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Home My WebLink AboutSW8051243_COMPLIANCE_20061025STORMWATER DIVISION CODING SHEET POST -CONSTRUCTION PERMITS PERMIT NO. SW DOC TYPE ❑ CURRENT PERMIT ❑ APPROVED PLANS ❑ HISTORICAL FILE COMPLIANCE EVALUATION INSPECTION DOC DATE YYYYMMDD SAND FILTER DESIGN FILENAME: S:IWQSISTORMWATERISPREADSHEETSISFILTER1051243.WK1 DATE: 25-Oct-06 PROJECT# SWB 051243 PROJECT NAME: Walgreens Swansboro DRAINAGE BASIN: White Oak REVIEWER: L. Lewis RECEIVING STREAM: *White Oak River CLASS: SA Index No.: WOK01 20-18 If ORW, is site within the 575' AEC? 'includes the ICWW SITE AREA: 1.74 acres DRAINAGE AREA: ;62920 SF IMPERVIOUS AREA CALCULATION BUILDINGS 14490 SQUARE FEET PARKING/WALKS 47850 SQUARE FEET CONCRETE 580 SQUARE FEET OTHER SQUARE FEET TOTAL ifi 62920 SQUARE FEET %IMPERVIOUS, 1= RV= .05+.009 (I) BOTTOM OF FILTER 2642 FEET MSL TOP OF SAND 29i42 FEET MSL OVERFLOW WEIR .... 29'92 FEET MSL SURFACE AREA Sediment Chamber Sand Chamber REQUIRED SURFACE AREA FILTER WIDTH PROVIDED FILTER LENGTH PROVIDED PROVIDED SURFACE AREA 520 00 SF 520005F FEET 4 ii 4' FEET FEET I' I!I 130 FEET SF IIIII� �,ii 520 SF 4' "';"'!';' " 130. 520. VOLUME ORIFICE DESIGN PROPOSED ORIFICE DIAMETER AVERAGE HEAD NUMBER OF ORIFICES FLOWRATE FOR 24 HOURS FLOWRATE PROVIDED TIME TO DRAWDOWN ;',,, 6 INCHES FEET EACH CFS CFS HRS Al pi,'i{hEilhli'f;' ..:..., 1 4i!I ;''"" hI ' 0017 3 Oa! h',i'". ....0036111„ 3 3'I 0;3'' COMMENTS Volume, surface area and drawdown are (not) within Design Requirements, Surface Area is deficient. Calculations: Filter Basin Sizing: 130' x 4' x 3' (each chamber) Drainage Area: 62,920 SF = 1.44 AC Surface Area calculation: 1.44 AC * 360 SFIAC = 518 SF required 520 SF provided Volume Calculation: 1.44 AC * 540 CF/AC = 778 CF required 1,560 CF provided Drawdown Calculation: Assumption: 0.04 gal/min/ft2 .04 gal/min/ft2 *520 ft2 = 20.8 gal/min * 60 min * 24 hrs = 29;952`gal°iri°a'24 hour I eriod Sand chamber volume = 520 sf * 3 ft = 1,560 CF = 11,670 gal Drawdown time = 11,670/29,952 = .39 24 hrs * .39 = 9.36 hrs. RECEIVED SEP 2 0 2006 DWQ �Roa # swJost Z43 GREENHORNS & O'MARA CONSULTING ENGINEERS June 9, 2006 Ms. Linda Lewis, Environmental Engineer North Carolina Department of Environment and Natural Resources 127 Cardinal Dr Wilmington, NC 28405-3845 RE: SW8 051243 Walgreens- Old Hammock Road Swansboro, North Carolina Dear Linda: 9zfoa�(e OVERNIGHT Please see attached the storm water permit application and review fee check for S 420 for plan amendment approval to the existing developed site. Following up your letter dated June 2, 2006 we have designed sand filters for the site as requested to the extent practical for our site conditions. Please find the enclosed documents: l . Three (3) copies of revised drawings 2. Three (3) copies of sealed calculations 3. Three (3) copies of the signed Operation and Maintenance Plan. If you have any questions please feel free to contact me at (919) 532-2312 or dpibhsog-_and-o.com. Sincerely yours, 7Dona E O'MARA, INC. ibbs, Jr, PE Senior Project Manager JUN 12 M6 5565 Cenlerview Drive Suite 107 . Raleigh, NC 27606 Phone 919 851 1919 ■ fax 919 851 8393 www.G-and-O.com GREENHORN & O'MARA CONSULTING ENGINEERS This letter is being written to explain the reason for not meeting the surface area .requirement. G& O has made every attempt to utilize sand filters to the maximum practical extent. Due to site characteristics, there is only one practical area where a sand filter will function properly. All other areas place the outlet of the sand filter below the invert elevations of the existing drainage structures. While not meeting the minimum surface area requirement, we have exceeded the required sand volume by 12%. Given that the sand filter