SW6110501_HISTORICAL FILE_20110509

STORMWATER DIVISION CODING SHEET
POST -CONSTRUCTION PERMITS
PERMIT NO.
SW &,y
DOC TYPE
❑ CURRENT PERMIT
❑ APPROVED PLANS
HISTORICAL FILE
❑ COMPLIANCE EVALUATION INSPECTION
DOC DATE
&50 /
e
YYYYMMDD

North Carolina
Beverly Eaves Perdue
Governor
Mr. David Arnold, PE
Timmons Group
5420 Trinity Road, Suite 112
Raleigh, NC 27607
WDERR
Department of Environment and
Division of Water Quality
Colleen H. Sullins
Director
May 9, 2011
Natural Resources
Subject: Request for Additional Information
Stormwater Project No. SW6110501
Scott Street Parking Lot
Cumberland County
Dee Freeman
Secretary
The Division of Water Quality Central Office received a Stormwater Management Permit Application for
the subject project on May 2, 2011. A preliminary review of that information has determined that the
application is not complete. The following information is needed to continue the stormwater review:
Please revise the table in item 10 of the SW- 101 application form. The values for existing
BUA should be only the amount that will remain after development. The current values do not
seem to be consistent with the plan sheets.
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 May 23, 2011, 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 need additional time to submit the information, please mail or fax your request for a time extension
to the Division at the address and fax number at the bottom of this letter. The request must indicate the
date by which you expect to submit the required information. The Division is allowed 90 days from the
receipt of a completed application to issue the permit.
Please reference the State assigned project number on all correspondence. If you have any questions
concerning this matter please feel free to call me at [phone].
Sincerely,
Brian Lowther
Enviromnental Engineer
cc: Fayetteville Regional Office
SW6110501 File
Wetlands and Stomlwater Branch
One
1617 Mail Service Center, Raleigh, North Carolina 27699-1617 -
t, n:alOrtlIla
i��Ol Ll1l,
iv
Location: 512 N. Salisbury St. Raleigh, North Carolina 27604
Phone: [phone] FAX: [phone] Customer Service: 1-877-623-6748
Naturally
Internet: www.ncivaterquality.org
An Equal Opportunity 1 Affirmative Action Employer

To: Lowther, Brian
Subject: RE: add info for Scott Street parking Lot- SW6110501
Brian,
I think you might have forgotten to send the attachment.
Thanks,
David Arnold, PE
Project Engineer
TIMMONS GROUP I www.timmons.com
5410 Trinity Road, Suite 112 1 Raleigh, NC 27607
Office: 919.866.4938 Fax: [phone]
Mobile: [phone] david.arnold cDtimmons.com
Your Vision Achieved Through Ours
From: Lowther, Brian fmailto:brian.lowtherCalncdenr.gov]
Sent: Monday, May 09, 2011 11:17 AM
To: David Arnold
Subject: add info for Scott Street parking Lot- SW6110501
David,
Attached is the additional information request I sent out today. Let me know if you have any questions.
Brian
Brian C. Lowther
Environmental Engineer
NCDENR I DWQ J Stor nwater Permitting Unit
1617 Mail Service Center, Raleigh, NC 27699-1617
512 N. Salisbury St, Raleigh, NC 27604
Phone: [phone]
Email: brian.lowther a ncdenr.
Website: http:Hportal.nedenr.org/web/wq/ws/su/ws/su
E-mail correspondence to and from this address may be subject to the North Carolina Public Records
Law and may be disclosed to third parties.

Lowther, Brian
From: David Arnold [David,[e-mail]]
Sent: Tuesday, May 10, 2011 9:49 AM
To: Lowther, Brian
Subject: RE: add info for Scott Street parking Lot- SW6110501
Attachments: Revised Stormwater Narrative 5-10-11.pdf
Brian,
In response to your comment and our phone conversation this morning, I have revised the narrative of the storrnwater
report to clarify what Built -Upon -Areas are to be retained and removed as part of this project. Please reference the end
of the "Drainage Areas" section on page 6 for this revision. Please let me know if you need anything else or further
clarification.
Thanks,
David Arnold, PE
Project Engineer
TIMMONS GROUP I www.timmons.com
5410 Trinity Road, Suite 112 1 Raleigh, NC 27607
Office: 919.866.4938 1 Fax: [phone]
Mobile: [phone] david.arnold(o)timmons.com
Your Vision Achieved Through Ours
From: Lowther, Brian [mailto:brian.lowtherCdncdenr.00vl
Sent: Monday, May 09, 2011 11:30 AM
To: David Arnold
Subject: RE: add info for Scott Street parking Lot- SW6110501
Thanks David. See attached.
Brian C. Lowther
Environmental ]Engineer
NCDENR I DWQ I Stormwater Permitting Unit
1617 Mail Service Center, Raleigh, NC 27699-1617
512 N. Salisbury St, Raleigh, NC 27604
Phone: [phone]
Email: brian.lowthercr,neclenr.gov
Website: http://portal.nedenr.org/web/wq/ws/su
E-mail correspondence to and from this address may be subject to the North Carolina Public Records
Law and may be disclosed to third parties.
From: David Arnold [mailto:David.Arnold(cbtimmons.coml
Sent: Monday, May 09, 2011 11:20 AM

'I \' RiF,1lded 7d Tle IRA'/ /,t J Act
-+ -R. in/TA4.e ,f-- R/ms .s£7-10,p
Application Completeness Review
a� First Submittal ❑ Re -submittal Date
Development/Project Name: Scams
Receiving stream name REA \fr R
Date Reviewed: _T 1 By Bill Diuguid J
For post -construction requirements, a program will be deemed compliant for the areas where it is
implementing any of the following programs: WS-I, WS-II, WS-III, WS-IV, HQW, ORW, Neuse River Basin
NSW, Tar -Pamlico River Basin NSW, and the Randleman Lake Water Supply Watershed Nutrient
High Density Projects that require a 401/404 within an NSW require 85% TSS, 30%.TN and 30% TP removal.
T&E Species (Goose Creek, Waxhaw Creek or Six Mile Creek Water Sheds): �ZA
Latitude and Longitude:3 OQ 0 —'18 S8 . J tn/ Jurisdiction J-027- goC&,9 sit �
Project Address: AL[" rw eitcectroy 0-F �yqc sf:t�F t SCVH 5fR,cc-F
ZJ Engineer name and firm: A4 D A/otD} T07fnms G,eaccP� 7CQL£ica
dsrlo(. azro /d(§) .1�7i,+modr, coin 9r 9 — 0 5 9 -- 64,03
❑ Low Density (no curb and gutter) ❑ Low Density with curb and gutter outlets O High Density ❑ Other
N�r9 —EP 401/404 impacts o surface waters, wetlands, and buffers (add language to cover letter and/or addinfo letter)
❑ BUA O./ o
ul�Checlk for $505.00 included
iginal signature (not photocopy) on application
Legal signature (Corporation-VP/higher, Partnership -General Partner/higher, LLC-member/manager, Agent).
Check spelling, capitalization, punctuation: http://www.secretary.state.nc.us/corporations/thepage.aspx
If an agent signs the application, a signed letter of authorization from the applicant must be provided which
includes the name, title, mailing address and phone number of the person signing the letter.
❑ ,For subdivided projects, a signed and notarized deed restriction statement
:a /Sealed, signed & dated calculations
' Correct supplement and O&M provided for each BMP on site (check all that were provided & number of each)
❑ Bioretention
❑ Dry Detention Basin
❑ Filter Strip
❑ Grass Swale
❑ Infiltration Basin
❑ Infiltration Trench
❑ Level Spreader
❑ Permeable Pavement
❑ Restored Riparian Buffer
❑ Rooftop Runoff Management
❑ Sand Filter
❑ Stormwater Wetland
Wet Detention Basin
❑ Low Density
❑ Curb Outlet
❑ Off -Site
❑ NCDOT Linear Road
9"Two sets of sealed, signed & dated layout & finish grading plans with appropriate details
VNarrative Description of stormwater management provided
Wis
provided
/�T�❑/ elineated or a note on the plans that none exist on site and/or adjacent property
tro7Eb cf ,Dhe roads, parking area, cul-de-sac'_radii;.-sidewalk widths, curb and gutter;
5� Dimensions & slopes provided
❑ jPrainage areas delineated ❑ Pervious and impervious reported for each ❑ Areas of high density
Fv spection and maintenance agreements provided
or Application complete ❑ Application Incomplete Returned:
Fi)(MrF V' A-, N, f� TpG ✓
Comments J,�o a-ne..�as 7'7) iiw✓e_. _..,a w�t���c�s aK Ar"o A
(Date)
February 9, 2009 Revision

,-j k1 r T"I
rl-j-
CV
"EN'S
tr-12
------ --I- "W01-
BVILLE - "
NO
i�!�TAYET-T
Al
rn.

I
TIMMONS GROUP .000060
YOUR VISION ACHIEVED THROUGH OURS. • • •
5410 Trinity Road, Suite 112, Raleigh, NC 27607
To: NCDENR Fayetteville Regional Office, SWP
Attn: Mr. Mike Lawyer
225 Green Street, Suite 714
Fayetteville, NC 28301-5043
From: David Arnold, PE
Project: Scott Street Parking Lot
Enclosed Please Find:
DATE
2
3-23-11
Stormwater Construction Drawings
2
Application Forms
1
O&M Forms BMP Supplements
1
Calculation Package w/Narrative, Quad Map, Soils Information
1
Geotech Report
1
Project Narrative
1
Check for $505
Comments:
Mr. Lawyer,
Please let me know if you have any questions.
Thanks,
SIGNED: JJ
D id Arnold, PE
MAY 0 2 201
1ANR • WATER QUALITY
SANDSMUWATM9k U

Storm Water Calculations
SCOTT STREET PARKING LOT
Fort Bragg, NC
Prepared, f6r:
,US "y Engii Corp6f S Dist , fi9t
p,eers,,.1ava.pna-
may:2o I I
Qyfinfilqtis Qr6u0:201 1,
DEt-v i t
JUN 2 1 lUjj
DWQ
j
PROPERTY OF THE UNITED STATES
GOVERNMENT
FOR OFFICIAL USE ONLY

Or 14
SCOTT STREET PARKING LOT
FORT BRAGG, NC
STORM WATER CALCULATIONS
Prepared; for:
US ARMY CORP OF ENGINEERS
SAVANNAH DISTRICT
Prepared by:
TIMMONS GROUP
5410 TRINITY ROAD, SUITE 112
RALEIGH, NORTH CAROLINA 27607
Revised: May 2011
April 2011
Timmons Project No: 26232

i
This document, together with the concepts and designs presented herein, as an instrument of
service, is intended only for the specific purpose and client for which it was prepared. Reuse of
and improper reliance on this document without written authorization and adaptation by
Timmons Group shall be without liability to Timmons Group.

TABLE OF CONTENTS
STORMWATER NARRATIVE
FIGURES
USGS QUADRANGLE MAP
SOILS SURVEY
SCOTT STREET PARKING LOT WET POND CALCULATIONS
WATER QUALITYCALCULATIONS
WATER QUANTITY CALCULATIONS
APPENDICIES
EROSION CONTROL MATFING'
,GEO-COMPOSITE CLAY LINER

Storm Water Narrative
Background
This report contains the approach and results of a stormwater analysis conducted for the
proposed Scott Street Parking Lot project located on Fort Bragg in Fayetteville, North Carolina. The
project consists of a new parking lot to be added on the north side of Scott Street just east of Knox
Street. This report outlines the measures necessary for this parking addition.
Scott Street Parking Lot is bounded by Knox Street, Macomb Street, Scott Street, and an
existing railroad. The site currently is occupied by a variety of old trailers and gravel/asphalt parking
areas that are all to be removed as part of this project. The site is approximately 10 acres in size.
Soils
The Cumberland County Soils Survey indicates that the primary near surface soil present on
the site is Wagram-Urban land complex (WgB) and is classified as hydrologic group "A" by the Soils
Survey. In light of the existing soil types, the overall lack of topographic relief of the site (generally
flat), and the fact that the vast majority of the soils are sandy, Curve Numbers for the site have been
determined based on "fair" conditions in undisturbed areas and "good" conditions in proposed
development areas.
Site Stabilization
After final grading is completed, permanent vegetation shall be applied to stabilize the site
until further work commences.
Drainage Areas
This site has been separated into two separate drainage basins. Sub -basin "A" is located to the
eastern portion of the site and outlets into the existing storm drainage system of the main headquarters
facility. Sub -basin `B" outlets into the existing storm drainage network located along Knox Street and
Macomb Street.
Pre -Development Areas
Sub -Basin
Drainage Area
Impervious Area 1
; Pervious Area
(ac)..
(ac).
(ac)
A
5.90
2.52 "f
3.38
B
5.72 11
4.40 l
it 1.32

