20081048 Ver 1_More Info Received_20080806

Horvath Associates, PA
Civil Engineers • Planners • Landscape Architects
16 Consultant Place Ste. 201 Durham, NC 27707
PO. Box 51806 Durham, NC 27717-1806
[phone] Fax [phone]
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WE ARE SENDING YOU attached via CO(.rrW-,e the following items:
? Shop drawings PfPlans ? Specifications CT ILGI?OZL'TS
COPIES DATE NO. DESCRIPTION
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THESE ARE TRANSMITTED as checked below:
ZFor approval ? For your use ? As requested ? For review and comment
REMARKS
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AUG 6 2008
I)ENR yATER QUP•LiT? eANGH
WETLANDS AND STORIAWATER 3
COPY TO
SIGNED z??
If enclosures are not as noted, kindly notify us at once.
August 5, 2008
71 Ms. Cyndi Karoly, Supervisor
401 Oversight/Express Review Permitting Unit
2321 Crabtree Blvd
HORVATH
A S S O C I A T E 5 Raleigh, NC 27604
Civil Engineers Subject: Chatham Pointe -
Land crape Architects Response to July 23, 2008 "Request for more information"
Dear Ms. Karoly,
The following responses and attached items are in response to the
"Request for more information," dated July 23, 2008. If you have
any questions please contact us, at the number listed below.
1. Please provide cross section details showing the provisions for
aquatic life passage.
The details have been provided. Please see "Culvert Detail
Plans" report.
2. Per the requirements of the Neuse River Riparian Buffer Rule, you
must show that this site meets diffuse flow requirements with a level
spreader or other BMP per Chapter 8 of the BMP Manual.
The site meets diffuse flow requirements through use of BMP's.
Please see "Stormwater Management Plan" report and associated
drawings.
3. Please provide documentation of the local government's
approval of the Stormwater management plan (SMP) for this project
by providing EITHER:
4. A valid approval letter and one copy of the approved
SMP (including plans and calculations), OR
5. One set of stormwater plan details and calculations
stamped as "Approved" by the local government.
A 401 Permit is required for SMP approval by the local
government. Per phone conversation with Ian McMillan on August
5, 2008, SMP approval will be a condition of the 401 permit and the
approved SMP will be forwarded when received. Please see the
above response for SMP items.
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? North Carolina
16 Consultant Place, Suite 201
Durham, NC 27707
Bill Price, E.I . p 919.490.4990 / f 919.490.8953
Tennessee
537 Market Street Suite LL20
Chattanooga, TN 37402
p 423.266.4990 / f 423.266.5700
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HORVATH
ASSOCIATES
CIVIL ENGINEERS PLANNERS LANDSCAPE ARCHITECTS
Chatham Pointe
Culvert Detail Plans
August 5, 2008
Job 0360
North Carolina Tennessee
16 Consultant Place, Suite 201 537 Market Street Suite LL20
Durham, NC 27707 Chattanooga, TN 37402
p 919.490.4990 / f 919.490.8953 p 423.266.4990 / f 423.266.5700
6 2008
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HORVATH DRAWN BY:
ASSOCIATES CULVERT PLAN VIEW CHECKED BY:
JES
' 16 CONSULTANT PLACE, SURE 201
DURHAM. NORTH CAROLINA 27707 SCALE
P 919.490.4990 F 919.490.8953 CHATHAM P O I N TE 120'
537 MARKET STREET, SURE LL20 901 WEST CHATHAM STREET DATE
CHATTANOOGA, TENNESSEE 37402 7-31-2008
' P 423.266.4990 F 423.266.5700 PROJECT NO
www.horvathassociates.com CARY, NORTH CAROLINA 0360
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HORVATH
A S S O C I A T E S CULVERT PROFILE VIEW CHECKED BYES
1 16 CONSULTANT PLACE, SURE 201 SCALE
DURHAM. NORTH CAROLINA 27707 CHATHAM POINT E P 919.490.4990 F 919.490.8953 I" = 20
537 MARKET STREET, SURE Ll20 901 WEST CHATHAM STREET DATE
CHATTANOOGA. TENNESSEE 37402 7-31-2008
' P 423.266.4990 F 423.266.5700 PROJECT NO
www.horvathassociates.com CARY, NORTH CAROLINA 0360
VISTA CREEK PLACE (W R/W)

