SW8910806_Historical File_19911119 (2)

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?roiect #: 910806 File Name: DET806 Reviewer:Alexis Finn
vroi;:ct Name: PEMBROKE AT LANDFALL Date: 11/18/91
#xx*vx*x*xxkvv►***DETENTION POND ANALYSIS*1$I******$********$stt$
POND to, 1 OF 3
Iota; Site Aria, TA; TA: 215905 ft"2 If
[TA ;acre!] / [43560 ft"2/acre]= TA: 4.956496 Acres
Total Crainage A.°ea, DA: DA: 215905 ft"2 It
[{;A ,acre)] / [43560 ft"2/acre]: DA: 4.956496 Acres
IMPERVIAS SURFACE AREA CALCULATIONS:
Structure Surface Area, A Runoff Coef., C
st
Buildings: 46303 1 Adjusted Surface Area : A s C : 46303 ft"2 If
Parking/sidewalks/streets: 35290 0.95 Adjusted Surface Area : A $ C : 33525.5 ft"2 If
ftsiti (developed): 100188 0.8 Adjusted Surface Area : A e C : 80150.4 ft"2 ##
'Wrenn Areas: 134312 0.2 Adjusted Surface Area : A '* C : 26862.4 ft"2 if
TOTAL: 186841.3 ft"2 ft
eroent impervious, %I: note: SA:(BUILDING+PARKING+OFFSITE):159918.9 sf
tSSA/TA1*100:
[ 159978,9 / 215905 18100: SI: 74,10%%
Note: It %I < 30%i check Density Option.
If %I > 30%, require engineered system to minimize non-point stream degradation.
POND SUING;
Ainimum Required Storage Volume, VOLreq; note: SA has been multiplied by runoff coefficients
[SA (ft-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 SIINS.
Bottom Elevation, ELb: ELb : 16.81 ft It
Permanent Pool Elevation, ELpp: Elpp: 22.3 ft If
Area of Permanent Pool, App: App : 41856 ft"2 ##
Storage Pond Elevation, Esp: ELsp: 23.3 ft #t
Area of Storage Pond, Asp; Asp : 43902 ft"2 ##
Runott Storage Depth, d:
(via project engineer's design; d : ELsp - ELpp) d: 1 ft ft
Storage Volume Provided, VOLpro: Side Slope: 3:1 ####
Volume 1, Viz App * d : 41856 ft"2 * 1 ft : VI: 41856 ft"3
Vo a e 2, V2: (Asp - App) * d e 0.5 : V2: 1023 ft"3
VOLpro : V1 + V2 : 41856 ft"3 + 1023 ft"3 VOLpro: 42819 ft"3
,e&te; Iareo ( VOI nrn: 2YCeSS Storaml iS availahie, therefore Pond Size is Armen+361c,

i 1
DETENTION POND ANALYSIS CONTINUED: PAGE TWO
PERHENANT POOL:
Perm. Pool at Normal Level: 22.3 ft
Bottom of Pond = 16.61 ft
Depth Provided, D = 5.43 ft < Okay, depth > OR = 3 ft.
SA; A CALCULATION:
By Chart 44; 0 90% TSS:
Depth, 0 - 5.43 ft
% Impervious : 74.10%
DA - 4.956496 Acres Where DA is the Draninage Area
SA/DA % : 4.78 lift
Area of Permanent Pool Required = (SA/DA %) * DA
Aica of Permanent Pool Required = 4.78 * 4.289286 Acres
Area of Permanent Pool Required = 0.236920 Acres
Arca of Permanent Pool Required = 10320.25 ft"2
-:rea of PEWi'iEiiT POOL Required: 10320.25 sf < provided area of 41856 sf <--OKAY: sufficient stor
ORIFICE i OUTLET SIZING:
VOLpro = 42879
Orifice outflow, 2 Day Drawdown = Volpro/[(2 day) * (86400 sec/day)]
Orifice o;Atlow, 2 Day Drawdown = 42879 ft"3 / 172800 sec : Q2: 0.240142 cfs
Orifice C.S. Area, A:
A: 11/[Cd((2gh)"0.5))]
A= 0.248142 / [0.6*((2x32.2t1.0)"0.5))]: A2: 0.051535 ft"2
A2: 7.421115 inch"2
Pipe diameter, d: d2: 3.073899 inch
Note: Head, h = maximum pond level - permanent pond level : 1 ft
Coeficient of Discharge, Cd : 0.6
ur1fi e outflow, S Day Drawdown : Volpro/[(5 day) # (86400 sec/day)]
'iriticc outflow, 5 Day Drawdown = 42879 ft"3 / 432000 sec = Q5: 0.099256 cfs
Orifice L.S. Ares. A!