In the post -development condition, the majority of site drainage will exit the site through sub -basin
"A". There are 5 different outlet locations for this sub -basin. Four of these (A2-AS), are existing
drainage structures that will primarily capture areas that are not to be disturbed as part of this
construction (existing road surfaces, existing building rooftops, existing open space, and some new
impervious area for driveway entrances). These areas have been designed to sheet flow offsite. Sub -
basin Al will capture the majority of the new development work and will drain into the proposed wet
detention basin. The area remaining in sub -basin B will consist of existing road surfaces, existing
open space, and some new impervious area for driveway entrances.
Post -Development Areas
Sub -Basin
Drainage Area
(ac)
Impervious Area
(ac)
Pervious Area
(ac)
A] _
6.67
5.12
1.55
A2,A3,A4-,A5
2.72
0.83
1.89
A (TOTAL)
9.39
5.95
3.44
B
2.23
1.03
1.20
As part of this project a large amount of built upon area is to be removed. The majority of old trailers
and existing parking are to be demolished and replaced with the new parking lot. A small amount of
BUA is to remain consisting of the existing roadways and two on -site trailers. Drainage Sub -Basin
"A" will have a net increase of 3.43 acres of impervious and will treat 5.12 acres of impervious in the
proposed wet detention pond. Drainage Sub -Basin `B" will have a net decrease of 3.37 acres from the
existing conditions.
Existing
Existing
Existing
BUA
BUA
Proposed
Total BUA
Net BUA
Treated
Drainage
BUA
to be
to
BUA
after
after
BUA
Basin
removed
Remain
construction
construction
(ac)
(ac)
(ac)
(ac)
(ac)
(ac)
(ac)
A
2.52
1.62
0.90
5.05
5.95
3.43
5.12
B
4.4
1 3.59
0.81
1 0.22
1.03 1
-3.37
0
Wet Detention Pond Water Quality.
The wet detention pond located on the eastern side of the Scott Street parking lot has been designed to
treat the "first flush" (1" rainfall) of runoff of the site at an 85% TSS removal efficiency. This adheres
to regulations and requirements set forth by Fort Bragg and NCDWQ.
The wet detention pond has a permanent pool elevation of 285.50 and a temporary water quality
elevation of 287.00. A 2" orifice has been placed at elevation 285.50 to allow the water quality
volume to draw down over a period of 2-5 days as required.

Wet Detention
Surface Area
Surface Area
Water Quality
Water Quality
Drawdown
Basin
Required
Provided
Volume
Volume
Time
Time
(sf)
(sf)
Required (ef)
Provided (et)
Scott Street
9,303
9,850
17,938
18,065
2.76
The remaining runoff will be stored and released in the wet detention pond by a concrete riser
structure. A ten foot (10') vegetated safety bench has been included per NCDWQ requirements from
elevation 285.00 to elevation 286.00. A geo-composite clay liner is to be installed below the
vegetated safety bench to help ensure the wet detention pond is able to retain water and preserve
aquatic plant growth.
The wet detention basin has been designed to treat 5.12 acres of impervious area which is 150% of the
required 3.43 acre net BUA increase. Using a 90% TSS removal and SA/DA ratio, a surface area of
6,613 sf is required for our net BUA increase. Our design has provided for 9,850 sf in surface area
which again is 150% of the required area. Similarly, the required storage volume below the temporary
pool is provided at 150% of the required volume.
To further help achieve the 90% TSS removal efficiency and provide a higher water quality onsite, a
form of pre-treatment has been provided before runoff enters the wet detention facility. Site runoff
will sheet flow off of the proposed parking lot and travel over a 12" wide x 24" deep gravel verge
filled with #57 stone. The runoff will then flow into grassed trapezoidal swales with a bottom width
of 3.5'. These swales will have a slope of 0.5% and are intended to aid in TSS removal and encourage
infiltration of the 1" rainfall event prior to entering the storm network. Drop inlets are included at the
downstream end of these swales to convey this runoff to the wet detention basin. We believe that this
form of pretreatment should give the remaining 5% of the 90% TSS removal required in excess of the
85% provided by the wet detention basin.
The BUA for Drainage Basin "B" has been reduced 3.37 acres below that of pre -development levels.
The overall drainage area for this portion of the site has also been reduced with a large amount being
diverted to the new wet detention facility. Approximately 75% of the BUA in Drainage Basin "B" is
that left from existing conditions, primarily consisting of existing roadways and buildings. Due to the
fact that so much impervious area is being removed from this sub -basin, and that most of the
remaining area is being diverted to the wet detention basin, we feel that the water quality leaving the
site has been improved and no additional water quality measures are required.
Please reference the water quality calculations of this report for further details and calculations;:

