SW8910806_Historical File_19911119

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?roiect #: 910806 File Name: DET806 Reviewer:Alexis Finn
Proj;:ct .Jame; PENBROKE AT LANDFALL Date: 11/18/91
##############►###DETENTION POND ANALYSIS########################
POND t o, 1 OF 3
TotV S ite Arsa, TA;
TA:
215905
ft"2 It
;acre!] J (43560 ft'`2Jacrel:
TA:
4.956496
Acres
Total Crainage A,,ea, DA:
DA=
215905
ft"2 It
tDA (acre)] J (43560 ft"2/aerel:
v
DA:
4.956496
Acres
I1iPEf viwl �I;RFACE AREA CALCULATIONS:
Structure Surface Area, A
Runoff Coef., C
sf
Buildings: 46303
1 Adjusted
Surface
Area
: A
# C :
46303
ft"2 It
ParkugJsidewalks/streets; 352SO
0.95 Adjusted
Surface
Area
: A
# C :
33525.5
ft-2 if
f tsitG ;aevelop4d;; 100138
0.8 Adjusted
Surface
Area :
A
# C :
80150.4
ft"2 It
Wren^ Areas: 134312
0,2 Adjusted
Surface
Area
: A
# C :
26862.4
ft-2 ##
TOTAL;
MUM
ft"2 ##
2r srt Impery uus, %I: note: SA:(BUILDING+PARKING+OFFSITE):159978.9 sf
[SSA/TA]#iOO:
[ 159978,9 J 215905 1#100: SI: 14.10%%
Note; It %I < 30% check Density Option.
If %I 7 30%, require engineered system to minimize non -point stream degradation.
Pv1D i:d;;;
Ainimum, Required Storage Volume, VOLreq; note; SA has been multiplied by runoff coefficients
[SA (f"2) # (1 inch of runoff) # (1 ft/12 inch)]:
[ 186841.3 ft-2 # 1 inch # 0.083333 ft/inch]: VOLreq: 15570.10 ft"3
##
POND SKIN,,;
Botlom Elevation, ELb: ELb = 16.81 ft If
lermanent Pool Elevation, ELpp:
ELpp:
22.3
ft
It
Area of
Permanent Pool, App;
App :
4i856
ft"2
##
tor,ags
Pond Elevation, Esp:
ELsp:
23.3
ft
##
Area of
Storage Pond, Asp:
Asp =
43902
ft"2
##
sunof 4,
:brag:• Depth, d:
(via project engineer's
design; d : ELsp - ELpp)
d:
1
ft
##
.forage
'o:ume Provided, VOLpro:
Side Slope: 3:1
####
Volume 1, V1: App # d
: 4i856 ft"2 # 1 ft :
V1:
41856
ft"3
Ve ame 2; 1,12: (Asp - App) # d # 0.5 =
V2:
1023
ft"3
VOLpro : V1 + V2 :
41856 ft"3 + 1023 ft"3
VOLpro:
42M
ft"3
,eVte
iULrea V01orf,: 2YCegs
StoraGR iS availahla, tharafnra Dnnd
Si7a is ACC4.^+��la.

4.1, ., D . L•,..5. , , - -r. -, -. :dG 5J JLor -tje ° 0i.DslC------.-
DETENTION POND ANALYSIS CONTINUED: PAGE TWO
PERNENANT P40L:
Perm, Pool at Normal level= 22.3 ft
Botiom of Pond = 16.91 ft
Depth Prcyided, D = 5.43 ft <----- Okay, depth > OR = 3 ft.
SA;;A CALCULATION:
By .-hart #4; b 90% TSS:
Depth, D - 5.43 ft
% Impervious = 74.10%
DA - 4.956496 Acres Where DA is the Oraninage Area
SA/DA % = 4.78 U H
Area of Permanent Pool Required = (SA/DA %) '► DA
Aiea of Permanent Pool Required = 4.79 x 4.289286 Acres
Area of Permanent Pool Required = 0.236920 Acres
Arca of Permanent Pool Required : 10320.25 ft"2
=:rea of PM AfiERT POOL Required: 10320.25 sf < provided ares of
ORIFICE j OUTLET SIZING:
VOLpro = 42879
Orifice autflow, 2 Day Drawdown = Voipro/[(2 day) * (86400 sec/day)]
Oriti-.e o;ttlow, 2 Day Drawdown = 42879 ft-3 / 172000 sec =
Orifice C.S. Area, A:
A= Q/[Cd((2gh)"0.5))]
41856 sf <--OKAY: sufficient stor
Q2= 0.248142 cfs
A= 0.248142 / [0.6A{(2x32.2m1.0)"0.5))]= A2--
A2=
Pipe diameter, d: d2=
Note: Head, h = maximum pond level - permanent pond level =
Coeficient of Discharge, Cd = 0.6
0,051535 ft"2
7.421115 inch"2
3,073099 inch
1 ft
<outtiow, 5 Day Drawdown = Volpro/[(5 day) # (86400 sec/day)]
it tice outflow, 5 Day Drawdown = 42879 ft-3 / 432000 sec =
.?rifice L... Area. A:
Q5-- 0.099256 cfs