BURY LEFT BOX 1'
CONCRETE BOX CULVERTS
741 X 13WN X SH ® 2.97%
BURIED 1'
If .?
UPSTREAM - CROSS-SECTION VIEW

HORVATH
A S S O C I A T E S
' 16 CONSULTANT PLACE, SURE 201
DURHAM, NORTH CAROLINA 27707
P 919.490.4990 F 919.490.8953
537 MARKET STREET, SUITE LL20
CHATTANOOGA, TENNESSEE 37402
' P 423.266.4990 F 423.266.5700
www.horvathassocl(3tes.com
.......................................................
DRAWN BY:
CULVERT CROSS-SECTION VIEW CHECKED BY:
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HORVATH
ASSOCIATES
CIVIL ENGINEERS PLANNERS LANDSCAPE ARCHITECTS
Chatham Pointe
Stormwater Management Plan
August 5, 2008
Job 0360
North Carolina Tennessee
16 Consultant Place, Suite 201 537 Market Street Suite LL20
Durham, NC 27707 Chattanooga, TN 37402
p 919.490.4990 / f 919.490.8953 p 423.266.4990 / f 423.266.5700
U2@20YON
AUG 6 2008
WETLM?DS AND ST ER QUALITY
ORMWATER BRANCH
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C) g- i-D42
CHATHAM POINTE
STORM WATER MANAGEMENT PLAN
CHATHAM POINTE
West Chatham Street
Cary, North Carolina
Horvath Associates Project Number: 0360
MAY 28, 2008
?OQ:•oFESSio• ?
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Prepared for: T.O.W. INC.
105 West Main Street
Durham, North Carolina 27701
[phone]
Prepared by: Horvath Associates, P.A.
Engineers - Planners - Landscape Architects
P.O. Box 51806
Durham, North Carolina 27717
[phone]
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TABLE OF CONTENTS
1. NARRATIVE
' II. SUMMARY OF RESULTS
III. FLOW CALCULATIONS
IV. WATER QUALITY CALCULATIONS
' V. 401 CERTIFICATION APPLICATION FORMS
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NARRATIVE

