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HomeMy WebLinkAboutSW8970713_OTHER_19971003STORMWATER MANAGEMENT & EROSION CONTROL CALCULATIONS for ANTIQUA prepared for SANCO of WILMINGTON, INC. D E C E I V E OCT 0 31997 D PRO a A O'al3 Hanover Design Services, P.A. 319 Walnut Street Wilmington, NC 28401 ,r``••� CARO/ , a•'• �\ l� •FESSIpy�q ��O q SEAL i 20007 % 'o :Ft'�i�E....�� 3. IZ4 g7 EROSION AND SEDIMENT CONTROL PLAN for ANTIQUA SANCO of WILMINGTON, Inc. MARCH, 1997 NARRATIVE NOTE: To be reviewed in conjunction with "Erosion and Sediment Control Plan for ANTIQUA", Hanover Design Services, P.A., Drawing No. 4893ESC and 4893ESC1, Sheets 1 & 2 of 2. PROJECT DESCRIPTION - The purpose of this project is to construct a residential community of condominium buildings and the associated development infrastructure. The Erosion and Sediment Control Plan is to identify measures to be implemented to control erosion during construction of the roads, utilities, and land grading associated with this development. The site is located off U.S. 421 WEST of ECHO FARMS BOULEVARD, in the City of Wilmington, New Hanover County, and is approximately 15.186 acres in size, of which about 11 acres are proposed to be disturbed. The site is wooded over most of its area and has a rolly topography. It is bordered on the East and partially on the North by residential development, to the West by Titanium Road, and to the South by wooded property, as per the approved "Antiqua Preliminary Plan". SOILS - The soil in the project area is primarily Seagate and Wakulla, both sandy soil ( Se ) and(Wa); sands that are poorly drained, rapidly permeable, with an erosion "K" factor of 0.10, moderate to severe erodibility. The hydrologic classification of the soil is A/D. Because of the topography and the amount of paving proposed, curbing and a storm sewer system will be the means of stormwater transport for the 10- year event to the proposed pond/ basin. (Soils Map attached) f L No Be I Wr No lVeLottaAovec M'9p NEW HANOVER COUNTY, NORTI Ur Ur k L Ay. Se fl, Y 14 r. e Ly C Ls Ll It, .4 Be Kr M�N ,* M'lltwl Map Bp .4 STORMWATER MANAGEMENT AND DRAINAGE CALCULATIONS for ANTIQUA prepared for SANCO of WILNHNGTON, INC. CAR01 j''• �*!OFESSIQ,' 9 Hanover Design Services, P.A. fay SEAL 20007 319 Walnut street ° Wilmington, NC 28401 a �NGINE�fr� -3 .24 -c�)7 IA'f;vjq Rec eiv,n< 0A(-uci ure I Pond ►, �3 a ► ai5 a 3% 3 l,c,36 `+ 1. as 6 .qua 631 �I k ,6C5 JD I iv 22 1 13 r1_ i.S95 l�r 13 ,`IIS TIM 10,-23 AlGli E'•^ HANOVER DESIGN SERVICES/ PA LAND SURVEYORS, ENGINEERS, LAND PLANNERS 319 WALNUT STREET, WILMINGTON, NC 28401 SHEET ► OF re # ac' ,u •-- CfGUe:•) U-Iy►raln '�- io f lrr�-o ` (L q 111/1n kLk�lC% ►9 �. Pre-de✓"o/ f �. loi ) G_G,:rp -�_O�wI 11 rP iqn •: L' Q/iS.,�. c,a: &0 �• Cy�-r. iQF .coi — `b I�C�'� irh erv%VMS `18 ;4fe I CO= HANOVER DESIGN SERVICES, PA LAND SURVEYORS, ENGINEERS, LAND PLANNERS 319 WALNUT STREET, WILMINGTON, NC 28401 SHEET a OF oUS dIi co5o0 Roqj sr d prrvew� y /'A710 ^'lLcs,' 17 Yl /yc' S F (q,D Secl ; �' P!, oh r; 5 MPn ran ky< l D, J 3 at.,,;-.