20081832 Ver 2_Stormwater Info_20101015

BASS, NIXON & KENNEDY, INC., CONSULTING ENGINEERS
6310 CHAPEL HILL ROAD, SUITE 250, RALEIGH, NC 27607
919/851-4422 ¦ FAX [phone] [e-mail]
DOWNSTREAM CHANNEL, CONSTRUCTED WETLANDS AND
CONCEPTUAL STORMWATER PLAN CALCULATIONS
FOR
SOUTHEAST 40 CENTRE
RALEIGH, NORTH CAROLINA
DEVELOPED BY:
APMWvLLC
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© !' 029993 n
PREPARED By
DANNY L. HOWELL, JR.% PE.
BASS, NIXON & KENNEDY INC.
REV. OCTOBER 15, 201 0
OCT1510+0
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BASS, NIXON & KENNEDY, INC., CONSULTING ENGINEERS ? ;
rNk 6310 CHAPEL HILL ROAD, SUITE 250, RALEIGH, NC 27607 4 0
919/8514422 FAX [phone] www.BNKinc.com
69-7%%
CALCULATION NARRATIVE
FOR
SOUTHEAST 40 CENTRE
RALEIGH, NORTH CAROLINA
1. BACKGROUND AND PURPOSE
The purpose of this report is to outline the calculations which were performed by Bass,
Nixon & Kennedy, Inc. at the project known as Southeast 40 Centre in Raleigh, NC.
These calculations are being performed at the request of NC DWQ as part of the
resolution of a Notice of Violation (NOV - DWQ Project 08-1832) which was issued for
the project.
The calculations for this resolution consist of 3 parts:
• Channel Velocity Calculations (pre-developed and post-developed)
• Constructed Wetlands Design Calculations
• Conceptual Stormwater Calculations Per Lot (bioretention areas)
The above calculations will have accompanying illustrations and drawings.
2. CHANNEL VELOCITY CALCULATIONS
The storm drainage conveyance system for the project collects stormwater from
approximately 23 acres of drainage area, which includes all street drainage and a large
portion of the lot drainage. Approximately 3.93 acres of impervious surface is included
in the 23 acres of drainage (17.1% Impervious). The 23 acres of drainage which are
collected into the stormwater conveyance system are discharged at a single discharge
point shown as Structure 1 on the approved plans. The discharge point includes an
energy dissipater consisting of Class B rip-rap extending from the pipe termination to
the start of the Neuse River Buffer.
Previous calculations performed by Bass, Nixon & Kennedy, Inc. reflected as-built 2-
year velocities in the receiving stream which exceeded levels acceptable to the NC
Division of Water Quality. The purpose of the channel calculations included herein is to
demonstrate that by rearranging and redirecting drainage areas within the development,
velocities in the receiving stream mentioned above can be reduced to approximately
pre-developed levels.
There are numerous changes that will be required to the approved and constructed
plan in order to accomplish the redirection of flow. The changes required will include
additional piping, storm drainage inlets, and grading for ditches and are shown on the
plans referenced below.
Page 2 of 4
October 15, 2010
The following illustrations and attachments are included as part of this calculation:
• DRAWING Q1.0 - Pre-developed Drainage Area at Discharge
• DRAWING Q1.1 - Post-developed Drainage Area at Discharge
• DRAWING Q1.2 - Drainage Areas after Modification (including site changes to
redirect flow)
• FIGURE 1 - Location of channel section measurement used in calculation
• Receiving channel 2-Year velocity calculations after drainage area modification
2.1. Methodology
Data was collected about the receiving channel, including channel section and
channel/floodplain lining and roughness coefficients. The data was used to
determine the velocity and depth of flow in the channel based on Manning's formula
for open channel flow. A more detailed breakdown of the channel section and
Roughness coefficients is provided in the attached calculations.
Flow quantity calculations were calculated based on the Rational Method. The time
of concentration was taken from storm drainage conveyance system calculations
which were performed as part of the original plan set generation.
2.2. Rational "C" Value Calculation
As part of the Stormwater Management Plan approved by the City of Raleigh, no
stormwater quantity attenuation was required for the lots which were created by this
subdivision; however, each lot is required by the City to reduce its nitrogen export to
levels acceptable under City code by limiting the amount of impervious surface, buy-
down, stormwater quality treatment, or any combination of the three. Nitrogen
export calculations for each lot must include the lot itself and also must account for
areas within the public right of way (including impervious surface) along the lot's
frontage up to the centerline of that road.
Despite the fact that no quantity attenuation is required for these lots, a significant
amount of small storm (2-Year) quantity attenuation benefit will likely be provided by
the quality treatment measures which may, depending on the nitrogen export
calculations, be proposed on each lot (wet ponds, bioretention areas, constructed
wetlands, etc). It is therefore assumed that since the channel velocity and normal
depth calculations are for the 2-Year storm events, most lots will passively attenuate
their post-developed flows to pre-developed levels through the quality measures
they may be providing. Furthermore, the owner will require the developer of lots
which drain to the existing discharge point 1 (after modifications) to attenuate their
post-developed flows to pre-developed levels for the 2-Year event (Lots 2, 3, 4,16,
and 17), in order to contribute to the flow reduction to the discharge point. This
would be accomplished by using the nitrogen reduction BMP selected for each lot
(as part of the City's approved Stormwater Management Plan) to also control
quantity and would be provided at time of lot development. On this basis, the
Page 3 of 4
October 15, 2010
Rational "C" values were calculated based on the drainage area being comprised of
the already constructed street infrastructure and the undeveloped lots.
