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Home My WebLink About20110156 Ver 1_Stormwater Info_201110111\ - 01 5 LO Michael Baker Engineering, Inc. 7800 Airport Center Drive, Ste. 100 Greensboro, NC 27409 336-931-1500 FAX 336-931-1501 October 10, 2011 Ms. Annette M. Lucas, PE, Environmental Engineer N.C. Department of Environment and Natural Resources Division of Water Quality Wetlands and Stormwater Branch 512 N. Salisbury St, 9th Floor Raleigh, NC 27604 Re: Mount Airy - Surry County Airport Holly Springs Road Relocation Dear Ms. Lucas, OCT 1 1 2011 DENR • WATER QUALITY WENWQSAND STORMMMATER BRANCH For your review and comment, please find enclosed the following: • One (1) copy of the Stormwater Management Plan (Binder), which includes the revised detailed narrative, calculations, and other requested information. • One (1) set of Stormwater Management Plan plansheets • One (1) set of the permitted Erosion and Sedimentation Plans (36x48) • One (1) set of the 100% Submitted Road Plans to NCDOT for the Holly Springs Road Relocation. NCDOT comments have not been received at this time. • One (1) CD of Stormwater Management Plan (Binder) and Plansheets; Permitted Erosion and Sedimentation Plans (36x48); and 100% Submitted Road Plans to NCDOT for the Holly Springs Road Relocation. If you have any questions or need additional information, please feel free to call. Sincerely, Michael Baker Engineering, Inc. Timothy S. Ke 'erly, P.E. Project Engineer Enclosures cc: Ed Smail, Environmental Specialist, LPA/Baker ATA oa?FWATp9QG WDENR O Y STORMWATER MANAGEMENT PERMIT APPLICATION FORM 401 CERTIFICATION APPLICATION FORM LEVEL SPREADER - VEGETATED FILTER STRIP (LS-VFS) SUPPLEMENT This form must be completely filled out, printed, initialed, and submitted. I. PROJECT INFORMATION Project name Mt. Airy Airport - Stormwater Management Plan Contact name Tim Kennerly, PE Phone number 336.662.4251 Date September 19, 2011 Drainage area number Taxiway'A' South Extension II. DESIGN INFORMATION The purpose of the LS-VFS Pollutant removal: 40% TSS, 30% TN, 35% TP Stormwater enters LS-VFS from The drainage area Type of VFS Engineered filter strip (graded & sodded, slope < 8%) Explanation of any "Other" response s above Vegetated Filter Strip consists of the taxiway Safety Area If Stormwater Enters the LS-VFS from the Drainage Area Drainage area 450,846 ft2 Impervious surface area 153,767 ftz Percent impervious 34.11 % Rational C coefficient 0.70 Peak flow from the 1 in/hr storm 7.25 cfs Time of concentration 5.00 min Rainfall intensity, 10-yr storm 0.218 in/hr Peak flow from the 10-yr storm 1.58 cfs Design storm 10-year storm Maximum amount of flow directed to the LS-VFS 1.58 cfs Is a flow bypass system going to be used? N (Y or N) Explanation of any "Other" responses above If Stormwater Enters the LS-VFS from a BMP Type of BMP Peak discharge from the BMP during the design storm Peak discharge from the BMP during the 10-year storm Maximum capacity of a 100-foot long LS-VFS Peak flow directed to the LS-VFS Is a flow bypass system going to be used? Explanation of any "Other" responses above Rainfall intensity is based on a 10 YR - 24 HR Storm Event Do not complete this section of the form. cfs cfs Do not complete this section of the form. 10 cfs cfs Do not complete this section of the form. (Y or N) Form SW401 - LS-VFS - 27Ju12011 - Rev.9 page 1 of 3 LS-VFS Design Forebay surface area Depth of forebay at stormwater entry point Depth of forebay at stormwater exit point Feet of level lip needed per cfs Computed minimum length of the level lip needed Length of level lip provided Width of VFS Elevation at downslope base of level lip Elevation at the end of the VFS that is farthest from the LS Slope (from level lip to the end of the VFS) Are any draws present in the VFS? Is there a collector swale at the end of the VFS? Bypass System Design (if applicable) Is a bypass system provided? Is there an engineered flow splitting device? Dimensions of the channel (see diagram below): M B W y (flow depth for 10-year storm) freeboard (during the 10-year storm) Peak velocity in the channel during the 10-yr storm Channel lining material Does the bypass discharge through a wetland? Does the channel enter the stream at an angle? Explanation of any "Other" responses above 0 sq ft Forebay is undersized. 