A: 0,099256 / [0.6*((2$32,2*1.0)"0.5))]: A5: 0.020814 ft"2
A5: 2.968446 inch"2
Pipe diameter, d: d5: 1.944104 inch
dprovided < d2 : 1,9 < 2,0 < 3,1 < OKAY..,; Orifice is sized correctly.
FW No. 2 OF 3
T,:ta :Me Area, TA: TA= 441142 ft"2 ##
ttA (acre)] / [43560 ft"2/acre)= TA: 10,12122 Acres
Total Drainage Area, DA: DA= 148329 ft"2 ##
[DA (acre)] / [43560 ft"2/acre): DA: 3.405165 Acres
IN ERVIO1S SURFACE AREA CALCULATIONS:
St'uctu,e Surface Area, A Runoff Coef., C
sf
Buildi:gs: 66102 1 Adjusted Surface Area : A * C : 66102 ft"2 ##
Parking/s;d:walks/streets: 61009 0.95 Adjusted Surface Area = A $ C = 63658.55 ft"2 ##
G:: n Areas: 15218 0.2 Adjusted Surface Area : A ; C : 3043.8 ft"2 ##
TOTAL: 132804.1 ft"2 ##
Percent impervious, %I: note: SA:(BUILOING + PARKING.,): 133111 sf
[SA/TA]x100:
[ 133111 / 441142 1*100: %I: 30.11%%
Note: If tI < 30% check Density Option.
If %I ) 30%, require engineered system to minimize non-point stream degradation.
SIr G:
Minimum Required Storage Volume, VOLreq: note: SA has been multiplied by runoff coefficients
iA (ft-2' * (1 inch of runoff) $ (1 ft/12 inch)]:
l 132804.1 ft-2 * 1 inch * 0.083333 ft/inch]: VOLreq: 11061.01 ft"3
If

r OND SIZIN :
Bottom Elevation, ELb: Elb = 17 ft ##
Permanent Pool Elevation, ELpp: ELpp: 22 ft If
Area of Permanent Pool, App: App : 36977 ft"2 ##
Storage Pund Elevation, Esp: ELsp: 23 ft If
Area of Storage Pond, Asp: Asp = 49947 ft"2 if
urott Storage Depth, d:
(via project engineer's design: d : ELsp - ELpp) d: 1 ft #f
Storage Volume Provided, VOLpro: Side Slope: 3:1 ####
Volume 1, Viz App * d : 36977 ft"2 * 1 ft = V1: 36977 ft"3
Volume 2, V2: (Asp - App) ' d * 0,5 : V2: 6485 ft"3
VOLpro : V1 + V2 : 36977 ft"3 + 6485 ft"3 VOLpro: 43462 ft"3
Note: ;;;lroq VOLpro; excess storage is available, therefore Pond Size is Acceptable.
% Excess Storage :(VOLreq J VOLpro) $ 100 % Excess Storage : 74.54%<
DETENTION POND ANALYSIS CONTINUED: PAGE TWO
PE4ENAt;1 PC L
Perm. Pool at Normal Level: 22 ft
Bottom of Pond : 17 ft
I:t2th 5ft < Okay, depth > OR - 3ft.
SA/DA CALCULATION:
By chart #4; @ 90% TSS:
Depth, D - 5 ft
% Impervious : 30.17%
DA : 3,405165 Acres Where DA is the Graninage Area
SA/DA % : 2.55 ####
Area of Permanent Pool Required : (SA/DA %) t DA
Area at Permanent Pool Required : 2.55 $ 3.048763 Acres
Area of Permanent Pool Required : 0.086831 Acres
Area of Permanent Pool Required : 3782.389 ft"2
Area of PERMANENT POOL Required: 3782.389 sf < provided area of 36977 sf <--OKAY: sufficient stor
;r:TTICE OUTLET SIZINGG:

VOLpro : 43462
Orifice outflow, 2 Day Drawdown = Volpro/[(2 day) * (86400 sec/day)]
v:'itic outflow, 2 Day Drawdown = 43462 ft"3 / 112800 sec : Q2= 0.251516 cfs
Orifice C.S. Area, A:
A: Qf[Cd((2gh)"0.5))]
A: 0,251516 / [0.6*((2 32,2*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 = 0.6
critic,. outflow, 6 Day Drawdown = Volpro/[(5 day) * (86400 sec/day)]
Or;lice outflow, 5 Day Drawdown : 43462 ft"3 / 432000 sec = O. 0.100606 cfs
Critice C,S, Area, A:
A= Q/[Cd((2gh)"0.5))]
A: 0.100606 / [0.6*((2*32,2*1,0)11.5))]= A5= 0.020894 ft"2
A5= 3.008806 inch"2
Pipe diameter, d: d5= 1.957276 inch
• i. 5 '°;. idcd ' : 2,0 < 2,0 < 3.1 < OKAY...; Orifice is sized correctly.