1,. - -a."r _.-e,i
A: 0.099256 / [0.6*((2*32.2$l.0)-0.5))]= A5: 0.020614 ft"2
A5= 2.968446 inch"2
Pipe diameter, d: d5: 1.944104 inch
Ca: da dprovided < d2 : 1.9 < 2.0 < 3.1 <------ OKAY ... ; Orifice is sized correctly.
Ev ! No. 2 OF 3
---------------
T,:ta Cite Area, TA:
TA--
441142
ft"2 ##
IPA (acre)] / [43560 ft°2/acre]=
TO
10,12722
Acres
Tctal Drainage Area, DA:
00
148329
ft"2 ##
IDA (acre)] / [43560 ft"2/acre]=
DA--
3.405165
Acres
M EiVIOUS SURFACE AREA CALCULATIONSS
StiucTu,a Surface Area, A Runoff Coef., C
sf
Buildi:gs: 66102 1 Adjusted Surface Area = A * C = 66102 ft-2 ##
Pcrt;:ngjs;da1s/streets: 61009 0.95 Adjusted Surface Area : A s C : 63658.55 ft"2 ##
G.T"U Areas: 15218 0.2 Adjusted Surface Area : A S C : 3043.6 ft"2 It
TOTAL: 132804.1 ft"2 ##
fvr gin;. impervious, %I: note: SA:(BUILDING + PARKING..): 133111 sf
[SA/TA]4100=
I 13311i / 441142 ]$M: %I= 30.13%
Note; If xI < 30% check Density option.
If %I ) 30%, require engineered system to minimize non -point stream degradation.
P:;;,) SIZ7.NC,
Minimum Required Storage Volume, VOLreq: note: SA has been multiplied by runoff coefficients
SA (ft 2' (i inch of runoff) (1 ft/12 inch)]--
1 132804.1 ft"2 $ 1 inch 0.083333 ft/inch]: VOLreq: 11067.01 ft"3
it

------------
Bottom Elevation, ELb:
ELb =
fermaneat
Pool Elevation, ELpp:
ELpp:
Area of
Permanent Pool, App:
App =
"Storage
Pload Elevation, Esp:
ELsp:
Area of
Storage Pond, Asp:
Asp =
urrff
boragG Depth, d:
(via project engineer's design: d = Elsp - ELpp)
d:
Storage
Volume P ovided, VGLpro: Side Slope: 3:1
####
Volume 1, Vi= App s d = 36977 ft"2 * 1 ft :
V1:
Volume 2, V2= (Asp - App) W d * 0.5 :
V2:
VGLpro : V1 + V2 = 36977 ft"3 + 6485 ft"3
VOLpro:
1lott:
;;lr y : VGLpro; excess Storage is available, therefore Pond
Size is Acceptable.
---
% Excess Storage --(VOLreq J VGLpro) $ 100 % Excess Storage =
DETENTION POND ANALYSIS CONTINUED: PAGE TWO
f'E ;ITtPlAN;l Pr' ;.:
Perm. Pool at Normal Level: 22 ft
bottom of Pond = 17 ft
-'h "rovid'd , D - 5 ft <----- Okay, depth > OR - 3 ft.
,3A/, A CALCULATION:
By ciil rt #4; @ 90% TSS:
Depth, D - 5 ft
S Impervious : 30.17%
DA : 3,405165 Acres Where DA is the Draninage Area
SA/DA % : 2.55 ####
Area of Permanent Pool Required : (SA/DA %) # DA
Araa of Permanent Pool Required = 2.55 3.048763 Acres
Area of Permanent Pool Required : 0.086031 Acres
_ ea of Permanent Pool Required : 3782,389 ft"2
Area of PERMANENT POOL Required: 3782.389 sf < provided area of
ft It
22 ft It
36977 ft"2 It
23 ft It
49947 ft"2 ##
i ft ##
36977 ft"3
6485 ft"3
43462 ft"3
<--------
74.54%<--------
36977 sf <--OKAY: sufficient stor

VOLpro
= 43462
Orifice outflow,
2 Day Drawdown =
Volproj[(2 day) x (86400 sec/day)]
v:'iti'ce outtlow,
2 Day Drawdown =
43462 ft-3 j 172800 sec =
Q2=
0,251516
cfs
Orifice
C.S. Area, A:
A= Q/[Cd((2gh)"0.5))]
A=
0,251516 ( [0.6*((2132.2*1.0)-0.5))]=
A2=
0.052236
ft"2
A2=
7.522016
inch"2
Pipe diameter, d:
d2=
3.094725
inch
Note:
Head, h = maximum pond level permanent pond level =
1 ft
Coefficient of Discharge, Cd = 0.8
critic,. cuttlow, W Day Drawdown = Volproj[(5 day) * (86400 sec/day)]
Or;tice. outflow, 5 Day Drawdown = 43462 ft"3 ( 432000 sec = Q5= 0.100606 cfs
Cr tics C.S. Area, A:
A= Qj[Cd((2gh)"0.5))]
A= 0,100606 j [0.6*((2*32.2t1,0)-0.5))]= A5= 0.020894 ft"2
A5= 3.008806 inch"2
Pipe diameter, d: d5= 1.957276 inch
• i. 5 '°;; i:cd ' �^ : 23 < 2,0 3.1 (------ OKAY ... ; Orifice is sized correctly.

