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HomeMy WebLinkAbout20072235 Ver 1_Stormwater Info_20080115WITHERS ~~y RAVENEL STORMWATER MANAGEMENT REPORT 5401 North Raleigh, North Carolina Prepared For: 5401 NORTH, LLC. 563o Bankers Avenue Baton Rouge, LA 70808 Attn : Carolyne E. Martin, V.P. Prepared By: WITHERS &RAVENEL, INC i1i MacKenan Drive Cary, North Carolina 275ii February 2008 W&R Project No. 2070102 C. Heath Wadsworth, PE 5401 NORTH STORMWATER MANAGEMENT REPORT RALEIGH, NORTH CAROLINA INTRODUCTION 5401 North is a planned development located in north Raleigh near the interchange of Louisburg Road and Interstate 540. The 39o-acre development proposes a mix of retail, office, and residential uses. The site is bounded to the east by the Neuse River and is subject to the North Carolina Division of Water Quality Neuse River Basin rules for stormwater management. The development will also be subject to the stormwater management ordinances of the City of Raleigh. The purpose of this report is to establish the minimum criteria for stormwater compliance that will apply to 54oi North and the overall proposed stormwater management approach to meet the requirements. STORMWATER MANAGEMENT REQUIREMENTS Because the proposed development is within the Neuse River Basin, the site must meet the site requirements relating to the Neuse River Basin rules. To meet these requirements, the nitrogen export from the site must be calculated and brought under 3.60 lbs/ac/yr using Best Management Practices (BMP) and/or a buy down payment. stormwater quantity leaving the proposed site must also be controlled. NC DWQ requires the attenuation of the 1-year, 24-hour storm. In addition to this requirement, the stormwater control regulations found in the City of Raleigh's Code of Ordinances state that the z-year, z4-hour storm and the io-year, z4-hour storm must be attenuated. Attenuation of the storm means that the post-development peak flow for the design storm cannot exceed the peak flow of the pre-development conditions. Exceptions to this requirement include cases where the post-developed peak flow for the z and io-year storms is less than 10% greater than the pre- 5401 North W&R Project zo7oioz stormwater Management Report February zoo8 Figure 1. Proposed 54oi North Development Boundary 5401 NORTH STORMWATER MANAGEMENT REPORT RALEIGH, NORTH CAROLINA developed peak flow for the 2 and 1o-year storms. The attenuation requirement is also exempt for sites or portions of sites that drain directly to FEMA mapped Special Flood Hazard Areas (SERA). The portion of the site that drains to another property before the stormwater reaches the SFHA will require attenuation ofthe 2-year, 2!}-hour storm and the 1o-year, 2!}-hour storm. Other stormwater management requirements include the establishment of a buffer around all streams that appear on the latest edition ofthe USGS Quadrangle map orthe NRCS Soil Survey map. Development within this buffer is limited by the table of uses found in the NC DWQ or City of Raleigh regulations. STORMWATER MANAGEMENT APPROACH To meet the requirements of the stormwater management regulations, Withers & Ravenel proposes an overall stormwater management plan. Under this plan approximately 23o acres of the 39o acre development would drain to Best Management Practices (BMP) devices. Each BMP design would conform to the NC DWQ stormwater Best Management Practices manual (BMP Manual). The primary function of the structural BMP's would be to treat stormwater to remove nitrogen and to attenuate the stormwater peak flow. To achieve nitrogen removal, z4 of the proposed BMP's will be either constructed stormwater wetlands or detention ponds with wetland fringes. A detention pond/wetland fringe combination has a nitrogen removal rate of 30% according to NC DWQ. stormwater wetlands have a removal rate of 40% of the nitrogen export according to the BMP Manual. Two of the BMP's are proposed to be bioretention cells, providing 35% nitrogen removal. The cumulative treatment of the i8 structural BMP devices would remove approximately 34% of the nitrogen export from the proposed site. We anticipate a decrease in the nitrogen export of the proposed site to 6.65 lbs/ac/yr. To receive credit to decrease the total nitrogen export to 3.60 lbs/ac/yr, an offset payment of approximately $i million will be made. The structural BMP devices will also be designed for peak flow attenuation, where necessary. The BMP's that discharge off-site and not to a SFHA will be designed so that the 2-year and io-year storm are attenuated at five analysis points. Four of these points are located where stormwater flow will leave the proposed site. One analysis point is located at an existing pond. The post-development peak flows for the 2 and io-year peak flows will not exceed the pre-development 2 and io-year peak flows at the analysis points. In addition to meeting the requirements in attenuating the 2 and 10- yearpeak flows, the i5-year storm will also be attenuated at the analysis points. The locations of the proposed BMP's and peak flow attenuation analysis points are shown on the attached map. Delineation of the drainage area to each BMP was based on existing terrain and a preliminary estimate of storm drainage design. The impervious area for each drainage area was estimated based on the proposed land use within the drainage area. To determine the surface area required for each BMP, the volume of run-off created by an inch of rainfall (the "first flush") was calculated for the drainage area. To calculate this water quality volume the Simple Method was used, as described in the DWQ BMP Manual. This method uses arun-off coefficient to calculate the volume of run-off given a depth of rainfall. The run-off coefficient is determined based on the percent imperviousness of the drainage area. stormwater wetlands are required to have less than a foot of depth for the water quality pool according to the DWQ BMP Manual. To determine the minimum surface area required for the stormwater wetlands, the water quality volume was divided by i foot. Bioretention cells are preferred by DWQ to be designed so that the water quality pool is 9 inches in depth. The water quality volume going to the bioretention cells was divided by 9 inches to calculate the minimum surface area required for the two bioretention cells. The minimum surface area 5401 North W&R Project zo7oioz stormwater Management Report February zoo8 5401 NORTH STORMWATER MANAGEMENT REPORT RALEIGH, NORTH CAROLINA necessary forthe two wet ponds with wetland fringes was determined as directed in the NC DWQ BMP manual. After completion of full grading plan the BMP outlet structures will be designed to meet the attenuation requirements set forth in the previous section. 