� x I kcoc r-, _ 11, 3/ `I C, F Volume pro✓;dea = `' = 30,b`I9. CF �o boiff,'1, ofweir / of 5/orc,, L--4 Ser imnact ne/sr a r CJ 1 ArRES Tc (p ='llm' l _�eveloied ) = AC_A/ ( Pos1-de✓el"I,"f") 70 Rafond �41411hlrd = Q - Cid a(-2)(1 lS,y c�"' p I I /�.� 1/ �I 1 Cr, a -I c1 /41,nnn1 ! elk' I Iob c4efo,r'',no rnot c�,�•. �i r,r9 r- � 1-cr �•ii..,r. Gig<<. a��d rr.,Alvr�yt� II5c rR 't�.� �of �;('fti-/}1� Iq n� rc••��. `c-'r J t-�(1 1'r(10 -1:=r; II it ibo " I , HANOVER DESIGN SERVICES, IAA LAND SURVEYORS, ENGINEERS, LAND PLANNERS 319 WALNUT STREET, WILMINGTON, NC 28401 SHEET = OF Q(lo) /)(e-'19.1cirped - 1 S / c �S L1)�fyl i C 'rnPve�o�7f�% = dG.l C 3 S1 3 Q(5o1 P'-t�LlVd "a) e)C@ �e,.Idr,oed . 49,(oc{s ri wS-- Pe %Ra0049.9"1. S Ce Ada,/,P,/ > ' linr /: c' 'S ,1 ch la. I5 Hanover Design Services, P.A. Land Surveyors, Engineers, Land Planners ANTIQUA Additional Calculation Summary for D.W.Q. - WATER QUALITY CONSIDERATIONS - Impervious area calcs: See Project Data Sheet SOME OFFSITE AREAS DRAIN TO POND IMPERVIOUS TO POND = 6.69 ACRES OPEN AREA = 3.83 ACRES TOTAL AREA TO POND = 10.52 acres use 10.6 n SEAL 20007 * Retention of first 1" of run-off: Id SA REQUIRED: 6.69 x 0.98 + 3.83 x 0.20 / 10.52 = 0.70 USE 70% At 7.5' depth, 90% TSS removal, from chart - SA factor = 2.3 10.6 x 0.01 x 2.3 = 0.2438 acres = 10,620 sf SA REQUIRED At Elev = 10.00 - 0.346 acres = 15,073 sf SA PROVIDED Factor of Safety = 1.42 VOLUME REQUIRED: ((6.69 x 0.98 + 3.83 x 0.20) x 1/12)43,560 = 26,580 cf REQUIRED STORAGE --------------------------- --------------------------- At Elev. = 11.5 - 30,699 cf PROVIDED STORAGE Factor of Safety = 1.15 Average head from storage elevation to CL oriface - 11.5 - 10.0 /2 = 0.75' * 2" PVC drain to drawdown pond: Oriface Eq'n: Q = CA(2gh)A1/2 Q = 0.6(.022)(2.0 X 32.2 X 0.75)A1/2 = 0.092 cfs T = 337,450 sec. = 3.9 days OKAY Forebay Comps: Volume required = 30,699 X 20% = 6,140 cf Volume provided = 7,623 cf area @ 11 ft. el. = 22,554 sf area @ 11.5 ft. el. = 23,770 sf 319 Walnut Street Wilmington, N.C. 28401 (910) 343-8002 8rora g0 HANOVER DESIGN SERVICES, PIA III LAND SURVEYORS, ENGINEERS, LAND PLANNERS 319 WALNUT STREET, WILMINGTON, NC 28401 SHEET OF c F5 r�6 SF CC�FrISG CPC kic-rR r E S o Pncy GFS Sto¢nc.� IS o73 O o a 0 O O O ,07 0 0 0 .0-1 01/1 as ss y i d 781(f I ,10 o a3�70 o c o a.� `It�S �4a sa4 ,Is l,4 b 0 o I.61 , 98 -d qq 5,706 . 6 4.13 j c 3 a�so3 �68xa4 I,Ig -),s8 f; o i o -7,7b 1,58 I ,Id6,'rbl I y 301107 017(,33,a( 4c 3�8i8- ,113547 �a I �,o S- 33154� lla9,s, .a3 �`I,o a3, 15 S7 3 I a %Y '111 iN o,ol.a5 i a0,gs :So. I J7,� 13^�.8 i �, 33 16 706 164 -3,?V 6.s 5 sti7► I:I5 i9gs!,a7 �ay,d�l iaa.s a��.� 4a4,3� �, a� V/,JRI a- I Is' 444 .. '),.