cross section is 4' x 3' in each chamber, we believe there is adequate area to properly settle out suspended solids in the sediment chamber. Please see the attached details and calculations. Please call Don Gibbs at (919)532-2312 if you have any questions. Calculations - Filter Basin Sizing: 60' x 4' x 3' (each chamber) Drainage Area: 46,024 SF = 1.06 AC Surface Area calculation: 1.06 AC * 360 SF/AC = 381 SF required 240 SF provided Volume Calculation: 1.06 AC * 540 CF/AC = 570 CF required 720 CF provided Drawdown Calculation: Assumption: 0.04 gal/min/ft2 04 gal/min/$2 *240 ft2 = 9.6 gal/min * 60 min * 24 hrs = Sand chamber volume = 240 sf * 3 ft = 720 CF = 5,386 gal Drawdown time = 5,386/13,824 = .38 24 hrs * .38 = 9.5 hrs. little N CAlpO 'a w � ; d l� E. G1�0�,�� 5565 Centerview Drive Suite 107 ■ Raleigh, INC 27606 Phone 919 851 1919 . Fax 919 851 B393 www.G-and-o.com Permit No. '�iA8U la's 3 State of North Carolina Department of Environment and Natural Resources Division of Water Quality STORMWATER MANAGEMENT PERMIT APPLICATION FORM SAND FILTER SUPPLEMENT This form may be photocopied for use as an original. DWQ Stormwater Management Plan Review: A complete stormwater management plan submittal includes a Sand Filter supplement for each proposed sand filter, design calculations, plans and specifications showing all sand filter details, and a fully executed operation and maintenance agreement. I. PROJECT INFORMATION (Please complete the following information): Project Name: W&(49{"' s)9 SMDgE 4 10436 Seat-31) FIU ,,, Contact Person: E)n p G t 1365 Phone Number:_( 13) 5 37-- 7-.31 Z For projects with multiple basins, specify which basin this worksheet applies to: Elevations Sediment Chamber Bottom:-Z-3 -� fmsl Top of Sand: NIA Weir: -ZA 5?3 fmsl Grate: 31.71.5_fmsl Areas Drainage Area: L16 0 74 ftz Bottom Area: Zip ft2 Design Storage Area: Abft2 Volumes Required Volume: _ft3 Volume Provided: '77 ft3 Total Volume Provided (both chambers) Other Parameters Sand Chamber Z12.33 fmsl Z9. 3-�k_fmsl 7 9.-$3--fmsl 3 ) . :1 5 fmsl (floor of the sand filter) (min. 18" above bottom) (weir into the sand chamber) (top of the grate) T 2AQ ft (min. 360 ft per acre of drainage area) Z.q-D ft2 (at the weir elevation of the sand filter) 5 7D ft3 (Min. 540 ft3 per acre of drainage area) '77'7�o W. (volume provided at the weir elevation) / !, 41) ft3 Drawdown Orifice Size: (o It _ (maximum 6" diameter) Orifice Invert Elevation: 2633 —fmsl (usually the floor of the sand filter) Time to drawdown: 9. 5hours (must be _<24 hours) a. REQUIRED ITEMS CHECKLIST The following checklist outlines design requirements per the latest version of the Stormwater Best Management Practices Manual (N.C. Department of Environment and Natural Resources) and Administrative Section 15A NCAC 2H.1008. Initial in the blank space provided in front of each item to indicate the following design requirements have been met and supporting documentation is attached. If the applicant has designated an agent in the Stormwater Management Permit Application Form, the agent may initial below. If a requirement has not been met, please attach written justification. Form SWU- Paae 1 of 3 Permit No. (Applicant or authorized agent- Please initial in the appropriate blanks or mark the blank N/A if it does not apply) SECAV°k� a. Each chamber (sediment and sand chamber) of the sand filter provides a minimum surface area of 360 square feet per acre of drainage area. JPS b Each chamber (sediment and sand chamber) of the sand filter provides a minimum volume of 540 cubic feet per acre of drainage area. WDS c. A minimum of 18" of sand is provided in the sand chamber d. Positive drainage to the sand filter has been provided either in conduit or surface drainage. . 