5401 North W&R Project zo7oioz Stormwater Management Report February zoo8 5401 NORTH STORMWATER MANAGEMENT REPORT RALEIGH, NORTH CAROLINA BMP SIZING CALCULATIONS 5401 North W&R Project 2o7oio2 Stormwater Management Report February zoo8 BMP Sizing Requirements (All BMP's Are Wetlands Unless Otherwise Noted) BMP Name Drainage Area (acres) Estimated % Impervious for DA Surface Area Req'd (acres) Water Quality Volume Req'd (cu. ft) BMP 1 28.12 70 1.60 69,702 BMP 2 7.72 85 0.52 22,839 BMP 3 (Wet Pond) 9.89 70 0.28 24,412 BMP 4 (Wet Pond) 18.19 85 0.65 53,814 BMP 5 42.88 78 2.70 117,443 BMP 6 7.98 75 0.48 21,001 BMP 7 17.6 45 0.67 29,069 BMP 8 (BioRet) 6.69 45 0.34 11,050 BMP 9 (BioRet) 11.96 45 0.60 19,754 BMP 10 14.72 45 0.56 24,312 BMP 11 21.26 45 0.40 35,114 BMP 12 14.55 55 0.66 28,785 BMP 13 10.82 65 0.57 24,941 BMP 14 20.9 65 1.11 48,176 BMP 15 9.53 55 0.43 18,854 BMP 16 6.97 55 0.32 13,789 Yellow denotes that 2, 10, & 15-year storm attenuation is needed at these BMPs. Additional storage above the WQ Volume will be required. Project Name: 5401 North Project #: 2070102 i /State: Raleigh, NC Date: 1-Feb-08 Table 1.1 Surface Area to Drainage Area Ratio for Permanent Pool Sizing for 85% Pollutant Qmm~var FfFirinn~v in fi/~a Piat/mnnt Impervious Cover Permanent Pool Dep 3.0 4.0 5.0 6.0 th (feet) 7.0 8.0 9.0 10 0.59 0.49 0.43 0.35 0.31 0.29 0.26 20 0.97 0.79 0.70 0.59 0.51 0.46 0.44 30 1.34 1.08 0.97 0.83 0.70 0.64 0.62 40 1.73 1.43 1.25 1.05 0.90 0.82 0.77 50 2.06 1.73 1.50 1.30 1.09 1.00 0.92 60 2.40 2.03 1.71 1.51 1.29 1.18 1.10 70 2.88 2.40 2.07 1.79 1.54 1.35 1.26 80 3.36 2.78 2.38 2.10 1.86 1.60 1.42 90 3.74 3.10 2.66 2.34 2.11 1.83 1.67 Source: NCDENK/DW(1 Stormwater best Management rracnces, pg. 5, Apra iyyy STORMWATER BMP #1 -WETLANDS (85% TSS Removal 8~ 40% TN Removal) Land Use Area (ac) % IA Imp. Area (ac) Commercial 22.14 65 14.39 Town Center 5.98 90 5.38 Totals 28.12 19.77 Total % Impervious Surface Area = 70.3 Normal Pool De th 3 4 5 6 7 8 9 SA/DA Ratio 2.90 2.25 2.06 1.80 1.47 1.37 1.35 Minimum Surface Area R wired Acres 0.81 0.63 0.58 0.51 0.41 0.38 0.38 Sq. Ft 35463.42 27550.35 25215.27 22018.88 17957.31 16728.52 16483.54 Surface Area of Permanent Pool: Assumed depth = 3 feet SA/DA ratio = 2.90 % From Table 1.1 Minimum pond surface area (SA) _ ( DA * SA/DA ratio)/100 SA = 0.814 acres 35463 sq. ft. Normal pool elevation = 0.00 feet To be determined Surface area provided = 0.000 acres 0 sq. ft. 1-Inch Runoff Volume Calculation Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987) Rv = 0.05 + 0.009(q where, Rv =Runoff coefficient, in./in. =Percent impervious Rv = 0.68 in./in. Total runoff volume from 1-inch precipitation: Runoff volume, S = (Design rainfall) (Rv) (Drainage Area) S = 1.600 acre-ft 69702 cu. ft. Water quality pool elevation= 0.00 feet To be determined Storage volume provided = 0.000 acre-ft 0 cu. ft. Project Name: 5401 North Project #: 2070102 Citk/State: #REF! Date: 2/8/2007 STORMWATER BMP #1 -WETLANDS (85% TSS Removal & 40% TN Removal) Orifice Calculator Variables WQ Volume: Head: Draw down time: 0 Acre-ft 0.00 ft 51 h rs 0 cf Oft 183600 s Constants g= Cd = 32.2 ft/s2 0.6 Orifice Area = #DIV/0! sq. ft Orifice Diameter = #DIV/0! in #DIV/0! sq. in Max Q= #DIV/0! cfs BMP2 Project Name: 5401 North Pr ' c #: 2070102 it / at :Raleigh, NC Date: 1-Feb-08 Table 1.1 Surface Area fo Drainage Area Ratio for Permanent Pool Sizing for 85% Pollutant Removal Efficiency in the Piedmont % Impervious Cover Permanent Pool Depth (feet) 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10 0.59 0.49 0.43 0.35 0.31 0.29 0.26 20 0.97 0.79 0.70 0.59 0.51 0.46 0.44 30 1.34 1.08 0.97 0.83 0.70 0.64 0.62 40 1.73 1.43 1.25 1.05 0.90 0.82 0.77 50 2.06 1.73 1.50 1.30 1.09 1.00 0.92 60 2.40 2.03 1.71 1.51 1.29 1.18 1.10 70 2.88 2.40 2.07 1.79 1.54 1.35 1.26 80 3.36 2.78 2.38 2.10 1.86 1.60 1.42 90 3.74 3.10 2.66 2.34 2.11 1.83 1.67 Source: NCDENR/DWQ Stormwater Best Management Practices, pg. 5, April 7999 STORMWATER BMP #2 -WETLANDS (85% TSS Removal & 40% TN Removal) Land Use Area (ac) % IA Imp. Area (ac) Commercial 7.72 85 6.56 Totals 7.72 6.56 Total % Impervious Surface Area = 85.0 Normal Pool De th 3 4 5 6 7 8 9 SA/DA Ratio 3.55 2.94 2.52 2.22 1.99 1.72 1.55 Minimum Surface Area Re wired Acres 0.27 0.23 0.19 0.17 0.15 0.13 0.12 Sq. Ft 11938.05 9886.73 8474.34 7465.49 6675.22 5767.26 5195.58 Surface Area of Permanent Pool: Assumed depth = 3 SA/DA ratio = 3.55 Minimum pond surface area (SA) _ (I SA = 0.274 11938 feet From Table 1.1 JA * SA/DA ratio)/100 acres sq. ft. Normal pool elevation = 0.00 feet To be determined Surface area provided = 0.000 acres 0 sq. ft. 1-Inch Runoff Volume Calculation Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987) Rv = 0.05 + 0.009(1) where, Rv =Runoff coefficient, in./in. I =Percent impervious Rv = 0.82 in./in. Total runoff volume from 1-inch precipitation: Runoff volume, S = (Design rainfall) (Rv) (Drainage Area) S = 0.524 acre-ft 22839 cu. ft. Water quality pool elevation= 0.00 feet To be determined Storage volume provided = 0.000 acre-ft 0 cu. ft. BMP3 Project Name: 5401 North Project #: 2070102 Ci tate: Raleigh, NC Date: 1-Fek~08 Table 1.1 Surface Area to Drainage Area