dotal Site Area, TA: TA= 202300 ft"2 If
(TA (acre)] / [43560 ft"2/acre]: TA= 4.644168 Acres
Total Drainage Area, DA: DA: 90283 ft"2 II
IDA (acre)] / 143560 ft"2/acre]: DA: 2.072612 Acres
WE lVIOUS SURFACE AREA CALCULATIONS:
tructurc Surface Area, A Runoff Coef,, C
sf
Buildin,s: 42260 1 Adjusted Surface Area : A * C : 42260 ft"2 tf
Parking/sidewalks/streets: 24057 0.95 Adjusted Surface Area : A * C : 22854.15 ft"2 II
Green Areas: 23986 0.2 Adjusted Surface Area : A * C : 4193.2 ft"2 ft
TOTAL: 69907.35 ft"2 It
ercer,t impervious, %I: note: SA:(BUILDING + PARKING..): 66311 sf
(SA/TA)*100:
( 66311 / 202300 ]x100: %I= 32.18%%
Note: if %I < 30% check Density Option.
If %I > 30%, require engineered system to minimize non-point stream degradation.
POND SIZING:
Ainiaum required Storage Volume, VOLreq: note: SA has been multiplied by runoff coefficients
ISA (ft`2) * ;1 inch of runoff) x (1 ft/12 inch)]:
( 69907.35 ft"2 x 1 inch $ 0,083333 ft/inch]: VOLreq: 5825.612 ft"3
rON `I!
Bcttsm Elevation, ELb: ELb : 13 ft It
Permanent tool Elevation, ELpp; Elpp: 18 ft It
r:;a . Permanent Pool, App: App = 6145 ft"2 It
Storage Pon.: Elevation, Esp: Elsp: 19 ft ft
Arca at Storage Pond, Asp: Asp : 9413 ft"2 It
unott ,forage Leptn, d:
(via project engineer's design: d : ELsp - ELpp) d: 1 ft ft
Storage Volume Provided, VOLpro: Side Slope: 3:1
Volume 1, V1: App * d : 6145 ft"2 x 1 ft : V1: 6145 ft"3
Volume 2, V2: (Asp - App) * d x 0,5 : V2= 1364 ft"3
VOLpro : V1 + V2 : 6145 ft"3 + 1364 ft"3 VOLpro: 8109 ft"3
Note: Vi7Lreq K volpro; excess storage is available, therefore Pond Size is Acceptable.
ti Excess Storage :(VOLreq / VOLpro) $ 100 t Excess Storage : 28.16%<
A DETENTION POND ANALYSIS CONTINUED: PAGE TWO
P E E N A:'i a r t 01:
Perm, Pool at Normal Level: 18 ft
Bottom of Pond : 13 ft
Lcpth Provided1, D : 5 ft < Okay, depth > OR : 3 ft.

..A/DA CALCULATION:
Sy Chart t4; @ 90% TSS:
Depth, D - 5 ft
t Impervious = 32.78%
DA = 2.072612 Acres Where DA is the Draninage Area
SA/DA % = 2.38 Hit
Area of Permanent Pool Required = (SA/DA %) # DA
Area of Permanent Pool Required = 2.38 * 1.604851 Acres
Area of Permanent Pool Required = 0.049328 Acres
Area of Permanent Pool Required = 2148.735 ft"2
Area of PER,iAMENT POOL Required: 2148,735 sf < provided area of 6745 sf <--OKAY: sufficient stor
JRIF10E , OUTIET SIZING:
VOLpro = 8109
Orifice outflow, 2 Day Drawdown = Volpro/[(2 day) * (86400 sec/day)]
cutflow, 2 Day Drawdown = 8109 ft"3 / 112800 sec = Q2= 0.046927 cfs
Orifice C.S. Area, A:
A= Q/[Cd((2gh)"0,5))]
A: 0,046927 / [0.6*((2*32.2*1.0)"0.5))1= A2: 0.009746 ft"2
A2= 1.403433 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
is outflow, 5 Day Drawdown = Volpro/[(5 day) a (86400 sec/day)]
Orifice outflow, 5 Day Drawdown = 8109 ft"3 / 432000 sec : Q5= 0.018110 cfs
Orifice C,S. Area, A:
A: Q/[Cd((2gh)"0.5))]
A. 0,018710 / [0.6w((2a32,2$1,0)"0.5))]= A5= 0.003898 ft"2
A5= 0,561313 inch"2
Pipe diameter, d: d5= 0.845436 inch
CHECK: d5 < dprovided < d2 : 0.8 < 1.0 < 1.3 < OKAY...; Orifice is sized correctly.

EXF LTRATION PIPE ANALYSIS
PROPOSED IMPERVIOUS AREA SUMMATION: EXISTING IMPERVIOUS AREA SUMMATION:
;as,n Paved Roof Sidewalk TOTAL Basin Paved Roof Sidewalk TOTAL
at sf sf sf sf sf sf sf sf sf
A 6400 0 0 6400 A 0 0 0 0
st 640' 0 0 6400 Total: sf 0 0 0 0
1ota1; ac 0.15 0,00 0.00 0.15 Total: ac 0,00 0,00 0.00 0.00
PROPOSED - EXISTING = TOTAL IMPERVIOUS AREA : 6400 SF
TOTAL IMPERVIOUS AREA = 0.146923 ACRES
Design for 1.0 inch of rainfall - recieving waterway is not classified SA.
Lt Determine average runoff coefficient:
Area Runoff
Type Coeff.
Root 1.00
Ureen 0.20
Pvmt. 0.90
Average (for 1" RF)
Basin Paved Root Green TOTAL Runoff Volume
sf sf sf sf sf Coeff. cf
A 4800 0 1600 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 < Yini_um Required
d Volne
Minimum RC1{YIIt:u tvi�wv, acres.

3, Trench Design:
Bottom Width, W= 6 ft
Sideslopes, H:V= 1 ft
Depth, d= 2 ft
Pipe Diameter, 0= 12 inches
Storage Capacity of Trench:RECTANGULAR
Area of Trench, At= (Ws(1)= 12 sf
Area of Pipe, Ap: (@Pi * 0"2)/576 0.785396 sf
Void Space = Porosity, P = 0.4
Effective gravel volume, Vg = P*(At*Ap) = 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
5,57 : Minimum Required Volume, cf
% difference = 8,31%
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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RECEIVED
NOV 1 tt
8. Keith Cooper, P.E.
6 Bahama Drive
Wrightsville Beach, NC 28480
(919) 256-8033
November 5, 1991
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 Pages 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.
IEuV
NOV 1 3 1991
D M
a o j # 9/o goy

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 tit [ V
t.
6 b
NOV1 3 1991
DIM
of 7,-----9� s— -..

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,
eith Coo r, P.E.
SKC/vc
Enclosure
DECE
it]
NOV 1 3 1991
DEM
no]. # gioso�f...

AT LANDF A L
BLAIR PROPERTIES, INC.
POST OFFICE BOX 468
WRIGHTSVILLE E BEACH, NC 28480 J i
TELEPHONE[phone] U
NOV 1 3 1991
November 5, 1991 D E P!
7.0j # 9lago&. .._
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,
(zal
Ilr
tF. Smith
B PROPERTIES, INC.
North Carolina, /a4,1t,i,A, uIE" County
, a Notary Public for the
Count a d State a oresal , certify that James F. Smith
personally came before me this day and acknowledged the due
execution of the foreg9ing instrument. Witness my hand and seal
this day of el/ , 1991.
My Commission Expires At /11
didesto-0 Notary Public
SEAL

S. Keith Cooper, P.E.
6 Bahama Drive
Wrightsville Beach , North Carolina 28480
(919) 256-8033
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. 910806
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,

•
4fiy� y.n:a
j' - `
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
✓ ic. What are the 3 pLpes which cross the property line
contributing to the detention pond? Provide invert
elevations, gra=de, type, size and flow.
ld. Flared end sections and rip rap at pond inlets or supporting
calculations which determine energy dispersion is
unnecessary.
Pond #2
I 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
Tcontinued-
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
1. North Arrow
v2 . Add development name to site plans
-3 . Notarized submittal authorization
Detail of pond inlets 0( .-- k
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 .
Sin ly,
Ms . Alexis I . Finn
Environmental Engineer
AIF: 910806.00T
cc : (2 ) Alexis Finn
Central Files