0 in 0 in Too shallow. 10 ft/cfs 16 ft 100 ft 50 It 1,203.00 fmsl 1,205.00 fmsl -4.00 % N (Y or N) OK N (Y or N) N (Y or N) N (Y or N) ft ft ft ft fusec Pick one: (Y or N) (Y or N) No Bypass System is Provided. W , r i P, j Form SW401 - LS-VFS - 27JU12011 - Rev.9 page 2 of 3 III. REQUIRED ITEMS CHECKLIST EDIT Please indicate the page or plan sheet numbers where the supporting documentation can be found. An incomplete submittal package will result in a request for additional information. This will delay final review and approval of the project. Initial in the space provided to indicate the following design requirements have been met. If the applicant has designated an agent, the agent may initial below. If a requirement has not been met, attach justification. Requried Item: 1. Plans (1" - 50' or larger) of the entire site showing: - Design at ultimate build-out, Off-site drainage (if applicable), Delineated drainage basins (include Rational C coefficient per basin), Forebay (if applicable), High flow bypass system, Maintenance access, Proposed drainage easement and public right of way (ROW), and Boundaries of drainage easement. Initials Page or plan sheet number and any notes: DA-5 Nom` 2. Plan details (1" = 30' or larger) for the level spreader showing: - Forebay (if applicable), High flow bypass system, One foot topo lines between the level lip and top of stream bank, Proposed drainage easement, and Design at ultimate build-out. 3. Section view of the level spreader (120' or larger) showing: - Underdrain system (if applicable), Level lip, Upslope channel, and Downslope filter fabric. 4. Plan details of the flow splitting device and supporting calculations (if applicable). 5. A construction sequence that shows how the level spreader will be protected from sediment until the entire drainage area is stabilized. 6. If a non-engineered VFS is being used, then provide a photograph of the VFS showing that no draws are present. ?-?"? NA NA NA 7. The supporting calculations. 8. A copy of the signed and notarized operation and maintenance (0&M) agreement. Tab TW'A' South EXT. BMP 0&M Agreements Form SW401 - LS-VFS - 27Ju12011 - Rev.9 page 3 of 3 Permit Number: (to be provided by DWQ) ®? O?O? wAT ?9pG r WDENR ` STORMWATER MANAGEMENT PERMIT APPLICATION FORM 401 CERTIFICATION APPLICATION FORM GRASSED SWALE SUPPLEMENT This form must be filled out, printed and submitted. The Required Items Checklist (Part III) must also be filled out, printed and submitted along with all of the required information. I. PROJECT INFORMATION Project name Mt. Airy Airport - Stormwater Management Plan Contact name Tim Kennerly, PE Phone number 336.662.4251 Date September 19, 2011 Drainage area number Taxiway'A' South Extension II. DESIGN INFORMATION Site Characteristics Drainage area 450,846.00 ft2 Impervious area 153,767.00 ft2 Percent impervious 34.1%% Design rainfall depth 1.00 inch Peak Flow Calculations 10-yr storm runoff depth 5.23 in 10-yr storm intensity 0.22 in/hr Post-development 10-yr storm peak flow 1.60 ft3/sec Velocity Maximum non-erosive velocity (peak 10-year storm) 5.50 ft/sec Soil characteristics (enter "x" below) Sand/silt (easily erodible) Clay mix (erosion resistant) X Grass Type (enter "x" below) Bermuda Tall fescue X Bahiagrass Kentucky bluegrass Grass-legume mixture Swale type: Fill out one of the options below: Option 1: Curb Outlet Swale: N (Y or N) Maximum velocity Side slopes :1 Swale length ft Option 2: Conveyance Swale, Seeking Pollutant Credit: Y (Y or N) Maximum velocity for 10-yr storm 5.50 ft/sec Side slopes 5.00 :1 Swale length 500.00 ft Insufficient maximum velocity. OK OK Form SW401-Grassed Swale-Rev.3 Parts I and II. Project Design Summary, Page 1 of 2 Permit Number: (to be provided by DWQ) Swale Characteristics Swale Shape: Enter an 'Y' in the appropriate cell below: Trapezoidal X Parabolic V-shaped Width of the bottom of the Swale 6.00 ft Width of the top of the swale 26.00 ft Additional Information Is the swale sized for all runoff from ultimate build-out? Y (Y or N) OK Is the BMP located in a proposed drainage easement with a N (Y or N) Insufficient ROW location. recorded access easement to a public Right of Way (ROW)? What is the distance from the bottom of the swale to the SHWT? #VALUE! ft #VALUE! What is the ground level elevation? 