Ratio for Permanent Pool Sizing for 85% Pollutant Removal Fffirienrv in the Piedmont °k Impervious Cover Permanent Pool Dept 3.0 4.0 5.0 6.0 h (feet) 7.0 8.0 9.0 10 0.59 0.49 0.43 0.35 0.31 0.29 0.26 20 0.97 0.79 0.70 0.59 0.51 0.46 0.44 30 1.34 1.08 0.97 0.83 0.70 0.64 0.62 40 1.73 1.43 1.25 1.05 0.90 0.82 0.77 50 2.06 1.73 1.50 1.30 1.09 1.00 0.92 60 2.40 2.03 1.71 1.51 1.29 1.18 1.10 70 2.88 2.40 2.07 1.79 1.54 1.35 1.26 80 3.36 2.78 2.38 2.10 1.86 1.60 1.42 90 3.74 3.10 2.66 2.34 2.11 1.83 1.67 Source: NCDENR/DWQ Stormwater best Management Practices, pg. 5, April 1 yyy STORMWATER BMP #3 -WET POND WITH WETLAND FRINGE (85% TSS Removal 8~ 30% TN Removal) Land Use Area (ac) % IA Imp. Area (ac) Commercial 9.89 70 6.92 Totals 9.89 6.92 Total % Impervious Surface Area = 70.0 Normal Pool De th 3 4 5 6 7 8 9 SA/DA Ratio 2.88 2.40 2.07 1.79 1.54 1.35 1.26 Minimum Surface Area Re wired Acres 0.28 0.24 0.20 0.18 0.15 0.13 0.12 Sq. Ft 12407.28 10339.40 8917.73 7711.47 6634.45 5815.91 5428.19 Surface Area of Permanent Pool: Assumed depth = 3 feet SA/DA ratio = 2.88 % From Table 1.1 Minimum pond surface area (SA) _ ( DA * SA/DA ratio)/100 SA = 0.285 acres 12407 sq. ft. Normal pool elevation = 0.00 feet To be determined Surface area provided = 0.000 acres 0 sq. ft. 1-Inch Runoff Volume Calculation Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987) Rv = 0.05 + 0.009(1) where, Rv =Runoff coefficient, in./in. I =Percent impervious Rv = 0.68 i n./i n. Total runoff volume from 1-inch precipitation: Runoff volume, S = (Design rainfall) (Rv) (Drainage Area) S = 0.560 acre-ft 24412 cu. ft. Water quality pool elevations 0.00 feet To be determined Storage volume provided = 0.000 acre-ft 0 cu. ft. BMP4 Project Name: 5401 North Project #: 2070102 it /State: Raleigh, NC Date: 1-Feb-08 Table 1.1 Surface Area to Drainage Area Ratio for Permanent Pool Sizing for 85% Pollutant Removal Efficiency in the Piedmont % Impervious Cover Permanent Pool Dept 3.0 4.0 5.0 6.0 h (feet) 7.0 8.0 9.0 10 0.59 0.49 0.43 0.35 0.31 0.29 0.26 20 0.97 0.79 0.70 0.59 0.51 0.46 0.44 30 1.34 1.08 0.97 0.83 0.70 0.64 0.62 40 1.73 1.43 1.25 1.05 0.90 0.82 0.77 50 2.06 1.73 1.50 1.30 1.09 1.00 0.92 60 2.40 2.03 1.71 1.51 1.29 1.18 1.10 70 2.88 2.40 2.07 1.79 1.54 1.35 1.26 80 3.36 2.78 2.38 2.10 1.86 1.60 1.42 90 3.74 3.10 2.66 2.34 2.11 1.83 1.67 Source: NCDENR/DWQ Stormwater Best Management Practices, pg. 5, April 1999 STORMWATER BMP #4 -WET POND WITH WETLAND FRINGE (85% TSS Removal & 30% TN Removal) Land Use Area (ac) ~° IA Imp. Area (ac) Commercial 18.19 85 15.46 Totals 18.19 15.46 Total % Impervious Surface Area = 85.0 Normal Pool Depth 3 4 5 6 7 8 9 SA/DA Ratio 3.55 2.94 2.52 2.22 1.99 1.72 1.55 Minimum Surface Area Re wired Acres 0.65 0.53 0.46 0.40 0.36 0.31 0.28 Sq. Ft 28128.65 23295.28 19967.38 17590.31 15728.27 13588.91 12241.91 Surface Area of Permanent Pool: Assumed depth = 3 feet SA/DA ratio = 3.55 % From Table 1.1 Minimum pond surface area (SA) _ (DA * SA/DA ratio)/100 SA = 0.646 acres 28129 sq. ft. Normal pool elevation = 0.00 feet To be determined Surface area provided = 0.000 acres 0 sq. ft. 1-Inch Runoff Volume Calculation Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987) Rv = 0.05 + 0.009(1) where, Rv =Runoff coefficient, in./in. =Percent impervious Rv = 0.82 i n./i n. Total runoff volume from 1-inch precipitation: Runoff volume, S = (Design rainfall) (Rv) (Drainage Area) S = 1.235 acre-ft 53814 cu. ft. Water quality pool elevation= 0.00 feet To be determined Storage volume provided = 0.000 acre-ft 0 cu. ft. BMP5 Project Name: 5401 North Project #: 2070102 it /State: Raleigh, NC Date: 1-Feb-08 Table 1.1 Surface Area to Drainage Area Ratio for Permanent Pool Sizing for 85% Pollutant Removal EffiriPnrv in thr PiPdmnnt Impervious Cover Permanent Pool Depth (feet) 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10 0.59 0.49 0.43 0.35 0.31 0.29 0.26 20 0.97 0.79 0.70 0.59 0.51 0.46 0.44 30 1.34 1.08 0.97 0.83 0.70 0.64 0.62 40 1.73 1.43 1.25 1.05 0.90 0.82 0.77 50 2.06 1.73 1.50 1.30 1.09 1.00 0.92 60 2.40 2.03 1.71 1.51 1.29 1.18 1.10 70 2.88 2.40 2.07 1.79 1.54 1.35 1.26 80 3.36 2.78 2.38 2.10 1.86 1.60 1.42 90 3.74 3.10 2.66 2.34 2.11 1.83 1.67 source: rv~utrvrouwtl arormwater tsest Management PracLCes, pg. S, Apnl 7999 STORMWATER BMP #5 -WETLANDS (85% TSS Removal 8~ 40% TN Removal) Land Use Area (ac) °~ IA Imp. Area (ac) Commercial 25.13 70 17.59 Town Center 17.75 90 15.98 Totals 42.88 33.57 Total % Impervious Surface Area = 78.3 Normal Pool Depth 3 4 5 6 7 8 9 SA/DA Ratio 3.28 2.71 2.33 2.05 1.80 1.56 1.39 Minimum Surface Area R wired Acres 1.41 1.16 1.00 0.88 0.77 0.67 0.60 Sq. Ft 61216.78 50704.71 43458.33 38228.34 33713.35 29081.96 26009.15 Surface Area of Permanent Pool: Assumed depth = 3 feet SA/DA ratio = 3.28 % From Table 1.1 Minimum pond surface area (SA) _ ( DA * SA/DA ratio)/100 SA = 1.405 acres 61217 sq. ft. Normal pool elevation = 0.00 feet To be determined Surface area provided = 0.000 acres 0 sq. ft. 1-Inch Runoff Volume Calculation Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987) Rv = 0.05 + 0.009(1) where, Rv =Runoff coefficient, in./in. I =Percent impervious Rv = 0.75 in./in. Total runoff volume from 1-inch precipitation: Runoff volume, S = (Design rainfall) (Rv) (Drainage Area) S = 2.696 acre-ft 117443 cu. ft. Water quality pool elevation= 0.00 feet To be determined Storage volume provided = 0.000 acre-ft 0 cu. ft. BMP6 Project Name: 5401 North Project #: 2070102 i /State: Raleigh, NC Date: 1-Fek~08 Table 1.1 Surface Area to Drainage Area Ratio for Permanent Pool Sizing for 85% Pollutant Removal Efficiency in the Piedmont Impervious Cover Permanent Pool Dept 3.0 4.0 5.0 6.0 h (feet) 7.0 8.0 9.0 10 0.59 0.49 0.43 0.35 0.31 0.29 0.26 20 0.97 0.79 0.70 0.59 0.51 0.46 0.44 30 1.34 1.08 0.97 0.83 0.70 0.64 0.62 40 1.73 1.43 1.25 1.05 0.90 0.82 0.77 50 2.06 1.73 1.50 1.30 1.09 1.00 0.92 60 2.40 2.03 1.71 1.51 1.29 1.18 1.10 70 2.88 2.40 2.07 1.79 1.54 1.35 1.26 80 3.36 2.78 2.38 2.10 1.86 1.60 1.42 90 3.74 3.10 2.66 2.34 2.11 1.83 1.67 Source: NCDENR/DWQ Stormwater Best Management Practices, pg. 5, April 1999 STORMWATER BMP #6 -WETLANDS (85% TSS Removal & 40% TN Removal) Land Use Area (ac) % IA Imp. Area (ac) Commercial 7.98 75 5.99 Totals 7.98 5.99 Total % Impervious Surface Area = 75.0 Normal Pool De th 3 4 5 6 7 8 9 SA/DA Ratio 3.12 2.59 2.23 1.95 1.70 1.48 1.34 Minimum Surface Area Re wired Acres 0.25 0.21 0.18 0.16 0.14 0.12 0.11 Sq. Ft 10845.39 9003.07 7734.30 6760.99 5909.35 5127.23 4657.96 Surface Area of Permanent Pool: Assumed depth = 3 feet SA/DA ratio = 3.12 % From Table 1.1 Minimum pond surface area (SA) _ (DA * SA/DA ratio)/100 SA = 0.249 acres 10845 sq. ft. Normal pool elevation = 0.00 feet To be determined Surface area provided = 0.000 acres 0 sq. ft. 1-Inch Runoff Volume Calculation Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987) Rv = 0.05 + 0.009(1) where, Rv =Runoff coefficient, in./in. I =Percent impervious Rv = 0.73 in./in. Total runoff volume from 1-inch precipitation: Runoff volume, S = (Design rainfall) (Rv) (Drainage Area) S = 0.482 acre-ft 21001 cu. ft. Water quality pool elevation= 0.00 feet To be determined Storage volume provided = 0.000 acre-ft 0 cu. ft. BMP7 Proiect Name: 5401 North Project #: 2070102 Cit State: Raleigh, NC Date: 1-Feb-08 Table 1.1 Surface Area to Drainage Area Ratio for Permanent Pool Sizing for 85% Pollutant Removal Efficiency in the Piedmont °~ Impervious Cover Permanent Pool Dept 3.0 4.0 5.0 6.0 h (feet) 7.0 8.0 9.0 10 0.59 0.49 0.43 0.35 0.31 0.29 0.26 20 0.97 0.79 0.70 0.59 0.51 0.46 0.44 30 1.34 1.08 0.97 0.83 0.70 0.64 0.62 40 1.73 1.43 1.25 1.05 0.90 0.82 0.77 50 2.06 1.73 1.50 1.30 1.09 1.00 0.92 60 2.40 2.03 1.71 1.51 1.29 1.18 1.10 70 2.88 2.40 2.07 1.79 1.54 1.35 1.26 80 3.36 2.78 2.38 2.10 1.86 1.60 1.42 90 3.74 3.10 2.66 2.34 2.11 1.83 1.67 Source: NCDENR/DWQ Stormwater Best Management Practices, pg. 5, April 1999 STORMWATER BMP #7 -WETLANDS (85% TSS Removal & 40% TN Removal) Land Use Area (ac) ~° IA Imp. Area (ac) Residentia 17.60 45 7.92 Totals 17.60 7.92 Total °'° Impervious Surface Area = 45.0 Normal Pool De th 3 4 5 6 7 8 9 SA/DA Ratio 1.90 1.58 1.38 1.18 1.00 0.91 0.85 Minimum Surface Area Required Acres 0.33 0.28 0.24 0.21 0.18 0.16 0.15 Sq. Ft 14528.13 12113.16 10541.52 9008.21 7628.23 6976.57 6478.24 Surface Area of Permanent Pool: Assumed depth = 3 feet SA/DA ratio = 1.90 % From Table 1.1 Minimum pond surface area (SA) _ (DA * SA/DA ratio)/100 SA = 0.334 acres 14528 sq. ft. Normal pool elevation = 0.00 feet To be determined Surface area provided = 0.000 acres 0 sq. ft. 1-Inch Runoff Volume Calculation Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987) Rv = 0.05 + 0.009(1) where, Rv =Runoff coefficient, in./in. =Percent impervious Rv = 0.46 in./in. Total runoff volume from 1-inch precipitation: Runoff volume, S = (Design rainfall) (Rv) (Drainage Area) S = 0.667 acre-ft 29069 cu. ft. Water quality pool elevation= 0.00 feet To be determined Storage volume provided = 0.000 acre-ft 0 cu. ft. BMP 8 (BioRet) Project Name: 5401 North Project #: 2070102 City/State: Raleigh, NC Da e: 1-Feb-08 Table 1.1 Surface Area to Drainage Area Ratio for Permanent Pool Sizing for 85% Pollutant Removal Efficiency in the Piedmont % Impervious Cover Permanent Pool Dept 3.0 4.0 5.0 6.0 h (feet) 7.0 8.0 9.0 10 0.59 0.49 0.43 0.35 0.31 0.29 0.26 20 0.97 0.79 0.70 0.59 0.51 0.46 0.44 30 1.34 1.08 0.97 0.83 0.70 0.64 0.62 40 1.73 1.43 1.25 1.05 0.90 0.82 0.77 50 2.06 1.73 1.50 1.30 1.09 1.00 0.92 60 2.40 2.03 1.71 1.51 1.29 1.18 1.10 70 2.88 2.40 2.07 1.79 1.54 1.35 1.26 80 3.36 2.78 2.38 2.10 1.86 1.60 1.42 90 3.74 3.10 2.66 2.34 2.11 1.83 1.67 Source: NCDENR/DWQ Stormwater Best Management Practices, pg. 5, April 1999 STORMWATER BMP #8 - BIORETENTION (85% TSS Removal & 35% TN Removal) Land Use Area (ac) % IA Imp. Area (ac) Residential 6.69 45 3.01 Totals 6.69 3.01 Total % Impervious Surface Area = 45.0 Normal Pool Depth 3 4 5 6 7 8 9 SA/DA Ratio 1.90 1.58 1.38 1.18 1.00 0.91 0.85 Minimum Surface Area R wired Acres 0.13 0.11 0.09 0.08 0.07 0.06 0.06 Sq. Ft 5522.34 4604.38 4006.98 3424.14 2899.59 2651.89 2462.47 Surface Area of Permanent Pool: Assumed depth = 3 feet SA/DA ratio = 1.90 % From Table 1.1 Minimum pond surface area (SA) _ (DA * SA/DA ratio)/100 SA = 0.127 acres 5522 sq. ft. Normal pool elevation = 0.00 feet To be determined Surface area provided = 0.000 acres 0 sq. ft. 1-Inch Runoff Volume Calculation Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987) Rv = 0.05 + 0.009(1) where, Rv =Runoff coefficient, in./in. I =Percent impervious Rv = 0.46 in./in. Total runoff volume from 1-inch precipitation: Runoff volume, S = (Design rainfall) (Rv) (Drainage Area) S = 0.254 acre-ft 11050 cu. ft. Water quality pool elevation= 0.00 feet To be determined Storage volume provided = 0.000 acre-ft 0 cu. ft. Project Name: 5401 North Project #: i /State: Raleigh, NC Date: Table 1.1 Surface Area to Drainage Area Ratio for Permanent Pool Sizing for 85% Pollutant RPmnval FffiriPnrv in the PiPr/mnnt BMP 9 (BioRet) 2070102 1-Feb-08 Impervious Cover Permanent Pool Depth (feet) 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10 0.59 0.49 0.43 0.35 0.31 0.29 0.26 20 0.97 0.79 0.70 0.59 0.51 0.46 0.44 30 1.34 1.08 0.97 0.83 0.70 0.64 0.62 40 1.73 1.43 1.25 1.05 0.90 0.82 0.77 50 2.06 1.73 1.50 1.30 1.09 1.00 0.92 60 2.40 2.03 1.71 1.51 1.29 1.18 1.10 70 2.88 2.40 2.07 1.79 1.54 1.35 1.26 80 3.36 2.78 2.38 2.10 1.86 1.60 1.42 90 3.74 3.10 2.66 2.34 2.11 1.83 1.67 Source: NCDENR/DWQ Stormwater Best Management Practices, pg. 5, April 1999 STORMWATER BMP #9 - BIORETENTION (85% TSS Removal 8 35% TN Removal) Land Use Area (ac) % IA Imp. Area (ac) Residential 11.96 45 5.38 Totals 11.96 5.38 Total ~° Impervious Surface Area = 45.0 Normal Pool De th 3 4 5 6 7 8 9 SA/DA Ratio 1.90 1.58 1.38 1.18 1.00 0.91 0.85 Minimum Surface Area R uired Acres 0.23 0.19 0.16 0.14 0.12 0.11 0.10 Sq. Ft 9872.53 8231.45 7163.44 6121.49 5183.73 4740.90 4402.26 Surface Area of Permanent Pool: Assumed depth = 3 feet SA/DA ratio = 1.90 % From Table 1.1 Minimum pond surface area (SA) _ (DA * SA/DA ratio)/100 SA = 0.227 acres 9873 sq. ft. Normal pool elevation = 0.00 feet To be determined Surface area provided = 0.000 acres 0 sq. ft. 1-Inch Runoff Volume Calculation Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987) Rv = 0.05 + 0.009(1) where, Rv =Runoff coefficient, in./in. =Percent impervious Rv = 0.46 i n./i n. Total runoff volume from 1-inch precipitation: Runoff volume, S = (Design rainfall) (Rv) (Drainage Area) S = 0.453 acre-ft 19754 cu. ft. Water quality pool elevation= 0.00 feet To be determined Storage volume provided = 0.000 acre-ft 0 cu. ft. BMP 10 Project Name: 5401 North Project #: 2070102 it /S ate: Raleigh, NC Date: 1-Feb-08 Table 1.1 Surface Area to Drainage Area Ratio for Permanent Pool Sizing for 85% Pollutant Removal Efficiency in the Piedmont Impervious Cover Permanent Pool Dep 3.0 4.0 5.0 6.0 th (feet) 7.0 8.0 9.0 10 0.59 0.49 0.43 0.35 0.31 0.29 0.26 20 0.97 0.79 0.70 0.59 0.51 0.46 0.44 30 1.34 1.08 0.97 0.83 0.70 0.64 0.62 40 1.73 1.43 1.25 1.05 0.90 0.82 0.77 50 2.06 1.73 1.50 1.30 1.09 1.00 0.92 60 2.40 2.03 1.71 1.51 1.29 1.18 1.10 70 2.88 2.40 2.07 1.79 1.54 1.35 1.26 80 3.36 2.78 2.38 2.10 1.86 1.60 1.42 90 3.74 3.10 2.66 2.34 2.11 1.83 1.67 Source: NCDENR/DWQ Stormwater Best Management Practices, pg. 5, April 1999 STORMWATER BMP #10 -WETLANDS (85% TSS Removal & 40% TN Removal) Land Use Area (ac) ~° IA Imp. Area (ac) Residential 14.72 45 6.62 Totals 14.72 6.62 Total % Impervious Surface Area = 45.0 Normal Pool De th 3 4 5 6 7 8 9 SA/DA Ratio 1.90 1.58 1.38 1.18 1.00 0.91 0.85 Minimum Surface Area R uired Acres 0.28 0.23 0.20 0.17 0.15 0.13 0.12 Sq. Ft 12150.80 10131.01 8816.54 7534.14 6379.97 5834.95 5418.17 Surface Area of Permanent Pool: Assumed depth = 3 feet SA/DA ratio = 1.90 % From Table 1.1 Minimum pond surface area (SA) _ ( DA * SA/DA ratio)/100 SA = 0.279 acres 12151 sq. ft. Normal pool elevation = 0.00 feet To be determined Surface area provided = 0.000 acres 0 sq. ft. 1-Inch Runoff Volume Calculation Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987) Rv = 0.05 + 0.009(1) where, Rv =Runoff coefficient, in./in. =Percent impervious Rv = 0.46 i n./i n. Total runoff volume from 1-inch precipitation: Runoff volume, S = (Design rainfall) (Rv) (Drainage Area) S = 0.558 acre-ft 24312 cu. ft. Water quality pool elevation= 0.00 feet To be determined Storage volume provided = 0.000 acre-ft 0 cu. ft. BMP 11 Project Name: 5401 North Project #: 2070102 Cit~State: Raleigh, NC Date: 1-Feb-08 Table 1.1 Surface Area to Drainage Area Ratio for Permanent Pool Sizing for 85% Pollutant Removal Efficiency in the Piedmont Impervious Cover Permanent Pool Depth (feet) 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10 0.59 0.49 0.43 0.35 0.31 0.29 0.26 20 0.97 0.79 0.70 0.59 0.51 0.46 0.44 30 1.34 1.08 0.97 0.83 0.70 0.64 0.62 40 1.73 1.43 1.25 1.05 0.90 0.82 0.77 50 2.06 1.73 1.50 1.30 1.09 1.00 0.92 60 2.40 2.03 1.71 1.51 1.29 1.18 1.10 70 2.88 2.40 2.07 1.79 1.54 1.35 1.26 80 3.36 2.78 2.38 2.10 1.86 1.60 1.42 90 3.74 3.10 2.66 2.34 2.11 1.83 1.67 Source: NCDENR/DWQ Stormwater Best Management Practices, pg. 5, April 1999 STORMWATER BMP #11 -WETLANDS (85% TSS Removal & 40% TN Removal) Land Use Area (ac) °~ IA Imp. Area (ac) Residential 21.26 45 9.57 Totals 21.26 9.57 Total % Impervious Surface Area = 45.0 Normal Pool De th 3 4 5 6 7 8 9 SA/DA Ratio 1.90 1.58 1.38 1.18 1.00 0.91 0.85 Minimum Surface Area Re uired Acres 0.40 0.34 0.29 0.25 0.21 0.19 0.18 Sq. Ft 17549.32 14632.15 12733.68 10881.51 9214.55 8427.38 7825.42 Surface Area of Permanent Pool: Assumed depth = 3 feet SA/DA ratio = 1.90 % From Table 1.1 Minimum pond surface area (SA) _ (DA * SA/DA ratio)/100 SA = 0.403 acres 17549 sq. ft. Normal pool elevation = feet To be determined Surface area provided = acres 0 sq. ft. 1-Inch Runoff Volume Calculation Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987) Rv = 0.05 + 0.009(1) where, Rv =Runoff coefficient, in./in. I =Percent impervious Rv = 0.46 in./in. Total runoff volume from 1-inch precipitation: Runoff volume, S = (Design rainfall) (Rv) (Drainage Area) S = 0.806 acre-ft 35114 cu. ft. Water quality pool elevation= 0.00 feet To be determined Storage volume provided = 0.000 acre-ft 0 cu. ft. BMP 12 Project Name: 5401 North Proeec #: 2070102 i / to :Raleigh, NC Date: 1-Feb-08 Table 1.1 Surface Area to Drainage Area Ratio for Permanent Pool Sizing for 85% Pollutant Removal Efficiency in the Piedmont °~ Impervious Cover Permanent Pool Dept 3.0 4.0 5.0 6.0 h (feet) 7.0 8.0 9.0 10 0.59 0.49 0.43 0.35 0.31 0.29 0.26 20 0.97 0.79 0.70 0.59 0.51 0.46 0.44 30 1.34 1.08 0.97 0.83 0.70 0.64 0.62 40 1.73 1.43 1.25 1.05 0.90 0.82 0.77 50 2.06 1.73 1.50 1.30 1.09 1.00 0.92 60 2.40 2.03 1.71 1.51 1.29 1.18 1.10 70 2.88 2.40 2.07 1.79 1.54 1.35 1.26 80 3.36 2.78 2.38 2.10 1.86 1.60 1.42 90 3.74 3.10 2.66 2.34 2.11 1.83 1.67 Source: NCDENR/DWQ stormwater Best Management Practices, pg. S, April 1999 STORMWATER BMP #12 -WETLANDS (85% TSS Removal & 40% TN Removal) Land Use Area (ac) % IA Imp. Area (ac) Residential 14.55 55 8.00 Totals 14.55 8.00 Total ~° Impervious Surface Area = 55.0 Normal Pool De th 3 4 5 6 7 8 9 SA/DA Ratio 2.23 1.88 1.61 1.41 1.19 1.09 1.01 Minimum Surface Area Re wired Acres 0.32 0.27 0.23 0.20 0.17 0.16 0.15 Sq. Ft 14133.70 11915.40 10172.46 8904.86 7542.20 6908.40 6401.36 Surface Area of Permanent P Assumed depth = 3 feet SA/DA ratio = 2.23 % From Table 1.1 Minimum pond surface area (SA) _ ( DA * SA/DA ratio)/100 SA = 0.324 acres 14134 sq. ft. Normal pool elevation = 0.00 feet To be determined Surface area provided = 0.000 acres 0 sq. ft. 1-Inch Runoff Volume Calculation Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987) Rv = 0.05 + 0.009(1) where, Rv =Runoff coefficient, in./in. I =Percent impervious Rv = 0.55 in./in. Total runoff volume from 1-inch precipitation: Runoff volume, S = (Design