dotal Site Area, TA:
TA:
202300
ft-2
##
(TA (acre)] / 1,43560 ft"2/acre]:
TA:
4.644168
Acres
Total Drainage Area, DA:
00
90263
ft-2
#$
[bA1 (acre)] ; (43560 tt"2/acre):
DA:
2.072612
Acres
IA',*11 cVIOUS SURFACE AREA CALCULATIONS:
tructury Surface Area, A Runoff Coef., C
sf
Buildin,s: 42260 1 Adjusted
Surface Area :
A C :
42260
ft"2
##
Parkingsidewalksjtreets: 24057 0.95 Adjusted
Surface Area :
A a C :
22854.15
ft"2
##
Sreen Areas: 23966 0.2 Adjusted
Surface Area :
A # C :
4793.2
ft-2
##
TOTAL:
69907.35
ft"2
##
"ercint impervious, %I, note: SA:(BUILDING + PARKING..):
66317 sf
(SA/TA]1100:
( 66317 / 202300 1t100:
%I:
32.78%%
Mote: It %I < 30% check Density Option.
If %I > 30%, require engineered system to minimize non -point
stream degradation,
POND SLZING:
------------
Ainimum required Storage Volume, VOLreq: note: SA has been
multiplied by
runoff coefficients
I3A (tt`211 # ;1 inch of runoff) t (t ft/12 inch)]:
{ 69907.35 ft-2 x 1 inch 0,083333 ft/inch]:
VOLreq:
5825.612
ft"3
Bc.tsm elevation, ELb:
ELb :
13
ft
It
Pefwaner;t roof Elevation, ELpp:
ELpp:
18
ft
##
r:;a =' Perma,,ient Pool, App:
App :
6745
ft"2
##
�.orage Pon,.' Elevation, ESP:
ELsp=
19
ft
##
Arc; at Storage Pond, Asp:
Asp :
9473
ft"2
##
uncit �,to,'age Lepth, d:
(via project engineer's design: d : ELsp - ELpp)
d:
1
ft
#f
'to rag Volume Provided, VOLpro: Side Slope:
3:1 fill
Volume 1, V1: App s d : 6745 ft"2 s 1
ft :
V1:
6745
ft"3
Vclume 1', V2: (Asp - App) 4 d x 0.5 :
V2:
1364
ft"3
VOLpro = V1 + V2 : 6145 ft"3 + 1364
ft"3
VOLpro:
8109
ft"3
Note: Vi7Lreq t VOLpro; excess storage is available, therefore Pond Size is
Acceptable.
<--------
- -- I Excess Storage :(VOLreq / VOLpro) t 100
% Excess Storage
:
28.16%<--------
DETENTION POND ANALYSIS CONTINUED: PAGE TWO
PL01NAN N0 �1UL:
Perm, Pool at Normal Level: le ft
B„=tom of Pond 13 ft
Ecpth Provide: 0 : 5 ft <----- Okay, depth > OR : 3 ft.

�A,'DA CALCULATION:
Sy Chart t4; @ 90% TSS:
Depth, D - 5 ft
% Impervious = 32.78%
DA = 2.072612 Acres Where DA is the Draninage Area
'.A/DA % = 2.38 111#
Area
of
Permanent
Pool
Required =
(SA/DA 4) * DA
Area
of
Permanent
Pool
Required
= 2.38 # MUM Acres
Area
of
Permanent
Pool
Required =
0,049328 Acres
Area
of
Permanent
Pool
Required
= 2140.735 ft"2
Area of PPRNAMENT POOL Required: 2148,735 sf < provided area of
ANTFICE , JTIET SI7ING:
VOLpro = 8109
Orifice outflow, 2 Day Drawdown = Volpro/[(2 day) r (86400 sec/day)]
cutflow, 2 Day Drawdown = 8109 ft"3 / 172800 sec =
Orifice C.S. Area, A:
6745 sf <--OKAY: sufficient stor
Q2= 0.046927 cfs
A= Q/[Cd((29h)"0.5))]
A= 0.046927 / [0.6t((2*32.2*l.0)"0.5))]= A2= 0.009746 ft"2
A2= MOM33 inch"2
Pipe diameter, d: d2= 1.336752 inch
Note: Head, h = maximum pond level - permanent pond level = 1 ft
Coeficient of Discharge, Cd = 0.6
r: is auttlow, 5 Day Drawdown = Volpro/[(5 day) $ (86400 sec/day)]
vrit,.we outflow, 5 Day Drawdown = 8109 ft"3 / 432000 sec = Q5= 0.018170 cfs
=rifice G.S. Area, A:
A= Q/[Cd((2gh)"0.5))1
A= 0.018770 / [0.6w((2e32.2e1,0)-0.5))]= A5-- 0.003898 ft"2
AS- 0.561373 inch"2
Pipe diameter, d: d5= 0.945436 inch
NEU : d5 � dprovided C d2 : 0.8 < 1.0 < 1.3 <------ OKAY...; Orifice is sized correctly.