Wet Detention Pond Water Quantity
The wet detention pond has been designed to reduce the post -development peak flow onsite to below
the pre -development levels for the 1-year, 24-hour storm event per NCDWQ.
Drainage Basin "A"
Storm Event Cyr)
Pre -development Rate (cfs)
Post -development Rate (cfs)
1
7.00
3.49
2
-" 9.61
10.83
10 -"
21.80
38.56
25
30.17
52.28
100
45.49
75.48
Drainage Basin `B"
Storm Event (yr)
Pre -development Rate (cfs)
Post -development Rate (cfs)
1
16.57
1.94
2
20.10
2.80
10
34.79
7.07
25 -
44.03
10.08
100
59.38
15.51
Due to site and topographical constraints an earthen emergency spillway was not feasible. Therefore
the 5' x 5' concrete riser structure has been designed to accommodate up to the 100-year storm event.
The top of this riser structure has been set at the top of the temporary storage volume (elevation
287.00). The 100 year storm even has been designed to stage to a maximum water surface elevation
of 288.01 which provides 3 feet of freeboard to the top of the wet detention basin.
Please reference the corresponding section of this report for further details and calculations.
Conclusion.
Based on the analysis provided herein, the proposed storm water measures and facilities will
be adequate to address the storm water requirements of Fort Bragg and the NCDWQ. We believe that
the conditions of this site have been improved from its existing state. From a site containing no storm
water management, we are now providing an environment that promotes water quality and quantity
control. These measures not only improve our site but that of those downstream.

Lowther, Brian
From: David Arnold [[e-mail]]
Sent: Monday, May 16, 2011 3:14 PM
To: Lowther, Brian
Subject: RE: add info for Scott Street parking Lot- SW6110501
Attachments: Revised Stormwater Narrative.pdf
Brian,
Attached is the revised storm water narrative. Please reference the water quality section as well as the conclusion
section for changes. Please let me know if you have any additional comments or questions. If all goes well, do you have
a date as to when our permit should be issued?
Thanks,
David Arnold, PE
Project Engineer
TIMMONS GROUP I www.timmons.com
5410 Trinity Road, Suite 112 1 Raleigh, NC 27607
Office: 919.866.4938 1 Fax: [phone]
Mobile: [phone] david.arnold(LDtimmons.com
Your Vision Achieved Through Ours
From: Lowther, Brian[mailto:[e-mail]]
Sent: Monday, May 16, 2011 12:54 PM
To: David Arnold
Subject: RE: add info for Scott Street parking Lot- SW6110501
David,
I think that is fine. I would include information on drainage area B as well though.
Let me know if you have any more questions.
Brian
Brian C. Lowther
Environmental Engineer
NCDENR I DWQ � Stormwater Permitting Unit
1617 Mail Service Center, Raleigh, NC 27699-1617
512 N. Salisbury St, Raleigh, NC 27604
Phone: [phone]
Email: brian.lowtheru,ncdenr."ov
Website: http://portal.ncdenr.org/wcb/hvq/\vs/su
E-mail correspondence to and from this address map be subject to the North Carolina Public Records
Lair and may be disclosed to third parties.

From: David Arnold [mailto:[e-mail]]
Sent: Monday, May 16, 2011 11:15 AM
To: Lowther, Brian
Subject: RE: add info for Scott Street parking Lot- SW6110501
Brian,
I wanted to run a few things by you before I updated the narrative. The points I wish to highlight will be the following:
• Treated Imp Area: 5.12 ac, Net BUA increase: 3.43 ac. We are treating 150% of the increase of BUA.
The SA/DA value for 90%TSS removal using the BUA increase (3.43 ac) on our site is 2.276. This requires a
surface area of 6,613 sf. Our pond is sized for a surface area of 9,850 sf which is 150% of the required area.
Similarly, the required storage volume to the temporary pool is provided at 150% of the required amount.
Not previously mentioned, there is a form of pre-treatment into the pond. Runoff will sheet flow off of the
proposed parking lot and travel over a 12" wide by 24" deep gravel verge filled with #57 stone. The runoff will
then flow into trapezoidal swales with a bottom width of 3.5'. The slope of these swales is at 0.5%. This gravel
verge and grassed swales are intended to aid in TSS removal and to encourage infiltration of the 1" event prior
to entering the storm network. Drop inlets are included at the downstream end of these swales to convey this
runoff to the wet detention basin. We believe this form of pretreatment should give the remaining 5% of the
TSS removal required in excess of the 85% provided by the wet detention basin.
In summary, we believe that the conditions of this site have been improved from its existing state. From a site
containing no storm water management, we are now providing an environment that promotes water quality and
quantity control. These measures not only improve our site but that of those downstream.
Please let me know if this will suffice for what you are looking for. If so, I will get it worked into our narrative and sent
back over to you.
Thanks!
David Arnold, PE
Project Engineer
TIMMONS GROUP I www.timmons.com
5410 Trinity Road, Suite 112 1 Raleigh, NC 27607
Office: 919.866,4938 1 Fax: 919,859,5663
Mobile: [phone] david.arnold(cDtimmons.com
Your Vision Achieved Through Ours
From: Lowther, Brian [mailto:[e-mail]]
Sent: Monday, May 16, 2011 9:54 AM
To: David Arnold
Subject: RE: add info for Scott Street parking Lot- SW6110501
Hey David,
I touched on this subject on the phone last week but the only concern left I have with this project is that the pond is
designed for 85%TSS with no filter strip. Normally, we require at filter strip or sizing the pond for 90% TSS. Therefore,
you can modify to design to 90%TSS removal or add a filter strip for approval. However, I do think that since you are
over treating the difference from the pre -development to post -development that it may be more protective of water
quality. If you would like to leave the project as it is, please submit a revised narrative to describe why you feel over

treating with a 85% pond is better protecting water quality than a 90% pond or adding a filter strip. Please let me know
if you have any questions.
Brian C. 1.ow her
Environmental Engineer
NCDINR I DWQ I Stormwater Permitting Unit
1617 Mail Sen�ice Center, Raleigh, NC 27699-1617
512 N. Salisbury St, Raleigh, NC 27604
Phone: [phone]
Email: brian.lowthcro,ncdenr.�,ov
Website: htth:�/portal.ncdenr.ora/web/wq/ws/su
E-mail correspondence to and from this address may be subject to the North Carolina Public Records
La,vi, and may be disclosed to third parties.
From: David Arnold [mailto:[e-mail]]
Sent: Tuesday, May 10, 2011 9:49 AM
To: Lowther, Brian
Subject: RE: add info for Scott Street parking Lot- SW6110501
Brian,
In response to your comment and our phone conversation this morning, I have revised the narrative of the stormwater
report to clarify what Built -Upon -Areas are to be retained and removed as part of this project. Please reference the end
of the "Drainage Areas' section on page 6 for this revision. Please let me know if you need anything else or further
clarification.
Thanks,
David Arnold, PE
Project Engineer
TIMMONS GROUP I www.timmons.com
5410 Trinity Road, Suite 112 1 Raleigh, NC 27607
Office: 919.866.4938 1 Fax: [phone]
Mobile: [phone] david.arnold(cDtimmons.com
Your Vision Achieved Through Ours
From: Lowther, Brian [mailto:[e-mail]]
Sent: Monday, May 09, 2011 11:30 AM
To: David Arnold
Subject: RE: add info for Scott Street parking Lot- SW6110501
Thanks David. See attached.
Brian C. Lowther
Environmental Engineer
NCDENR I DWQ I Stormwater Permitting Unit

1617 Mail Service Center, Raleigh, NC 27699-1617
512 N. Salisbury St, Raleigh, NC 27604
Phone: [phone]
Email: brian.lowthcra,nalcnr.uov
Website: http://i)ortal.ncdenr.or,,/web/wq/ws/su
E-mail correspondence to and from this address may he subject to the North Carolina Public Records
Law and may be disclosed to third parties.
From: David Arnold [mailto:[e-mail]]
Sent: Monday, May 09, 2011 11:20 AM
To: Lowther, Brian
Subject: RE: add info for Scott Street parking Lot- SW6110501
Brian,
I think you might have forgotten to send the attachment.
Thanks,
David Arnold, PE
Project Engineer
TIMMONS GROUP I www.timmons.com
5410 Trinity Road, Suite 112 1 Raleigh, NC 27607
Office: 919.866.4938 1 Fax: [phone]
Mobile: [phone] david.arnold(aDtimmons.com
Your Vision Achieved Through Ours
From: Lowther, Brian [mailto:[e-mail]]
Sent: Monday, May 09, 2011 11:17 AM
To: David Arnold
Subject: add info for Scott Street parking Lot- SW6110501
David,
Attached is the additional information request I sent out today. Let me know if you have any questions.
Brian
Brian C. Lowther
Environmental Engineer
NCDENR I DWQ I Stormwater Permitting Unit
1617 Mail Service Center, Raleigh, NC 27699-1617
512 N. Salisbury St, Raleigh, NC 27604
Phone: [phone]
Email: brian.lowther(c�ncdenr.gov
Website: httn://um tal.ncdenr.ora/webhvq/ws/su

E-mail correspondence to and from this address may be subject to the North Carolina Public Records
Law and may be disclosed to third parties.

Storm Water Calculations
SCOTT STREET PARKING LOT
Fort Bragg, NC
7 ;9%
g A. r
— 03fi665 _
:!VG{NE O
DAV16 I
Preparcd Por:
US Army Corp of Enginecrs, Savannah District
May 2011
stl'inminn - Gaup, 2011
JUN Z t iUll
PROPERTY OF THE UNITED STATES
GOVERNMENT
FOR OFFICIAL USE ONLY

SCOTT STREET PARKING LOT
FORT BRAGG, NC -
STORM WATER CALCULATIONS
Prepared for:
US ARMY CORP OF ENGINEERS
SAVANNAH DISTRICT
.. . L't s.
Prepared by:
TIMMONS GROUP
5410 TRINITY ROAD, SUITE 112
tALEiM NORTA CAROLINA'27607
Revised: May 2011
April 2011
Timmons Project No: 26232,

This document, together with the concepts and designs presented herein, as an instrument of
service, is intended only for the specific purpose and client for which it was prepared. Reuse of
and improper reliance on this document • without written authorization and adaptation by
Timmons Group shall be without liability to Timmons Group.

TABLE OF CONTENTS
STORMWATER NARRATIVE
FIGURES
USGS QUADRANGLE MAI'
t:
SOILS'SURUEY
SCOTT STREET PARKING LOT WET POND CALCULATIONS
WATER QUALITY CALCULATIONS'
WATER QUANTITY CALCULATIONS
APPEVDICIES
EROSION CONTROI, MATTING
GEO-COMPOSITE CLAY INNER

Storm Water Narrative
Background
This report contains the approach and results of a stormwater analysis conducted for the
proposed Scott Street Parking Lot project located on Fort Bragg in Fayetteville, North Carolina. The
project consists of a new parking lot to be added on the north side of Scott Street just east of Knox
Street. This report outlines the measures necessary for this parking addition.
Scott Street Parking Lot is bounded by Knox Street, Macomb Street, Scott Street, and an
existing railroad. The site currently is occupied by a variety of old trailers and gravel/asphalt parking
areas that are all to be removed as part of this project. The site is approximately 10 acres in size.
Soils
The Cumberland County Soils Survey, indicates that the primary near surface soil present on
the site is Wagram-Urban land complex (WgB) and is classified as hydrologic group "A" by the Soils
Survey. In light of the existing soil types, the overall lack of topographic relief of the site (generally
flat), and the fact that the vast majority of the soils are sandy, Curve Numbers for the site have been
determined based on "fair" conditions in undisturbed areas and "good" conditions in proposed
development areas.
Site Stabilization
After final grading is completed, permanent vegetation shall be applied to stabilize the site
until further work commences.
Drainaee Areas
This site has been separated into two separate drainage basins. Sub -basin "A" is located to the
eastern portion of the site and outlets into the existing storm drainage system of the main headquarters
facility. Sub -basin `B" outlets into the existing storm drainage network located along Knox Street and
Macomb Street.
Pre -Development Areas
Sub -Basin
Drainage Area
(ac)
Impervious Area
(ac)
Pervious Area
(ac)
A
5.90
2.52
3.38
B
5.72
4.40
1.32
+ic