rainfall) (Rv) (Drainage Area) S = 0.661 acre-ft 28785 cu. ft. Water quality pool elevation= 0.00 feet To be determined Storage volume provided = 0.000 acre-ft 0 cu. ft. BMP 13 Project Name: 5401 North Project #: 2070102 i /State: Raleigh, NC Date: 1-Feb-08 Table 1.1 Surface Area to Drainage Area Ratio for Permanent Pool Sizing for 85% Pollutant Removal Efficiency in the Piedmont Impervious Cover Permanent Pool Dept 3.0 4.0 5.0 6.0 h (feet) 7.0 8.0 9.0 10 0.59 0.49 0.43 0.35 0.31 0.29 0.26 20 0.97 0.79 0.70 0.59 0.51 0.46 0.44 30 1.34 1.08 0.97 0.83 0.70 0.64 0.62 40 1.73 1.43 1.25 1.05 0.90 0.82 0.77 50 2.06 1.73 1.50 1.30 1.09 1.00 0.92 60 2.40 2.03 1.71 1.51 1.29 1.18 1.10 70 2.88 2.40 2.07 1.79 1.54 1.35 1.26 80 3.36 2.78 2.38 2.10 1.86 1.60 1.42 90 3.74 3.10 2.66 2.34 2.11 1.83 1.67 Source: NCDENR/DWQ Stormwater Best Management Practices, pg. 5, April 7999 STORMWATER BMP #13 -WETLANDS (85% TSS Removal 8~ 40% TN Removal) Land Use Area (ac) % IA Imp. Area (ac) Residential/Commercial 10.82 65 7.03 Totals 10.82 7.03 Total % Impervious Surface Area = 65.0 Normal Pool De th 3 4 5 6 7 8 9 SA/DA Ratio 2.64 2.22 1.89 1.65 1.42 1.27 1.18 Minimum Surface Area Re wired Acres 0.29 0.24 0.20 0.18 0.15 0.14 0.13 Sq. Ft 12442.83 10439.72 8907.93 7776.77 6669.17 5962.19 5561.57 Surface Area of Permanent Pool: Assumed depth = 3 feet SA/DA ratio = 2.64 % From Table 1.1 Minimum pond surface area (SA) _ (DA * SA/DA ratio)/100 SA = 0.286 acres 12443 sq. ft. Normal pool elevation = 0.00 feet To be determined Surface area provided = 0.000 acres 0 sq. ft. 1-Inch Runoff Volume Calculation Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987) Rv = 0.05 + 0.009(1) where, Rv =Runoff coefficient, in./in. 1 =Percent impervious Rv = 0.64 i n./i n. Total runoff volume from 1-inch precipitation: Runoff volume, S = (Design rainfall) (Rv) (Drainage Area) S = 0.573 acre-ft 24941 cu. ft. Water quality pool elevation= 0.00 feet To be determined Storage volume provided = 0.000 acre-ft 0 cu. ft. BMP 14 Project Name: 5401 North Project #: 2070102 City/State: Raleigh, NC Date: 1-Feb-08 Table 1.1 Surface Area to Drainage Area Ratio for Permanent Pool Sizing for 85% Pollutant Removal Efficiency in the Piedmont % Impervious Cover Permanent Pool Dept 3.0 4.0 5.0 6.0 h (feet) 7.0 8.0 9.0 10 0.59 0.49 0.43 0.35 0.31 0.29 0.26 20 0.97 0.79 0.70 0.59 0.51 0.46 0.44 30 1.34 1.08 0.97 0.83 0.70 0.64 0.62 40 1.73 1.43 1.25 1.05 0.90 0.82 0.77 50 2.06 1.73 1.50 1.30 1.09 1.00 0.92 60 2.40 2.03 1.71 1.51 1.29 1.18 1.10 70 2.88 2.40 2.07 1.79 1.54 1.35 1.26 80 3.36 2.78 2.38 2.10 1.86 1.60 1.42 90 3.74 3.10 2.66 2.34 2.11 1.83 1.67 Source: NCDENR/DWQ Stormwater Best Management Practices, pg. 5, April 1999 STORMWATER BMP #14 -WETLANDS (85% TSS Removal & 40% TN Removal) Land Use Area (ac) % IA Imp. Area (ac) Residential/Commercial 20.90 65 13.59 Totals 20.90 13.59 Total % Impervious Surface Area = 65.0 Normal Pool De th 3 4 5 6 7 8 9 SA/DA Ratio 2.64 2.22 1.89 1.65 1.42 1.27 1.18 Minimum Surface Area Re wired Acres 0.55 0.46 0.40 0.34 0.30 0.26 0.25 Sq. Ft 24034.67 20165.45 17206.64 15021.67 12882.22 11516.61 10742.77 Surface Area of Permanent Pool: Assumed depth = 3 feet SA/DA ratio = 2.64 % From Table 1.1 Minimum pond surface area (SA) _ (DA * SA/DA ratio)/100 SA = 0.552 acres 24035 sq. ft. Normal pool elevation = 0.00 feet To be determined Surface area provided = 0.000 acres 0 sq. ft. 1-Inch Runoff Volume Calculation Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987) Rv = 0.05 + 0.009(1) where, Rv =Runoff coefficient, in./in. I =Percent impervious Rv = 0.64 i n./i n. Total runoff volume from 1-inch precipitation: Runoff volume, S = (Design rainfall) (Rv) (Drainage Area) S = 1.106 acre-ft 48176 cu. ft. Water quality pool elevation= 0.00 feet To be determined Storage volume provided = 0.000 acre-ft 0 cu. ft. BMP 15 Proiect Name: 5401 North Project #: 2070102 it /State: Raleigh, NC Date: 1-Fek1-08 Table 1.1 Surface Area to Drainage Area Ratio for Permanent Pool Sizing for 85% Pollutant Removal Efficiency in the Piedmont ~° Impervious Cover Permanent Pool Dept 3.0 4.0 5.0 6.0 h (feet) 7.0 8.0 9.0 10 0.59 0.49 0.43 0.35 0.31 0.29 0.26 20 0.97 0.79 0.70 0.59 0.51 0.46 0.44 30 1.34 1.08 0.97 0.83 0.70 0.64 0.62 40 1.73 1.43 1.25 1.05 0.90 0.82 0.77 50 2.06 1.73 1.50 1.30 1.09 1.00 0.92 60 2.40 2.03 1.71 1.51 1.29 1.18 1.10 70 2.88 2.40 2.07 1.79 1.54 1.35 1.26 80 3.36 2.78 2.38 2.10 1.86 1.60 1.42 90 3.74 3.10 2.66 2.34 2.11 1.83 1.67 Source: NCDENR/DWQ Stormwater Best Management Practices, pg. 5, April 1999 STORMWATER BMP #15 -WETLANDS (85% TSS Removal ~ 40% TN Removal) Land Use Area (ac) % IA Imp. Area (ac) Residential 9.53 55 5.24 Totals 9.53 5.24 Total ~° Impervious Surface Area = 55.0 Normal Pool De th 3 4 5 6 7 8 9 SA/DA Ratio 2.23 1.88 1.61 1.41 1.19 1.09 1.01 Minimum Surface Area Required Acres 0.21 0.18 0.15 0.13 0.11 0.10 0.10 Sq. Ft 9257.33 7804.38 6662.79 5832.53 4940.01 4524.88 4192.78 Surface Area of Permanent Pool: Assumed depth = 3 feet SA/DA ratio = 2.23 % From Table 1.1 Minimum pond surface area (SA) _ (DA * SA/DA ratio)/100 SA = 0.213 acres 9257 sq. ft. Normal pool elevation = 0.00 feet To be determined Surface area provided = 0.000 acres 0 sq. ft. 1-Inch Runoff Volume Calculation Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987) Rv = 0.05 + 0.009(1) where, Rv =Runoff coefficient, in./in. =Percent impervious Rv = 0.55 in./in. Total runoff volume from 1-inch precipitation: Runoff volume, S = (Design rainfall) (Rv) (Drainage Area) S = 0.433 acre-ft 18854 cu. ft. Water quality pool elevation= 0.00 feet To be determined Storage volume provided = 0.000 acre-ft 0 cu. ft. BMP 16 Project Name: 5401 North Project #: 2070102 i /State: Raleigh, NC Date: 1-Feb-08 Table 1.1 Surface Area to Drainage Area Ratio for Permanent Pool Sizing for 85% Pollutant Removal E-fficiencv in the Piedmont Impervious Cover Permanent Pool Dept 3.0 4.0 5.0 6.0 h (feet) 7.0 8.0 9.0 10 0.59 0.49 0.43 0.35 0.31 0.29 0.26 20 0.97 0.79 0.70 0.59 0.51 0.46 