SW8980611_Historical File_20010326

TRIPP ENGINEERING, P.C.
419 Chestnut Street
Wilmington, North Carolina. 28401
Phone: [phone] • FAX: [phone]
February 12, 2001
NCDENR
Division of Environmental Management
Water Quality Section
127 Cardinal Drive
Wilmington, NC 28405-3845
Attn: Mr. Scott Vinson
Re: HMF Northchase
SW8 980611Mod
New Hanover County, NC
TE 00137
Dear Scott:
FEB 13 Z001
In response to your correspondence dated January 30, 2001, we offer the
following:
1. A note that no wetlands exist has been provided
2. Sealed pond calculations are enclosed.
3. The sediment basin cleanout level on the supplement has been revised.
4. The outlet structure detail has been revised.
5. The site data chart now corresponds with the application and supplement.
Please review for approval and contact us with any questions or comments.
Thank you.
Sincerely,
Tripp Engineering, P.C.
aa 4�i
Charles D. Cazier E.L
cdc
Enc.

2112101 HMF NORTHCHASE 00137
CDC Stormwater Calculations
Total Drain a Area
s . ft.
acres
425145
9.76
Impervious Area
Land Use
sq. ft.
acres
EXISTING BUILDING
1 75,000
1.72
EXISTING CONCRETE
3,000
0.07
PROPOSED ASPHALT
59,888
1.37
PROPOSED CONCRETE
7,908
0.18
PROPOSED STONE
48,979
1.12
Total
194,775
4.47
Stormwater Calculations:
Time of Concentration:
Hydraulic Length (L) = 1,300 ft.
change in Height (H) = 3 ft.
Tc = (La /H).yee / 128
20.22 min.
Flow for 10 year, 6 hour Storm (Qio):
QPRE _ (CPRE) x (ii0) x (Area)
13.30 cis
QPow = (CPosr) x (110) x (Area)
= 30.36 cis
eon Mora a..a ac Tor w yew azorm:
CN = (98)(% Imp.) + (60)(1-% imp.)
78
P = 4.80 in. for 10 yr, 6 hr storm
S - 1000/CN - 10
2.82
Depth (D)= [P-(0.2)(S)12I [P+(0.8)(8)]
= 2.54 in.
Time to Peak Flow.
TP = [(43.5)(D)(Area)] I Qio,Posr
35.56 min.
Detention Pond Design:
Pond Size:
Elevation
(IL)
Surface Area
(sq. It.
Normal Pool
29.50
21,165
Flood Pool
30.50
24,142
To of Bank
32.00
32,852
Bottom of Pool
25.50
1 7,700
Total Provided Storage Volume:
Vol. _ [(Normal pool SA + Flood Pool SA) / 2]
x (Flood Pool elev. - N.P. elev.)
22,654 cu. It.
00137POND
1 of 2
% impervious = 0.458
= 45.8%
CPRE =
0.25
CPosr = (% imp.)(.95)+(1-% imp.)(.25)
=
0.57
110 =
5.45 in/hr
1, =
6.75 in/hr
Flow for 50 year, 6 hour Storm (Q5@:
QPRE _ (CPRE) x 050) x (Area)
16.47 cfs
QPosT = (CPosr) x (150) x (Area)
= 37.60 cis
blorm:
CN = (98)(% imp.) + (60)(1 -%imp.)
78
P = 8.42 in. for 50 yr, 6 hr storm
S = 1000/CN -10
= 2.82
Depth (D)= [P-(0.2)(SV' I [P+(0.8)(S)1
Time to Peak Flow:
TP = [(43.5)(D)(Area)] I QN,Posr
44.63 min.
ware
Pond side slopes = 3 :1
Depth below N.P. = 4 1t.
SAIDA = 0.0398
(Chart for 90% TSS Removal for Wet Detention
Pond without Veaetative Filter)
State Volume Requirement for first 1" of runoff.
Vol. = [(1/12) x (DA) x (% imp.)] +
[(1/12) x (DA) x (1-% imp.) x C]
C = 0.2
20,071 cu.ft.
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FEB �c310pf
PAW # DWO
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2/12101 HMF NORTHCHASE 00137
CDC Stormwater Calculations
Fore
Required Volume
Vol. = 20% of state storage volume
= 4.014 cu. ft.
Outlet Structure Design:
Flow for 2-day drawdown:
for 1st 1" of stormwater,
Q = Required Vol. / 172,800 see. (2-days)
= 0.116 cfs
Required Area of Pipe for 2-day drawdown:
A= 0/[CdxSQRT(2xgxh)]
Cd = 0.6
9 = 32.2 ft./32
h - (F.P. elev.- N.P. elev.) /2
= 0.5 ft.
A = 0.0341 sq. ft.
Diameter of Pipe for 2-day drawdown:
DIA. = SQRT[(A x 4) / pi]
= 0.2084 It.
2.50 in.
USE: 2.5 in ORIFICE
Outlet Structure Check:
Using a 4' x 4' Basin,
Perimeter = 16 It.
Q = CIA
C = (% imp.)(.95) + (1-% imp.)(.25)
0.57
1= 5.45 in. for a 10 yr. Storm
A = 9.76 Acres
30.36 cis
Q= CwxLxH'-5
H = [Q / (Cw x L)p
Cw = 3
0.74 ft.
Peak elevation = flood pool elevation + H
31.24 ft.
Provided Volume
Bottom Pool SA = 1,957 sq. ft.
Normal Pool SA = 3,538 sq. ft.
Vol. _ [(N.P. SA + F.P. SA) / 2] x (F.P. el. - N.P. el.)
9,616 cu.ft.
---depth= 4 ft.
Flow for 5-day drawdown:
for 1st 1" of stonnwater,
Q = Required Vol. / 432,000 sec. (5-days)
= 0.046 cf5
Required Area of Pipe for 5-dav drawdown:
Am Q/[CdxSQRT(2xgxh)]
Cd = 0.6
g - 32.2 ft./s2
h = (F.P. elev. - N.P. elev.) / 2
0.5 ft.
A = 0.0136 sq. ft.
Diameter of Pipe for 5-day drawdown:
SQRT[(A x 4) / pi]
0.1318 ft.
= 1.58 in.
00137POND 2 of 2