`I ,fro S4q,-f cre5 ed WeLR fooh,u L=3,3 Q_ CL-N'', WEIR I d (40 HANOVER DESIGN SERVICES, PA LAND SURVEYORS, ENGINEERS, LAND PLANNERS 319 WALNUT STREET, WILMINGTON, NC 28401 SHEET OF i Table J-2 SCS curve Runbers for various coves conditions cover Description Fully developed urban area, PoSpace or condition (<50% grass) Fair condition (50-75% grass) Good condition (>75% grass) Impervious auras pavement, roofs Gravel Dirt Urban districts O mnercial and business Industrial Residential areas (by lot size) 1/8 acre (town houses) 1/4 acre 1/3 acre 1/2 acre 1 acre 2 acres Agricultural areas Pasture, grassland poor Fair Good Meadow (mowed) Brush poor Fair Good Woods and grass (orchard) poor Fail Good Woods Poor Fail Good Raw crops, straight, good ROW crops, contoured, good Small grain, good rn rntsteads Ba ed upon Sc5 TR-55 (SCS, 1966) Hydrologic Soil Group A g c Percent D lipervious 68 79 49 69 39 61 86 79 74 89 84 80 98 76 72 85 82 89 87 91 89 89 81 92 88 94 91 95 93 85 72 77 61 57 54 51 46 85 75 72 70 68 65 90 83 81 80 79 77 92 87 86 85 84 82 65 38 30 25 20 12 68 79 86 89 49 69 79 84 39 61 74 80 30 58 71 78 48 67 77 83 35 56 70 77 30 48 65 73 57 73 82 86 43 65 76 82 32 58 72 79 45 66 77 83 36 60 73 79 30 55 70 77 67 78 85 89 65 75 82 86 G3 75 83 87 59 74 82 86 T-9.58 FIG. /. 5. 000 900 800 700 600 500 v Paved .9 400 z D- . e 0 300 Of .� w Bare 200 _ Soil Poor \ Grass Q_ 5 Surface Average =_ 4 Grass U 100 Surface 90 \ BO Dense Grass a \ 70 \ 60 J 50 V 40 30 20 IN OVERLAND w z_ J I- 0 J D_ 0.5j w 35 30 25 20 w F- z ►0 ter. w N 0 15 ::E J / F- 2.0 �' / z 0 5.0 z w a /� 10 L W z 2 0 D_ *LOW TIME 11 0. REPRINTED WITH PERMISSION FROM 'DATA BOOK FOR CIVIL ENGINEERS' VOL. I - DESIGN 2Mo EDITION (1951) BY E.E.SEELYE JAN-08-1996 09;19 FROM ENNR WILM REG OFFICE 10 934syy41 r.ee 85% TSS REMOVAL 30 FOOT VEGETATED FILTER REQUIRED DEPTIi 3' 3.5' 4.0' 4.5' 5.0' 5.5' 6.0' 6.5' 7.0' 7.57 IMP � 10 % .9 .8 .7 .6 .5 0 1 0 0 0 0 20 % 1.7 1.3 1.2 1.1 1.0 .9 .8 .7 .6 .5 30 % 2.5 2.2 1.9 1.8 1.6 1.5 1.3 1.2 1.0 .9 40 % 3.4 3.0 2.6 2.4 2.1 1.9 1.6 1.4 1.1 1.0 50 % 4.2 3.7 3.3- 3.0 2.7 2.4 2.1 1.8 1.5 1.3 60 % 5.0 4.5 3.8 3.5 3.2 2.9 2.6 2.3 2.0 1.6 70 % 5.2 4.5 4.1 3.7 3.1 2.9 2.5 2.1 1.8 80 % F7.5 6.0 5.2 4.7 4.2 3.7 3.2 2.7 2.2 2.0 90 % 6.5 5.8 5.3 4.8 4.3 3.8 3.3100 % 7.4 6.8 6.2 5.6 5.0 4.4 3.8 90% TSS REMOVAL NO VEGETATED FILTER REQUIRED DEPTH 3 3.5' 4.0' 4.5' 5.0' 5.5' 6.0' 6.5' 7.0' 7.5' IMP % 10 % 1.3 1.0 .8 .7 .6 .5 .4 .3 .2 .1 20 % 2.4 2.0 L 8 1.7 1.5 1.4 1.2 1.0 .9 .6 30 % 3.5 3.0 2.7 2.5 2.2 1.9 1.6 1.3 1.1 .8 40 % 4.5 4.0 3.5 3.1 2.8 2.5 2.1 1.8 1.4 1.1 50 % 5.6 5.0 4.3 3.9 3.5 3.1 2.7 2.3 1.9 1.5 60 % 7.0 6.0 5.3 4.8 4.3 3.9 3.4 2.9 2.4 1.9 70 % 8.1 7.0 6.0 5.5 5.0 4.5 3.9 3.4 2.9 2.3 80 % 9.4 8.0 7.0 6.4 5.7 5.2 4.6 4.0 3.4 2.8 90 % 10.7 9.0 7.9 7.2 6.5 5.9 5.2 4.6 3.9 3.3 100 % 12.0 10.0 8.8 8.1 7.3 6.6 5.8 5.1 4.3 3.6 Note: The required surface area calculated from the tables is to be provided at the permanent pool elevation. s0 - .20 .10 4- 4- a .06 0 In 02 01 I I I I I 1 1 1 1 2 4 G 10 Average velocity, ft/sec Figure J-I,—�b'e ra Y.e rcln cil ies h,r eslim:rting tr:Ircl link f." shnllulc rnnrc111r:ded pn„'. ,1 0 (gln VI TR.5",, svrnw! ICI! ..Inns c0 Worksheeeet 3,: Time of concentration (Tc) or travel time V roJect �1�(J .l.�. gyC4. Dace Location I Checked_' y Dace circle one: RCCS<nt D<velooed Circle one: Tc T� through subarea NOTES: Space for as many as two aegments per flow type can be used for each workshcet. Include a cap, schematic, or description of flow segments. Sheer flow (Applicable to Te only) Segment ID 1. Surface description (table 3-1) ............ 