CHATHAM POINTE
' STORM WATER IMPACT ANALYSIS,
DETENTION AND WETLAND DESIGN
General Description
' Chatham Pointe is a proposed 8.475 acre project located on the southeast side
of West Chatham Street and northeast of the intersection of West Chatham
Street and Jason Court. It consists of single family homes and townhomes and is
' zoned RMF-B-CU. The site is located in the Swift Creek Watershed and is subject
to Town of Cary's Nitrogen Control Plan. The impervious percentage of the site
is approximately 38% in the post-development condition. Because the
' proposed project exceeds 12% impervious, 85% TSS removal is required.
Additionally, 1-year, post-development peak flow runoff and nitrogen loading
' control is required. Strategies to address these requirements are described
below.
85% TSS Removal
impervious surfaces associated with this project (including ROW area), will be
' directed to a constructed wetland and bioretention cell that are sized using the
latest North Carolina Division of Water Quality (DWQ) Best Management
Practices (BMP).
The bioretention cell provides 85% TSS removal for the town homes and the
access road in front of the town home area. A design summary showing
' compliance with surface area and volume requirements is included in the
design portion of this report.
' The wetland provides 85% TSS removal for the single family home portion of the
project and the portion of the access road that crosses the stream, which
passes through the middle of the site. This wetland also conforms to surface
' area and volume requirements as set forth by the DWQ.
Nitroaen Loadin
The composite post-development nitrogen loading for this project exceeds the
3.6 lb/acre/year limitation. Physical treatment of the nitrogen in the stormwater
' runoff will be accomplished using the wetlands as discussed above. The
wetland will provide removal of 40% and the bioretention cell will provide
' removal of 35% of the nitrogen in the runoff that drains to them. The portion of
impervious area that does not drain to either of the BMP's along with managed
and permanently protected open space is accounted for with separate
' nitrogen loading calculations. The total nitrogen loading for the site is then
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summed to provide the post-development nitrogen loading with treatment. The
post-development nitrogen loading rate is then based upon this loading rate
divided by the total land area. Payment to the Ecosystem Enhancement Fund is
required to reduce the effective nitrogen loading rate to 3.6 Ibs/acre/year. The
nitrogen loading and required payment are provided in the Summary of Results.
1-Year Peak Flow Detention
The 1-Year Peak Flow Analysis has been modified and the analysis now
measures the pre- and post-development peak flow rate in the stream which
passes through the property. The bioretention cell detains much of the peak
flow resulting from the 1-year rainfall event. The outlet structure is a 13' wide,
sharp-crested weir, set at the 1 "-inch rainfall water surface elevation. The
wetland detains the 1-year rainfall and the outlet structure consists of a sharp-
crested weir to pass rainfall events having a higher peak flow and lower
frequency.
The area draining to the bioretantion cell consists of the property and the
adjacent restaurant site. In order to be conservative, the restaurant is assumed
to not be constructed in the pre-development condition. It is considered to be
85% impervious in the post-development condition due to the fact that a
footprint of the constructed area is not provided. Detention of most of the peak
flow resulting from the 1-year storm event is accomplished by passing the
majority of the 1-year volume through the bioretention.
The area draining to the wetland is the onsite area draining to the buffered
stream on the southeast side of the stream. Updated topography and
planimetric information is not available, but a town home or apartment
complex appears to be present on the eastern boundary of the site.
Additionally, impervious surfaces that would otherwise drain to the buffered
stream on the southern portion of the site will be directed to the wetland, and
the flow into this buffered stream does not need to be characterized, because
the flow will be reduced (Drainage Point 3).
Conclusion
1-Year peak flow detention will be provided for this project using the wetland as
a detention facility. 85% TSS removal and reduction of nitrogen export will also
be accomplished with construction of the wetlands. Payment to the Ecosystem
Enhancement Fund in the amount of $6,918.35 will be required to reduce the
effective nitrogen loading rate to the 3.6 lb/acre/year threshold.
Methodology
• Soils are based upon USDA Soil Survey as determined using Wake County
GIS soil information. NRCS Curve Numbers were determined by importing
the soil information into AutoCAD and determining the limits of the HSG 'B'
and 'C' soils on the site. Each composite NRCS Curve Number in the pre-
and post-development condition should therefore have considerable
precision.
• Time of Concentration for each sub-basin in the pre-development
condition is determined using the NRCS TR-20 segmental approach in
HydroCAD Version 7.10. Post-development, developed sub-basins are
assumed to have the minimum time of concentration which is five
minutes.
• Pre- and post-development flow calculations are determined using the
SCS TR55 Method in HydroCAD Version 7.10. Routing of each wetland is
accomplished using HydroCAD Version 7.10, which utilizes the Storage-
Indication Method the route each facility.
• Nitrogen loading is determined using Town of Cary's methodology. Given
that the maximum impervious area for each single-family lot is known,
Method 2 is utilized for all of the nitrogen loading calculations. By using
the (maximum) square footage of impervious area per lot, a conservative
estimate is made for the nitrogen loading because the impervious
footprint for the majority of the single family homes is not likely to be
exceeded.
SUMMARY OF RESULTS
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FLOW CALCULATIONS
0360 - POST DEVELOPMENT Type// 24-hr 1-Year Rainfall=3.00"
Prepared by {enter your company name here} Page 2
HydroCAD® 7.10 s/n 003899 © 2005 HydroCAD Software Solutions LLC 5/19/2008
Time span=0.00-72.00 hrs, dt=0.01 hrs, 7201 points
Runoff by SCS TR-20 method, UH=SCS
Reach routing by Stor-Ind method - Pond routing by Stor-Ind method
Pond 1P: Bloretention Cell Peak EIev=422.00' Storage=5,093 cf Inflow=5.41 cfs 0.245 of
Outflow=1.37 cfs 0.141 of
Pond 2P: Wetland Peak EIev=419.06` Storage=6,105 cf Inflow=6.34 cfs 0.284 of
Outflow=0.69 cfs 0.234 of
0360 - POST DEVELOPMENT Type// 24-hr 9-Year Rainfall=3.00"
Prepared by (enter your company name here) Page 3
HydroCAD® 7.10 s/n 003899 © 2005 HydroCAD Software Solutions LLC 5/19/2008
Pond 1 P: Bioretention Cell
Inflow Area = 1.770 ac, Inflow Depth = 1.66" for 1-Year event
Inflow = 5.41 cfs @ 11.96 hrs, Volume= 0.245 of
Outflow = 1.37 cfs @ 12.09 hrs, Volume= 0.141 af, Atten= 75%, Lag= 7.6 min
Primary = 1.37 cfs @ 12.09 hrs, Volume= 0.141 of
Routing by Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.01 hrs
Peak Elev= 422.00'@ 12.09 hrs Surf.Area= 5,555 sf Storage= 5,093 cf
Plug-Flow detention time= 216.4 min calculated for 0.141 of (58% of inflow)
Center-of-Mass det. time= 101.9 min ( 923.2 - 821.3)
Volume Invert Avail.Storage Storag e Description
#1 421.00' 11,130 cf Custo m Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
(feet) (sq-ft) (cubic-feet) (cubic-feet)
421.00 4,623 0 0
421.50 5,082 2,426 2,426
422.00 5,554 2,659 5,085
422.50 6,041 2,899 7,984
423.00 6,542 3,146 11,130
Device Routing Invert Outlet Devices
#1 Primary 421.90' 13.0' long Emergency Spillway 2 End Contraction (s)
Primary OutFlow Max=1.37 cfs @ 12.09 hrs HW=422.00' (Free Discharge)
t-1=Emergency Spillway (Weir Controls 1.37 cfs @ 1.0 fps)