3. LEVEL SPREADER CALCULATIONS
The flows which are redirected away from the single discharge point will be discharged
onto Lot 9, which were lots 9-11 on the previously approved subdivision plan. These
lots were recombined into a single lot for an end user. Because this lot contains a
buffered stream and there is no ephemeral stream between the beginning of the
buffered stream and the buffer start, the flow will be diffused by using a level spreader
located at the end of the discharge pipe. The level spreader will be designed in
accordance with the latest requirements of the NCDWQ Best Management Practices
Manual (Chapter 8, 09-28-07 version).
The following illustrations and attachments are included as part of this calculation:
• DRAWING Q1.2 - Drainage Areas after Modification (shows drainage area to
level spreader)
• DRAWING D1.0 - Constructed Wetlands Detailed Area Plan
• Constructed Wetlands Calculations
4. CONCEPTUAL PER LOT STORMWATER PLAN
As part of the resolution to the NOV associated with this project, NC DWQ has
requested that the owner provide a conceptual stormwater plan showing a feasible
type, size, and location of BMP's for each of the lots in the development. NCDWQ staff
has confirmed that this is a conceptual plan and is not binding on the owner or end
users with respect to type, size, or location of any BMPs which are required as part of
the City of Raleigh's approved stormwater management plan.
The stormwater management strategy and plan for this site was approved under the
City of Raleigh's delegated program. The approved strategy requires each lot to meet
the City's nitrogen export requirements. Lots 2-8, and 16-17 must account for
impervious surfaces to the centerline of all streets on which they front such that all
impervious surface added as part of the development (including public street and
sidewalk) will be accounted for in nutrient export calculations. Lots 1 and 9-14
impervious surfaces to the centerline of all streets were accounted for in the design of
the constructed wetlands. Lot 15 has already been constructed and has accounted for
the treatment of the street impervious surfaces in a bioretention area. NCDWQ has
agreed to accept the City of Raleigh approved stormwater management strategy and
also to accept City's review and approval of each individual lot as lots are developed.
The following illustrations and attachments are included as part of this calculation:
• DRAWING CON1 - BMP Concept Plan showing bioretention areas on
undeveloped lots (bioretention areas are shown in concept only. Final type, size,
and location of BMPs required by the City's approved stormwater management
plan may vary).
Page 4 of 4
October 15, 2010
• Bioretention Area Calculations (assuming 85% impervious surface per lot with
entire lot draining to bioretention area and 12" ponding depth).
5. PERMITTING OF PLAN CHANGES
After a plan to resolve the NOV is approved by NC DWQ, the changes shown will
require approval by the City of Raleigh as a revision to previously approved construction
drawings and grading permit or may require new construction drawings and grading
permit for this work only. Upon NC DWQ approval of this plan, the owner will need to
submit plans to the City of Raleigh for approval prior to constructing the approved
changes. It is somewhat uncertain as to the timeframe with which these City approvals
can be obtained, but it is typical for the approval processes to take 6-8+ weeks.
CHANNEL VELOCITY
CALCULATIONS
SOLItheast 40 Centre
Rev: October 15, 2010
FIGURE 1
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BASS, NIXON & KENNEDY, INC. SOUTHEAST 40 CENTRE
CONSULTING ENGINEERS CHANNEL SECTION
• 6310 CHAPEL HILL ROAD, STE 250, RALEIGH, NORTH CAROLINA 27607
• 3319 HERITAGE TRADE DR, WAKE FOREST, NORTH CAROLINA 27587
TELEPHONE: [phone] or [phone] JOB NO. DRAWN BY DATE SHEET OF
FAX: [phone] (RALEIGH), [phone] (WAKE FOREST) 06839000 JTC 5-12-10 1 1
Pre-Developed Channel Flow Calculation:
Rational Method Flow Calculation:
Q = CIA
Drainage Area: 11.302 acres
Rational Coefficient (C): 0.2
Time of Concentration: 5 min
Storm Event: 2 yr
Rainfall Intensity (1): 5.76 in/hr
Flow (Q): 13.02 cfs
Manning's Channel Depth of Flow:
Channel Manning's n: 0.046
Longitudinal Slope: 0.0055 ft/ft
Base Width: 1.75 ft
Sideslope: 0.44 :1
Depth of Flow: 2.16 ft
Flow: 13.02 cfs
Velocity:
2.24 fps
Channel Section:
Station Elevation
46.71 235.66
48.28 232.06
50.03 232.11
52.13 236.83
Kirpich Time of Concentration Calculation
Length of Flow: 1126 ft
Highest Point on Length of Flow: 298.5 ft EL.
Lowest Point on Length of Flow: 240 ft EL.
Change in Height: 58.5 ft
Time of Concentration: 5.5 min
Channel Section:
238
237

236 52. 1
236. 3,
• 3
6.71,

235 35.66
234
233

232 50.0 ,

231 232.0
46 47 48 49 50 51 52 53
Sl,fl-
Post-Developed Channel Flow Calculation:
Rational Method Flow Calculation:
Q = CIA
Drainage Area: 11.966 acres
Rational Coefficient (C): 0.2
Time of Concentration: 6 min
Storm Event: 2 yr
Rainfall Intensity (1): 5.56 in/hr
Flow (Q): 13.31 cfs
Manning's Channel Depth of Flow:
Channel Manning's n: 0.046
Longitudinal Slope: 0.0055 ft/ft
Base Width: 1.75 ft
Sideslope: 0.44 :1
Depth of Flow: 2.19 ft
Flow: 13.31 cfs
Velocity: 2.25 fps
Channel Section:
Station Elevation
46.71 235.66
48.28 232.06
50.03 232.11
52.13 236.83
Kirpich Time of Concentration Calculation
Length of Flow: 1246 ft
Highest Point on Length of Flow: 302 ft EL.
Lowest Point on Length of Flow: 240 ft EL.
Change in Height: 62 ft
Time of Concentration: 6.0 min
Channel Section:
238

237

38
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236.
r
3
2 6.71,

235 35.66
234
233
50.0 ,
232 .

231 232.06
46 47 48 49 50 51 52 53
Station
CONSTRICTED WETLANDS
DESIGIN CALCULATIONS,
Southeast 40 Centre
Rev: October 15, 2010
Water Quality Wetland Calculations
Project Name: Southeast 40 Centre - Lot 9
Determine Drainage Area and Impervious Surface Percentage
Onsite Drainage Area: 15.72 ac
Onsite Impervious Area: 4.94 ac
Percent Impervious: 31.4%
Calculate the Volume Req uired to Treat the First Flush:
Rainfall to Treat:
1 in
Runoff Coefficient (Rv) = 0.05 + 0.009*(% Impervious)
Runoff Coefficient (RJ: 0.33 in/in
Runoff Volume (V) = Rainfall * (R„) * (Drainage Area)
Runoff Volume (V): 18,991 cf
Determine the Surface Area and Depth of Each Wetland Zone
Permanent Pool Elev. (PPE): 247.60
Elev. 1' Above PPE: 248.60
Volume Available at Elev. 1' Above PPE: 26,158 cf based on end area average
Depth of Temporary Pool: 1.00 ft
Depth of Temporary Pool: 12.00 in
Temporary Pool Elevation: 248.60
Total Surface Area Required: 18,991 sf (Runoff Volume / Depth Temp. Pool)
Surface Area Provided at Top Temp Pool: 19,080 sf
Determine the Orifice Size for 2-5 Dav Drawdown of Temporary Pool:
Orifice Invert Elevation:
Temporary Pool Elevation:
Orifice Diameter:
247.60
248.60
2.00 in
Use the orifice equation to determine flow and drawdown time:
Orifice Equation: Q = CA(2gh)0.5
Volume to Draw Down: 18,991 cf
C: 0.60
g:
A:
Depth of Temp Pool to CL Orifice (h)
Orifice Flow:
32.20 ft/sz
0.02 sf
0.917 ft
0.101 cfs
Drawdown Time: 2.186 days (OK - Drawdown is between 2 and 5 days)
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Wetland Zone Surface Area Percentage Calculations
Project Name: Southeast 40 Centre - Lot 9
2007 BMP Manual Requirements:

Wetland Zone
Depth (in) % o Total
Surface Area
Deep Pool
Foreba 18-36 10
Outlet Area 18-36 5-10
Shallow Land 12 Max 30-40
Shallow Water 3-6 40
Temporary Pool Elevation:
Total Surface Area at Temporary Pool:
Deep Pools:
Forebay Surface Area:
Forebay as Percent of Total Surface Area:
Outlet Area Surface Area:
Outlet Area as Percent of Total Surface Area
Shallow Water:
Surface Area of 3-6" Depth:
Shallow Water as Percent of Total Surface Area:
Shallow Land (Only wet during storm event):
Surface Area of 12" Depth:
Shallow Land as Percent of Total Surface Area:
248.60
19,080 sf
2,090 sf
11.0% OK -area approx 10%
1,395 sf
7.3% OK -area approx 5-10%
8,075 sf
42.3% OK - area approx 40%
7,520 sf
39.4% OK - area approx 40%
OF W ATF9 AGIII'Ar
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NCDENR °
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
401 CERTIFICATION APPLICATION FORM
WETLAND SUPPLEMENT
This form must be filled out, printed and submitted.
The Required Items Checklist (Part III) must be printed, filled out and submitted along with all the required information.
I. PROJECT INFORMATION
Project name SOUTHEAST 40 CENTRE
Contact name DANNY HOWELL, PE
Phone number [phone]
Date October 14, 2010
Drainage area number DRAINAGE AREA #2
II. DESIGN INFORMATION
Site Characteristics
Drainage area 684,571.00 ft2
Impervious area 215,187.00 ft2
Percent impervious 31.4%%
Design rainfall depth 1.00 inch
Peak Flow Calculations
1-yr, 24-hr rainfall depth 3.00 in
1-yr, 24-hr intensity 4.52 in/hr
Pre-development 1-yr, 24-hr runoff 14.21 ft3/sec
Post-development 1-yr, 24-hr runoff 31.26 ft3/sec
Pre/Post 1-yr, 24-hr peak control 17.05 ft3lsec
Storage Volume: Non-SA Waters
Minimum required volume 18,991.00 ft3
Volume provided (temporary pool volume) 19,080.00 ft3 OK
Storage Volume: SA Waters Parameters
1.5" runoff volume ft3
Pre-development 1-yr, 24-hr runoff volume ft3
Post-development 1-yr, 24-hr runoff volume ft3
Minimum volume required ft3
Volume provided ft3
Outlet Design
Depth of temporary pool/ponding depth (DPI,nts) 12.00 in OK
Drawdown time 2.19 days OK
Diameter of orifice 2.00 in OK
Coefficient of discharge (CD) used in orifice diameter

calculation 0.60 (unitless)
Driving head (Ho) used in the orifice diameter calculation 0.92 ft OK
Form SW401-Wetland-Rev.6-11/16/09 Parts I and II. Project Design Summary, Page 1 of 3
Surface Areas of Wetland Zones
Surface Area of Entire Wetland
Shallow Land
The shallow land percentage is:
Shallow Water
The shallow water percentage is:
Deep Pool
Forebay portion of deep pool (pretreatment)
The forebay surface area percentage is:
Non-forebay portion of deep pool
The non-forebay deep pool surface area percentage is:
Total of wetland zone areas
Add or subtract the following area from the zones
Topographic Zone Elevations
Temporary Pool Elevation (TPE)
Shallow Land (top)
Permanent Pool Elevation (PPE)
Shallow Water/Deep Pool (top)
Shallow Water bottom
Most shallow point of deep pool's bottom
Deepest point of deep pool's bottom
Design must meet one of the following two options:
This design meets Option #1,
Top of PPE is within 6" of SHWT, If yes:
SHWT (Seasonally High Water Table)
This design meets Option #2,
Wetland has liner with permeability < 0.01 in/hr, If yes:
Depth of topsoil above impermeable liner
Topographic Zone Depths
Temporary Pool
Shallow Land
Permanent Pool
Shallow Water
Deep Pool (shallowest)
Deep Pool (deepest)
Planting Plan
Are cattails included in the planting plan?
Number of Plants recommended in Shallow Water Area:
Herbaceous (4'cubic-inch container)
Number of Plants recommended in Shallow Land Area:
Herbaceous (4'cubic-inch container), OR
Shrubs (1 gallon or larger), OR
Trees (3 gallon or larger) and Herbaceous (4+ cubic-inch)
Number of Plants provided in Shallow Water Area:
Herbaceous (4'cubic-inch container)
Number of Plants provided in Shallow Land Area:
Herbaceous (4'cubic-inch container)
Shrubs (1 gallon or larger)
Trees (3 gallon or larger) and
Grass-like Herbaceous (4+ cubic-inch)
Form SW401-Wetland-Rev.6-11/16/09
19,080.00 ft2 OK
7,520.00 ft2 OK
39%%
8,075.00 ft2 Insufficient shallow water area.
42%%
2,090.00 ft2 OK
11% %
1,395.00 ft2 OK
7%%
19,080.00 ft2 OK
0.00 ft,
248.60 ft amsl
247.60 ft amsl
247.10 ft amsl
246.00 ft amsl
244.60 ft amsl
Y (Y or N)
242.60 ft amsl OK
N (Y or N)
in
12.00 in OK
6.00 in OK
19.20 in OK
36.00 in OK
N (Y or N) OK
2,050
1,900
304
38 and 1,520
2,050 OK
305 OK
Parts I and II. Project Design Summary, Page 2 of 3
Additional Information
Can the design volume be contained?
Does project drain to SA waters? If yes,
What is the length of the vegetated filter?
Are calculations for supporting the design volume provided in the
application?
Is BMP sized to handle all runoff from ultimate build-out?
Is the BMP located in a recorded drainage easement with a
recorded access easement to a public Right of Way (ROW)?
The length to width ratio is:
Approximate wetland length
Approximate wetland width
Approximate surface area using length and width provided
Will the wetland be stabilized within 14 days of construction?
Form SW401-Wetland-Rev.6-11/16/09
Y (Y or N) OK
N (Y or N) Excess volume must pass through filter.
ft
Y (Y or N) OK
Y (Y or N) OK
Y (Y or N) OK
1.86 :1 OK
195.00 ft
105.00 ft
20 ,475.00 ftZ This approx. surface area is within this number of square feet
of the entire wetland surface area reported above:
Y (Y or N) OK
Parts I and II. Project Design Summary, Page 3 of 3
Permit No.
(to be provided by DWQ)
ill.' REQUIRED CHECKLIST
Please indicate the page or plan sheet numbers where the supporting documentation can be found. An incomplete submittal package will
result in a request for additional information. This will delay final review and approval of the project. Initial in the space provided to
indicate the following design requirements have been met. If the applicant has designated an agent, the agent may initial below. If a
requirement has not been met, attach justification.
Initials Page/ Plan
41? Sheet No.
1•Z
0001?0 -+-1. 0
0-? -V. 0

dp?
.'?'" ale
SW401-Wetland-Rev.6-11 /16/09
1. Plarys i" - 50' or larger) of the entire site showing:
esign at ultimate build-out,
/Off-site drainage (if applicable),
,#offe'lineated drainage basins (include Rational C coefficient per basin),
VNetland dimensions (and length to width ratio),
pretreatment system,
,/Maintenance access,
Proposed drainage easement and public right of way (ROW),
/Overflow device, and
vnoundaries of drainage easement.
