20080187 Ver 2_More Info Received_20080418

Permit Number:
(to be provided by DWQ)
V D o?oe warFRQc
ARA A- P R I IS 2008 DNR °
NC ,
DENR W?1@I? nAANAGEMENT PERMIT APPLICATION FORM
WETLANDS ANDS !VI ?",
RTIFICATION APPLICATION FORM
BIORETENTION CELL SUPPLEMENT
This form must be filled out, printed and submitted.
The Required Items Checklist (Part 111) must be printed, filled out and submitted along with all of the required information.
1. PROJECT INFORMATION
Project name Lake Gaston Pit Stop
Contact name N. Ray Watson, Jr, PE
Phone number 919-790-0879
Date April 11, 2008
Drainage area number 1
11. DESIGN INFORMATION
Site Characteristics
Drainage area 59,745.24 ft2
Impervious area 56,236.92 ft2
Percent impervious 94.1% %
Design rainfall depth 1.00 inch
Peak Flow Calculations
1-yr, 24-hr runoff depth 2.77 in
1-yr, 24-hr intensity 0.12 in/hr
Pre-development 1-yr, 24-hr peak flow 0.06 ft3/sec
Post-development 1-yr, 24-hr peak flow 0.16 ft3/sec
Pre/Post 1-yr, 24-hr peak control 0.10 ft3/sec
Storage Volume: Non-SR Waters
Design volume 4,729.83 ft3
Storage Volume: SR Waters
Pre-development 1-yr, 24-hr runoff N/A ft3
Post-development 1-yr, 24-hr runoff N/A ft3
Minimum volume required #VALUE! ft3
Volume provided N/A ft3 #VALUE!
Cell Dimensions
Ponding depth of water 12.00 inches OK
Ponding depth of water 1.00 ft
Surface area of the top of the bioretention cell 4729.83 ft2 OK
Length: 101.00 ft OK
Width: 51.00 ft OK
-or- Radius ft
Soils Report Summary
Drawdown time, ponded volume 8.00 hr OK
Drawdown time, to 24 inches below surface 16.00 hr OK
Drawdown time, total: 24.00 hr
In-situ soil:
Soil permeability 0.00 in/hr Insufficient. Increase infiltration rate.
Planting media soil:
Soil permeability 1.50 in/hr OK
Soil composition
% Sand (by weight) 87% OK
% Fines (by weight) 10% OK
% Organic (by weight) 3% OK
Total: 100%
Form SW401 -Bioretention-Rev. 3 Parts I and II. Design Summary, Page 1 of 2
Permit Number:
(to be provided by DWQ)
Phosphorus Index (P-Index)
Basin Elevations
Temporary pool elevation
Planting elevation (top of the mulch)
Bottom of the cell
Planting depth
Depth of mulch
SHWT elevation
Are underdrains being installed?
How many clean out pipes are being installed?
What factor of safety is used for sizing the underdrains? (See
BMP Manual Section 12.3.6)
Additional distance between the bottom of the planting media and
the bottom of the cell to account for underdrains
Bottom of the cell required
Distance from bottom to SHWT
Type of bioretention cell (answer "Y" to only one of the two
following questions):
Is this a grassed cell?
Is this a cell with trees/shrubs?
Planting Plan
Number of tree species
Number of shrub species
Number of herbaceous groundcover species
Additional Information
Does volume in excess of the design volume bypass the
bioretention cell?
Does volume in excess of the design volume flow evenly distributed
through a vegetated filter?
What is the length of the vegetated filter?
Does the design use a level spreader to evenly distribute flow?
Is the BMP located at least 30 feet from surface waters (50 feet if
SA waters)?
Is the BMP located at least 100 feet from water supply wells?
Are the vegetated side slopes equal to or less than 3:1?
Is the BMP located in a recorded drainage easement with a
recorded access easement to a public Right of Way (ROW)?
Inlet velocity (from treatment system)
Is the area surrounding the cell likely to undergo development in
the future?
Are the slopes draining to the bioretention cell greater than 20%?
Is the drainage area permanently stabilized?
Pretreatment Used
(Indicate Type Used with an "X" in the shaded cell)
Gravel and grass
(8'inches gravel followed by 3-5 It of grass)
Grassed Swale
Forebay
20 (unitless) OK
82.00 fmsl
81.00 fmsl OK
79.00 fmsl
2.00 ft
0.00 inches Insufficient mulch depth.
73.00 fmsl OK
Y (Y or N)
7 OK
8.00 OK
1ft
78.00 fmsl
5.00 ft OK
Y (Y or N) OK
N (Y or N)
Y (Y or N) OK
N (Y or N) Excess volume must pass through filter.
N/A ft
n (Y or N) Show how flow is evenly distributed.
Y (Y or N) OK
Y (Y or N) OK
Y (Y or N) OK
y (Y or N) OK
0.37 ft/sec OK
N (Y or N) OK
N (Y or N) OK
Y (Y or N) OK
OK
X
Form SW401 -Bioretention-Rev. 3 Parts I and II. Design Summary, Page 2 of 2
Underdrain Design
flow through soil media (in/hr) 1.5 1 u 2008
factor of safety 8 DENR - WATER QUALITY
WETLUS AND STQRMWATER RRO'h
bioretention area (sf) 4729.83
design flow (cfs) 1.313842
pipe size 8.82143
USE 3-6" PVC
Table 5-1

site area (so
site impervious area (so
road widening impervious area (so
% impervious
Drainage Area (square feet)
Volume of runoff
Runoff coefficient
Design rainfall depth (inches)
Volume of runoff (cubic ft)
Bioretention area design
design depth inches
surface area required (square feet)
forebay 20% of required volume
forebay depth average (ft)
rough forebay area (so
remaining bioretention area (cubic ft)
Forebay volume
contour elevation
bioretention elevation
total bioretention volume
average velocity in cell
width in center
length
area (so
flow cfs)
velocity (fps)
82
81
80
82
81
35
1
35
13
0.371429
137,217.23
56,236.92
12,597.56
50.2
59, 745.24
0.95
1
4,729.83
12
4729.83
945.97
2
473
3783.87
incremental vol total volume
799 626 950.5
453 324.5 324.5
196 0 0
4203 3802.5
3402 0
4753