The URL can be used to link to this page

Home My WebLink About20080610 Ver 1_Stormwater Info_20080602www.st*wart-ong.com C S T E WA R T June 2, 2008 Annette Lucas, PE NC Division of Water Quality 401 Oversight / Express Permitting Unit 2321 Crabtree Boulevard, Suite 250 Raleigh, NC 27604 Q[R@[RBW?R JUN 2 2008 DENR - MATER QUAD I I WETLANDS AND STORMYVATER BRANCH Re: Swift Creek Commons Buffer Encroachment DWQ Project number 08-0610 Ms. Lucas, Thank you for your comments and review of the Swift Creek Project. I feel we have a good system now and have included your comments by email along with responses to ease your review of the documents attached. I've included 5 copies of the plan changes, revised level spreader detail, and revised level spreader calc sheets. I'm hopeful that we can have a conditional 401 issued this week. 1. Level spreader A appears is placed only 35 feet away from the receiving stream. Please relocate the level such that it is a minimum of 50 feet from the receiving stream. In addition, please provide an updated Level Spreader Supplement Form. I've relocated the level spreader outside the buffer so that there is a min. of 50' to the receiving channel. I've also included an updated level spreader supplemental form. 2. At level spreader B, the slope from the proposed level spreader(s) lip to the top of bank of the stream exceeds the allowable slope for level spreaders (6% for wooded vegetation and 8% for thick ground coverand grass). Please relocate the level spreader to a location where the filter strip slope is appropriate. In addition, please provide an updated Level Spreader Supplement Form. I've relocated this level spreader to below the fill slope to an area with natural slopes of 6% mixed wooded vegetation and thick ground cover. 3. Please provide documentation of the Town of Cary's approval of the stormwater management plan (SMP) for this project by providing EITHER: * A valid approval letter and one copy of the approved SMP (including plans and calculations), OR * One set of stormwater plan details and calculations stamped as "Approved" by the Town of Cary. Once I get the conditional 4011 can obtain Cary SMP approval. 4. You will want to make sure that the level spreader at Pond A is only receiving the design flow and that larger flows are routed to another location (this is also an important consideration for Pond B as well). Please take a look at my sketch and revised detail of the level spreader. We have diverted the low flow's into the level spreader through small pipes (2" for pond A, 3/4" for pond B) ENGINEERING. INNOVATION. SOLUTIONS.'"" 421 FAYETTEVILLE STREET RALEIGH, NC T 919.380.8750 SUITE 400 27601 F 919.380.8752 C S T E WA R T designed to take only the 1" drawdown from the pond into the level spreader. The remaining storms will fill up the diverter box and spill out the front and into the channels. I think this is pretty close to the way the BMP manual shows it in Figure B-1 and how we have done it on past projects. Thank you for your help on this and please email or call if you think there is anything I can do to expidite your review and the actual processing of the conditional 401. Sincerely, Ryan A. Hambleton, PE Project Engineer Rhambleton@stewart-eng.com Enclosures 2 of 2 a f ac,--4 PROJ PAGE OF I S REFERENCE PROJECT NO. t?, Crc l;? jaa? :? I C -?T CLIENT DESIGNER DATE STEWART I I I f???? CHECKER DATE ENGINEERING. INNOVATION. SOLUTIONS.'" 421 AV[TTEVILI I '11 RALOGH, NC T oi' - www.stewart-eng.com SUITf_ ?!)C) 21601 c ?W) ?y ?O? W ATFgO ? O G h r NCDENR STORMWATER MANAGEMENT PERMIT APPLICATION FORM 401 CERTIFICATION APPLICATION FORM LEVEL SPREADER, FILTER STRIP AND RESTORED RIPARIAN BUFFER SUPPLEMENT This form must be completely filled out, printed and submitted. DO NOT FORGET TO ATTACH THE REQUIRED ITEMS CHECKLIST AND ALL REQUIRED ITEMS (NEXT WORKSHEET)I L PROJECT INFORMATION Project name Swift 'C reek Commons 4artmenls (Greenway trail) Contact name Ryan Hambleton Phone number 919-866-4819 Date May 29, 2008 Drainage area number Pond IL DESIGN, INFORMATION For Level Spreaders Receiving Flow From a BMP Type of BMP Wet Pond Drawdown flow from the BMP 0.11 cfs For Level Spreaders Receiving Flow from the Drainage Area Do not complete this section of the worksheet. Drainage area fe Do not complete this section of the worksheet. Impervious surface area fe Do not complete this section of the worksheet. Percent impervious % Do not complete this section of the worksheet. Rational C coefficient Do not complete this section of the worksheet. Peak flow from the 1 in/hr storm cfs Do not complete this section of the worksheet. Time of concentration min Rainfall intensity, 10-yr storm in/hr Do not complete this section of the worksheet. Peak flow from the 