1,206.00 fmsl What is the elevation of the bottom of the swale? 1,204.00 fmsl What is the SHWT elevation? NA fmsl What is the longitudinal slope of the swale? 1.50 % OK What is the depth of freeboard? 1.00 ft OK Form SW401-Grassed Swale-Rev.3 Parts I and II. Project Design Summary, Page 2 of 2 r Permit No: (to be assigned by DWQ) III. REQUIRED ITEMS CHECKLIST Please indicate the page or plan sheet numbers where the supporting documentation can be found. An incomplete submittal package will result in a request for additional information. This will delay final review and approval of the project. Initial in the space provided to indicate the following design requirements have been met. If the applicant has designated an agent, the agent may initial below. If a requirement has not been met, attach justification. Initials Page/ Plan Sheet No. '.&6 DP-2 /y a DP-2 Plans (1" = 50' or larger) of the entire site showing: - Design at ultimate build-out, - Off-site drainage (if applicable), Delineated drainage basins (include Rational C coefficient per basin), - Swale dimensions (width, length, depth), - Maintenance access, - Proposed drainage easement and public right of way (ROW), - Grass species, and - Boundaries of drainage easement. 2. Plan details (1" = 50' or larger) for the grassed swale showing: - Swale dimensions (width, length, depth), - Maintenance access, - Proposed drainage easement and public right of way (ROW), - Design at ultimate build-out, - Grass species, - Off-site drainage (if applicable),and - Boundaries of drainage easement. 3. Section view of the grassed swale (1" = 20' or larger) showing: - Side slopes, - Longitudinal slope, - Freeboard - Swale dimensions, and - SHWT level(s) T'$ _rW 'A' 4. Supporting calculations (including maximum velocity calculations for applicable storms) s O n•r 01KI. (3Av?' Attached 5. A copy of the signed and notarized operation and maintenance (0&M) agreement. NA NA 6. A copy of the deed restrictions (if required). SW401-Grassed Swale-Rev.3 Part III, Page 1 of 1 Permit No. (to be provided by DWQ) o?OF WATF,9OG RIMA STORMWATER MANAGEMENT PERMIT APPLICATION FORM o 1 WDENR 401 CERTIFICATION APPLICATION FORM DRY EXTENDED DETENTION BASIN SUPPLEMENT This form must be filled out, printed and submitted. The Required Items Checklist (Part Ill) must be printed, filled out and submitted along with all the required information. 1. PROJECT INFORMATION Project name Mt. Airy Airport - Stormwater Management Plan Contact person Tim Kennerly, PE Phone number 336.662.4251 Date 9/19/2011 Drainage area number Taxiway 'A' Extension South Drainage Area II. DESIGN INFORMATION Site Characteristics Drainage area 450,846.00 ft2 Impervious area 153,767.00 ft2 % Impervious 0.34 Design rainfall depth 1.00 in Peak Flow Calculations 1-yr, 24-hr rainfall depth 2.89 in Rational C, pre-development 0.71 (unitless) Rational C, post-development 0.71 (unitless) Rainfall intensity: 1-yr, 24-hr storm 0.12 in/hr Pre-development 1-yr, 24-hr peak flow 0.88 ft3/sec Post-development 1-yr, 24-hr peak flow 0.88 ft3/sec Pre/Post 1-yr, 24-hr peak control 0.00 ft3/sec Storage Volume: Non-SA Waters Minimum required volume 13,450.00 ff3 Provided volume 21,509.54 ft3 OK Sediment storage volume provided 5,378.00 ff3 OK Storage Volume: SA Waters 1.5" runoff volume ff3 Pre-development 1-yr, 24-hr runoff volume ff3 Post-development 1-yr, 24-hr runoff volume ff3 Minimum required volume ff3 Provided volume ff3 Sediment storage volume provided ff3 Basin Design Parameters Drawdown time 3.24 days OK SHWT elevation fmsl Basin bottom elevation 1186.75 fmsl OK Storage elevation 1189.00 fmsl Basin side slopes 3.0 :1 OK Top elevation 