P. 1
* COMMUNICATION RESULT REPORT ( JAN.30.2001 5:15PM )
FILE MODE --- OPTION
---------------
860 MEMORY TX
REASON FOR ERROR
E-1) HANG UP OR LINE FAIL
E-3) NO ANSWER
ADDRESS (GROUP)
-------------r-----------
9-7635631 OK
P` r
E-2) BUSY
E-4) NO FACSIMILE CONNECTION
WIRO
State of North Carolina
Depaitment of Environment and Natural Resources
Division of Water Quality
Wilmington Regional Office
Michael F, Easley, Governor William G. Ross Jr., Secretary
FAX COVER SHEET
Date: January 30, 2001
To: Phil Tripp, P.E.
Company: Tripp Engineering, P.C.
FAX #: [phone]
No. of Pa: 1
Fr m: Scott Vikion
Water li
ty S on - Stormwater
FAX N.-910
1! 00!
Phone #: [phone]
DWQ Stormwater Project #SWS 980611MOD
Project Name: IMF NorthChase
MESSAGE:
Phil,
please address the following items in order to continue the review process of the above
mentioned application for Stormwater;
1, Delineate wetlands on -site or note on the plans that none exist,
2. Please include a sealed set of calculations for the design of tho pond.

State of North Carolina
Department of Environment and Natural Resources
Division of Water Quality
Wilmington Regional Office
Michael F. Easley, Governor William G. Ross Jr., Secretary
FAX COVER SHEET
Date: January 30, 2001 No. of Pages: 1 ff
To: Phil Tripp, P.E. From: Scott Vinson
Company: Tripp Engineering, P.C. Water Quality Section - Stormwater
FAX #: [phone] FAX #: [phone]
Phone #: [phone]
DWQ Stormwater Project #SW8 980611MOD
Project Name: HMF NorthChase
MESSAGE:
Phil,
please address the following items in order to continue the review process of the above
mentioned application for Stormwater:
1. Delineate wetlands on -site or note on the plans that none exist.
2. Please include a sealed set of calculations for the design of the pond.
3. At your request I would like to change the sediment benchmark pond depths
on page 3 of 4 of the supplement form from 1.0 foot permanent pool depth
to a 3.0 foot permanent pool depth. (For both main pond and fore bay.)
4. Please correct the temporary pool elevation (Flood Pool) on the "Detention
Pond Outlet Structure" detail from 32.0 to 30.50 located on sheet C2.
5. Please correct the Total Impervious Area from 269,116 SF to 194,116 SF on
the Site Data Chart located on sheet C1.
SAWQS\STORMWAT\ADDINFO\980611.JAN
127 Cardinal Drive Extension, Wilmington, NC 28405-3845 Telephone [phone] FAX [phone]
An Equal Opportunity Affirmative Action Employer

TRIPP ENGINEERING, P.C.
419 Chestnut Street
Wilmington, North Carolina 28401
Phone: [phone] • FAX: [phone]
December 7, 2000
NCDENR
Division of Environmental Management
Water Quality Section
127 Cardinal Drive
Wilmington, NC 28405-3845
Attn: Ms. Linda Lewis
Re: HMF Northchase
SW8 980611 MOD
New Hanover County, NC
TE 00137
Dear Linda:
Enclosed please find two (2) sets of plans, one (1) signed original and one (1)
copy of the application form with narrative, one (1) wet detention basin supplement and
one check for the application fee for the modification of existing permit SW8 980611.
Please review for approval and contact us with any questions or comments.
Thank you.
Sincerely,
Tripp Engineering, P.C.
A�VFXut� )Omwy
Katherine Powell
KAP: dcb
E nc.

December 7, 2000
Stormwater Narrative
HNT Northchase
New Hanover County, NC
TE 00137
The total drainage area of this project is 9.76 acres. This site contains an existing building
with area of 75,000 sf. An asphalt and stone parking area for this existing building will
total 119,116 sf. A complete 1,116 sf (1,965 sf of sidewalk) brings the total built upon
area to 45.7% impervious. I 14 rib
Stormwater runoff will be handled by an on -site wet detention pond designed to exceed
the states requirement of the first one inch of runoff. This pond will drain to Smith Creek
with a classification of C-SW.