10-yr storm cfs Do not complete this section of the worksheet. Where Does the Level Spreader Discharge? To a grassed bioretention cell? N (Y or N) To a mulched bioretention cell? N (Y or N) To a wetland? N (Y or N) To a filter strip or riparian buffer? Y (Y or N) Please complete filter strip characterization below. Other (specify) Filter Strip or Riparian Buffer Characterization (if applicable) Width of grass ft Width of dense ground cover 20.00 It Width of wooded vegetation 30.00 ft Total width 50.00 ft Elevation at downslope base of level lip 427.00 fmsl Elevation at top of bank of the receiving water 424.00 fmsl Slope (from level lip to to top of bank) 6.00 % OK Are any draws present? N (Y or N) OK Level Spreader Design Forebay surface area sq ft No forebay is needed. Feet level lip needed per cfs 44 fUcfs 1 Q?/72 p R 6 `51 Answer "Y" to one of the following: _1 . L 7r+ Length based on the 1 in/hr storm? Y (Y or N) Length based on the 10-yr storm? N (Y or N) JUN 2 2008 Length based on the BMP discharge rate? Y (Y or N) Design flow 0.11 cfs DENR-WATER QUAIJTY WETLANDS AND STORMWATER BRANCH Is a bypass device provided? Y (Y or N) OK Form SW401-Level Spreader, Filter Strip, Restored Riparian Buffer-Rev.5 Parts I. and Il. Design Summary, page 1 of 2 x • • Length of the level lip 13.00 ft Are level spreaders in series? N (Y or N) Bypass Channel Design (if applicable) Does the bypass discharge through a wetland? N (Y or N) Does the channel enter the stream at an angle? Y (Y or N) Dimensions of the channel (see diagram below): M ft B It W ft y ft Peak velocity in the channel during the 10-yr storm cfs Channel lining material #VALUE! • • i4 W ?? , 1 ------------ Y - - a 1 M M B Form SW401-Level Spreader, Filter Strip, Restored Riparian Buffer-Rev.5 Parts I. and II. Design Summary, page 2 of 2 o?o? WArF?oy ? r NCDENR a STORMWATER MANAGEMENT PERMIT APPLICATION FORM 401 CERTIFICATION APPLICATION FORM LEVEL SPREADER, FILTER STRIP AND RESTORED RIPARIAN BUFFER SUPPLEMENT This form must be completely filled out, printed and submitted. DO NOT FORGET TO ATTACH THE REQUIRED ITEMS CHECKLIST AND ALL REQUIRED ITEMS (NEXT WORKSHEET)! 1. PROJECT INFORMATION Project name Swift Creek Commons Apartments (Greenway trail) Contact name Ryan Hambleton Phone number 919-866-4819 Date May 29, 2008 Drainage area number Pond A IL DESIGN INFORMATION For Level Spreaders Receiving Flow From a BMP Type of BMP Wet Pond Drawdown flow from the BMP 0.60 cfs For Level Spreaders Receiving Flow from the Drainage Area Do not complete this section of the worksheet. Drainage area fe Do not complete this section of the worksheet. Impervious surface area ft2 Do not complete this section of the worksheet. Percent impervious % Do not complete this section of the worksheet. Rational C coefficient Do not complete this section of the worksheet. Peak flow from the 1 in/hr storm cfs Do not complete this section of the worksheet. Time of concentration min Rainfall intensity, 10-yr storm in/hr Do not complete this section of the worksheet. Peak flow from the 10-yr storm cfs Do not complete this section of the worksheet. Where Does the Level Spreader Discharge? To a grassed bioretention cell? N (Y or N) To a mulched bioretention cell? N (Y or N) To a wetland? N (Y or N) To a filter strip or riparian buffer? Y (Y or N) Please complete filter strip characterization below. Other (specify) Filter Strip or Riparian Buffer Characterization (if applicable) Width of grass ft Width of dense ground cover 5.00 ft Width of wooded vegetation 45.00 ft Total width 50.00 ft Elevation at downslope base of level lip 432.00 fmsl Elevation at top of bank of the receiving water 430.50 fmsl Slope (from level lip to to top of bank) 3.00 % OK Are any draws present? N (Y or N) OK Level Spreader Design Forebay surface area sq ft No forebay is needed. Feet of level lip needed per cfs 60 ft/cfs Answer "Y" to one of the following: Length based on the 1 in/hr storm? Y (Y or N) Length based on the 10-yr storm? N (Y or N) Length based on the BMP discharge rate? Y (Y or N) Design flow 0.59 cfs Is a bypass device provided? Y (Y or N) OK Form SW401-Level Spreader, Filter Strip, Restored Riparian Buffer- Rev. 5 Parts I. and II. Design Summary, page 1 of 2 Length of the level lip 36.00 ft Are level spreaders in series? N (Y or N) Bypass Channel Design (if applicable) Does the bypass discharge through a wetland? N (Y or N) Does the channel enter the stream at an angle? Y (Y or N) Dimensions of the channel (see diagram below): M ft B ft W ft y ft Peak velocity in the channel during the 10-yr storm cfs Channel lining material #VALUE! • • a w n 1 +------------ M i B i M Form SW401-Level Spreader, Filter Strip, Restored Riparian Buffer-Rev.5 Parts I. and II. Design Summary, page 2 of 2