1192.00 fmsl OK Freeboard provided 2.00 ft OK Form SW401-Dry Extended Detention Basin-Rev.3 Parts I. & It. Design Summary, Page 1 of 2 Permit Basin Bottom Dimensions Basin length 117.00 ft Basin width 46.00 ft Length to width ratio 2.54 :1 OK Additional Information Total runoff volume captured by basin 30.80 ac-in Forebay is required Forebay provided N (Y or N) Is basin in a recorded drainage easement? N (Y or N) Need to a recorded drainage easement Does basin capture all runoff at ultimate build-out? Y (Y or N) OK Is a sediment depth indicator included? Y (Y or N) OK Does the basin include a drain? Y (Y or N) OK (to be provided by DWQ) Form SW401-Dry Extended Detention Basin-Rev.3 Parts I. & II. Design Summary, Page 2 of 2 Permit No. (to be provided by DWQ) III. REQUIRED ITEMS CHECKLIST Please indicate the page or plan sheet numbers where the supporting documentation can be found. An incomplete submittal package will result in a request for additional information. This will delay final review and approval of the project. Initial in the space provided to indicate the following design requirements have been met. If the applicant has designated an agent, the agent may initial below. If a requirement has not been met, attach justification. Page/ Plan Initials Sheet No. DA-5 1. Plans (1" 50' or larger) of the entire site showing: Design at ultimate build-out, Off-site drainage (if applicable), Delineated drainage basins (include Rational C coefficient per basin), Basin dimensions, Pretreatment system, Maintenance access, Proposed drainage easement and public right of way (ROW), Overflow device, and Boundaries of drainage easement. G-6 2. Plan details (1" = 30' or larger) for the bioretention cell showing: Basin dimensions Pretreatment system, Maintenance access, Outlet structure, Overflow device, Flow distribution detail for basin inflow, and Vegetation specifications. ? 3. Section view of the basin (1" = 20' or larger) showing: .? /? ??p Z Side slopes, 3:1 or lower, Pretreatment and treatment areas, and Inlet and outlet structures. NA NA 6. A construction sequence that shows how the dry detention basin will be protected from sediment until the entire drainage area is stabilized. // ?,e%? ?? ?tW7. The supporting calculations. So'fFrr1 ??j, 4ntP. ,??? Attached 8. A copy of the signed and notarized operation and maintenance (0&M) agreement. NA NA 9. A copy of the deed restrictions (if required). NA NA 10. A soils report that is based upon an actual field investigation, soil borings, and infiltration tests. County soil maps are not an acceptable source of soils information. Form SW401-Dry Extended Detention Basin-Rev.3 Part III. Required Items Checklist, Page 1 of 1 o?oF wnrfROG ? r AV HCDENR STORMWATER MANAGEMENT PERMIT APPLICATION FORM 401 CERTIFICATION APPLICATION FORM LEVEL SPREADER - VEGETATED FILTER STRIP (LS-VFS) SUPPLEMENT This form must be completely filled out, printed, initialed, and submitted. I. PROJECT INFORMATION Project name Mt. Airy Airport - Stormwater Management Plan Contact name Tim Kennerly, PE Phone number 336.662.4251 Date September 19, 2011 Drainage area number Runway / Taxiway / Future Development Drainage Area II. DESIGN INFORMATION The purpose of the LS-VFS Pollutant removal: 40% TSS, 30% TN, 35% TP Stormwater enters LS-VFS from The drainage area Type of VFS Engineered filter strip (graded & sodded, slope < 8%) Explanation of any "Other" responses above If Stormwater Enters the LS-VFS from the Drainage Area Drainage area Impervious surface area Percent impervious Rational C coefficient Peak flow from the 1 in/hr storm Time of concentration Rainfall intensity, 1 0-yr storm Peak flow from the 10-yr storm Design storm Maximum amount of flow directed to the LS-VFS Is a flow bypass system going to be used? Explanation of any "Other" responses above If Stormwater Enters the LS-VFS from a BMP Type of BMP Peak discharge from the BMP during the design storm Peak discharge from the BMP during the 10-year storm Maximum capacity of a 100-foot long LS-VFS Peak flow directed to the LS-VFS Is a flow bypass system going to be