2. ;?eettl tails (1" = 50' or larger) for the wetland showing:
dimensions (and length to width ratio)
system,
aintenance access,
OfIrbsed drainage easement and public right of way (ROW),
psi n at ultimate build-out,
si drainage (if applicable),
WKSgew device, and
undaries of drainage easement.
wetlands: Shallow land depth, shallow water depth, deep pool depth
Option 1, no clay liner: SLWT depth
Option 2, clay liner: Depth of topsoil on top of liner, liner specifications
3. Sect n view of the wetland (1" = 20' or larger) showing:
VIM slopes, 3:1 or lower
etland layers
4. A detailed planting plan (1" = 20' or larger) prepared by a qualified individual showing:
t:seof
riseveral suitable species (not including cattails),
, spacing and locations of plantings,
-ief?gy?aritity of each type of plant specified,
*017bnUaq " detail,
ursery for the plants, and
Ilizer and watering requirements to establish vegetation.
5. A construction sequence that shows how the wetland will be protected from sediment until the entire
drainage area is stabilized.
6. The supporting calculations (including drawdown calculations).
7. A copy of the signed and notarized operation and maintenance (0&M) agreement.
8. A copy of the deed restrictions (if required).
9. A soils report that is based upon an actual field investigation and soil borings. County soil maps are not
an acceptable source of soils information.
Part III, page 1 of 1
Permit Number:
(to be provided by DWQ)
Drainage Area Number:
Stormwater Wetland Operation and Maintenance Agreement
I will keep a maintenance record on this BMP. This maintenance record will be kept in a
log in a known set location. Any deficient BMP elements noted in the inspection will be
corrected, repaired or replaced immediately. These deficiencies can affect the integrity
of structures, safety of the public, and the removal efficiency of the BMP.
Important maintenance procedures:
- Immediately after the stormwater wetland is established, the wetland plants will
be watered twice weekly if needed until the plants become established
(commonly six weeks).
- No portion of the stormwater wetland will be fertilized after the first initial
fertilization that is required to establish the wetland plants.
- Stable groundcover will be maintained in the drainage area to reduce the
sediment load to the wet detention basin.
- Once a year, a dam safety expert will inspect the embankment.
After the wet detention pond is established, I will inspect it once a month and within 24
hours after every storm event greater than 1.0 inches (or 1.5 inches if in a Coastal
County). Records of operation and maintenance will be kept in a known set location
and will be available upon request.
Inspection activities shall be performed as follows. Any problems that are found shall
be repaired immediately.
BMP element: Potential problem: How I will remediate the problem:
The entire BMP Trash/debris is resent. Remove the trash/ debris.
The perimeter of the Areas of bare soil and/or Regrade the soil if necessary to
wetland erosive gullies have formed. remove the gully, and then plant a
ground cover and water until it is
established. Provide lime and a
one-time fertilizer application.
Vegetation is too short or too Maintain vegetation at a height of
long. approximately six inches.
The inlet device: pipe or The pipe is clogged (if Unclog the pipe. Dispose of the
swale applicable). sediment off-site.
The pipe is cracked or Replace the pipe.
otherwise damaged (if
applicable).
Erosion is occurring in the Regrade the swale if necessary to
swale (if applicable). smooth it over and provide erosion
control devices such as reinforced
turf matting or riprap to avoid
future problems with erosion.
Fonn SW401-Wetland O&M-Rev.3 Page 1 of 4
BMP element:
The forebay
The deep pool, shallow
water and shallow land
areas
Potential problem:
Sediment has accumulated in
the forebay to a depth that
inhibits the forebay from
functioning well.
Erosion has occurred
Weeds are present.
Algal growth covers over
50% of the deep pool and
shallow water areas.
Cattails, phragmites or other
invasive plants cover 50% of
the deep pool and shallow
water areas.
Shallow land remains flooded Unclog the outlet device
more than 5 days after a immediately.
storm event.
Plants are dead, diseased or
dying.
Best professional practices
show that pruning is needed
to maintain optimal plant
health.
Sediment has accumulated
and reduced the depth to 75%
of the original design depth
of the deep pools.
How I will remediate the
Search for the source of the
sediment and remedy the problem if
possible. Remove the sediment and
dispose of it in a location where it
will not cause impacts to streams or
the BMP.
Provide additional erosion
protection such as reinforced turf
matting or riprap if needed to
prevent future erosion problems.
Remove the weeds, preferably by
hand. If a pesticide is used, wipe it
on the plants rather than spravinq.
Consult a professional to remove
and control the algal growth.
Remove the plants by wiping them
with pesticide (do not spray) -
consult a professional.
Determine the source of the
problem: soils, hydrology, disease,
etc. Remedy the problem and
replace plants. Provide a one-time
fertilizer application to establish the
ground cover if a soil test indicates
it is necessary.
Prune according to best professional
practices.
Search for the source of the
sediment and remedy the problem if
possible. Remove the sediment and
dispose of it in a location where it
will not cause impacts to streams or
the BMP.
