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Stormwater Management Report FILL STORMWATER MANAGEMENT REPORT FOR ABMAST INC. - WAREHOUSE Queensbury, New York Warren County Prepared by: NACE ENGINEERING, P.C. 169 HAVILAND ROAD QUEENSBURY,NY 12804 V Thomas W.Nace, P.E. August 2003 File: #47382 STORMWATER MANAGEMENT REPORT FOR ABMAST INC. -WAREHOUSE CARY INDUSTRIAL PARK INTRODUCTION The site of the proposed Abmast warehouse is in the Cary Industrial Park Subdivision on the south side of Corinth Road, in the Town of Queensbury, NY. The site is in the southern end of the subdivision loop road and contains 1.68 acres. This report addresses drainage issues pertaining to the development of a warehouse building and associated roads, parking and site improvements on this lot. EXISTING CONDITIONS The site is wooded and is slightly lower than the adjacent Cary Road. Soils on this site are Windsor sandy loams. Test pits and percolation tests done for the original subdivision showed consistently well drained soils with no evidence of seasonal high groundwater to a depth of over 8 feet. Percolation rates were slightly less than one minute. Due to the permeable surface soils, all of the existing stormwater soaks into the ground. There are no drainage patterns developed from existing runoff. DRAINAGE METHODOLOGY Since the soils are deep and well drained, all runoff from new impervious surfaces will be routed to infiltration devices to allow it to filter into the ground as it now does. Runoff from the building roof will be stored and infiltrated by means of stone filled eave trenches. The eave trenchs will be a minimum 3.5 feet wide and 3 feet deep. Runoff from all pavement, walks and lawn areas around the building will sheet flow into shallow stormwater basins. There will be two basins. One will be located in the lawn area adjacent to the employee parking lot and will receive drainage from the entrance road and the parking lot. The second will be located adjacent to the truck dock loading area and will receive drainage from the truck maneuvering and docking area and the exit driveway. CALCULATIONS All computations SCS TR-20 HydroCAD. I 50 year storm event—Type II rainfall=4.9" Soil conditions—Oakville sandy loam— SCS soil group A - -- Existing stormwater runoff assumed to be zerodue to permeable soils & good groundcover. Runoff rate and volume computations for the 50 year storm event have been completed for developed conditions. The eave trenches and detention basins have been sized to maintain adequate freeboard during a 50 year design storm. See attached HydroCAD analysis for all computations. CONCLUSIONS Based upon the attached HydroCAD analysis, the eave trenches and detention basins have sufficient capacity to manage all runoff generated by the proposed site development during a 50 year storm event and post development runoff will be maintained at or below pre-developed level. 2 • STORMWATER MANAGEMENT REPORT FOR ABMAST INC. - WAREHOUSE HydroCAD RESULTS DEVELOPED CONDITIONS E N W T U) 7 0 a? M co s N E W o p o Q U Q U n. � aCL Q Q _co N N 0 O W � W U co f0 tm Z O T j] C O -p N Clio C CX(D pa ¢ U 0 T c J 0 d vJ n _ r r in 47382- ABMAST WAREHOUSE Type 11 24-hr Rainfall=4.90" Prepared by Nace Engineering, P.C. Page 1 u droCAD®6 00 s/n 000768 © 1986-2001 Applied Microcomputer Systems 8/17/2003 Time span=5.00-20.00 hrs, dt=0.05 hrs, 301 points Runoff by SCS TR-20 method, UH=SCS, Type II 24-hr Rainfall=4.90" Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 1S: BUILDING ROOF Tc=0.8 min CN=98 Area=10,000 sf Runoff-- 1.79 cfs 0.082 of Subcatchment 2S: TRUCK DOCK AREA PAVING Tc=1.7 min CN=98 Area=12,114 sf Runoff=2.08 cfs 0.099 of Subcatchment 3S: PARKING LOT & ENTRY DRIVE Tc=0.9 min CN=98 Area=3,563 sf Runoff- 0.63 cfs 0.029 of Pond 1 P: BUILDING EAVE TRENCHES Peak Storage=676 cf Inflow= 1.79 cfs 0.082 of Primary= 0.85 cfs 0.082 of Outflow=0.85 cfs 0.082 of Pond 2P: DETENTION/INFILTRATION BASIN Peak Storage=481 cf Inflow=2.08 cfs 0.099 