used? Explanation of any "Other" responses above Vegetated Filter Strip consists of the Runway/ Taxiway Safety Area 2,810,491 ftz 322,344 fe 11.47 % 0.63 40.65 cfs 5.00 min 0.218 in/hr 8.86 cfs ear storm 8.86 cfs N (Y or N) Rainfall intensity is based on a 10YR - 24 HR Storm Event Do not complete this section of the form. cfs cis Do not complete this section of the form. 10 cfs cfs Do not complete this section of the form. (Y or N) Form SW401 - LS-VFS - 27Ju12011 - Rev.9 page 1 of 3 LS-VFS Design Forebay surface area Depth of forebay at stormwater entry point Depth of forebay at stormwater exit point Feet of level lip needed per cfs Computed minimum length of the level lip needed Length of level lip provided Width of VFS Elevation at downslope base of level lip Elevation at the end of the VFS that is farthest from the LS Slope (from level lip to the end of the VFS) Are any draws present in the VFS? Is there a collector swale at the end of the VFS? Bypass System Design (if applicable) Is a bypass system provided? Is there an engineered flow splitting device? Dimensions of the channel (see diagram below): M B W y (flow depth for 10-year storm) freeboard (during the 10-year storm) Peak velocity in the channel during the 10-yr storm Channel lining material Does the bypass discharge through a wetland? Does the channel enter the stream at an angle? Explanation of any "Other" responses above 0 sq ft 0 in 0 in 10 fvcfs 89 ft 100 ft 100 ft 1,246.00 fmsl 1,249.00 fmsl -3.00 % N (Y or N) Y (Y or N) N (Y or N) N (Y or N) ft ft ft ft ft ft/sec Pick one: (Y or N) (Y or N) No Bypass System is Provided. W Forebay is undersized. Too shallow. OK E Form SW401 - LS-VFS - 27Ju12011 - Rev.9 page 2 of 3 III. REQUIRED ITEMS CHECKLIST EDIT Please indicate the page or plan sheet numbers where the supporting documentation can be found. An incomplete submittal package will result in a request for additional information. This will delay final review and approval of the project. Initial in the space provided to indicate the following design requirements have been met. If the applicant has designated an agent, the agent may initial below. If a requirement has not been met, attach justification. Requried Item: Initial Page or plan sheet number and any notes: 1. Plans (1" - 50' or larger) of the entire site showing: ??k Plansheet DA-4 & DA-6 - Design at ultimate build-out, Off-site drainage (if applicable), Delineated drainage basins (include Rational C coefficient per basin), Forebay (if applicable), High flow bypass system, Maintenance access, Proposed drainage easement and public right of way (ROW), and Boundaries of drainage easement. ? " ' h t DA 6 Pl or larger) for the level spreader showing: ? 2. Plan details (1 = 30 - ans ee - Forebay (if applicable), High flow bypass system, One foot topo lines between the level lip and top of stream bank, Proposed drainage easement, and Design at ultimate build-out. 3. Section view of the level spreader (1"= 20' or larger) showing: - Underdrain system (if applicable), Level lip, Upslope channel, and Downslope filter fabric. 4. Plan details of the flow splitting device and supporting calculations (if applicable). ,? 5. A construction sequence that shows how the level spreader will be protected from Nom( sediment until the entire drainage area is stabilized. 6. If a non-engineered VFS is being used, then provide a photograph of the VFS showing n/ t that no draws are present. 7. The supporting calculations. N? /C Tab RW & TW EXT. BMP, Tab RW & TW & Future Development BMP 8. A copy of the signed and notarized operation and maintenance (0&M) agreement. L_?