Form SW401-Wetland O&M-Rev.3 Page 2 of 4
BMP element: Potential problem: How I will remediate the problem:
The embankment A tree has started to grow on Consult a dam safety specialist to
the embankment, remove the tree.
An annual inspection by an Make all needed repairs.
appropriate professional
shows that the embankment
needs repair.
Evidence of muskrat or Use traps to remove muskrats and
beaver activity is present. consult a professional to remove
beavers.
The micropool Sediment has accumulated Search for the source of the
and reduced the depth to 75% sediment and remedy the problem if
of the original design depth. possible. Remove the sediment and
dispose of it in a location where it
will not cause impacts to streams or
the BMP.
Plants are growing in the Remove the plants, preferably by
micropool. hand. If a pesticide is used, wipe it
on the plants rather than s ra in .
The outlet device Clogging has occurred. Clean out the outlet device. Dispose
of the sediment off-site.
The outlet device is damaged Repair or replace the outlet device.
The receiving water Erosion or other signs of Contact the NC Division of Water
damage have occurred at the Quality 401 Oversight Unit at 919-
outlet. 733-1786.
Form SW401-Wetland O&M-Rev.3 Page 3 of 4
Permit Number.
(to be provided by DWQ)
I acknowledge and agree by my signature below that I am responsible for the
performance of the maintenance procedures listed above. I agree to notify DWQ of any
problems with the system or prior to any changes to the system or responsible party.
Project name: Southeast 40 Centre
BMP drainage area number:Drainage Area #2
Print name:Allen Pipkin
Title:Manager, APMW, LLC
Address: 10320-113 Durant Road, Raleigh NC 27614
Phone
Signat
Date: 1 D l f1 QO C)
Note: The legally responsible party should not be a homeowners association unless more than 50% of
the lots have been sold and a resident of the subdivision has been named the president.
I,Q r a L-) Lehr , a Notary Public for the State of
r?.?n? , County of b06.1 do hereby certify that
O l e v- I I O Y__I n personally appeared before me this Ih `
day of LAC+bbey- , --?20)0 , and acknowledge the due execution of the
forgoing stormwater wetland maintenance requirements. Witness my hand and official
seal,
.
« A,
.may
SEAL
My commission expires Pi _ Iq -,:20B
Form SW401-Wetland O&M-Rev.3 Page 4 of 4
PONCEPTUAL ST ORM WA i ER
CALCULATIONS PER.LOIT
Southeast 40 Centre
Rev: October 15, 2010
Conceptual Bioretention Calculations
Project Name: Southeast 40 Centre
Design Criteria: 2007 DWQ BMP Manual (Updated)
Lot Number: 1
Step 1: Determine. Drainage Area and Impervious Surface
Drainage Area:
Impervious Area:
2.01 ac Assumes Entire Lot as D.A.
1.71 ac 85% of Lot Area
Drainage Area Percent Impervious: 85%
Step 2: Determine the Volume of Water to Treat
Rainfall to Treat: (First Flush) 1 in
Runoff Coefficient (Rv) = 0.05 + 0.009*(% Impervious)
Runoff Coefficient (Rv): 0.82 in/in
Runoff Volume (WQV) = Rainfall * (Rv) * (Drainage Area)
Runoff Volume (WQV): 5,955 cf
Step 3: Determine the Surface Area and Depth Required
Ponding Depth:
Required Surface Area:
12.00 in = 1.00 ft
5,955 sf
RA2006jobs\06839000\NOV StufflBioretention for Concept PlanAs
Conceptual Bioretention Calculations
Project Name: Southeast 40 Centre
Design Criteria: 2007 DWQ BMP Manual (Updated)
Lot Number: 2
Step 1. Determine Drainage Area and Impervious Surface
Drainage Area: 1.63 ac Assumes Entire Lot as D.A.
Impervious Area: 1.39 ac 85% of Lot Area
Drainage Area Percent Impervious: 85%
Step 2: D termine the Volume of Water to Treat
Rainfall to Treat: (First Flush) 1 in
Runoff Coefficient (Rv) = 0.05 + 0.009*(% Impervious)
Runoff Coefficient (Rv): 0.82 in/in
Runoff Volume (WQV) = Rainfall * (Rv) * (Drainage Area)
Runoff Volume (WQV): 4,836 cf
Step 3: Determine the Surface Area and Depth Required
Ponding Depth: 12.00 in = 1.00 ft
Required Surface Area: 4,836 sf
RA2006jobs\06839000\NOV StufflBioretention for Concept Plan.xis
Conceptual Bioretention Calculations
Project Name: Southeast 40 Centre
Design Criteria: 2007 DWQ BMP Manual (Updated)
Lot Number: 3
Step 1: Determine Drainage Area and Impervious' Surface
Drainage Area: 1.74 ac Assumes Entire Lot as D.A.