2. Ranning's roughness eoeff., ❑ (table 3-1) .. 3. Flow length„L (total L;< 300jj ft) .......... ft 4. Tuo-yr 24-hr rainfall, P�... )LJ.^..1. ... in (0 5. Land slope, s fe/ft 6. T _ 0'.007 (nL)0.8 0.S 0.4 Compute T t .. hr c P1 c Shallow concentrated flow Segment ID 7. Surface description (paved or unpaved) ..... B. Flow length, L ............................. ft, 9. Watercourse slope, s ....................... ft/ft 10. A-,erage velocity, V (figure 3-1) ........... fc/s 11. Tr ' J600 V .. Compute :Tt....... hr .Channel flowSegment ID 12. Croce sectional flow area; a ............... ft 13. Wetted perimeter, pw .............. 1......... ft 14. Hydraulic radius, r - Compute r .. ..... ft pv 15. Channel slope, a ft/ft 16. Harming'& roughness coeff., ❑ ............:: 2/J 1/2 17. V - 1'•49 r. a Compute V ....... fc/c r 16. Flow lcogch, L ............................. ft Q F1.2 19. Tc 3600 v Compu c< i' ...... hr 8 + . L - 20. Watershed or eubarea Te or Tc (add Tr in steps 6, 11, and 19) ....... hr vn ivl . (?IONI-TR-55, Second Ed- June 1986) D-3 Appendices 3 3 5 10 20 50 100 200 500 1000 Discharge(P/sec) Curves may not be extrapolated. Figure 0.06a Design of outlet protection protection from a round pipe flowing full, minimum tallwater condition (T., <0.5 diameter). Rt . 12/93 8.06.3 HANOVER DESIGN SERVICES, PA LAND SURVEYORS, ENGINEERS, LAND PLANNERS 319 WALNUT STREET, WILMINGTON, NC 28401 SHEET OF OY 4 aff IC+i = Tool ys Or Niv. O o HANOVER DESIGN SERVICES, PA LAND SURVEYORS, ENGINEERS, LAND PLANNERS 319 WALNUT STREET, WILMINGTON, NC 28401 SHEET OF C Y-...�q'p'" V. 'vil"., r so _ 3a.78 c�S c 11 1—FE Precast Concrete Flared End Sections REINFORCED Q Oldcastle Flexible Plastic Type Joints Specifications: N.C. Department of Transportation OD rl C r FALL A NCP ID WALL OD L A B C E F C H J K M WT 12 2 16 7 75 4 23 z 51 s 23 2 14 13 4 a 13 s e 13 � a 1 -' a 1 -' 722 15 21 194 74 i 7 274 472 30 17a 164 17 162 2 2 1038 18 2 z 23 2 74 i 9 27 47 36 20 e 20 ; 20 ; 19 z 2 e 2 1 426 24 3 30 a 80 9 43 37 47 27 z 27 e 26 26 4 2 2 2 2 2137 30 3z 37 ; 77 12 54 2 22 i 60 34 33 33 s 32 z 3 3 2990 36 4 44 97 s 16 50 37 71 40 e 40 39 ; 39 3 i 3 z 3960 42 1 4 z 52 z J 98 e 22 , ] 51 e 37 77 1 47 z J 46 a 1 46 a 45 8 4 , 3 2 5160 48 5 59 i 99 1 25 2 701 29 83 a 53 3 52 7 52 a 51 3 4 q 3 z 6480 54 5 i 65 s 104 26 65 39 i 89 59 T 58 1 58 1 57 Z 4 L 4 i 9370 60 6 72 103 i 28 z 57 z 46 56 65 -' 65 64 � 64 4 4 11650 N.C. PRODUCTS P.O. BOX 27077 RALEIGH, NC 27611 (919) 772-6301 1-800-662-1983 POND PEAK DISCHARGE SUMMARY - Q(10) post -developed = 13.7 32.8 cfs @ cfs @ WSEL = 13.8 WSEL = 14.7 Q(50) post -developed 0(100)post-developed = = 48.6 cfs @ WSEL = 14.9 GRATE TOP 0. 5.0' \WELDED BAR TRASH RACK EL=14.25 BOLTED /N PLACE 90' ELBOW DOWN 8" BELOW WSEL 13 ' 4 4 1.25' WEIR 4 WSEL70.0 *30,699c( SB 2" PERFORATED PVC W/ GRAVEL POND BOTTOM AND FABRIC FILTER EL= 5.25 ELEV= 2.5 POND MAY BE OVEREXCAVATEO TO PROVIDE SEDIMENT STORAGE FOUR STANDARD 2'%3' GRATES NCDO7 OR EOUAL 713 — GRATE TOP EL= 11.5 2 — 24"'RCP INV= ® 0.31 7 10.0 1. CONC. INV= 10.0 or GROUT OUTLET PIPES 0 1 2.5' SUMP =BASE 4'x 10'Precosf Conc. Box, Tindall UV0410 OR EOUIVALEf% SECTION VIEW WE W —4' —0 TYP. nM SEE DEFOR L, 14 NPLAN VIEW CRATE PLAN VIEW •5. 