SW6100904_HISTORICAL FILE_20101015

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

Wilk
ffGREENHORNE & O'MARA
CONSULTING INGINIIRS
Letter of Transmittal
Greenhorne & O'Mara, Inc.
5565 CENTERVIEW DRIVE, SUITE 107, RALEIGH, NC 27606
Attn: Mike Randall
NCDENR DWQ Permitting Unit
512 N. Salisbury Street
Raleigh, NC 27601
DATE: September 17, 2010
RE: 24th STS — Fort Bragg
PHONE NO: 919-807-6374
JOB NO: 140581.006
WE ARE SENDING YOU THE FOLLOWING ITEMS:
X ATTACHED
CALCULATIONS UNDER SEPARATE COVER ®C9N�—F��
BLUEPRINTS SPECIFICATIONS 9�1 f
CD COST ESTIMATE OCT 15 2010
MYLARS/SEPIAS COPY OF LETTER
DVVW�p�
Q
VIA: 0REGULAR MAIL OVERNIGHT MAIL M BY HAND [:] PICKUP 0 MESSENGER
COPIES I DATE or NO.
2 DESCRIPTION
8/11/2010 Stormwater Management Permit Application Form (original + copy
1 8/11/2010 Infiltration Basin Supplement and 0&M document
1 8/6/2010 Permit Application Fee - $505.00
1 9/17/2010 Project Narrative
1 USGS Map Showing Site Location
1 9/17/2010 Stormwater Management Calculations
1 7/2010 Soils Report
2 9/24/2010I Sets of Plans (only sheets pertaining to stormwarP_r a_�rl
THESE ARE 'MANS -.___ w
r��� I nHrv�Ivu I I LU AS CHECKED BELOW:
X FOR APPROVAL
X FOR REVIEW AS APPROVED BY:
FOR YOUR USE AS SUBMITTED FOR APPROVAL TO:
FOR YOUR RECORDS
AS REQUESTED BY: REMARKS: H PLEASE RETURN TO US AFTER USING
CC: Lee Ward — DPW/Water Management Branch
SIGNED: Timothy J. Same PE
ANNAPOLIS, MD ATLAN I A, GA BALTIMORE, MD BRAGE NTIN, FL BONIFAY, FL FAIRMONT, WV
FREDERICKSBURG, VA CHANTILLY, VA GERMANTON, MD JACKSONVILLE, FL LAUREL, MD PANAMA CITY, FL
RALEIGH, NC RICHMOND, VA, WEST PALM BEACH, FL TALLAHASSEE, FL CLEARWATER, FL

WATER QUALITY/STORMWATER CONTROL
PROJECT NARRATIVE
SOF OPERATIONS SUPPORT FACILITY
241h SPECIAL TACTICAL SQUADRON
Fort Bragg, North Carolina
G&O Project #140677.D09
September 17, 2010
Project Description:
®ENR-FRO
OCT 15 2010
®WQ
The Department of the Army at Fort Bragg is proposing to construct a new SOF
Operations Support Facility for the 24th Special Tactical Squadron (STS), Joint Special
Operations Command (JSOC) on an undeveloped site at the Aberdeen Training Facility
(ATF) on Fort Bragg, North Carolina. The entire project is located within the SOF ATF,
which is a controlled access site within Fort Bragg.
This project includes all improvements necessary within the scope of the Government's
RFP to begin the construction of a new campus for the 24th STS onto the Aberdeen
Training Facility (ATF). This scope includes roadwork, water supply for domestic and
fire use, sanitary sewer service currently planned through use of a septic tank and leach
field, a geothermal well field for energy conservation, power/communications utility
lines, and storm water management using a large infiltration basin on the south end of the
site with a spillway on its east side directing flow toward the wetland. The construction
of this project will be phased (Phase 1 and II).
The disturbed area covers a total area of 9.77 acres and all the properties surrounding the
project are owned by Fort Bragg (The disturbed area is referred to as the Project Limits
on the construction plans). Approximately 2.8 acres of additional impervious area is
being added to the site as a result of the proposed Phase I development. The design intent
is to capture the runoff from all of the proposed impervious surfaces in a closed drainage
system. The closed drainage system will outlet into the forebay of the proposed
infiltration basin.
The U.S. Army Corps of Engineers — Savannah District performed the geotechnical
evaluation of the site for this project. An infiltration rate of 1.22 inches per hour was
used in the design calculations based upon the information provided in the report entitled
"Foundation Design Report", dated July 2010.
The infiltration basin has been designed to capture and control runoff for all storm events
up to and including the 100 year. The water quality volume (15,627 CF) was calculated
using the simple method and the I" rainfall depth. The basin has been designed such that
the primary outlet is infiltration and the secondary/emergency outlet is a 15' wide
spillway constructed in the basin's embankment. The available volume below the invert
of the spillway (433.8) is approximately 67,430 Cl,. According to the calculations,
outflow through the spillway will occur only for the 25 year and larger storm events.