In the post -development condition, the majority of site drainage will exit the site through sub -basin
"A". There are 5 different outlet locations for this sub -basin. Four of these (A2-A5), are existing
drainage structures that will primarily capture areas that are not to be disturbed as part of this
construction (existing road surfaces, existing building rooftops, existing open space, and some new
impervious area for driveway entrances). These areas have been designed to sheet flow offsite. Sub -
basin Al will capture the majority of the new development work and will drain into the proposed wet
detention basin. The area remaining in sub -basin B will consist of existing road surfaces, existing
open space, and some new impervious area for driveway entrances.
Post -Development Areas
Sub -Basin
Drainage Area
(ac) J;:(ac)
Impervious Area
Pervious Area
(ac)
Al
6.67
—' 5.12
1.55
A2,A3,A4,A5
2.72
0.83
1.89
A (TOTAL)
9.39
5.95
3.44
B
2.23
1.03
1.20
As part of this project a large amount of built upon area is to be removed. The majority of old trailers
and existing parking arc to be demolished and replaced with the new parking lot. A small amount of
BUA is to remain consisting of the existing roadways and two on -site trailers. Drainage Sub -Basin
"A" will have a net increase of 3.43 acres of impervious and will treat 5.12 acres of impervious in the
proposed wet detention pond. Drainage Sub -Basin "B" will ,Its ve a net decrease of 3.37 acres from the
existing conditions.
Existing
Existing
Existing
BUA
BUA
Proposed
Total BUA
Net BUA
Treated
Drainage
BUA
to be
to
BUA
after
after
BUA
Basin
removed
Remain
construction
construction
(ac)
(ac)
(ac)
(ac)
(ac)
(ac)
(ac)
A
2.52
1.62
0.90
;5.05.
5.95
3.43
5.12
B
4.4
3.59
0.81
0.22
1.03
1 -3.37
1 0
Wet Detention Pond Water Ouality
The wet detention pond located on the eastern side of the Scott Street parking lot has been designed to
treat the "first flush" (I" rainfall) of runoff of the site. This adheres to regulations and requirements
set forth by Fort Bragg and NCDWQ.
The wet detention pond has a permanent pool elevation of 285.50 and a temporary water quality
elevation of 287.00. A 2" orifice has been placed at elevation 285.50 to allow the water quality
volume to draw down over a period of 2-5 days as required.

Wet Detention
Surface Area
Surface Area
Water Quality
Water Quality
Drawdown
Basin
Required
Provided
Volume
Volume
Time
(so
(so
Required (co
Provided (cf)
(Days)
Scott Street
9,303
9,850 ,`
17,938
18,065
2.76
r
The remaining runoff will be stored and released in the wet detention pond by a concrete riser
structure. A ten foot (10') vegetated safety bench has been included per NCDWQ requirements from
elevation 285.00 to elevation 286.00. A geo-composite clay liner is to be installed below the
vegetated safety bench to help ensure the wet detention pond is able to retain water and preserve
aquatic plant growth.
Please reference the water quality calculations of this report for further details and calculations.
Wet Detention Pond Water Ouantity
The wet detention pond has been designed to reduce the post -development peak now onsite to below
the pre -development levels for the 1-year, 24-hour storm event per NCDWQ.
Drainage Basin "A"
Storm Event (yr)
Pre -development Rate (cfs)
Post -development Rate (cfs)
1
7.00
3.49
10.83
10
2180
38.56
25
30.17
52.28
100
45.49
75.48
Drainage Basin "B"
Storm Event (yr)
Pre -development Rate (cfs)
Post -development Rate (e£s)
1
" LtL 1.16.57
1.94
2
20.10
2.80
10
34.79
7.07
25
44.03
10.08
100
59.38
15.51

Due to site and topographical constraints an earthen emergency spillway was not feasible. Therefore
the 5' x 5' concrete riser structure has been designed to accommodate up to the 100-year storm event.
The top of this riser structure has been set at the top of the temporary storage volume (elevation
287.00). The 100 year storm even has been designed to -stage to a maximum water surface elevation
of 2,88.01 which provides 3 feet of freeboard to the top of the wadetention basin.
JPleaserreference the corresponding section of Otis report for further details, and calculations.
Conclusion
Based on the analysis provided herein, the proposed storn water measures and facilities will
be adequate to address the storm water requirements of Fort Bragg and the NCDWQ.
:71