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0360 - POST DEVELOPMENT Type 11 24-hr 1-Year Rainfall=3.00"
Prepared by {enter your company name here} Page 4
HydroCAD®7 10 s/n 003899 © 2005 HydroCAD Software Solutions LLC 5/19/2008
Pond 1 P: Bioretention Cell
Hydrograph
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F-31 nflow
10 Primary 10 11 12 13 14
Time (hours)

' 0360 - POST DEVELOPMENT Type// 24-hr 1-Year Rainfall=3.00"
Prepared by {enter your company name here} Page 5
HydroCAD® 710 s/n 003899 0 2005 HydroCAD Software Solutions LLC 5/19/2008
Pond 2P: Wetland
' Inflow Area = 2.470 ac, Inflow Depth = 1.38" for 1-Year event
Inflow 6.34 cfs @ 11.96 hrs, Volume= 0.284 of
Outflow = 0.69 cfs @ 12.36 hrs, Volume= 0.234 af, Atten= 89%, Lag= 23.9 min
' Primary = 0.69 cfs @ 12.36 hrs, Volume= 0.234 of
Routing by Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.01 hrs
Peak Elev= 419.06' @ 12.36 hrs Surf.Area= 6,245 sf Storage= 6,105 cf
' Plug-Flow detention time= 831.8 min calculated for 0.234 of (83% of inflow)
Center-of-Mass det. time= 754.6 min ( 1,589.8 - 835.3 )
Volume Invert Avail Storage Storage Description
' #1 418.00' 20,082 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation Surf.Area Inc.Store Cum.Store
' (feet) (sq-ft) (cubic-feet) (cubic-feet)
418.00 5,248 0 0