/ ITab 0&M Agreements in Calculation Maunal Form SW401 - LS-VFS - 27Ju12011 - Rev.9 page 3 of 3 Permit Number: (to be provided by DWQ) O?OF W ATF9OG ARA p Y NCDENR STORMWATER MANAGEMENT PERMIT APPLICATION FORM 401 CERTIFICATION APPLICATION FORM GRASSED SWALE SUPPLEMENT This form must be filled out, printed and submitted. The Required Items Checklist (Part III) must also be filled out, printed and submitted along with all of the required information. I. PROJECT INFORMATION Project name Mt. Airy Airport - Stormwater Management Plan Contact name Tim Kennerly, PE Phone number 336.662.4251 Date September 19, 2011 Drainage area number Runway / Taxiway / Future Development Drainage Area II. DESIGN INFORMATION Site Characteristics Drainage area 2,810,491.00 ft2 Impervious area 1,273,259.00 fe Percent impervious 45.3%% Design rainfall depth 1.00 inch Peak Flow Calculations 10-yr storm runoff depth 5.23 in 10-yr storm intensity 0.22 in/hr Post-development 10-yr storm peak flow 9.93 fe/sec Velocity Maximum non-erosive velocity (peak 10-year storm) 5.50 ft/sec Soil characteristics (enter "x" below) Sand/silt (easily erodible) Clay mix (erosion resistant) X Grass Type (enter "x" below) Bermuda Tall fescue X Bahiagrass Kentucky bluegrass Grass-legume mixture Swale type: Fill out one of the options below: Option 1: Curb Outlet Swale: Curb Outlet Swale: N (Y or N) Maximum velocity Side slopes :1 Swale length ft Option 2: Conveyance Swale, Seeking Pollutant Credit: Y (Y or N) Maximum velocity for 10-yr storm 5.50 ft/sec Insufficient maximum velocity. Side slopes 5.00 :1 OK Swale length 1,100.00 ft OK Form SW401-Grassed Swale-Rev.3 Parts I and II. Project Design Summary, Page 1 of 2 Swale Characteristics Swale Shape: Enter an Y in the appropriate cell below: Trapezoidal Parabolic V-shaped Width of the bottom of the swale Width of the top of the swale Additional Information Is the swale sized for all runoff from ultimate build-out? Is the BMP located in a proposed drainage easement with a recorded access easement to a public Right of Way (ROW)? What is the distance from the bottom of the swale to the SHWT? What is the ground level elevation? What is the elevation of the bottom of the swale? What is the SHWT elevation? What is the longitudinal slope of the swale? What is the depth of freeboard? Form SW401-Grassed Swale-Rev.3 Permit Number: (to be provided by DWQ) X 6.00 ft 26.00 ft Y (Y or N) OK N (Y or N) Insufficient ROW location. ifVHLVC! It 1,248.00 fmsl 1,245.00 fmsl NA fmsl 1.50% OK 1.00 ft OK #VALUE! Parts I and II. Project Design Summary, Page 2 of 2 Permit No: (to be assigned by DWQ) III. REQUIRED ITEMS CHECKLIST Please indicate the page or plan sheet numbers where the supporting documentation can be found. An incomplete submittal package will result in a request for additional information. This will delay final review and approval of the project. Initial in the space provided to indicate the following design requirements have been met. If the applicant has designated an agent, the agent may initial below. If a requirement has not been met, attach justification. Initials Page/ Plan Sheet No. DA-4 1. Plans (1" = 50' or larger) of the entire site showing: ?? - Design at ultimate build-out, - Off-site drainage (if applicable), - Delineated drainage basins (include Rational C coefficient per basin), - Swale dimensions (width, length, depth), - Maintenance access, - Proposed drainage easement and public right of way (ROW), - Grass species, and - Boundaries of drainage easement. DP-2 2. Plan details (1" = 50' or larger) for the grassed swale showing: - Swale dimensions (width, length, depth), - Maintenance access, - Proposed drainage easement and public right of way (ROW), - Design at ultimate build-out, - Grass species, - Off-site drainage (if applicable),and - Boundaries of drainage easement. " ' DP-2 3. Section view of the grassed swale (1 = 20 or larger) showing: - Side slopes, - Longitudinal slope, - Freeboard - Swale dimensions, and - SHWT level(s) Je 'TA/b PUJ S`-7%/ 4 S i l l i )cr. . upport ng ca cu at ons (including maximum velocity calculations for applicable storms) Hill, ATTACHED 5. A copy of the signed and notarized operation and maintenance (0&M) agreement. "&/( NA 6. A copy of the deed restrictions (if required). SW401-Grassed Swale-Rev.3 Part III, Page 1 of 1 Permit No. (to be provided by DWQ) A ? O?O? W ATF9OG " STORMWATER MANAGEMENT PERMIT APPLICATION FORM NCDENR 401 CERTIFICATION APPLICATION FORM DRY EXTENDED DETENTION BASIN SUPPLEMENT This form must be filled out, printed and submitted. The Required Items