0.44 30 1.34 1.08 0.97 0.83 0.70 0.64 0.62 40 1.73 1.43 1.25 1.05 0.90 0.82 0.77 50 2.06 1.73 1.50 1.30 1.09 1.00 0.92 60 2.40 2.03 1.71 1.51 1.29 1.18 1.10 70 2.88 2.40 2.07 1.79 1.54 1.35 1.26 80 3.36 2.78 2.38 2.10 1.86 1.60 1.42 90 3.74 3.10 2.66 2.34 2.11 1.83 1.67 Source: NCDENR/DWQ Stormwater Best Management Practices, pg. 5, April 1999 STORMWATER BMP #16 -WETLANDS (85% TSS Removal & 40% TN Removal) Land Use Area (ac) °~ IA Imp. Area (ac) Residential 6.97 55 3.83 Totals 6.97 3.83 Total % Impervious Surface Area = 55.0 Normal Pool De th 3 4 5 6 7 8 9 SA/DA Ratio 2.23 1.98 1.68 1.50 1.24 1.03 0.80 Minimum Surface Area Re uired Acres 0.16 0.14 0.12 0.10 0.09 0.07 0.06 Sq. Ft 6770.57 6011.54 5100.70 4554.20 3749.62 3112.04 2413.72 Surface Area of Permanent Pool: Assumed depth = 3 feet SA/DA ratio = 2.23 % From Table 1.1 Minimum pond surface area (SA) _ (DA * SA/DA ratio)/100 SA = 0.155 acres 6771 sq. ft. Normal pool elevation = 0.00 feet To be determined Surface area provided = 0.000 acres 0 sq. ft. 1-Inch Runoff Volume Calculation Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987) Rv = 0.05 + 0.009(1) where, Rv =Runoff coefficient, in./in. I =Percent impervious Rv = 0.55 in./in. Total runoff volume from 1-inch precipitation: Runoff volume, S = (Design rainfall) (Rv) (Drainage Area) S = 0.317 acre-ft 13789 cu. ft. Water quality pool elevation= 0.00 feet To be determined Storage volume provided = 0.000 acre-ft 0 cu. ft. 5401 NORTH STORMWATER MANAGEMENT REPORT RALEIGH, NORTH CAROLINA NITROGEN LOADING CALCULATION S 5401 North W&R Project zo7o1o2 Stormwater Management Report February 2008 Nitrogen Control Plan Commercial /Industrial /Residential Sites with Known Impervious Area Project Title: 5401 North (Preliminary Overall Stormwater Management) Part I. Riparian Buffers Area includes riparian buffers? [ ] No [ X ]Yes [ ]Exempt If yes, [ X ] 50 foot [ ] 100 foot River Basin? [ X ] Neuse [ ]Cape Fear Basis for Exemption Show buffers on site plan. Part II. Nitrogen Calculations (Method 2, Appendix C): a. Site Information Total Area of Property incl. RNV Denuded Area Impervious Area incl. RNV Managed open space Protected open space b. Pre-development loading: 389.63 acres 327.33 acres 181.05 acres 146.28 acres 60.17 acres Type of Land Cover Permanently protected undisturbed open space (forest, unmown meadow) Permanently protected managed open space (grass, landscaping, etc.) Impervious Area TOTAL Nitrogen Loading Rate (Ibs/ac/yr) _ c. Post-development loading: TN Export Area TN export coeff from use acres (Ibs/ac/ r Ibs/ r 235.55 0.6 141.33 154.08 1.2 184.896 0 21.2 0 389.63 326.23 0.84 Type of Land Cover Permanently protected undisturbed open space (forest, unmown meadow) Permanently protected managed open space (grass, landscaping, etc.) Impervious Area TOTAL Nitrogen Loading Rate (Ibs/ac/yr) = 9.44 TN Export Area TN export coeff from use (acres) (Ibs/ac/yr) (Ibs/yr) 60.17 0.6 36.10 167.06 1.2 200.47 162.4 21.2 3442.88 389.63 3679.45 Proposed BMP(s) 13 Wetlands, 2 Wet Ponds w/ Wetland Fringes, & 2 Bioretention Cells Nitrogen Load after BMPs = 6.81 Ibs/ac/yr Nitrogen Load offset by Payments = 3.21 Ibs/aGyr Estimated Buy Down = $1,065,052 Net change in on-site NLoad = 5.84 Ibs/ac/yr Part III. Control of Peak Stormwater Flow (for 1 year, design storm) Calculated Pre-development Peak Flow Calculated Post-development Peak Flow Proposed BMP(s) Post BMP Peak Flow I, the undersigned, certify to the best of my knowledge that the above information is correct (affix seal). 0 cfs To be determined 0 cfs Supply notes & details showing control of Nitrogen and peak Stormwater runoff. Nitrogen Control Plan Commercial /Industrial /Residential Sites with Known Impervious Area Project Name: 5401 North Project #: 2070102 TOTAL TRACT (Excluding Townhomes) Total Area: 16,372,283 sgft. = 389.63 ac. Impervious Area .7;562,018 sgft. = 173.60 ac. Natural Open Space Area: 2,521,005 sgft. = 60.17 ac. Managed Open Space Area: 8,789,262 sgft. = 155.86 ac. Estimated Pre-Development TN Loading Date: 1 /3 012 0 0 8 Computed by: PC Type of Land Cover Acres TN Export Cceff. (Ibs/aGyr) TN EXPORT (Ibs/yr) Permanently Protected Undisturbed Area 2 7.68 0.6 142.61 Permanently Protected Managed Area 151.95 1.2 182.34 Impervious Surface O.OD 21.2 0.00 ota 5 32 . Estimated Post-Development TN Loading Drainage Area I: WETLANDS Type of Land Cover Acres TN Export Cceff. (Ibs/aGyr) TN EXPORT (Ibs/yr) Permanently Protected Undisturbed Area D DO 0.6 0.00 Permanently Protected Managed Area 8.35 1.2 10.02 Impervious Area 19.77 21.2 419.12 otals 2 .1 4 9.14 Estimated BMP Reduction for Wetlands: 40 Estimated Drainage Area I Nitrogen Loading Reduction: 171.66 Ibstyr Drainage Area II: WETLANDS Type of Land Cover Acres TN Export oeff. (Ibs/aGyr) TN EXPORT (Ibs/yr) Permanently Protected Undisturbed Area D.oO 0.6 0.00 Permanently Protected Managed Area 1.16 1.2 1.39 Impervious Area 8.56 21.2 139.07 Totals 7.72 .4 Estimated BMP Reduction for Wetlands 40 % Estimated Drainage Area II Nitrogen Loading Reduction: 56.19 Ibs/yr Drainage Area III: WET POND WITH WETLAND FRINGE Type of Land Cover Acres Ibs/a Oe ' TN EXPORT (Ibs/yr) Permanently Protected Undisturbed Area 0 DD 0.6 0.00 Permanently Protected Managed Area 2.97 1.2 3.56 Impervious Area 6.82 21.2 146.70 ota s 1 Estimated BMP Reduction for Wet Pond with Wetland Fringe 30 % Estimated Drainage Area 111 Nitrogen Loading Reduction: 45.08 Ibs/yr Drainage Area IV: WET POND WITH WETLAND FRINGE Type of Land Cover Acres Ibya ce ' TN F~(PORT (Ibs/yr) Permanently Protected Undisturbed Area 0.00 0.6 0.00 Permanently Protected Managed Area 2.73 1.2 3.28 Impervious Area 15.46 21.2 327.75 Totals 78.19 Estimated BMP Reduction for Wet Pond with Wetland Fdnge 30 % Estimated Drainage Area IV NlVogen Loading Reduction: 99.31 Ibs/yr Drainage Area V: WETLANDS Type of Land Cover Acres ~~ ° TN EXPORT (Ibs/yr) Permanently Protected Undisturbed Area 0.00 0.6 0.00 Permanently Protected Managed Area 9.31 1.2 11.17 Impervious