Impervious Area: 1.48 ac 85% of Lot Area
Drainage Area Percent Impervious: 85%
Step 2: Determine the Volume of Water to Treat
Rainfall to Treat: (First Flush) 1 in
Runoff Coefficient (Rv) = 0.05 + 0.009*(% Impervious)
Runoff Coefficient (Rv): 0.82 in/in
Runoff Volume (WQV) = Rainfall * (Rv) * (Drainage Area)
Runoff Volume (WQV): 5,134 cf
Step 3: Determine the Surface Area and Depth Required
Ponding Depth: 12.00 in =
Required Surface Area: 5,134 sf
1.00 ft
R:\2006jobs\06839000\NOV Stuff\Bioretention for Concept PlanAs
Conceptual Bioretention Calculations
Project Name: Southeast 40 Centre
Design Criteria: 2007 DWQ BMP Manual (Updated)
Lot Number: 4
Step 1: Determine Drainage Area and Impervious Surface
Drainage Area: 1.36 ac Assumes Entire Lot as D.A.
Impervious Area: 1.16 ac 85% of Lot Area
Drainage Area Percent Impervious: 85%
Step 2: Determine the;Volume of Water to Treat
Rainfall to Treat: (First Flush) 1 in
Runoff Coefficient (Rv) = 0.05 + 0.009*(% Impervious)
Runoff Coefficient (Rv): 0.82 in/in
Runoff Volume (WQV) = Rainfall * (Rv) * (Drainage Area)
Runoff Volume (WQV): 4,021 cf
Step 3: Determine the Surface Area and Depth Required
Ponding Depth: 12.00 in = 1.00 ft
Required Surface Area: 4,021 sf
R:\2006jobs\06839000\NOV Stuft\Bioretention for Concept Plan.xis
Conceptual Bioretention Calculations
Project Name: Southeast 40 Centre
Design Criteria: 2007 DWQ BMP Manual (Updated)
Lot Number: 5
Step 1: Determine Drainage Area and Impervious Surface
Drainage Area: 1.01 ac
Impervious Area: 0.86 ac
Drainage Area Percent Impervious: 85%
Step 2: Determine the Volume of Water to Treat
Rainfall to Treat: (First Flush) 1 in
Runoff Coefficient (Rv) = 0.05 + 0.009*(% Impervious)
Runoff Coefficient (Rv): 0.82 in/in
Runoff Volume (WQV) = Rainfall * (Rv) * (Drainage Area)
Runoff Volume (WQV): 2,991 cf
Step 3: Determine the Surface Area and Depth Required
Ponding Depth:
Required Surface Area:
Assumes Entire Lot as D.A.
85% of Lot Area
12.00 in = 1.00 ft
2,991 sf
RA2006jobs\06839000\NOV Stuff\Bioretention for Concept Plan.xls
Conceptual Bioretention Calculations
Project Name: Southeast 40 Centre
Design Criteria: 2007 DWQ BMP Manual (Updated)
Lot Number: 6
Step 1: Determine Drainage Area and Impervious Surface
Drainage Area: 1.93 ac Assumes Entire Lot as D.A.
Impervious Area: 1.64 ac 85% of Lot Area
Drainage Area Percent Impervious: 85%
Step 2: Determine the Volume of Water to Treat
Rainfall to Treat: (First Flush) 1 in
Runoff Coefficient (Rv) = 0.05 + 0.009*(% Impervious)
Runoff Coefficient (Rv): 0.82 in/in
Runoff Volume (WQV) = Rainfall * (Rv) * (Drainage Area)
Runoff Volume (WQV): 5,707 cf
Step 3: Determine the Surface Area and Depth Required
Ponding Depth: 12.00 in = 1.00 ft
Required Surface Area: 5,707 sf
RA2006jobs\06839000\NOV Stuff\Bioretention for Concept Plan.xls
Conceptual Bioretention Calculations
Project Name: Southeast 40 Centre
Design Criteria: 2007 DWQ BMP Manual (Updated)
Lot Number: 7
Step 1: Determine Drainaae Area and Impervious Surface
Drainage Area: 2.47 ac Assumes Entire Lot as D.A.
Impervious Area: 2.10 ac 85% of Lot Area
Drainage Area Percent Impervious: 85%
Step 2: Determine the Volume of Water to Treat
Rainfall to Treat: (First Flush) 1 in
Runoff Coefficient (Rv) = 0.05 + 0.009*(% Impervious)
Runoff Coefficient (Rv): 0.82 in/in
Runoff Volume (WQV) = Rainfall * (Rv) * (Drainage Area)
Runoff Volume (WQV): 7,305 cf
Step 3: Determine the Surface Area and Depth Required
Ponding Depth: 12.00 in = 1.00 ft
Required Surface Area: 7,305 sf
R:\2006jobs\06839000\NOV Stuff\Bioretention for Concept PlanAs
Conceptual Bioretention Calculations
Project Name: Southeast 40 Centre
Design Criteria: 2007 DWQ BMP Manual (Updated)
Lot Number: 8
Step 1: Determine Drainage Area and Impervious' Surface
Drainage Area:
Impervious Area:
2.01 ac Assumes Entire Lot as D.A.
