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Home My WebLink AboutSW8050703_COMPLIANCE_20050718STORMWATER DIVISION CODING SHEET POST -CONSTRUCTION PERMITS PERMIT NO. SW DOC TYPE ❑ CURRENT PERMIT ❑ APPROVED PLANS ❑ HISTORICAL FILE COMPLIANCE EVALUATION INSPECTION DOC DATE YYYYMMDD DETENTION POND ANALYSIS FILE NAME: G:\DATA\WPDATA\WQS\POND1050703.WKI PROJECT#: SW8 050703 , REVIEWER: P.Bartlett PROJECT NAME: Receiving Stream" Drainage Basin: Site Area Drainage Area Dollar General - Boiling Spring Lakes 0, DATE: 18-Jul-05 1( Allen Creek Class: B: Sw Cape Fear Index No. 18-85-1-(1) 0 f D� IMPERVIOUS AREAS buildings parking/asphalt sidewalks TOTAL 2.07 acres square feet Area = 2.07 acres SURFACE AREA CALCULATION % IMPERVIOUS 50.34% Des. Depth 6 TSS: 90 Rational C 13950.00 square feet 0.95 29833.00 square feet 0.95 1608.00 square feet 0.95 square feet square feet square feet square feet Rational Cc= 0.58 SA/DA Ratio 2.72% Req. SA 2456 sf Prov. SA ii6971 sf VOLUME CALCULATION * place a "'I" in the box if Rational is used Rational ?* Des. Storm inches Rv= 0.50 Bottom 38 msl Perm. Pool msl Design Pool 46 msl Design SA 10632 sf Req. Volume cf cf Prov. Volume ORIFICE CALCULATION Avg. Head = Flow Q2, cfs Flow Q5, cfs No. of Orifices Diameter, inches Drawdown = ze-TOMMAVA Perm, Pool Volume= 27375 Req. Forebay Volurne= 5475 Provided Volume= 5600-00 Percent= SA @ = 7697 10632 11933.00 Elevation=: 44 46 47.00 Q2 Area = Q5 Area = Orifice Area Q= COMMENTS Surface Area , Volume and Orifice are within Design Guideline in 0.66 sq. in. 0.26 sq, in. 0.44 sq. in. 0.015 cfs x in f 7/13/2005 JWH Dollar General Boiling Springs Lake, NC 05032 Total Drainage Area s . ft. acres 90,169 2.07 Impervious Area Land Use s . ft. acres buildin s 13,950 0.32 arkin las halt 29,833 0.68 sidewalks 1,608 0.04 Total ✓45,391 1.04 Stormwater Calculations: Time of Concentration Hydraulic Length (L) = 355 ft, change in Height (H) = 5 ft. To = (L' /H)'" 1 128 3.71 min. Flow for 2 year, 6 hour Storm (Q2): QPRE _ (CPRE) x (I,p) x (Area) 2.20 cfs QPosT - (CPOST) x (110) x (Area) 5.37 cfs sou storage �apaCffy Tor z Xear zworm: CN = (98)(% imp.) + (60)(1-% imp.) = 80 P = 3.30 in. fo2yr, 6 hr storm S = 1000IC N - 10 = 2.50 Depth (D)= [P-(0.2)(S)]2 ! [P+(0.8)(S)] = 1.48 in. Time to Peak Flow: TP = ](43.5)(D)(Area)] / Q2,POST - 24.82 min. 7 Detention Pond Design: Pond Size: Elevation ft. Surface Area (sq. ft. Normal Pool 44.00 7,697 Flood Pool 46.00 10,632 Top of Bank 47.00 11,933 Bottom of Pool 38.00 1,428 % impervious = 0.503 = 50.3% say 51.0% CPRE = 0.25 CPasT = (% imp.)(.95)+(1-% imp.)(.25) Iz = 4.25 in/hr 110 = 4.92 inlhr Flow for 10 year, 6 hour Storm (Q,a) QPRE - (CPRE) x (115) x (Area) _ = 2.55 cfs Q POST = (CP05T) x (125) x (Area) = 6.21 cfs Soil Storaqe Caoacitv for 10 Year Storm CN = (98)(% imp.) + (60)(1-% imp.) 80 P = 4.82 in. for 10 yr, 6 hr storm S = 1000/CN - 10 = 2.50 Depth (D)= [P-(0.2)(S)f I [P+(0.8)(S)] = 2.74 in. Time to Peak Flow: TP = ((43.5)(D)(Area)] 1 Q10POST 39.66 min. State Surface Area Requirement at nofmal pool Pond side slopes = 3 :1 Depth below N.P. = 6 ft. SAIDA = 0.0277 (Chart for 90% TSS Removal for Wet Detention Pond without Vegetative Filter Required SA = (SAIDA) x (Total Drainage Area) 2,498 s . ft. Provided Storage Volume: State Volume Required for Storage of first 1" of runoff: Vol. _ [(Normal pool SA + Flood Pool SA) 121 Rv = .05+ .009(% imp) x (F.P. elev, - N.P. eiev.) = 0.503058 18,329 cu. ft. ,# j%%J1111111 V= (Design rainfall)(Rv)(Drainage Area) CARo = 3,780 cu. ft. SEAL -� 173741- JUL [. Luo �iA �j •. ,G1NE - - - GREGO 05032pond M 3Lvr f 711312005 Dollar General JWH Boiling Springs Lake, NC 05032 Pond Volume: Bottom SA = 1,428 sq. ft. Normal Pool SA = 7,697 sq. ft. Vol. _ ](N.P. SA + Bottom SA)12] x (N.P. el. - Bottom et.) = 27,375 cu, ft, Forebay: Required Volume Vol. = 20% of storage volume 5,475 cu. ft. Outlet Structure Design: Flow for 2-day drawdown: for 1 st 1 " of stormwater, Q = Required Vol. / 172,300 sec. (2-days) 0.022 cfs Required Area of Pipe for 2-day drawdown: A= Q 1 [Cd x SQRT(2 x g x h)] Cd = 0.6 g = 32.2 ft.ls2 h = (F.P. elev.- N.P. elev.)/2 A = 0.0045 sq. ft. Diameter of Pine for 2-dav drawdown: DIA. = SQRT[(A x-4) t pi] 0.0761 ft. = 0.91 in. 