Checklist (Part 111) must be printed, filled out and submitted along with all the required information. I. PROJECT INFORMATION Project name Mt. Airy Airport - Stormwater Management Plan Contact person Tim Kennedy, PE Phone number 336.662.4251 Date 9/19/2011 Drainage area number Runway / Taxiway / Future Development Drainage Area II. DESIGN INFORMATION Site Characteristics Drainage area 2,810,491.00 ft2 Impervious area 1,273,259.00 ft2 % Impervious 0.45 Design rainfall depth 1.00 in Peak Flow Calculations 1-yr, 24-hr rainfall depth 2.89 in Rational C, pre-development 0.70 (unitless) Rational C, post-development 0.70 (unitless) Rainfall intensity: )-yr, 24-hr storm 0.12 in/hr Pre-development 1-yr, 24-hr peak flow 5.42 ft3/sec Post-development 1-yr, 24-hr peak flow 5.42 ft3/sec Pre/Post 1-yr, 24-hr peak control 0.00 ft3/sec Storage Volume: Non-SA Waters Minimum required volume 192,228.00 ft3 Provided volume 209,178.00 ft3 OK Sediment storage volume provided 52,295.00 ft3 OK Storage Volume: SA Waters 1.5" runoff volume ft3 Pre-development 1-yr, 24-hr runoff volume ft3 Post-development 1-yr, 24-hr runoff volume ft3 Minimum required volume ft3 Provided volume ft3 Sediment storage volume provided ft3 Basin Design Parameters Drawdown time 2.58 days OK SHWT elevation 1195.00 fmsl Basin bottom elevation 1200.50 fmsl OK Storage elevation 1206.50 fmsl Basin side slopes 3.0 :1 OK Top elevation 1209.00 fmsl OK Freeboard provided 2.50 ft OK Form SW401-Dry Extended Detention Basin-Rev.3 Parts I. & II. Design Summary, Page 1 of 2 Basin Bottom Dimensions Basin length Basin width Length to width ratio Additional Information Total runoff volume captured by basin Forebay provided Is basin in a recorded drainage easement? Does basin capture all runoff at ultimate build-out? Is a sediment depth indicator included? Does the basin include a drain? 251.00 ft 80.00 ft 3.13 :1 211.50 ac-in N (Y or N) N (Y or N) Y (Y or N) Y (Y or N) Y (Y or N) Permit No OK Forebay is required Need to a recorded drainage easement OK OK OK (to be provided by DWQ) Form SW401-Dry Extended Detention Basin-Rev.3 Parts I. & II. Design Summary, Page 2 of 2 Permit No (to be provided by DWQ) III. REQUIRED ITEMS CHECKLIST Please indicate the page or plan sheet numbers where the supporting documentation can be found. An incomplete submittal package will result in a request for additional information. This will delay final review and approval of the project. Initial in the space provided to indicate the following design requirements have been met. If the applicant has designated an agent, the agent may initial below. If a requirement has not been met, attach justification. Pagel Plan Initials Sheet No. DA-4 1. Plans (1" 50' or larger) of the entire site showing: Design at ultimate build-out, Off-site drainage (if applicable), Delineated drainage basins (include Rational C coefficient per basin), Basin dimensions, Pretreatment system, Maintenance access, Proposed drainage easement and public right of way (ROW), Overflow device, and Boundaries of drainage easement. G-5 2. Plan details (1" = 30' or larger) for the bioretention cell showing: Basin dimensions Pretreatment system, Maintenance access, Outlet structure, Overflow device, Flow distribution detail for basin inflow, and Vegetation specifications. 3. Section view of the basin (1" = 20' or larger) showing: •? d` p?y2 Side slopes, 3:1 or lower, Pretreatment and treatment areas, and Inlet and outlet structures. NA NA 6. A construction sequence that shows how the dry detention basin will be protected from sediment until the entire drainage area is stabilized. s?/?c l TA'5 7 The supporting calculations. RW f'9'ti?i?G?'. .7A,.b c) 8. A copy of the signed and notarized operation and maintenance (0&M) agreement. Ae,/RC&'*%aW7g NA NA 9. A copy of the deed restrictions (if required). NA NA 10. A soils report that is based upon an actual field investigation, soil borings, and infiltration tests. County soil maps are not an acceptable source of soils information. Form SW401-Dry Extended Detention Basin-Rev.3 Part III. Required Items Checklist, Page 1 of 1