The stormwater management design calculations were performed using PondPack design
software.
For design and construction purposes, we have provided a phased Soil Erosion Control
Plan (sheet CG101 and CG102) clearly showing and demonstrating the existing
characteristics and stabilization measures. These plans also include all the project Erosion
and Sedimentation notes and Construction Sequencing of both phases for the project. In
addition, soil erosion control details have been provided on sheets C-501 thru C-505.
There will be (1) one stabilized construction entrance which will be located at the
northwest comer of the project site near the existing unnamed asphalt roadway. The
stabilized construction entrance will control tracking of mud, dirt or other debris from the
construction site onto adjacent roads and streets. The temporary stabilized stone pad
shall be constructed at the point where vehicular traffic will be leaving the construction
site and moving directly onto a paved road or street. It shall extend the full width of the
vehicular ingress and egress area and have a minimum length of 50 feet. The entrance
shall be maintained in a condition that will prevent tracking or flow of'mud onto adjacent
roads or streets. If conditions on the site are such that the majority of the mud is not
by the echiC tCS tra":Ciing O',Cr Ui c StOnc, the tires Of the Vehicles shall be 11'aJIt U
before entering the road or street. Any mud, which is tracked onto roads or streets, shall
be removed on a regular basis.
There will be (1) one temporary sediment trap and (1) temporary skimmer basin as part
of the erosion control measures. Runoff from the northwest side of the project site will
be conveyed via sheet flow using temporary diversion ditches to the trap located south of
the construction entrance. The temporary sediment trap will be removed near the end of
Phase 11. The temporary sediment trap will collect runoff from approximately 1.4 acres
of disturbed area and help prevent sediment from leaving the project site. The temporary
skimmer basin will control runoff from an additional 5.6 acres of disturbed area of the
project. Runoff wilt be conveyed via sheetflow using temporary diversion ditches and
check dams to the basin located on the south side of the project area. The skimmer basin
will be converted to an infiltration basin with a forebay at the end of the project.
Another measure to be used to minimize sediment transport in storm water discharges
associated with construction activity at the construction site is silt fence. Silt fence with
silt fence outlets shall be installed below disturbed areas where erosion would occur in
the form of sheet and rill erosion. The silt fence and silt fence outlets will be installed
during phase I of the project. The general drainage characteristics of the site are from
north to south. Therefore, we have installed silt fence with outlets along the south side of
the project site.
As part of phase I construction, temporary cross culverts are being utilized so
construction of the site is able to continue while temporary diversions ditches are present.
In order to protect these culverts, rock pipe inlet protection will be used to prevent
siltation and debris from construction activities. As part of phase 11 construction, storm
drain inlet protection shall be installed around all proposed storm drain inlets that will
become operational before permanent stabilization of the corresponding disturbed
drainage area has occurred. In order to achieve this, installation of hardware cloth inlet