1 e. The sediment chamber has no other outlet except to the sand chamber. O V 5 f. The outlet from the sediment chamber to the sand chamber results in a sheet flow condition. g. An outlet drain has been provided in the sand chamber which will completely empty the sand chamber within 24 hours. h. No single outlet pipe is sized greater than 6", to maintain a minimum of 12" of sand depth above the orifice. 3 IDS i. The drainage area to the sand filter does not exceed 50 acres. NlAj. Where stormwater quantity control is required by local ordinance, runoff that will flow over the sand filter has been considered in addition to the runoff flowing from the normal outlet of the sand filter. ,t6 k. Methods to capture trash have been provided at each inlet to prevent premature failure. III. SAND FILTER OPERATION AND MAINTENANCE AGREEMENT Regular maintenance is essential to the long-term performance and durability of the sand filter, as it is with all stormwater BMP's. The Sand Filter system is defined as the sediment chamber, the sand chamber, and the flow regulator or outlet device. This system (check one) ❑ does does not incorporate a vegetated filter. This system (check one) ❑ does does not incorporate non-integrated pretreatment. At a minimum, the following maintenance activities shall be performed: i. Depending on the types of activities occurring within the drainage area, most sand filters will show a decreased capacity for filtration after a few years. At least once a year, each filter must be inspected after a 1" design storm event to determine if the filter bed is passing the runoff within 24 hours. 2. if the filter is not passing the runoff completely within 24 hours, the first 2"-3" of discolored sand must be removed and replaced with new sand. The removed sand must be dewatered and disposed of properly. 3. At the same time that maintenance is performed on the sand chamber, the sediment chamber shall be pumped and cleaned. Remove accumulated sediment when it reaches a height of 6" in the sediment chamber. The removed sediment should be dewatered and disposed of properly. 4. At least once every quarter, check that the drawdown orifice is clear of obstruction. 5. Vegetation within an open sand filter must be mowed regularly to limit the height to 12". Vegetation within a closed sand filter must be removed. 6. Direct access to the sand and sediment chambers must be provided for maintenance and inspection. Form SwU- Page 2 of 3 1 Jun. 4. 2006 4:28PM KELLEYWSTIN PROPERTIES; LLC 06i n v tnno 10:'ab �:tm=-4HOF , & Q' MORA F ac 02/02 RIM-09--2006 FRI 02!46 PI, Myatt Reganoy Cobridge FAX C IE]r4.01HUG 1 02 $6/09/2006 15:21 919IMM93 k-'� � : i� C' @Ad4ii�, PAM 0; 52 F e03s%Wdv* and MUM by MY mdmaermtr: pm=dUmU5Ieddyxm lag= to row DWQ of ffw wlft t l4iall my am Prot to system of to lbr, ror-m" #ISI PtWift Rome: Fax IID3� Aro 4y poM JAO nai bo a hclda"atw ussa �r 4 Jun acrtW7 Ahe a wJgper me l e - bad r a , ertiy t d a ufthe xbAldo>s A= bten mma-d Ifi, j ruiaerrc; or apmjlcmcom bone ho b en amqud by kwlsaot tad WOW t > 1dm? C�91 o � Nc4,.yPUCIc,iSa:tir�3ro;utA ' COUNTY OF FOASYTtf hf; Canmlu!ar. E,yrura Fri*ur;r tfi, 4G1�,1 NahA Ood+�M'WnM�ytra`c�nti�yx�gei'�n� Form sQ'iPil- FF —Ep 3 of 1�1 Greenhorne & O'Mara, Inc. STORM SEWER COMPUTATION SHEET ZQ YEAR STORM -JUST FULL �^ JQ YEAR HYDRAULIC CHECK LOCATION: Swansboro. NC Calc'd by: 61.R JOB NO. 140290 Date: 12I12105 PROJECT: Walareens - SwansboraNC STREET: Manning's 'n' for hydraulc slope: min. acceptable cover (ft): Pipe thickness for cover calc. (in): FORM BASED ON U.S. DEPT OF COMMERCE, TP NO. 25. 1of1 0.0130 1.50 0.50 ��, • � ��®�®�®®gym � � mom � , �■ � � ��m�® ��®, • � � � � �■�■��m�■n�am�m�m��®mom® ®�®®�■��■■��a ��®®��®■ram®■� CARO�'�ya STOR Mcalcs.xls