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RECEIVT7n
OUT 'i 1991
±illi::ingtcai M.-grata! CAW
•-nM
8. Keith Cooper, P.E.
6 Bahama Drive
Wrightsville Beach, NC 28480
(919) 256-8033
EM
16
October 3, 1991 u V 1
OCT 8 1991
Ms. Alexis I. Finn D M
Environmental Engineer )110J # O
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:
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
r`«atof) Permit 26 [33CFR 330.5(a) (26) ] . Notification of less than
e�oF-txsa►'[�' - --
J
(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. Keith Cooper,("P.E.
SKC/vc RECIEllvitgb
Enclosure OCT 8 1991
DEM
'ROJ # y108067

14e.
State of North Carolina
Department of Environment, Health, 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 •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 ( 919 ) 395-3900 .
Sincere ,
c!-..4I
Ms . Alexis I . Finn
Environmental Engineer
AIF: 910806 . SEP
cc: (2) Alexis Finn
Bill Mills
Central Files

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1mbikAT LAN
BLAIR PROPERTIES, INC._____ 1ra Orb
rt
POST OFFICE BOX 468 �' �'^
WRIGHTSVILLE VILLE BEACH,NC 28480
TELEPHONE[phone] !!�� AI If '.
k
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 (919) 256-2700.
Sincerely,
--A ,CZA1
J m F. Smith
B Properties, Inc.
JFS/vc
Enclosure
jij\ E C E 11 V E Ili j
AUG 12 1991
PRoj # 9'iowr-,

•
PEMBROKE AT LANDFALL
NEW HANOVER COUNTY, NORTH CAROLINA
OWNER: BLAIR PROPERTIES, INC.
POST OFFICE BOX 468
1322 AIRLIE ROAD
WRIGHTSVILLE BEACH, NC 28480
(919) 256-2700
ENGINEER: S. KEITH COOPER, P.E.
6 BAHAMA DRIVE
WRIGHTSVILLE BEACH, NC 28480
(919) 256-8033
vollsimistr.sQ,'� CA RQe�•,'
4•.• �.44 E ssto,��,2y''-.
SEAL
12564
ir'J ° a
)1 t 0,
DULY, 1991 (0 IL � U � lijj
IR th.
AUG 1 1991.
DEM
'Ro' # 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
shall be stabilized within 48 hours of aradinq.

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 '4"'::'', 416 i'.,,.;. , .,„.
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• Table 1 • `••*44'w« rx
'gip `�'.
Runoff Coefficients for Use in Rational Formula • :y .
t
for
(slopes flatter (slopes steeper _.:.
Tyne of Land Use _ than 7%) than 7� .
Commercial 0.85 . - ,,.
Industrial 0.60-0. 5 - r slw'
Apartments, schools, churches 0.60 0.70
Residences, duplexes 0.45 0.55
Residences, 5000-7000 sq ft lots 0,,40 ' 0.50
Residences, 1/4-acre lots 0.38 0.48 .••
0.35 0.45 t -
Residences, 1/2-acre. lots f, ,;
41: Park 0,3 0.4: w ,-, L
` 4'' • Woodland 0.2 0 2 , , • . ,`4. -
7
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by following dashed line.
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CHART 3
/
_ NORTH CAROLlNA COASTAL REGIONS
SA/DA PERCENTAGES FOR WET DETENTION BASIN ', '
DESIGNED TO REMOVE 85X TSS (l " STORM) .� � .
°
�
SA/DA % For Basin Depths
X 3 Ft 3, � Pt 4 FFt
- _--~~-' LFt
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30 2. 5 2, 2 . 1 .9'� .1 .6
40
3, 4 2 .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. `
80 .6 :8 6 .0 5�2 4. `
90 7`5 6 . 5 5.B ' ' . .` '
. `
`
. .
'
CHART 4
SA/DA PERCE�TAGES FOR WET DETENTION BASINS
DISCHARGING DIRECTLY TO A STREAM '
NO VEGETATIVE FILTER , `PO9T-DEVELOPMENT DISCHARGE
RATE �� P�E-DEV�LOPM�NT RATE .B]R 10 . YEAR STORM) '
'
-
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.
.
SA/DA K For 8asin Depths
2lt' V Iou 5L-X 3,<5 Ft 4 Ft 5 Ft ' Ft
�----- ---r-- -----
' 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 ��� 2,7
60 7 ' 0 6 5.3 4. 3 3.4
_ 70 6 . 1 7 6.0 5 ,
.� ��] 9
\ BO 9 ' 4 8 7.0 ,7 4.6
90 1.0 . 7 q 7 .9 6 .�5 . ��.B
. .
Interpolate in6ermediate values
� SA/DA X = surfmce area basin/drainage area to ,b,a%in-x, ,l0(
,
`
36A
-- `
`