'Use: 0.75 in diameter pipe Outlet Structure Check Using a 4' x 4' Basin, Perimeter (L) = 16 ft. Q = CIA C = (% imp.)(.95) + (1-% imp.)(.25) 0.61 1 = 4.92 in. for a 25 yr. Storm A = 2.07 Acres 6.21 cfs Q= CwxLxH H = [Q / (Cw x L)]73 Cw = 3 0.26 ft. Peak elevation = flood pool elevation + H 46.26 ft. Provided Volume Bottom SA = 1,041 sq. ft. Normal Pool SA = 2,692 sq. ft. Vol. _ [(N.P. SA + Bottom SA) 12] x (N.P. el. - Bottom el.) 5,600 cu. ft. Flow for 5-day drawdown: for 1st 1" of stormwater, Q = Required Vol. 1432,000 sec. (5-days) = 0.009 cfs Required Area of Pipe for 5-day drawdown: A= Q 1 [Cd x SQRT(2 x g x h)] Cd = 0.6 g = 32.2 ft.ls2 h = (F.P. elev. - N.P. elev.)12 A = 0.0018 sq. ft. Diameter of Pipe for 5-day drawdown: DIA, = SQRT[(A x 4) 1 pi] 0.0481 ft. 0.58 in. JUL 1 4 ZOU5 05032pond 2 of 2 07/13/2005 13:49 (�) �Vq 9102560515 JTV MGMT PAGE 02/03 COASTAL ENVIRONMENTAL CONSULTING, INC. P.O. BOX 16102, WILMINGTON, NC 28408 PHONE: (910) 791-6411 FAX: (910} 791.077 CELL: 1910) 233-4730 Jon T. Vincent 1508 Military Cutoff Road, Suite 302 Wilmington, NC 28403 Preliminary Wetland Ev con 4.645 + Acres Lots 1 & 2 West North Shore Commercial Property N.C. Highway 87 Boiling Spring Lakes, Brunswick County, NC Vincent: September 10, 2004 Coastal Environ onsulting, Inc_ (CEC) has conducted a preliminary evaluation of the status of jurisdiction 404 wetlands on the subject site using the U.S. Array Corps of Engineers (USAGE) Wetlands Manual — 1987 edition. The project was authorized by your letter of engagement, dated August 24, 2004. Based on the results of the site reconnaissance performed on September 9, 2004, which included a series of hand -auger borings, the following conclusions have been drawn concerning the subject site: • The subject site consists of very flat recently cleared land, formerly part of a pine forest. On the day of the site visit, ponding was observed in small depressional areas mostly across the southern one-half of the property, due to the cumulative effect of about 20 inches of rain falling during the past month. JUL 13,2005 01:47P The water table was encountered at a depth of about 1 foot below land surface (BLS) on the northern one-half of the subject site, adjacent to N.C. Highway 87 right-of-way. The average water table depth on the southern portion of the property was 6 inches BLS. However, these water levels are extremely elevated due to an unusually wet late summer. It is our best estimate that the water table would range from 12 to 24 inches BLS in the dry season. 9102560515 Al U page 2 BY: /_'i 07/13/2005 13:49 9102560515 JTV MGMT PAGE 03/03 Prellrninary Wetland Evaluation Lots t & 2 West North Shore Commercial Pmparty Page 2 The predominant type of soil on the subject site is Leon find sand, a nearly level, poorly drained soil, This soil typically has a layer of hardpan encountered at depths ranging from 13 to 17 inches BLS. The presence of the hardpan causes water to stand on the surface for several days following periods of heavy rainfall. No muck -coated sand grains were detected on the property. • The mostly brick commercial structures on the adjoining properties to the east, south, and west are all constructed on the same type of land as found on the subject site. It should be noted that the NRCS Sail Survey of Brunswick County indicates that the wetness of Leon fine sand requires hydrology manipulation to facilitate building site development. In order to overcome or minimize soil limitations, special planning and designs include substantial amounts of grading and filling and construction of both open and tiled ditches with drains. The ditching on the northern one-half of the property appears to be helping to drain the property at the present time. _ Based on our preliminary evaluation, it appears that no jurisdictional wetlands, as regulated by the USACE, or isolated wetlands as regulated by the North Carolina Department of Environment and Natural Resources, are located on the subject site. We appreciate this opportunity to be of service. Please call us if you have any questions. Thank you. Sincerely, Coastal Environmental Consulting, Inc. 4A--� <F_ � Harvey E. Clifton, Jr. Wetland Scientist HEC/jmc guff 105.eval JUL 13, 2005 01:47P 9102560515 JUL 1 4 ZU0 page 3