SW8051117_COMPLIANCE_20051205

STORMWATER DIVISION CODING SHEET
POST -CONSTRUCTION PERMITS
PERMIT NO.
SW
DOC TYPE
❑ CURRENT PERMIT
❑ APPROVED PLANS
❑ HISTORICAL FILE
COMPLIANCE EVALUATION INSPECTION
DOC DATE
YYYYMMDD

�WK
/DICKSON
community infrastructure consultants
December 12, 2005
Mr Paul T Bartlett, P E
NC DENR Division of Water Quality
127 Cardinal Drive Extension
Wilmington, North Carolina 28405
RE Waccamaw Bank, Southport, NC
WKD Project Number 50243 00 WL
Dear Mr Bartlett
RECEIVED
DEC 1 2 2005
The following responses are In regard to comments from your letter to Mr Perry Dawson on
December 8, 2005
Comment
(1/11 Please clarify Cl #9 on Drawing C4 It appears that it should be Cl #6
Response- CI #9 was changed to read Cl #6
Comment
2 Please add notes to the Outlet Structure Detail on Drawing C7 that (a) grating bars will be 4"
q/ on center maximum, and (b) a pump will be provided for maintenance and to drain the pond
in emergencies
Response The outlet structure detail on sheet C7 was modified to include the following notes
a) Grating bars will be 4" o c maximum, and b) A pump will be provided for
maintenance and to drain the pond in emergencies
Comment
3/ Please clarify the temporary pool elevation The grate elevation on Drawing C7, Outlet
1/ Structure Detail, is given as 32 50' but the temporary pool elevation is given as 32 88' If the
1' design storm storage is limited to an elevation of only 32 50', approximately 2,550 cu ft will
be stored instead of the 3,634 cu ft reported on the supplement
Response The outlet structure detail on sheet C7 was modified to show the grate elevation at
32 88'
Comment
4 Please revise the calculations for the required forebay volume to be 20% of the forebay plus
mainbay volumes The reported result on the supplement, based on just the mainbay volume,
909 Market Slroet
Wilmingion, NC 28401
Tel [phone]
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www wkdickson com
North Carolina • South Carolina • Georgia • Florida

Mr Paul T Bartlett, P E
December 8, 2005
Page 2
is within the allowed tolerance (± 2%) for the result based on the mainbay plus forebay,
therefore, a pond design change is not required
Response The calculations have been revised and are attached for your review The forebay
volume proposed is now 18 1% of the mainbay and forebay combined This is still
within the +/- 2% tolerance
Should there be further comments or questions, please let me know
Sincerely,
W K. Dickson & Co, Inc
Robert P Balland
/pb
Enclosure

DETENTION POND ANALYSIS FILE NAME G IDATAIWPDATAIWQSIPOND1051117 WK1
PROJECT # SW8 051117 REVIEWER P Bartlett
PROJECT NAME Waccamaw Bank
DATE 07-Dec-05
Receiving Stream Jump and Run Crk Class SC, SW
Drainage Basin Cape Fear Index No 18-88-9-3-2
Site Area 1 46 acres
Drainage Area 5086 0fl I square feet Area = 1 26 acres
IMPERVIOUS AREAS
Rational C `
Bldgs 6331 00 square feet 095 ail
Prkg 2705200 square feet 095
sidewalks 1591 00 square feet 095 0 a
Offsite 800000 square feet 095 n
square feet
square feet
TOTAL square feet Rational Cc= 079
SURFACE AREA CALCULATION
ft
% IMPERVIOUS 78 30%
SA/DA Ratio 6 83% 0 , (4
Des Depth 4
Req SA
3749 sf
�-
TSS 90
Prov SA
48'3 sf
VOLUME CALCULATION
" place a "1"
in the box if Rational is used
Rational ?*
Des Storm
1,00
inches
Rv=
075
Bottom
28
msl
Perm Pool
32 00
msl
Design Pool
32 88
msl
Design SA
5556
sf (@32 7)
Req Volume
N52
cf
Prov Volume
4571 I
cf
ORIFICE CALCULATION
Avg Head =
Flow Q2, cfs
Flow Q5, cfs
No of Orifices
Diameter, inches
Drawdown =
042 ft
0 020 cfs
0 008 cfs
A.
0.75 weir HxW
4.2 days
FOREBAY
Perm Pool Volume=
Req Forebay Volume=
Provided Volume=
Percent=
SA @ -
Elevation=
10241 (MB only)
20482
226200
22 1d/o (18 1%, MB+Fig
Q2 Area = 0 92 sq in
05 Area = 0 37 sq in
Orifice Area 0 44 sq in
Q= 0 010 cfs
F. in x I in
COMMENTS
Surface Area , Volume and Orifice are within Design Guideline: