater Recharge Standard: Met with the infiltration basin iii) Water Quality Treatment Standard (WQV): Met with the infiltration basin iv) Channel Protection Standard (CPV): Met with the infiltration basin via the Hydrologic Condition Method v) Overbank Flood Protection Standard (QP10): Met with the infiltration basin via the Hydrologic Condition Method vi) Extreme Flood Protection Standard (QP100): Waiver requested due to less than 10 acres of impervious cover The following items are included for review: · eNOI form submitted via ANROnline · Narrative: Narrative, Location Map, Soils Map and Soils Report · Workbooks: STP Selection Tool and Standards Compliance Workbook · Worksheets: STP and Waiver Worksheets · Modeling: Runoff modeling and calculations · Plans: Pertinent plan sheets · Plan Set Reference: List of all plans applicable POI1Sheet Title:Project Title:EV Project #Date:Scale:Drawn By:Checked By:208 Flynn Avenue, Suite 2A, Burlington, VT 05401 s 802-863-622585 Mechanic Street, Suite E2-3, Lebanon, NH 03766 s 603-442-9333414 Union Street, Schenectady, NY 12305 s 518-630-9614www.engineeringventures.comFigure:224372022 ELEMENTARY SCHOOL ZEMsSOUTH BURLINGTONSCHOOL DISTRICT550 DORSET STREETSOUTH BURLINGTON, VT05403ENGINEERINGVENTURESPCJG1"=30'2022-10-31RICK MARCOTTE CENTRAL SCHOOLPRE-DEVELOPMENT DRAINAGE PLANSW1PBLEGENDPOI POI1Sheet Title:Project Title:EV Project #Date:Scale:Drawn By:Checked By:208 Flynn Avenue, Suite 2A, Burlington, VT 05401 s 802-863-622585 Mechanic Street, Suite E2-3, Lebanon, NH 03766 s 603-442-9333414 Union Street, Schenectady, NY 12305 s 518-630-9614www.engineeringventures.comFigure:224372022 ELEMENTARY SCHOOL ZEMsSOUTH BURLINGTONSCHOOL DISTRICT550 DORSET STREETSOUTH BURLINGTON, VT05403ENGINEERINGVENTURESPCJG1"=30'2022-10-31RICK MARCOTTE CENTRAL SCHOOLPOST-DEVELOPMENT DRAINAGE PLANSW2PBLEGENDPOI Type II 24-hr Tv Rainfall=1.92"22437 - Marcotte Printed 12/7/2022Prepared by BEK Page 1HydroCAD® 10.10-7a s/n 02107 © 2021 HydroCAD Software Solutions LLC Summary for Pond 1P: IB Inflow Area = 0.353 ac, 50.14% Impervious, Inflow Depth = 0.85" for Tv event Inflow = 0.37 cfs @ 12.05 hrs, Volume= 0.025 af Outflow = 0.10 cfs @ 11.80 hrs, Volume= 0.025 af, Atten= 72%, Lag= 0.0 min Discarded = 0.10 cfs @ 11.80 hrs, Volume= 0.025 af Primary = 0.00 cfs @ 1.00 hrs, Volume= 0.000 af Routed to Link 2L : POI1B Routing by Stor-Ind method, Time Span= 1.00-48.00 hrs, dt= 0.05 hrs Peak Elev= 312.82' @ 12.29 hrs Surf.Area= 0.009 ac Storage= 0.005 af Plug-Flow detention time= 10.9 min calculated for 0.025 af (100% of inflow) Center-of-Mass det. time= 10.8 min ( 782.6 - 771.7 ) Volume Invert Avail.Storage Storage Description #1 310.00' 0.002 af 6.00'W x 20.00'L x 2.00'H Prismatoid 0.006 af Overall x 33.0% Voids #2 312.00' 0.015 af 6.00'W x 20.00'L x 2.00'H Prismatoid Z=3.0 0.017 af Total Available Storage Device Routing Invert Outlet Devices #1 Primary 311.08'10.0" Round