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Home My WebLink About20061042 Ver 3_More Info Received_20120112WITHERS &' RAVENEL C 832 January 11 2012 Ms Annette Lucas NCDENR Division of Water Quality 512 N Salisbury Street Raleigh NC 27626 Re Ashton Hall Subdivision — Phases 3 & 4 Durham NC DWQ Project # o6 1042 v 3 W &R Project # 02090500 0 Dear Ms Lucas ENGINEERS 1 PLANNERS I SURVEYORS D JAN 12 2012 DENR WATER QUALITY nANDS AND STORMWATER BRANCH Please find attached three (3) copies of the revised Level Spreader Vegetated Filter Strip Supplement forms forthe above referenced project This information is provided in responseto your JanuaN3 2012 letter requesting additional information We have revised the supplement forms per the direction you provided during our phone conversation with you this morning The comments listed in your letter are listed below followed by a response to each Additional information Requested s ForLS VFS #7 the Supplement Form states that the peak flow durmgthe design storm is40 55 cfs while the peak flow from the io year storm is 29 45 cfs There appears to be an error Please provide the correct value for the peak flow from the design storm so that the DWQ can review yourproposed level spreader Response Per our conversation the values listed forthe design storm have been revised so as to reflect the actual discharge directed to the level spreader during the design storm ratherthan the previously listed total peak discharges from the BMP itself Note that the design storm for this level spreader is the water quality event Water is diverted to the level spreader through a small orifice therefore the peak flow for larger storms including the 10 year storm 1s o 93 cfs Storm events above the water quality storm will result in bypass flows not directed to the level spreader z For BMP #8 please provide an explanation as to why a diffuse flow device has not been provided at the outlet Response Per our conversation the requested explanation was provided with our previous submittal dated October 20 2011 following the September 23 2o11 Request for Additional Information (The runoff from this outlet enters a natural wetland outside of the NRB) 3 ForLS VFS #io the SupplementForm states that the peak flow dunngthe designstonn is5815 cfs while the peak flow from the io year storm is 2515 cfs There appears to be an error Please provide the correct value for the peak flow from the design storm so that the DWQ can review your proposed level spreader Response Per our conversation the values listed for the design storm have been revised so as to reflect the actual discharge directed to the level spreader during the design storm ratherthan iii MacKenan Drive 1 Cary NC 27511 1 tel 919 469 3340 1 fax 919 238 2099 I www withersravenel com 1410 Commonwealth Drive I Suite 1o1 1 Wilmington NC 284031 tel 910 256 92771 fax 910 256 2584 06 D Gallimore Dairy Road 1 Greensboro NC 27409 1 tel 336 993 5504 the previously listed total peak discharges from the BMP itself Note that the design storm for this level spreader is the water quality event Water is diverted to the level spreaderthrough a small orifice therefore the peak flow for larger storms Including the 10 year storm is o 78 cfs Storm events above the water quality storm will result in bypass flows not directed to the level spreader 4 ForLS VFS #ii the Supplement Form states that the peak flow dunng the design storm is 64 58 cfs while the peak flow from the io year storm is 42 27 cfs There appears to bean error Please provide the correct value for the peak flow from the design storm so that the DWQ can reviewyourproposed level spreader Response Per our conversation the values listed for the design storm have been revised so as to reflect the actual discharge directed to the level spreader during the design storm ratherthan the previously listed total peak discharges from the BMP Itself Note that the design storm for this level spreader Is the waterquahty event Water is diverted to the level spreaderthrough a small orifice therefore the peak flow for larger storms Including the io year storm Is o 95 cfs Storm events above the water quality storm will result in bypass flows not directed to the level spreader If you need any additional Information or have any questions please give me a call at 919 469 3340 Sincerely WITHERS & RAV INC lfiz,,�Al Bradley D Ha PE cc Patrick Allen — Beazer Homes Corp file iii MacKenan Drive I Cary NC 275211 tel 919 469 3340 1 fax 929 238 2099 1 www withersravenel com 1410 Commonwealth Drive I Suite 101 1 Wilmington NC 284031 tel 910 256 92771 fax 910 256 2584 06 D Gallimore Dairy Road I Greensboro NC 27409 1 tel 336 993 5504 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 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 Wet detention pond 093 cfs 093 ATA 10 cfs ICDENR JAN 1 2 201 2 < STORMWATER MANAGEMENT PERMIT A TAPORMQUALITY 401 CERTIFICATION APPLICATION F WATERBRANCH 30 LEVEL SPREADER VEGETATED FILTER STRIP (LS -VFS) SUPPLEMENT fmsl This form must be completely filled ou4 pnnted