-XF LTRATION PIPE ANALYSIS
---------------------
PROiPOSED IMPERVIOUS AREA SUMMATION:
uas;A Paved Roof Sidewalk TOTAL
st sf sf sf sf
--------------- -------------------------------
A 6400 0 0 6400
;eta'; tit 6400 0 0 6400
10:81; ac 0.'5 0100 0.00 0,15
PROPOSED - EXISTING
EXISTING IMPERVIOUS AREA SUMMATION;
Basin Paved Roof Sidewalk TOTAL
sf sf sf sf sf
---------------------------------------------
A 0 0 0 0
Total; sf 0 0 0 0
Total: ac 0,00 0,00 0.00 0.00
TOTAL IMPERVIOUS AREA : $400 SF
TOTAL IMPERVIOUS AREA = 0,148923 ACRES
Desgr for 1.0 inch of rainfall - recieving waterway is not classified SA.
Determine average runoff coefficient:
Area Runoff
Type Coeff,
Root 1.00
Urein 0,20
Pvmt. 0.90
Average (for P RF)
Basin Paved Root Green TOTAL Runoff Volume
sf sf sf sf sf Coeff. cf
------------------------------------------------------------------
A 4800 0 16DO 6400.00 0.73 386.67
---- ---- ---- ---- ---- ----
Total: sf 4800 0 1600 6400 0.725 386,6666 <----- Minimum Required Volume, cf
Total: ac 0.1i 0.00 0,04 0.15 n Al a-- L,,,
0 11" Illum KcW l Cu tv i �wv, acr,��
e$

3, Trench Design:
Ecttom width, W= 6 ft
Sideslopes, H:V= 1 ft
'?eatIt, d= 2 ft
Pipe Diameter, D= 12 inches
'storage Capacity of Trench:RECTANGULAR
Area of Trench, At: (Wsd)= 12 sf
Area at Pipe, Ap: (@Pi $ DA2)/576 0.785398 sf
Void Space = Porosity, P = 0.4
ctfective gravel volume, Vg = P$(AtsAp) = 4.485840 Cf/Lf
Total Storage Volume: Vg +(Ap $1 ft) = 5,271238 Cf/Lf
Linear feet of pipe provided = 80 ft
Total Storage Provided = L ► Vt = 421.6991 cf
,ko5,�7 :-----Hi;imum, Required Volume, cf
% difference = 8,31li
Note: Project Engineer has a excess of 35.03244 cf of volume.
This is equivalent to 6.645960 LF of combined trench and pipe.

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90
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4 DI RIM 22.5'
CONSTRUCTION
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L GRADI(1) GRADING CONTRACTOR NG PLAN
SHALL ADJUST EX.
MH RIM TO 0.2'i.

S. Keith Cooper, P.E.
6 Bahama Drive
Wrightsville Beach, NC 28480
[phone]
November 5, 1991
ReCEIVED
A10V t t
Ms. Alexis I. Finn
Environmental Engineer
N.C. Department of Environment, Health and Natural Resources
127 Cardinal Drive Extension
Wilmington, North Carolina 28405
RE: Pembroke at Landfall
Stormwater Project No. 910806
Dear Ms. Finn:
This package is in response to your October 21 review comments.
POND #1
la. The four elevations on Sheet 3 ranging from 16.39 to 16.87
are actual bottom elevations. These are now labeled as
such.
lb. Pond contour elevations have been labeled.
lc. The three existing pipes emptying into the north end of Pond
#1 drain from the adjacent tennis facility. The three
pipes, plus surface runoff from a small area west of the
pond, generate an estimated 12.9 CFS from 2.3 acres of
previously developed property. See Paces 3, 6 and 10 of the
calculation package (July, 1991) for discussion and
calculations. Inverts have been added.
id. The comment is noted. No changes made.
lI\1 NOV 13 1991 LJ
DEM
Oj # 9/0g061

POND #2
2a. The continuous contour at normal pool elevation 22.0 is
labeled as such. Elevations at the storage elevation were
already labeled.
2b. The catch basin rim elevation has been revised to 25.0
POND #3
3a. Catch basin invert elevations are labeled on Profile Sheets
5, 6 and 7.
GENERAL
1. North arrows added as necessary.
2. Development name added as necessary.
3. Notarized submittal authorization enclosed.
4. The detail of pond inlets is on Sheet 8.
5. Due to the amount of information required to show roof drain
locations on these drawings, we can not do so. The original
and now the two subsequent answers to review comments have
noted the need for some roof drains. That should be
satisfactory.
6. The FES between Units 32 and 33 does not pick up off -site
runoff.
7. As noted on Sheet 7, the FES in front of Unit 26 has an
invert of 23.5.
8. The detail of the exfiltration trench is shown on Sheet 3.
9. As we discussed last week, I ask that the NCDEHNR soils
scientist schedule a time to perform the soils
investigation.
10. As shown on Sheet 3, the existing ground elevation at the
exfiltration trench is approximately 27.
11. The area contributing to the exfiltration trench
delineated on an enclosed print of that s f: �0 [ � V
t.
3 1991
D t ivl

12. The invert of the exfiltration trench is shown on Sheet 5.
13. The observation well detail is shown on 9. The well is
sited on Sheet 3, adjacent to Unit 57.
In addition, we have enclosed a copy of the wetlands delineation
of the site performed in March 1991 using 1989 delineation
methods. The wetlands impact based on this delineation will be
0.98 acres or less. The development will create in excess of 1
acre of deep water wetlands systems as part of the stormwater
permitting requirements.
The statement ending your letter that the "file is on hold
subject to 401" water quality certification disturbs us greatly.
The project was initially submitted August 5, 1991. We
understand 401 water quality certification is part of your
considerations; however, we do not feel the review should be put
on hold. The two should continue concurrently.
Sincerely,
, :�e;ith Coo r, P.E.
SKC/vc
Enclosure
p E V'
U
NOV 13 1991
DEM
®J io o�

q ik
V
F A L
BLAIR PROPERTIES, INC.
POST OFFICE BOX 468
WRIGT-ITSVII T E BEACH, NC 28480
TELEPHONE [phone]
November 5, 1991
NOV 13 1991 U
U E IVI
Ms. Alexis I. Finn
Environmental Engineer
N.C. Department of Environment, Health and Natural Resources
127 Cardinal Drive Extension
Wilmington, North Carolina 28405
RE: Pembroke at Landfall
Stormwater Project No. 910806
Dear Ms. Finn:
This letter is to advise the North Carolina Department of
Environment, Health and Natural Resources that S. Keith Cooper is
authorized to submit plans and specifications on behalf of Blair
Properties, Inc.
Sincerely,
tme F. Smith
B PROPERTIES, INC.
North Carolina, �`�i�te County
I, , a Notary Public for
Coun a S a e aforesaid, certify that James F. Smith
personally came before me this day and acknowledged the
execution of the foregoing instrument. Witness my hand
this day of e'7/�¢._� , 1991.
My Commission Expires
4-q'0�'&'.Notary Public
SEAL
the
due
and seal

S. Keith Cooper, P.E.
6 Bahama Drive
Wrightsville Beach, North Carolina 28480
[phone]
Ms. Alexis I. Finn
Environmental Engineer
North CArolina Department of Environment,
Health & Natural Resources
127 Cardinal Drive Extension
Wilmington, North Carolina 28405
Re: Pembroke at Landfall
Stormwater Permit No. V10806
Dear Ms. Finn:
As previously discussed we are submitting three copies
each of Sheets 3 and 5 showing revisions to the
exfiltration trench. The trench has been redesigned to be
above the apparent seasonal high water table as measured
by the NCDEM soils scientist.
Please advise if there are nany questions regarding this
matter.
Sincerely,
'
co
Z ith C OPKITEn

State of North Carolina
Department of Environment; Health; and Natural Resources
Wilmington Regional Office
James G. Martin, Governor Bob Jamieson
William W. Cobey, Jr., Secretary Regional Manager
October 21, 1991
DIVISION OF ENVIRONMENTAL MANAGEMENT
Mr. S. Keith Cooper, P.E.
6 Bahama Drive
Wrightsville Beach, North Carolina 28480
Subject: Additional Information
Stormwater Project No. 910806
Pembroke @ Landfall
New Hanover County
Dear Mr. Cooper:
The Wilmington Regional Office received additional
information submittal for Pembroke @ Landfall on October 8, 1991.
A review of that information has determined that the following is
needed to complete the stormwater review:
Pond #1
✓ la. Bottom elevation
lb. Identify elevations on pond contours of site plan
✓ lc. What are the 3 pipes which cross the property line
contributing tC Lhe detention pond? Provide invert
elevations, grade, type, size and flow.
1d. Flared end sections and rip rap at pond inlets or supporting
calculations which determine energy dispersion is
unnecessary.
Pond #2
✓ 2a. Provide a continuous contour at the storage elevation or
higher
✓2b. Catch basin in front of buildings 19 & 20 has rim elevation
noted as 21.0 and invert noted at 23.08.
Pond #3
I
-/3a. Provide invert elevations of all catch basins
-continued-
127 Cardinal Drive Extension, Wilmington, N.C. 28405-3845 • Telephone [phone] • Fax [phone]
An Equal Opportunity Affirmative Action Employer

Mr. S. Keith Cooper
October 21, 1991
Stormwater Project #910806
Page Two
General
11 1. North Arrow
„2. Add development name to site plans
-3. Notarized submittal authorization
Detail of pond inlets
i�6'.,t✓ 5. Provide roof drains and locate connections.
6. Does the inlet between buildings 32 & 33 pick up any offsite
water?
7. What is the invert elevation of the flared end section
beside building #26?
8. Provide a detail of the exfiltration trench.
9. Provide soils data from the proposed location of exfiltration
trench with seasonal high water table elevation and
infiltration capacity.
10. What is the existing elevation of the area which is proposed
to contain exfiltration piping?
11. Delineate area contributing runoff to the exfiltration pipe.
12. Provide proposed elevation of exfiltration pipe invert and
grade.
13. Provide an observation well (and detail) down gradient of the
exfiltration pipe.
Please note that this file is on hold subject to 401 Wetland
review and approval by this Office. This information should be
received by this office no later than November 21, 1991. If you
have any questions, please call me at telephone number (919)
395-3900.
AIF: 910806.00T
cc: (2) Alexis Finn
Central Files
'Sin ly,
Ms. Alexis I. Finn
Environmental Engineer

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S. Keith Cooper, P.E.
6 Bahama Drive
Wrightsville Beach, NC 28480
[phone]
October 3, 1991
Ms. Alexis I. Finn
Environmental Engineer
North Carolina Department of Environment
Health and Natural Resources
Wilmington Regional Office
127 Cardinal Drive Extension
Wilmington, North Carolina 28405-3845
RE: Stormwater Permit No. 910806
Pembroke at Landfall
Dear Ms. Finn:
01-'T'f 1991
•-n M
D ECEIV(
OCT 8 1991
'AQJ 9io M
This letter and the enclosed package address the comments in your
September 6, 1991 letter to Mr. James F. Smith.
(1) Two drawings delineating the subdrainage areas of the
ponds are enclosed.
(2) offsite runoff will be routed through pond 1. Notes on
offsite runoff are made on pages 3 and 4 of the
calculations.
(3) The pipes discharging into ponds 1 and 2 near the outlet
structures have been relocated to eliminate short
circuiting.
(4) The site contains some 404 wetlands regulated by the U.S.
Army Corps of Engineers. Most of these wetlands lie in or
near the existing cypress pond., Wetland impacts will be
less than the 1 acre exemption allowed by Nationwide
Permit 26 [33CFR 330.5(a)(26)]. Notification of less than
oF-�rlesa►'[�E' _-
(5) Energy dissipaters at pond inlets have been added to the
grading plans (sheets 3 and 4), and a detail has been
added to sheet 8.

(6) Details of pond inlets and outlets are shown on sheet 8.
(7) Excess runoff is routed to an unnamed tributary of the
Baby's Hospital Pond.
If there are any questions regarding this package, please call.
Sincerel ,
�S-<th Cooper,P.E.
SKC/vc p I5 Q v I I
U.
Enclosure OCT 8 1991
D E M

State of .North Carolina
Department of Environment, Hlealth, and Natural Resources
Wilmington Regional Office
lames G. Martin, Governor Bob Jamieson
William W. Cobey, Jr., Secretary Regional Manager
September 6, 1991
DIVISION OF ENVIRONMENTAL MANAGEMENT
Mr. James F. Smith
Blair Properties, Inc.
Post Office Box 468
Wrightsville Beach, North Carolina 28480
Subject: Additional Information
Stormwater Project No. 910806
Pembroke at Landfall
New Hanover County
Dear Mr. Smith:
The Wilmington Regional Office received a stormwater
submittal for Pembroke at Landfall on August 12, 1991. A
preliminary review has determined that the submittal for the
subject project is not complete. The following information is
needed to continue the stormwater review:
1. Delineate subdrainage areas for each pond.
2. Is offsite runoff proposed to be routed through the
basins?
3. Please maximize the distance between the pond inlets
and outlets. Short circuiting the pond is of concern.
4. Are wetlands located on -site? If, so please indicate
type and location on the site plan.
5. Show energy dissipation at pond inlets on plans.
6. Provide details of pond inlets and outlets with energy
dissipation and relevant elevations noted.
7. Where is runoff (in excess of design volume) routed?
What is the receiving waterway?
-continued-
127 Cardinal Drive Extension, Wilmington, N.C. 28405-3845 9 Telephone [phone] • Fax [phone]

Mr. Smith
September 6, 1991
Page Two
Stormwate.r. Project #910806
----------------------------
Please note that this is a preliminary review. This
information should be received by this office no later than
October 7, 1991. If you have any questions, please call me at
telephone number [phone].
Sincere ,
r
Ms. Alexis I. Finn
Environmental Engineer
AIF: 910806.SEP
cc: (2) Alexis Finn
Bill Mills
Central Files

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A T L AND F A L
BLAIR PROPERTIES, INC.
POST OFFICE BOX 468
WR11GHTS v TT E BEA - NC 2S4S0 _
TELEPHONE [phone] Al If
August 5, 1991
Ms. Alexis I. Finn
N.C. Division of Environmental Management
125 Cardinal Drive Extension
Wilmington, North Carolina 28405
RE: Pembroke at Landfall
Storm Detention Review
Dear Ms. Finn:
In accordance with Division of Environmental Management rules, we
are submitting herewith for your review the following:
Three sets of construction plans
-- Three sets of construction specifications
One set of stormwater calculations
- Executed Operation and Maintenance Manual
If there are any questions regarding these items, do not hesitate
to call me at [phone].
Sincerely,
Jr m F. Smith
B Properties, Inc.
JFS/vC
Enclosure
E C E u V � D
AUG 1.2 1991
U E M

PEXBRORE AT LANDFALL
NEW HANOVER COUNTYj, NORTH CAROLINA
OWNER: BLAIR PROPERTIES, INC.
POST OFFICE BOX 468
1322 AIRLI.E ROAD
WRIGHTSVILLE BEACH, NC 28480
[phone]
ENGINEER: S. KEITH COOPER, P.E.
6 BAHAMA DRIVE
WRIGHTSVILLE BEACH, NC 28480
[phone]
+, `rrrrrrn rrr�r,
C ARge
4•.• ��44 E ssto,��,29'',.
S EAL
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ULY, 1991(�� U� 6
AUG I
D E M
.1,O j # 9