Culvert L= 25.0' CPP, mitered to conform to fill, Ke= 0.700 Inlet / Outlet Invert= 311.08' / 310.83' S= 0.0100 '/' Cc= 0.900 n= 0.010 PVC, smooth interior, Flow Area= 0.55 sf #2 Device 1 312.83'2.0" Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #3 Device 1 313.52'10.0" Horiz. Orifice/Grate C= 0.600 Limited to weir flow at low heads #4 Discarded 310.00'37.500 in/hr Exfiltration over Surface area below 310.01' Discarded OutFlow Max=0.10 cfs @ 11.80 hrs HW=310.07' (Free Discharge) 4=Exfiltration (Exfiltration Controls 0.10 cfs) Primary OutFlow Max=0.00 cfs @ 1.00 hrs HW=310.00' (Free Discharge) 1=Culvert ( Controls 0.00 cfs) 2=Orifice/Grate ( Controls 0.00 cfs) 3=Orifice/Grate ( Controls 0.00 cfs) Type II 24-hr Tv Rainfall=1.92"22437 - Marcotte Printed 12/7/2022Prepared by BEK Page 2HydroCAD® 10.10-7a s/n 02107 © 2021 HydroCAD Software Solutions LLC Stage-Area-Storage for Pond 1P: IB Elevation (feet) Surface (acres) Storage (acre-feet) 310.00 0.003 0.000 310.05 0.003 0.000 310.10 0.003 0.000 310.15 0.003 0.000 310.20 0.003 0.000 310.25 0.003 0.000 310.30 0.003 0.000 310.35 0.003 0.000 310.40 0.003 0.000 310.45 0.003 0.000 310.50 0.003 0.000 310.55 0.003 0.001 310.60 0.003 0.001 310.65 0.003 0.001 310.70 0.003 0.001 310.75 0.003 0.001 310.80 0.003 0.001 310.85 0.003 0.001 310.90 0.003 0.001 310.95 0.003 0.001 311.00 0.003 0.001 311.05 0.003 0.001 311.10 0.003 0.001 311.15 0.003 0.001 311.20 0.003 0.001 311.25 0.003 0.001 311.30 0.003 0.001 311.35 0.003 0.001 311.40 0.003 0.001 311.45 0.003 0.001 311.50 0.003 0.001 311.55 0.003 0.001 311.60 0.003 0.001 311.65 0.003 0.001 311.70 0.003 0.002 311.75 0.003 0.002 311.80 0.003 0.002 311.85 0.003 0.002 311.90 0.003 0.002 311.95 0.003 0.002 312.00 0.006 0.002 312.05 0.006 0.002 312.10 0.006 0.002 312.15 0.006 0.002 312.20 0.006 0.002 312.25 0.006 0.003 312.30 0.007 0.003 312.35 0.007 0.003 312.40 0.007 0.003 312.45 0.007 0.003 312.50 0.008 0.004 312.55 0.008 0.004 Elevation (feet) Surface (acres) Storage (acre-feet) 312.60 0.008 0.004 312.65 0.008 0.004 312.70 0.008 0.005 312.75 0.009 0.005 312.80 0.009 0.005 312.85 0.009 0.006 312.90 0.009 0.006 312.95 0.010 0.006 313.00 0.010 0.007 313.05 0.010 0.007 313.10 0.010 0.007 313.15 0.011 0.008 313.20 0.011 0.008 313.25 0.011 0.009 313.30 0.012 0.009 313.35 0.012 0.009 313.40 0.012 0.010 313.45 0.012 0.010 313.50 0.013 0.011 313.55 0.013 0.011 313.60 0.013 0.012 313.65 0.014 0.012 313.70 0.014 0.013 313.75 0.014 0.014 313.80 0.015 0.014 313.85 0.015 0.015 313.90 0.015 0.015 313.95 0.016 0.016 314.00 0.016 0.017 Type II 24-hr 1-YR Rainfall=1.88"22437 - Marcotte Printed 12/7/2022Prepared by BEK Page 1HydroCAD® 10.10-7a s/n 02107 © 2021 HydroCAD Software Solutions LLC Summary for Pond 1P: IB Inflow Area = 0.353 ac, 50.14% Impervious, Inflow Depth = 0.83" for 1-YR event Inflow = 0.36 cfs @ 12.05 hrs, Volume= 0.024 af Outflow = 0.10 cfs @ 11.80 hrs, Volume= 0.024 af, Atten= 71%, Lag= 0.0 min