24 " RCP OUTLET STRUCTURE DETAILS NOT TO SCALE State of North Carolina Department of Environment, Health, and Natural Resources Wilmington Regional Office James B. Hunt, Jr. Division of Water Quality Wayne McDevitt Governor Water Quality Section Secretary September 16, 1997 Mr. Jeff Malpass Hanover Design Services 319 Walnut Street Wilmington, NC 28401 Subject: REQUEST FOR ADDITIONAL INFORMATION Stormwater Project No. SW8 970713 Antiqua Apartments New Hanover County Dear Mr. Malpass: The Wilmington Regional Office received previously requested information for the Stormwater Management Permit Application for Antiqua Apartments on August 19, 1997. A preliminary review of that information has determined that the application is not complete. The following information is needed to continue the stormwater review: �1. I never received a copy of the calculation booklet, however, with a few modifications, the single sheet you have submitted is sufficient. Add the surface areas provided at 11 and 11.5. 2. Have you added the area of the sidewalks from the parking lot to the front doors to the permit application and calculations? 3. The footprint you have submitted is not complete. The footprint only shows one of the 4 building sizes. Please add complete dimensions for all four buildings to the plans. 4. The 65.76' dimension provided for the permanent pool appears to be for contour 11, not 10. Please add dimensions for each side of the figure created by the permanent pool contour. 2 5. Raise the forebay weir elevation to at least the permanent pool. Aesthetics cannot be considered in pond design. With proper design and maintenance, the weir section will not be an eyesore. See detail, enclosed. 127 Cardinal Drive Extension, Wilmington, N.C. 28405-3845 • Telephone 910-395-3900 • Fax 910-350-2004 An Equal Opportunity Affirmative Action Employer Mr. Malpass September 16, 1997 Stormwater Project No. SW8 970713 6. Add the cul-de-sac detail with pavement and right-of-way radii noted. 7. The street section shows both 12' and 15' lane widths. Please specify which width is used for this project. The street section also shows sidewalk, but the rest of the sidewalks on the project, per the parking section detail, ar 4' Is this correct? e8. What does the 174,100 square feet listed under "Other" on the permit application represent? 9. The building area on the application is 96,000, but the Sheet 1 summary shows 87,610. If you want to account for more built -upon area call it "Future", don't just add a Factor of Safety to your overall total. 