1.71 ac 85% of Lot Area
Drainage Area Percent Impervious: 85%
Step 2: Determine the'Volume of Water to Treat
Rainfall to Treat: (First Flush) 1 in
Runoff Coefficient (Rv) = 0.05 + 0.009*(% Impervious)
Runoff Coefficient (Rv): 0.82 in/in
Runoff Volume (WQV) = Rainfall * (Rv) * (Drainage Area)
Runoff Volume (WQV): 5,957 cf
Step 3: Determine the Surface Area and Depth Required
Ponding Depth:
Required Surface Area:
12.00 in = 1.00 ft
5,957 sf
R:\2006jobs\06839000\NOV Stuft\Bioretention for Concept Plan.xis
Conceptual Bioretention Calculations
Project Name: Southeast 40 Centre
Design Criteria: 2007 DWQ BMP Manual (Updated)
Lot Number: 12
Step 1: Determine Drainage Area and Impervious Surface
Drainage Area: 1.94 ac
Impervious Area: 1.65 ac
Drainage Area Percent Impervious: 85%
Step 2: Determine the Volume of Water to Treat
Rainfall to Treat: (First Flush) 1 in
Runoff Coefficient (Rv) = 0.05 + 0.009*(% Impervious)
Runoff Coefficient (Rv): 0.82 in/in
Runoff Volume (WQV) = Rainfall * (Rv) * (Drainage Area)
Runoff Volume (WQV): 5,742 cf
Step 3: Determine the Surface Area and Depth Reauired
Ponding Depth: 12.00 in =
Required Surface Area: 5,742 sf
Assumes Entire Lot as D.A.
85% of Lot Area
1.00 ft
RA2006jobs\06839000\NOV Stuff\Bioretention for Concept PlanAs
Conceptual Bioretention Calculations
Project Name: Southeast 40 Centre
Design Criteria: 2007 DWQ BMP Manual (Updated)
Lot Number: 13
Step 1: Determine Drainage Area and Impervious Surface
Drainage Area: 1.47 ac Assumes Entire Lot as D.A.
Impervious Area: 1.25 ac 85% of Lot Area
Drainage Area Percent Impervious: 85%
Step 2: Determine the Volume of Water to Treat
Rainfall to Treat: (First Flush) 1 in
Runoff Coefficient (Rv) = 0.05 r 0.009*(% Impervious)
Runoff Coefficient (Rv): 0.82 in/in
Runoff Volume (WQV) = Rainfall * (Rv) * (Drainage Area)
Runoff Volume (WQV): 4,361 cf
Step 3: Determine the Surface Area and Depth Required
Ponding Depth: 12.00 in = 1.00 ft
Required Surface Area: 4,361 sf
R:\2006jobs\06839000\NOV Stuff\Bioretention for Concept Plan.xis
Conceptual Bioretention Calculations
Project Name: Southeast 40 Centre
Design Criteria: 2007 DWQ BMP Manual (Updated)
Lot Number: 14
Step 1: Determine Drainage Area and Impervious Surface
Drainage Area: 1.29 ac Assumes Entire Lot as D.A.
Impervious Area: 1.09 ac 85% of Lot Area
Drainage Area Percent Impervious: 85%
Step 2: Determine the Volume of Water to Treat
Rainfall to Treat: (First Flush)
1 in
Runoff Coefficient (Rv) = 0.05 + 0.009*(% Impervious)
Runoff Coefficient (Rv): 0.82 in/in
Runoff Volume (WQV) = Rainfall * (Rv) * (Drainage Area)
Runoff Volume (WQV): 3,807 cf
Step 3: Determine the Surface Area and Depth Required
Ponding Depth:
Required Surface Area:
12.00 in = 1.00 ft
3,807 sf
R:\2006jobs\06839000\NOV Stuff\Bioretention for Concept Plan.xis
Conceptual Bioretention Calculations
Project Name: Southeast 40 Centre
Design Criteria: 2007 DWQ BMP Manual (Updated)
Lot Number: 16
Step 1: Determine Drainage Area and Impervious Surface
Drainage Area: 1.40 ac
Impervious Area: 1.19 ac
Drainage Area Percent Impervious: 85%
Step 2: Determine the Volume of Water to Treat
Rainfall to Treat: (First Flush) 1 in
Runoff Coefficient (Rv) = 0.05 + 0.009*(% Impervious)
Runoff Coefficient (Rv): 0.82 in/in
Runoff Volume (WQV) = Rainfall * (Rv) * (Drainage Area)
Runoff Volume (WQV): 4,153 cf
Step 3: Determine the Surface Area and Depth Required
Assumes Entire Lot as D.A.
85% of Lot Area
Ponding Depth: 12.00 in = 1.00 ft
Required Surface Area: 4,153 sf
RA2006jobs\06839000\NOV Stuff\Bioretention for Concept PlanAs
Conceptual Bioretention Calculations
Project Name: Southeast 40 Centre
Design Criteria: 2007 DWQ BMP Manual (Updated)
Lot Number: 17
Step 1: Determine Drainage Area and Impervious Surface
Drainage Area: 1.28 ac Assumes Entire Lot as D.A.
Impervious Area: 1.08 ac 85% of Lot Area
Drainage Area Percent Impervious: 85%
Step 2: Determine the Volume of Water to Treat
Rainfall to Treat: (First Flush) 1 in
Runoff Coefficient (Rv) = 0.05 + 0.009*(% Impervious)
Runoff Coefficient (Rv): 0.82 in/in
Runoff Volume (WQV) = Rainfall * (Rv) * (Drainage Area)
Runoff Volume (WQV): 3,776 cf
Step 3: Determine the Surface Area and Depth Required
Ponding Depth: 12.00 in = 1.00 ft
Required Surface Area: 3,776 sf
R:\2006jobs\06839000\NOV StufflBioretention for Concept PlanAs