Discarded = 0.10 cfs @ 11.80 hrs, Volume= 0.024 af Primary = 0.00 cfs @ 1.00 hrs, Volume= 0.000 af Routed to Link 2L : POI1B Routing by Stor-Ind method, Time Span= 1.00-48.00 hrs, dt= 0.05 hrs Peak Elev= 312.79' @ 12.29 hrs Surf.Area= 0.009 ac Storage= 0.005 af Plug-Flow detention time= (not calculated: outflow precedes inflow) Center-of-Mass det. time= 10.3 min ( 782.6 - 772.3 ) Volume Invert Avail.Storage Storage Description #1 310.00' 0.002 af 6.00'W x 20.00'L x 2.00'H Prismatoid 0.006 af Overall x 33.0% Voids #2 312.00' 0.015 af 6.00'W x 20.00'L x 2.00'H Prismatoid Z=3.0 0.017 af Total Available Storage Device Routing Invert Outlet Devices #1 Primary 311.08'10.0" Round Culvert L= 25.0' CPP, mitered to conform to fill, Ke= 0.700 Inlet / Outlet Invert= 311.08' / 310.83' S= 0.0100 '/' Cc= 0.900 n= 0.010 PVC, smooth interior, Flow Area= 0.55 sf #2 Device 1 312.83'2.0" Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #3 Device 1 313.52'10.0" Horiz. Orifice/Grate C= 0.600 Limited to weir flow at low heads #4 Discarded 310.00'37.500 in/hr Exfiltration over Surface area below 310.01' Discarded OutFlow Max=0.10 cfs @ 11.80 hrs HW=310.06' (Free Discharge) 4=Exfiltration (Exfiltration Controls 0.10 cfs) Primary OutFlow Max=0.00 cfs @ 1.00 hrs HW=310.00' (Free Discharge) 1=Culvert ( Controls 0.00 cfs) 2=Orifice/Grate ( Controls 0.00 cfs) 3=Orifice/Grate ( Controls 0.00 cfs) 1A Existing 1 2A Existing 2 1L POI1A Routing Diagram for 22437 - Marcotte Prepared by BEK, Printed 12/7/2022 HydroCAD® 10.10-7a s/n 02107 © 2021 HydroCAD Software Solutions LLC Subcat Reach Pond Link Type II 24-hr 10-YR Rainfall=3.22"22437 - Marcotte Printed 12/7/2022Prepared by BEK Page 2HydroCAD® 10.10-7a s/n 02107 © 2021 HydroCAD Software Solutions LLC Summary for Subcatchment 1A: Existing 1 Runoff = 0.08 cfs @ 12.04 hrs, Volume= 0.005 af, Depth= 0.36" Routed to Link 1L : POI1A Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 1.00-48.00 hrs, dt= 0.05 hrs Type II 24-hr 10-YR Rainfall=3.22" Area (ac) CN Adj Description 0.153 39 39 >75% Grass cover, Good, HSG A 0.021 98 98 Unconnected pavement, HSG A 0.174 Weighted Average 0.153 87.93% Pervious Area 0.021 12.07% Impervious Area 0.021 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 13.4 141 0.0150 0.18 Lag/CN Method, Summary for Subcatchment 2A: Existing 2 Runoff = 0.02 cfs @ 12.10 hrs, Volume= 0.002 af, Depth= 0.12" Routed to Link 1L : POI1A Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 1.00-48.00 hrs, dt= 0.05 hrs Type II 24-hr 10-YR Rainfall=3.22" Area (ac) CN Adj Description 0.190 39 39 >75% Grass cover, Good, HSG A 0.008 98 98 Unconnected pavement, HSG A 0.198 Weighted Average 0.190 95.96% Pervious Area 0.008 4.04% Impervious Area 0.008 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 18.2 176 0.0150 0.16 Lag/CN Method, Summary for Link 1L: POI1A Inflow Area = 0.372 ac, 7.80% Impervious, Inflow Depth = 0.23" for 10-YR event Inflow = 0.10 cfs @ 12.05 hrs, Volume= 0.007 af Primary = 0.10 cfs @ 12.05 hrs, Volume= 0.007 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 1.00-48.00 hrs, dt= 0.05 hrs 1B Proposed 1 2B Proposed 2 1P IB 2L POI1B Routing Diagram for 22437 - Marcotte Prepared by BEK, Printed 12/7/2022 HydroCAD® 10.10-7a s/n 02107 © 2021 HydroCAD Software Solutions LLC Subcat Reach Pond Link Type II 24-hr 10-YR Rainfall=3.22"22437 - Marcotte Printed 12/7/2022Prepared by BEK Page 2HydroCAD® 10.10-7a s/n 02107 © 2021 HydroCAD Software Solutions LLC Summary for Subcatchment 1B: Proposed 1 Runoff = 0.03 cfs @ 11.95 hrs, Volume= 0.001 af, Depth= 0.94" Routed to Link 2L : POI1B Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 1.00-48.00 hrs, dt= 0.05 hrs Type II 24-hr 10-YR Rainfall=3.22" Area (ac) CN Description 0.013 39 >75% Grass cover, Good, HSG A 0.006 98 Unconnected pavement, HSG A 0.019 Weighted Average 0.013 68.42% Pervious Area 0.006 31.58% Impervious Area 0.006 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 60 0.0150 0.20 Lag/CN Method, Summary for Subcatchment 2B: Proposed 2 Runoff = 0.63 cfs @ 12.04 hrs, Volume= 0.044 af, Depth= 1.50" Routed to Pond 1P : IB Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 1.00-48.00 hrs, dt= 0.05 hrs Type II 24-hr 10-YR Rainfall=3.22" Area (ac) CN Description 0.176 39 >75% Grass cover, Good, HSG A 0.177 98 Roofs, HSG A 0.353 Weighted Average 0.176 49.86% Pervious Area 0.177 50.14% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 13.4 294 0.0150 0.37 Lag/CN Method, Summary for Pond 1P: IB Inflow Area = 0.353 ac, 50.14% Impervious, Inflow Depth = 1.50" for 10-YR event Inflow = 0.63 cfs @ 12.04 hrs, Volume= 0.044 af Outflow = 0.20 cfs @ 12.26 hrs, Volume= 0.044 af, Atten= 69%, Lag= 13.2 min Discarded = 0.10 cfs @ 11.70 hrs, Volume= 0.039 af Primary = 0.09 cfs @ 12.26 hrs, Volume= 0.005 af Routed to Link 2L : POI1B Routing by Stor-Ind method, Time Span= 1.00-48.00 hrs, dt= 0.05 hrs Type II 24-hr 10-YR Rainfall=3.22"22437 - Marcotte Printed 12/7/2022Prepared by BEK Page 3HydroCAD® 10.10-7a s/n 02107 © 2021 HydroCAD Software Solutions LLC Peak Elev= 313.53' @ 12.27 hrs Surf.Area= 0.013 ac Storage= 0.011 af Plug-Flow detention time= (not calculated: outflow precedes inflow) Center-of-Mass det. time= 17.0 min ( 776.3 - 759.3 ) Volume Invert Avail.Storage Storage Description #1 310.00' 0.002 af 6.00'W x 20.00'L x 2.00'H Prismatoid 0.006 af Overall x 33.0% Voids #2 312.00' 0.015 af 6.00'W x 20.00'L x 2.00'H Prismatoid Z=3.0 0.017 af Total Available Storage Device Routing Invert Outlet Devices #1 Primary 311.08'10.0" Round Culvert L= 25.0' CPP, mitered to conform to fill, Ke= 0.700 Inlet / Outlet Invert= 311.08' / 310.83' S= 0.0100 '/' Cc= 0.900 n= 0.010 PVC, smooth interior, Flow Area= 0.55 sf #2 Device 1 312.83'2.0" Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #3 Device 1 313.52'10.0" Horiz. Orifice/Grate C= 0.600 Limited to weir flow