SECTION 700
EROSION CONTROL
GENERAL
The Contractor shall take all precautions necessary to
minimize soil erosion, siltation, water pollution, and air
pollution caused by his operations. The Contractor shall
comply with the applicable regulations of all legally
constituted authorities relating to pollution prevention and
control. The Contractor shall keep himself fully informed of
all such regulations which in any way affect the conduct of
the work and shall at all times observe and comply with all
such regulations. In the event of conflict between such
regulations and the requirements of the specifications, the
more restrictive requirements shall apply.
The Contractor shall exercise every reasonable precaution
throughout the life of the project to prevent the eroding of
soil and the silting of rivers, streams, lakes, reservoirs,
other water impoundments, ground surfaces, or other property.
Prior to suspension of operations on the project or any
portion thereof, the Contractor shall take all necessary
precautions to protect the construction area from erosion
during the period of suspension.
Unless otherwise approved in writing by the Engineer,
construction operations in rivers, streams, and water
impoundments shall be restricted to those areas where channel
changes are shown on the plans and to those areas which must
be entered for the construction or removal of temporary or
permanent structures.
Excavated materials shall not be deposited, nor shall earth
dikes or other temporary earth structures be constructed, in
rivers, streams, impoundments, or areas classified as waters
of the United States or of this State, or so near to such
waters that they will be carried into any river, stream,
impoundment, or areas classified as waters of the United
States or of this State by stream flow or surface runoff. As
an exception to the above, confined earth materials will be
permitted when approved in writing by the Engineer. Frequent
fording of live streams with construction equipment will not
be permitted.

SECTION 700
Failure on the part of the Contractor to perform the required
erosion control measures will be just cause for the Engineer
to direct the suspension of operations. The suspension will
be effective until such time as the Contractor has
satisfactorily performed the required erosion control work.
CONSTRUCTION METHODS
EROSION AND SILTATION CONTROL
Temporary and permanent erosion control measures shall be
provided as shown on the plans or as directed by the
Engineer. Erosion control measures shall be coordinated
to assure economical, effective, and continuous erosion
control throughout the construction and post construction
period and to minimize siltation of rivers, streams,
lakes, reservoirs, other water impoundments, ground
surfaces, other property, or areas classified as waters
of the United States or of this State.
Materials for temporary erosion control measures shall
have been approved by the Engineer before being used or
shall be as directed by the Engineer.
Erosion control measures installed by the Contractor
shall be acceptably maintained by the Contractor.
If grading operations are suspended for any reason
whatsoever, partially completed cut and fill slopes shall
be brought to the required slope, and the work of seeding
and mulching or other required erosion control operations
shall be performed.
During construction and until final acceptance, the
Contractor shall maintain the work by shaping to provide
for the drainage of surface runoff along and throughout
the length of the project by constructing temporary
ditches, and by using any other methods necessary to
maintain the work covered by this article so that the
work will not contribute to excessive soil erosion.
AIR POLLUTION
The Contractor shall comply with all state and/or local
air pollution regulations throughout the life of the
project.

SECTION 700
DUST CONTROL
The Contractor shall control dust throughout the life of
the project within the project area and at all other
areas affected by the construction of the project,
including, but not specifically limited to, unpaved
secondary roads, haul roads, access roads, disposal
sites, borrow pits, and staging sites. Dust control
shall not be considered effective where the amount of
dust creates a potential or unsafe condition, public
nuisance, or condition endangering the value, utility, or
appearance of any property.
SEEDING AND MULCHING
Seeding and mulching are to be performed according to North
Carolina State Highway requirements, Section 880, with the
following special provisions: .
Seeding and mulching shall be done on earth areas
disturbed by construction or as designated by the
Engineer.
No seeding and mulching work shall be done between June
15 and August 15 unless otherwise approved by the
Engineer.
In order to prevent excessive soil erosion and siltation,
the Contractor shall complete grading to the proper cross
section and perform seeding and mulching work within 30
working days of final grading unless the Engineer
approved a specific permissible length of delay due to
circumstances beyond the control of the Contractor.
Special attention is called to the portion of Section 880-4
of the North Carolina State Highway Specifications dealing
with seedbed preparation on steep slopes. Superficial
scratching of the slope surface will not be sufficient
seedbed preparation. on 2:1 or 1 1/2:1 slopes, a seedbed
preparation will be required approaching the degree of
preparation required on flatter areas as far as depth is
concerned although the same degree of smoothness of seedbed
will not be required. Permanent slopes of 2:1 or steeper