mibaled and submitted fmsl I PROJECT INFORMATION Project name Ashton Hall Phases 3 & 4 Contact name Brad Hart PE Withers & Ravenel Inc Phone number (919) 4693340 Date 0111112 Drainage area number BMPft7 II DESIGN INFORMATION The purpose of the LS VFS Buffer Rule Diffuse Flow Stormwater enters LS VFS from A BMP Type of VFS Engineered filter strip (graded & sodded slope < 8 /6) Explanation of any Other" responses above If Stormwater Enters the LS VFS from the Drainage Area Drainage area fe Do not complete this section of the form Impervious surface area fe Do not complete this section of the form Percent impervious / Do not complete this section of the form Rational C coefficient Do not complete this section of the form Peak flow from the 1 in/hr storm cfs Do not complete this section of the form Time of concentration min Do not complete this section of the form Rainfall intensity 10 yr storm in/hr Do not complete this section of the form Peak flow from the 10 yr storm cfs Do not complete this section of the forth Design storm Maximum amount of flow directed to the LS VFS cfs Do not complete this section of the forth Is a flow bypass system going to be used? (Y or N) Do not complete this section of the forth 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 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 Wet detention pond 093 cfs 093 cfs 10 cfs 093 cfs Y (Y or N) sq ft Ten feet is the minimum level spreader length Form SW401 LS-VFS 27Ju12011 Rev 9 page 1 of 3 in in 10 fUcfs 9 ft 10 ft 30 ft 34600 fmsl 34470 fmsl Ten feet is the minimum level spreader length Form SW401 LS-VFS 27Ju12011 Rev 9 page 1 of 3 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 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 433 / N (Y or N) OK N (Y or N) Y (Y or N) Y (Y or N) Please provide plan details of flow splitter & supporting calcs 200 It 1000 It 1600 ft 103 ft 047 ft Provide at least one foot of freeboard 237 ftisec Pick one N (Y or N) N/A (Y or N) Plunge Basin provided below bypass outlet & upstream of riparian buffer tt 1 B 1 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 Requned ftem 1 Plans (1 50 or larger) of the entire site showing Design at ultimate build -out, Off site drainage (d applicable) Delineated drainage basins (include Rational C coefficient per basin) Forebay (d applicable) High flow bypass system Maintenance access Proposed drainage easement and public right of way (ROW) and Boundaries of drainage easement 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 tip and top of stream bank Proposed drainage easement, and Design at ultimate build -out Page or plan sheet number and any notes Sheets 41 4 2 81 8 2 Sheets 81 8 2 10 2 Form SW401 LS VFS 27Ju12011 Rev 9 page 2 of 3 3 Section view of the level spreader (1 20 or larger) showing Underdram system (d 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 7 The supporting calculations 8 A copy of the signed and notarized operation and maintenance (08M) agreement s81 102 81 81 Form SW401 LS-VFS 27M2011 Rev 9 page 3 of 3 T A A OFWATF9 C� h 078 cfs IDENR cis STORMWATER MANAGEMENT PERMIT APPLICATION FORM cis 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 fmsl Project name Ashton Hall Phases 3 & 4 Contact name Brad Hart, PE Withers & Ravenel Inc Phone number (919) 469 3340 Date January 11 2012 Drainage area number BMP#10 II DESIGN INFORMATION The purpose of the LS VFS Buffer Rule Diffuse Flow Stormwater enters LS VFS from A BMP Type of VFS Engineered filter strip (graded & sodded slope < 80/) Explanation of any Other" responses above If Stormwater Enters the LS VFS from the Drainage Area Drainage area IF Do not complete this section of the form Impervious surface area fe Do not complete this section of the form Percent impervious / Do not complete this section of the form Rational C coefficient Do not complete this section of the form Peak flow from the 1 in /hr storm cfs Do not complete this section of the form Time of concentration min Do not complete this section of the form Rainfall intensity 10 yr storm in/hr Do not complete this section of the form Peak flow from the 10 yr storm cfs Do not complete this section of the form Design storm Maximum amount of flow directed to the LS VFS cfs Do not complete this section of the form Is a flow bypass system going to be used? (Y or N) Do not complete this section of the form 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 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 Wet detention pond 078 cfs 078 cfs 10 cis 078 cis Y (Y or N) sq ft Ten feet is the minimum level spreader length Form SW401 LS-VFS 27Ju12011 Rev 9 page 1 of 3 in in 10 ft/cfs 8 ft 10 ft 30 ft 35920 fmsl 35850 fmsl Ten feet is the minimum level spreader length Form SW401 LS-VFS 27Ju12011 Rev 9 page 1 of 3 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 W y (flow depth for 10 -year storm) freeboard (during the 10 year storm) Peak velocity in the channel during the 10-yr stone 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 233 / N (Y or N) OK N (Y or N) Y (Y or N) Y (Y