Area 33.57 21.2 711.68 otals 4 Estimated BMP Reduction for Wetlands 40 % Estimated Drainage Area V Nitrogen Loading Reduction: 289.14 Ibs/yr Nitrogen Control Plan Commercial /Industrial /Residential Sites with Known Impervious Area Drelnage Area VI: WETLANDS Type of Land Cover Acres ~ ~ rJ °e ' TN EXPORT (Ibs/yr) Permanently Protected Undisturbed Area 0.00 0.6 0.00 Permanently Protected Managed Area 1.99 1.2 2.39 Impervious Area 6.99 21.2 126.99 Totals .98 1 Estimated BMP Reduction for Wetlands 40 Estimated Drainage Area VI Nitrogen Loading Reduction: 51.75 Ibstyr Drainage Area VII: WETLANDS Type of Land Cover Acres I xPO d Oe ' TN EXPORT (Ibstyr) Permanently Protected Undisturbed Area o 00 0.6 0.00 Permanently Protected Managed Area 9.68 1.2 11.62 Impervious Area 7.92 21.2 167.90 Totals 71.60 1 Estimated BMP Reduction for Wetlands 40 % Estimated Drainage Area VII Nitrogen Loading Reduction: 71.81 Ibstyr Drainage Area VIII: BIORETENTION Type of land Cover Acres Ibs/aG Oe TN EXPORT (Ibstyr) Permanently Protected Undisturbed Area 0.00 0.6 0.00 Permanently Protected Managed Area 3.6e 1.2 4.42 Impervious Area 3.01 21.2 63.01 ola s o. a Estimated BMP Reduction for Bioretention 35 % Estimated Drainage Area VIII Nitrogen Loading Reduction: 23.88 Ibstyr Drainage Area IX: BIORETENTION Type of Land Cover Acres Ibyad Oe ' TN EXPORT (Ibstyr) Permanently Protected Undisturbed Area 0.00 0.6 0.00 Permanently Protected Managed Area 6.58 1.2 7.90 Impervious Area 5.38 21.2 114.06 ota s 1 1 Estimated BMP Reduction for Bioretention 35 % Estimated Drainage Area IX Nitrogen Loading Reduction: 42.68 Ibstyr Drainage Area X: WETLANDS Type of Land Cover Aces ~O °e ' Ibs/arJ r TN EXPORT (Ibstyr) Permanently Protected Undisturbed Area D.0o 0.6 0.00 Permanently Protected Managed Area 8.10 1.2 9.72 Impervious Area 6.62 21.2 140.34 Totals 14.72 Estimated BMP Reduction for Wetlands 40 % Estimated Drainage Area X Nitrogen Loading Reduction: 60.03 Ibstyr Drainage Area XI: WETLANDS Type of Land Cover Aces Ibs/aG TN EXPORT (Ibstyr) Permanently Protected Undisturbed Area 0.00 0.6 0.00 Permanently Protected Managed Area 11 89 1.2 14.03 Impervious Area 9.57 21.2 202.88 Totals z1.2ti 1 Estimated BMP Reduction for Wetlands 40 % Estimated Drainage Area XI Nitrogen Loading Reduction: 86.76 Ibstyr Nitrogen Control Plan Commercial /Industrial /Residential Sites with Known Impervious Area Drainage Area XII: WETLANDS Type of Land Cover Acres Ib~ac/ Oe ' TN EXPORT (Ibs/yr) Permanently Protected Undisturbed Area o 00 0.6 0.00 Permanently Proteced Managed Area 5.55 1.2 7.66 Impervious Area 8.00 21.2 169.60 Totals 14.55 Estimated BMP Reduction for Wetlands 40 Estimated Drainage Area XII Nitrogen Loading Reduction: 70.98 Ibstyr Drainage Area XIII: WETLANDS Type of Land Cover Acres Ib~a Oe ' TN EXPORT (Ibs/yr) Permanently Proleded Undisturbed Area o 00 0.6 0.00 Permanently Protected Managed Area 3.79 1.2 4.55 Impervious Area 7 D3 21.2 149.04 otas tu.dz 1 Estimated BMP Reduction for Wetlands 40 Estimated Drainage Area XIII Nitrogen Loading Reduction: 61.43 Ibstyr Drainage Area XIV: WETLANDS Type of Land Cover Acres Ib~ac/ o TN EXPORT (Ibs/yr) Permanently Protected Undisturbed Area 0.!)0 0.6 0.00 Pemmanently Protected Managed Area 7 31 1.2 6.77 Impervious Area 13.59 21.2 288.11 otals 2u.9u 2 Estimated BMP Reduction for Wetlands 40 Estimated Drainage Area XIV Nitrogen Loading Reduction: 118.75 Ibstyr Drainage Area XV: WETLANDS Type of Land Cover Acres ~O Oe ' Ibs/aG r TN EXPORT (Ibstyr) Permanently Protected Undisturbed Area D o0 0.6 0.00 Permanently Protected Managed Area 4.29 1.2 5.15 Impervious Area 5.24 21.2 111.09 ola s a.o3 11 . Estimated BMP Reduction for Wetlands 40 Estimated Drainage Area XV Nitrogen Loading Reduction: 46.49 Ibstyr Drainage Area XVI: WETLANDS Type of Land Cover Acres Ib~a Oe ' TN EXPORT (Ibs/yr) Permanently Protected Undisturbed Area D o0 0.6 0.00 Permanently Protected Managed Area 3.14 1.2 3.77 Impervious Area 3 e3 21.2 81.20 otals ti.9 Estimated BMP Reduction for Wetlands 40 % Estimated Drainage Area XVI Nitrogen Loading Reduction: 33.99 Ibstyr Drainage Area XVII: LEVEL SPREADER Type of Land Cover Acres (Ibs/a ce TN EXPORT (Ibs/yr) Permanently Protected Undisturbed Area o 00 0.6 0.00 Permanently Protected Managed Area o_00 1.2 0.00 Impervious Area 6.93 21.2 146.92 Totals 6.93 146.92 Estimated BMP Reduction for Level Spreader to Stream Buffer: 20 Estimated Drainage Area XVII Nitrogen Loading Reduction: 29.38 Ibstyr Nitrogen Control Plan Commercial /Industrial /Residential Sites with Known Impervious Area Drainage Area XVIII: LEVEL SPREADER Type of Land Cover Acres TN Export Coeff. (ibsladyr) TN EXPORT (Ibs/yr) Permanently Protected Undisturbed Area 0:00 0.6 0.00 Permanently Protected Managed Area 0:56 1.2 0.67 Impervious Area 4,94 21.2 104.73 Totals 5.50 105.40 Estimated BMP Reduction for Level Spreader to Stream Buffer: 20 % Estimated Drainage Area XVIII Nitrogen Loading Reduction: 21.08 Ibstyr Drainage Area XIX: LEVEL SPREADER Type of Land Cover Acres TN Export Coeff. (IbslaGyr) TN EXPORT (Ibs/yr) Permanently Protected Undisturbed Area o oo 0.6 0.00 Permanently Protected Managed Area 0.20 1.2 0.24 Impervious Area 7.47 21.2 158.36 Totals 7.67 158.60 Estimated BMP Reduction for Level Spreader to Stream Buffer: 20 % Estimated Drainage Area XIX Nitrogen Loading Reduction: 31.72 Ibstyr Drainage Area XX: UNTREATED Type of Land Cover Acres TN Export Coeff. TN EXPORT (Ibs/yr) (Ibs/aGyr) Permanently Protected Undisturbed Area 60.17 0.6 36.10 Permanently Protected Managed Area 55.60 1.2 66.72 Impervious Area 398 21.2 84.38 Tolais 119.75 187.20 Estimated BMP Reduction: 0 % Estimated Drainage Area XX Nitrogen Loading Reduction: 0.00 Ibstyr Total Area: 389.63 Acres Estimated Protect Pre-BMP TN Export: 4067.05 Ibstyr Estimated Project BMP TN Removal: 1412.12 Ibstyr Estimated Project TN Load Rate After BMPs: 6.81 Ibs/aGyr Estimated Project Composite Nitrogen Loading Rate Reduction: 34.72 Estimated Project Buy Down: 51,065,052.40