of Discarded= 1.49 cfs 0.099 of Outflow= 1.49 cfs 0.099 of Pond 3P: DETENTION/INFILTRATION BASIN Peak Storage= 160 cf Inflow= 0.63 cfs 0.029 of Discarded= 0.43 cfs 0.029 of Outflow=0.43 cfs 0.029 of Runoff Area = 0.589 ac Volume= 0.210 of Average Depth = 4.28" 47382-ABMAST WAREHOUSE Type 11 24-hr Rainfall=4.90" Prepared by Nace Engineering, P.C. Page 2 HydroCADO 6.00 s/n 000768 © 1986-2001 Applied Microcomputer Systems 8/17/2003 Subcatchment 1S: BUILDING ROOF Runoff = 1.79 cfs @ 11.89 hrs, Volume= 0.082 of Runoff by SCS TR-20 method, UH=SCS, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type II 24-hr Rainfall=4.90" Area (sf) CN Description 10,000 98 ROOF Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 0.8 67 0.0400 1.5 Sheet Flow, ACROSS ROOF TO EAVE Smooth surfaces n= 0.011 P2= 2.40" Subcatchment 2S: TRUCK DOCK AREA PAVING Runoff = 2.08 cfs @ 11.91 hrs, Volume= 0.099 of Runoff by SCS TR-20 method, UH=SCS, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type II 24-hr Rainfall=4.90" Area (sf) CN Description 12,114 98 PAVEMENT Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 1.7 140 0.0250 1.4 Sheet Flow, ACROSS PAVEMENT TO BASIN Smooth surfaces n= 0.011 P2= 2.40" Subcatchment 3S: PARKING LOT & ENTRY DRIVE Runoff = 0.63 cfs @ 11.90 hrs, Volume= 0.029 of Runoff by SCS TR-20 method, UH=SCS, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type II 24-hr Rainfall=4.90" Area (sf) CN Description 3,563 98 PAVEMENT Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 0.9 60 0.0200 1.1 Sheet Flow, ACROSS PAVEMENT TO BASIN Smooth surfaces n= 0.011 P2= 2.40" 47382-ABMAST WAREHOUSE Type 1l 24-hr Rainfall=4.90" Prepared by Nace Engineering, P.C. Page 3 HydroCADO6.00 s/n 000768 © 1986-2001 Applied Microcomputer Systems 8/17/2003 Pond 1P: BUILDING EAVE TRENCHES Inflow = 1.79 cfs @ 11.89 hrs, Volume= 0.082 of Outflow = 0.85 cfs @ 11.98 hrs, Volume= 0.082 af, Atten= 52%, Lag= 5.0 min Primary = 0.85 cfs @ 11.98 hrs, Volume= 0.082 of Routing by Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 3.02' Storage= 676 cf Plug-Flow detention time= 5.4 min calculated for 0.082 of(100% of inflow) Elevation Cum.Store (feet) (cubic-feet) 0.00 0 1.00 224 2.00 448 3.00 672 Primary OutFlow (Free Discharge) t--1=INFILTRATION # Routing Invert Outlet Devices 1 Primary 0.00' INFILTRATION Elev. (feet) 0.00 0.10 1.00 2.00 3.00 Disch. (cfs) 0.00 0.31 0.49 0.67 0.85 Pond 2P: DETENTION/INFILTRATION BASIN Inflow = 2.08 cfs @ 11.91 hrs, Volume= 0.099 of Outflow = 1.49 cfs @ 11.96 hrs, Volume= 0.099 af, Atten= 28%, Lag= 3.4 min Discarded = 1.49 cfs @ 11.96 hrs, Volume= 0.099 of Routing by Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 381.09' Storage= 481 cf Plug-Flow detention time= 4.7 min calculated for 0.099 of (100% of inflow) Storage and wetted areas determined by Prismatic sections Elevation Surf.Area Inc.Store Cum.Store (feet) (sg-ft) (cubic-feet) (cubic-feet) 380.30 0 0 0 381.00 1,009 353 353 382.00 1,720 1,365 1,718 383.00 2,821 2,271 3,988 Discarded OutFlow (Free Discharge) t-1=Exfiltration # Routing Invert Outlet Devices 1 Discarded 0.00' 0.083330 fpm Exfiltration over entire Surface area 47382-ABMAST WAREHOUSE Type /I24-hrRainfall=4.90" Prepared by Nace Engineering, P.C. Page 4 HydroCADO 6.00 s/n 000768 © 1986-2001 Applied Microcomputer Systems 8/17/2003 Pond 3P: DETENTION/INFILTRATION BASIN Inflow = 0.63 cfs @ 11.90 hrs, Volume= 0.029 of Outflow = 0.43 cfs @ 11.95 hrs, Volume= 0.029 af, Atten= 32%, Lag= 3.5 min Discarded = 0.43 cfs @ 11.95 hrs, Volume= 0.029 of Routing by Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 385.12' Storage= 160 cf Plug-Flow detention time= 5.3 min calculated for 0.029 of(100% of inflow) Storage and wetted areas determined by Prismatic sections Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 384.20 0 0 0 385.00 270 108 108 386.00 590 430 538 Discarded OutFlow (Free Discharge) !1=Exfiltration # Routing Invert Outlet Devices 1 Discarded 0.00' 0.083333 fpm Exfiltration over entire Surface area