SECTION 700
The kind of seed, the rate of application of seed, fertilizer
and limestone, and the seasonal limitations shall be as
follows (all rates are in pounds/1000 square feet):
Aug.
15 - Oct. 30
Feb.
15 - June
15
Nov.
1 - Feb. 15
1.75
lbs. -
Fescue Kentucky 31
2.75
lbs.
- Fescue
1.2
lbs. -
Pensacola Behia
0.6
lbs.
- Rye Grain
0.8
lbs. -
Korean Lespedeza
0.6
lbs.
- Unhulled
0.6
lbs. -
Hulled Bermuda
Bermuda
0.3
lbs. -
Weeping Love Grass
23
lbs.
- Fertilizer
(Slopes Only)
90
lbs. -
Limestone
23
lbs. -
Fertilizer
45
lbs.
- 70 lbs. Straw
90
lbs. -
Limestone
Sufficient
Emulsified
45
lbs. -
70 lbs. Straw
Asphalt to
Hold Straw
Sufficient
Emulsified
Asphalt to
Hold Straw
* Under no circumstances shall common Bermuda Grass be
planted within 100 feet of existing golf course fairways.
Areas within 100 feet of existing fairway will be seeded
with a mixture approved in writing by the golf course
maintenance superintendent. Schedules for seeding with
special mixtures shall be the same as those stated herein.
Limestone shall contain not less'than 85% of calcium and
magnesium carbonates and shall conform to the following
minimum screening standards. Ninety percent must pass
through U.S. standard 20 mesh screen, and twenty-five percent
must pass through U.S. standard 100 mesh screen.
Mulching - Mulch shall be spread uniformly over the area by
hand or by means of appropriate mechanical spreaders or
blowers to obtain an application satisfactory to the
Engineer. No seeded areas shall be allowed to remain for
more than 24 hours without mulching having been completed.
The Contractor will be required -to take sufficient
precautions to prevent mulch entering catch basins or pipe
lines through displacement by wind, water, or other causes.
The Contractor shall apply a sufficient amount of asphalt
tack to insure that the mulch is properly held in place.

SECTION 700 .
For slopes of 2:1 or greater, the Contractor shall use an
erosion control method approved by the Engineer. Acceptable
methods include use of hydromulch with resins used for tack
and erosion control blankets. Other methods will be
considered on an individual basis.
Erosion Control Blankets shall be equal to North American
Green - SC150 - distributed by Construction Fabrics Plus,
Pineville, North Carolina, 1-800-533-0046 (NC).
During the application of fertilizer in seeding operations,
or the application of asphalt materials during mulching
operations, adequate precautions. shall be taken to prevent
damage to traffic, traffic signs, curb and gutter, or any
other concrete or metal structures.
Once an area has been seeded and mulched, the Contractor is
required to take adequate precautions to insure that all
future construction operations do not damage these areas. No
payment will be made for repairs of any kind that are due to
negligence of the Contractor.
APPLICATION OF SPECIFICATIONS
The provisions of this article shall apply to all
construction operations. Further references and detailed
requirements concerning erosion, siltation, and pollution
prevention and control are given in the plans and/or special
provisions as supplements to the general requirements of this
article.
METHOD OF..PAYMENT
Payment for erosion control measures shall be made as
provided for by the various contract items in the Proposal.
Items of erosion control work shown on the plans but for
which there is no specific pay item in the Proposal shall be
paid for only through the payment for other items of work
listed.
The Contractor shall supply receipts showing weights of seed,
fertilizer, and mulch as proof that appropriate quantities of
materials were used. Failure to supply documentation will
result in payment being denied.

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Tables and Charts
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Table 1
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Runoff Coefficients for Use in Rational Formule. :;�
of Land U
Commercial
Industrial
Apartments, schools, churches
Residences, duplexes
Residences, 5000-7000 sq ft lots
Residences, 1/4-acre lots
Residences,.1/2-acre lots
Park
Woodland
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0.85
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0.60
0.45
0., 40
0.38
0.35
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0.2
1

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900
800
700
600
500
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100
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EXAMPLE Given discharge 0- 4.4CIA
friction factor n=0.012 -
slope of 0.0039 per foot
FIND Diameter 15 inches and
velocity of 3.5 ff. per second,
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NOMOGRAPH FOR
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n= 0.012
1019
Adopted from Engineering Manuol, Woe Department, Corps of Engineers, Nrt XIII,Chopl. 1, June 1955,
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CHART 3„
NORTH CAROLINA COASTAL
REGIONS
SA/DA
PERCENTAGES FOR WET
DETENTION BASINS;
DESIGNED TO REMOVE 85X
TSS (I" STORM)
SA/DA % For Basin
Depths
ITZ rvioua
X 3 Ft
3.5 Ft
4 Ft
S Ft f
30
2.. 5
2.2.
1.9
1 .6 `
40
3.4
3.0
2.6•
2..1 `.
50
4.2
3.7
3.3' .,
2. 7';
60
5.0
4.5
.
3.8
3.2
70
6.0
5.2
4.5
3.7
(:1(+
6 : B
6.0
5.•2
4.2
90
7.5
6.5
5. B
4.13
CHART 4
SA/DA
PERC,ENTA GHS FOR WET
DETENTION BASINS
DISCHARGING DIRECTLY
TO A STREAM
NO VEGETATIVE FILTER, ..P09T-DEVELOPMENT DISCHARGE
RATE:
< faRE-1.)E'.'El-.!,i'1"1N'I RATE
.FOR 10. YEAR
STORM)'
SA/DA
'/, For Basin
Depths
:?�5 Ft3, 5 Ft
4 Ft
.5 Ft
6 Ft
30
3.5 3
2.7
2.2
1.6
40
4.5 4
- 3.5,
2.1
50
5.6 5
4.3
3.5
2.7
60
7.0 6
5.3
4.3
3.4
70
6.1 7
6.0
5.0
3.9
00
9.4 8
7.0.
5.7
4.6
90
10.7 9
7.9
6.5
5.2
Interpolate in6.?rmediate values
SA/DA % = Sur-'f.-)ce area basin/drainage area to:b.asin'•.x,,10(
36A

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