at low heads #4 Discarded 310.00'37.500 in/hr Exfiltration over Surface area below 310.01' Discarded OutFlow Max=0.10 cfs @ 11.70 hrs HW=310.04' (Free Discharge) 4=Exfiltration (Exfiltration Controls 0.10 cfs) Primary OutFlow Max=0.09 cfs @ 12.26 hrs HW=313.53' (Free Discharge) 1=Culvert (Passes 0.09 cfs of 3.30 cfs potential flow) 2=Orifice/Grate (Orifice Controls 0.08 cfs @ 3.77 fps) 3=Orifice/Grate (Weir Controls 0.00 cfs @ 0.24 fps) Summary for Link 2L: POI1B Inflow Area = 0.372 ac, 49.19% Impervious, Inflow Depth = 0.21" for 10-YR event Inflow = 0.10 cfs @ 12.26 hrs, Volume= 0.006 af Primary = 0.10 cfs @ 12.26 hrs, Volume= 0.006 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 1.00-48.00 hrs, dt= 0.05 hrs 1A Existing 1 2A Existing 2 1L POI1A Routing Diagram for 22437 - Marcotte Prepared by BEK, Printed 12/7/2022 HydroCAD® 10.10-7a s/n 02107 © 2021 HydroCAD Software Solutions LLC Subcat Reach Pond Link Type II 24-hr 25-YR Rainfall=1.88"22437 - Marcotte Printed 12/7/2022Prepared by BEK Page 2HydroCAD® 10.10-7a s/n 02107 © 2021 HydroCAD Software Solutions LLC Summary for Subcatchment 1A: Existing 1 Runoff = 0.04 cfs @ 12.05 hrs, Volume= 0.003 af, Depth= 0.20" Routed to Link 1L : POI1A Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 1.00-48.00 hrs, dt= 0.05 hrs Type II 24-hr 25-YR Rainfall=1.88" Area (ac) CN Adj Description 0.153 39 39 >75% Grass cover, Good, HSG A 0.021 98 98 Unconnected pavement, HSG A 0.174 Weighted Average 0.153 87.93% Pervious Area 0.021 12.07% Impervious Area 0.021 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 13.4 141 0.0150 0.18 Lag/CN Method, Summary for Subcatchment 2A: Existing 2 Runoff = 0.01 cfs @ 12.10 hrs, Volume= 0.001 af, Depth= 0.07" Routed to Link 1L : POI1A Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 1.00-48.00 hrs, dt= 0.05 hrs Type II 24-hr 25-YR Rainfall=1.88" Area (ac) CN Adj Description 0.190 39 39 >75% Grass cover, Good, HSG A 0.008 98 98 Unconnected pavement, HSG A 0.198 Weighted Average 0.190 95.96% Pervious Area 0.008 4.04% Impervious Area 0.008 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 18.2 176 0.0150 0.16 Lag/CN Method, Summary for Link 1L: POI1A Inflow Area = 0.372 ac, 7.80% Impervious, Inflow Depth = 0.13" for 25-YR event Inflow = 0.06 cfs @ 12.05 hrs, Volume= 0.004 af Primary = 0.06 cfs @ 12.05 hrs, Volume= 0.004 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 1.00-48.00 hrs, dt= 0.05 hrs 1B Proposed 1 2B Proposed 2 1P IB 2L POI1B Routing Diagram for 22437 - Marcotte Prepared by BEK, Printed 12/7/2022 HydroCAD® 10.10-7a s/n 02107 © 2021 HydroCAD Software Solutions LLC Subcat Reach Pond Link Type II 24-hr 25-YR Rainfall=1.88"22437 - Marcotte Printed 12/7/2022Prepared by BEK Page 2HydroCAD® 10.10-7a s/n 02107 © 2021 HydroCAD Software Solutions LLC Summary for Subcatchment 1B: Proposed 1 Runoff = 0.02 cfs @ 11.95 hrs, Volume= 0.001 af, Depth= 0.52" Routed to Link 2L : POI1B Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 1.00-48.00 hrs, dt= 0.05 hrs Type II 24-hr 25-YR Rainfall=1.88" Area (ac) CN Description 0.013 39 >75% Grass cover, Good, HSG A 0.006 98 Unconnected pavement, HSG A 0.019 Weighted Average 0.013 68.42% Pervious Area 0.006 31.58% Impervious Area 0.006 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 60 0.0150 0.20 Lag/CN Method, Summary for Subcatchment 2B: Proposed 2 Runoff = 0.36 cfs @ 12.05 hrs, Volume= 0.024 af, Depth= 0.83" Routed to Pond 1P : IB Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 1.00-48.00 hrs, dt= 0.05 hrs Type II 24-hr 25-YR Rainfall=1.88" Area (ac) CN Description 0.176 39 >75% Grass cover, Good, HSG A 0.177 98 Roofs, HSG A 0.353 Weighted Average 0.176 49.86% Pervious Area 0.177 50.14% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 13.4 294 0.0150 0.37 Lag/CN Method, Summary for Pond 1P: IB Inflow Area = 0.353 ac, 50.14% Impervious, Inflow Depth = 0.83" for 25-YR event Inflow = 0.36 cfs @ 12.05 hrs, Volume= 0.024 af Outflow = 0.10 cfs @ 11.80 hrs, Volume= 0.024 af, Atten= 71%, Lag= 0.0 min Discarded = 0.10 cfs @ 11.80 hrs, Volume= 0.024 af Primary = 0.00 cfs @ 1.00 hrs, Volume= 0.000 af Routed to Link 2L : POI1B Routing by Stor-Ind method, Time Span= 1.00-48.00 hrs, dt= 0.05 hrs Type II 24-hr 25-YR Rainfall=1.88"22437 - Marcotte Printed 12/7/2022Prepared by BEK Page 3HydroCAD® 10.10-7a s/n 02107 © 2021 HydroCAD Software Solutions LLC Peak Elev= 312.79' @ 12.29 hrs Surf.Area= 0.009 ac Storage= 0.005 af Plug-Flow detention time= (not calculated: outflow precedes inflow) Center-of-Mass det. time= 10.3 min ( 782.6 - 772.3 ) Volume Invert Avail.Storage Storage Description #1 310.00' 0.002 af 6.00'W x 20.00'L x 2.00'H Prismatoid 0.006 af Overall x 33.0% Voids #2 312.00' 0.015 af 6.00'W x 20.00'L x 2.00'H Prismatoid Z=3.0 0.017 af Total Available Storage Device Routing Invert Outlet Devices #1 Primary 311.08'10.0" Round Culvert L= 25.0' CPP, mitered to conform to fill, Ke= 0.700 Inlet / Outlet Invert= 311.08' / 310.83' S= 0.0100 '/' Cc= 0.900 n= 0.010 PVC, smooth interior, Flow Area= 0.55 sf #2 Device 1 312.83'2.0" Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #3 Device 1 313.52'10.0" Horiz. Orifice/Grate C= 0.600 Limited to weir flow at low heads #4 Discarded 310.00'37.500 in/hr Exfiltration over Surface area below 310.01' Discarded OutFlow Max=0.10 cfs @ 11.80 hrs HW=310.06' (Free Discharge) 4=Exfiltration (Exfiltration Controls 0.10 cfs) Primary OutFlow Max=0.00 cfs @ 1.00 hrs HW=310.00' (Free Discharge) 1=Culvert ( Controls 0.00 cfs) 2=Orifice/Grate ( Controls 0.00 cfs) 3=Orifice/Grate ( Controls 0.00 cfs) Summary for Link 2L: POI1B Inflow Area = 0.372 ac, 49.19% Impervious, Inflow Depth = 0.03" for 25-YR event Inflow = 0.02 cfs @ 11.95 hrs, Volume= 0.001 af Primary = 0.02 cfs @ 11.95 hrs, Volume= 0.001 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 1.00-48.00 hrs, dt= 0.05 hrs