10. Detail for Type A curb. Please note that this request for additional information is in response to a preliminary review. The requested information should be received by this Office prior to October 16, 1997, or the application will be returned as incomplete. The return of a project will necessitate resubmittal of all required items, including the application fee. RSS/arl cc If you have any questions concerning this matter please feel free to call me at (910) 395-3900. Sincerely, Ms. Linda, Lewis Environmental Engineer S:\WQS\STORMWAT\ADDINFO\970713. SEP Linda Lewis Central Files 127 Cardinal Drive Extension, Wilmington, N.C. 28405-3845 • Telephone 910-395-3900 • Fax 910-350-2004 An Equal Oppornmity Affirmative Action Employer HAiNOVER DESIGN SERVICES, P.A. (910) 343-8002 319 WALNUT ST. WILWNGTON, NC 28401 ro - DATE SUBJECT 7e (` (« Q. {- �i v �. L7 / SIGNED Please repty ❑ No repty necessary 'f. ,s a ; / � j\ �` i _ .� 1. J � \\_�I Hanover Design Services, P.A. Land Surveyors, Engineers, Land Planners AUGUST 7, 1997 Ms. Linda Lewis N.C.D.E.H.N.R. 127 Cardinal Drive Extension Wilmington, NC 28405-3845 nE C E I V E luu{ AUG 191997 D Re: ANTIQUA, revisions as per State request PROJN E vR-b%(3 Dear Linda: As per request number 1, the drainage calculations were included in hand written form and attached in the middle of the stormwater management & erosion control booklet, for ease of reading I typed the calculations. 2 As per request #2, the owner has provided us with a footprint of the buildings, in this package you will find the attached drawing. 0 8M f As per request #3, the new application has been filled out and signed by the owner. As per request #4, the dimensions for walks,parking and permanent pool have been added to attached drawing 1 of 2. As per request #5, the road section details have been added to drawing 1 of 2. As per request #6, the owner has provided us with a drawing that includes sidewalks approaching buildings, which have been added to drawing 1 of 2. As per request #7, the note stating that all roof drains must be directed so that the run off is sent to pond has been added to drawing 1 of 2. As per request #8, the nearest city has been added to the location map. As per request #9, the offsite runoff has been accounted for in the pond design. 319 Walnut Street Wilmington, N.C. 28401 (910) 343-8002 As per request #10, the drainage areas have been delineated and is attached on drawing 1 of 2. If you have any questions, or require any additional information, please feel free to contact me. Sincerely, Jeffrey B. Malpass, EIT k4g, 146 � �- 7-, STORMdHATER Hanover Design Services, P.A. nn E C E I V E Land Surveyors, Engineers, Land Planners R AUG 191997 EJ D E M ANTIQUA PROJN Additional Calculation Summary for D.W.Q. - WATER QUALITY CONSIDERATIONS - Impervious area calcs: See Project Data Sheet SOME OFFSITE AREAS DRAIN TO POND IMPERVIOUS TO POND OPEN AREA TOTAL AREA TO POND use 10.6 = 6.62 ACRES 3.9 ACRES 10.52 acres CARO(j''• .rook, .y4 CCIn: SE AL 20007 S. * Retention of first 1" of run-off: C.3-7 �c37 SA REQUIRED: 6.62 x 0.98 + 3.9 x 0.20 / 10.52 = 0.69 USE 70% At 7.5' depth, 90% TSS removal, from chart - SA factor = 2.3 10.6 x 0.01 x 2.3 = 0.2438 acres ----------------------------------- = 10,620 sf SA REQUIRED At Elev = 10.00 - ----------------------------------- 0.346 acres ----------------------------------- = 15,073 sf SA PROVIDED Factor of Safety = 1.42 