or N) Please provide plan details of flow spldter & supporting calcs 200 It 1000 ft 1600 ft 098 It 052 It Provide at least one foot of freeboard 214 ft/sec Pick one N (Y or N) N/A (Y or N) Plunge Basin provided below bypass outlet & upstream of riparian buffer R .4 L B Ill REQUIRED ITEMS CHECKLIST EDIT Please Indicate the page or plan sheet numbers where the supporting documentation can be found An incomplete submdtal package will result in a request for adddional informabon 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 Requned 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 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 or plan sheet number and any notes 142 85 86 85 86 102 Form SW401 LS-VFS 27Ju12011 Rev 9 page 2 of 3 3 Section view of the level spreader (1 20 or larger) showing Underdram system (d applicable) Level lip Upslope channel and Downslope filter fabric 4 Plan details of the flow splitting device and supporting calculations (d 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 7 The supporting calculations 8 A copy of the signed and notanzed operation and maintenance (08M) agreement. s86 102 85 85 Form SW401 LS VFS 27M2011 Rev 9 page 3 of 3 If Stormwater Enters the LS VFS from a BMP Type of BMP Wet detention pond Peak discharge from the BMP during the design storm 095 cfs Peak discharge from the BMP dunng the 10 year storm 095 cis Maximum capacity of a 100 foot long LS VFS 10 cfs Peak flow directed to the LS VFS 095 cfs Is a flow bypass system going to be used? Y (Y or N) Explanation of any Other' responses above LS VFS Design Forebay surface area �F WAtF9 h sq ft r W.DENR in STORMWATER MANAGEMENT PERMIT APPLICATION FORM 401 CERTIFICATION APPLICATION FORM LEVEL SPREADER VEGETATED FILTER STRIP (LS -VFS) SUPPLEMENT This form must be completely filled ot4 punted ►n►t►aled and submitted I PROJECT INFORMATION 10 Project name Ashton Hall Phases 3 & 4 Contact name Brad Hart, PE Withers & Ravenel Inc Phone number (919) 469 3340 Date January 11 2012 Drainage area number BMPff11 II DESIGN INFORMATION 37900 The purpose of the LS VFS Buffer Rule Diffuse Flow Stormwater enters LS VFS from A BMP Type of VFS Engineered filter strip (graded & sodded slope < 8 h) Explanation of any Other" responses above If Stormwater Enters the LS VFS from the Drainage Area Drainage area fe Do not complete this section of the form Impervious surface area fe Do not complete this section of the form Percent impervious / Do not complete this section of the form Rational C coefficient Do not complete this section of the form Peak flow from the 1 in/hr storm cfs Do not complete this section of the form Time of concentration min Do not complete this section of the form Rainfall intensely 10 yr storm in/hr Do not complete this section of the form Peak flow from the 10 yr storm cis Do not complete this section of the form Design storm Maximum amount of flow directed to the LS VFS cfs Do not complete this section of the form Is a flow bypass system going to be used? (Y or N) Do not complete this section of the form Explanation of any Other' responses above If Stormwater Enters the LS VFS from a BMP Type of BMP Wet detention pond Peak discharge from the BMP during the design storm 095 cfs Peak discharge from the BMP dunng the 10 year storm 095 cis Maximum capacity of a 100 foot long LS VFS 10 cfs Peak flow directed to the LS VFS 095 cfs Is a flow bypass system going to be used? Y (Y or N) Explanation of any Other' responses above LS VFS Design Forebay surface area sq ft Depth of forebay at stormwater entry point in Depth of forebay at stormwater exit point in Feet of level lip needed per cis 10 ft/cfs Computed minimum length of the level lip needed 10 ft Ten feet is the minimum level spreader length Length of level lip provided 10 ft Width of VFS 30 ft Elevation at downslope base of level lip 37940 fmsl Elevation at the end of the VFS that is farthest from the LS 37900 fmsl Form SW401 LS-VFS 27Ju12011 Rev 9 page 1 of 3 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 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 M 133 k N (Y or N) OK N (Y or N) Y (Y or N) Y (Y or N) Please provide plan details of flow spldter 8 supporting caks 200 It 1000 ft 1600 ft 117 ft 033 It Provide at least one foot of freeboard 294 ftlsec Pick one N (Y or N) N/A (Y or N) Plunge Basin provided below bypass outlet & upstream of riparian buffer a B • 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 Requned 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 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 ,Page or plan sheet number and any notes I Sheets 41 4 2 8 7 8 8 Sheets 8 7 8 8 10 2 Form SW401 LS VFS 27Ju12011 Rev 9 page 2 of 3 3 Section view of the level spreader (1 20 or larger) showing Underdram system (if applicable) Level lip Upslope channel and Downslope fitter 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 7 The supporting calculations 8 A copy of the signed and notarized operation and maintenance (08M) agreement 88 102 37 37 Form SW401 LS VFS 27M2011 Rev 9 page 3 of 3