VOLUME REQUIRED: ((6.62 x 0.98 + 3.9 x 0.20) x 1/12)43,560 = 26,382 cf REQUIRED STORAGE -------------------------- At Elev. = 11.5 - 30,699 cf PROVIDED STORAGE -------------------------- -------------------------- Factor of Safety = 1.16 Average head from storage elevation to CL oriface - 11.5 - 10.0 /2 = 0.75' * 2" PVC drain to drawdown pond: Oriface Eq'n: Q = CA(2gh)^1/2 Q = 0.6(.022)(2.0 X 32.2 X 0.75)^1/2 = 0.092 cfs T = 337,450 sec. = 3.9 days OKAY Forebay Comps: Volume required = 30,699 X 20% = 6,140 cf Volume provided = 7,623 cf 319 Walnut Street Wilmington, N.C. 28401 (910) 343-8002 a State of North Carolina Department of Environment, Health, and Natural Resources Wilmington Regional Office James B. Hunt, Jr. Division of Water Quality Jonathan B. Howes Governor Water Quality Section Secretary July 29, 1997 Mr. David Hollis, P.E. Hanover Design Services 319 Walnut Street Wilmington, NC 28401 Subject: ACKNOWLEDGEMENT OF RECEIPT AND REQUEST FOR ADDITIONAL INFORMATION Stormwater Project No. SW8 970713 Antiqua New Hanover County Dear Mr. Hollis: The Wilmington Regional Office received a Stormwater Management Permit Application for Antiqua on July 14, 1997. A preliminary review of that information has determined that the application is not complete. The following information is needed to continue the stormwater review: 1. The design calculations were not included in the submittal. 2. Provide a typical unit footprint and show all wood decks and concrete patio areas. 3. The Operation and Maintenance Plan has been revised. Note the inclusion of forebay and pond design depths, and the deletion of the notary requirement. 4. Provide dimensions for the walks, parking lot and permanent pool. 5. Provide a road section detail. 6. Why are there are no sidewalks shown from the parking lot to the front door? 7. Note on the plans that all roof drains must be directed so that the runoff is sent to the pond. 8. Please begin the habit of adding the nearest city or town name to the location map. 127 Cardinal Drive Extension, Wilmington, N.C. 284053845 • Telephone 910-395-3900 • Fax 910-350-2004 An Equal Oppormnity Affirmative Action Employer Mr. Hollis July 29, 1997 Stormwater Project No. SW8 970713 9. Has offsite runoff been accounted for in the pond design, or diverted? 10. Please delineate the drainage area to the pond, if offsite areas are included, or if it is different than the site area. Please note that this request for additional information is in response to a preliminary review. The requested information should be received by this Office prior to August 29, 1997, or the application will be returned as incomplete. The return of a project will necessitate resubmittal of all required items, including the application fee. If you have any questions concerning this matter please feel free to call me at (910) 395-3900. Sincerely, 4cbu " Ms. Linda Lewis Environmental Engineer RSS/arl: S:\WQS\STORMWAT\ADDINFO\970713.JUL cc: Linda Lewis Central Files ►J HANOVER DESIGN SERVICES, PJL (910)343-8002 319 WALNUT ST. 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