' 418.50
419.00 5,709 2,739 2,739
6,183 2,973 5,712
419.50 6,672 3,214 8,926
420.00 7,174 3,462 12,388
420.50 7,691 3,716 16,104
' 421.00 8,222 3,978 20,082
Device Routing Invert Outlet Devices
#1 Primary 416.50' 15.0" x 28.0' long OUTLET BARREL
RCP, square edge headwall, Ke= 0.500
Outlet Invert= 416.00' S=0.0179? Cc= 0.900
' n= 0.013 Concrete pipe, bends & connections
#2 Device 1 419.00' 48.0" Horiz. RISER Limited to weir flow C= 0.600
#3 Device 1 418.00' 1.0" Vert. ORIFICE C= 0.600
1 Primary OutFlow Max=0.68 cfs @ 12.36 hrs HW=419.06' (Free Discharge)
L1=OUTLET BARREL (Passes 0.68 cfs of 8.23 cfs potential flow)
2=RISER (Weir Controls 0.65 cfs @ 0.8 fps)
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' 3=ORIFICE (Orifice Controls 0.03 cfs @ 4.9 fps)

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0360 - POST DEVELOPMENT Type// 24-hr T-Year Rainfall=3.00"
Prepared by {enter your company name here} Page 6
HydroCADO 7.10 s/n 003899 © 2005 HydroCAD Software Solutions LLC 5/19/2008
Pond 2P: Wetland
Hydrograph
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? Primary
10 11 12 13 14
Time (hours)
0360 - POST DEVELOPMENT Type 11 24-hr 100-Year Rainfall=7.40"
Prepared by {enter your company name here} Page 7
HydroCAD(D 7.10 s/n 003899 © 2005 HydroCAD Software Solutions LLC 5/19/2008
Time span=0.00-72.00 hrs, dt=0.01 hrs, 7201 points
Runoff by SCS TR-20 method, UH=SCS
Reach routing by Stor-Ind method - Pond routing by Stor-Ind method
Pond 1P: Bioretention Cell Peak Elev=422.43' Storage=7,553 cf Inflow=17.50 cfs 0.848 of
Outflow=16.19 cfs 0.744 of
Pond 2P: Wetland Peak Elev=420.26' Storage=14,290 cf Inflow=23.04 cfs 1.089 of
Outflow= 10.46 cfs 1.040 of

0360 - POST DEVELOPMENT Type 11 24-hr 100-Year Rainfall=7.40"
Prepared by {enter your company name here) Page 8
HydroCADO 7.10 s/n 003899 © 2005 HydroCAD Software Solutions LLC 5/19/2008
' Pond 1 P: Bioretention Cell
' Inflow Area = 1.770 ac, Inflow Depth= 5.75" for 100-Year event
Inflow 17.50 cfs @ 11.96 hrs, Volume= 0.848 of
Outflow = 16.19 cfs @ 11.99 hrs, Volume= 0.744 af, Atten= 7%, Lag= 1.7 min
Primary = 16.19 cfs @ 11.99 hrs, Volume= 0.744 of
Routing by Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.01 hrs
Peak Elev= 422.43'@ 11.99 hrs Surf.Area= 5,971 sf Storage= 7,553 cf
' Plug-Flow detention time= 97.4 min calculated for 0.744 of (88% of inflow)
Center-of-Mass det. time= 38.0 min ( 824.3 - 786.2 )
Volume Invert Avail Storage Storag e Description
#1 421.00' 11,130 cf Custom Stage Data (Prismatic) Listed below (Recalc)
' Elevation
(feet) Surf.Area
(sq-ft) Inc.Store
(cubic-feet) Cum.Store
(cubic-feet)
421.00 4,623 0 0
421.50 5,082 2,426 2,426
' 422.00 5,554 2,659 5,085
422.50 6,041 2,899 7,984
423.00 6,542 3,146 11,130
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Device Routing Invert Outlet Devices
#1 Primary 421.90' 13.0' long Emergency Spillway 2 End Contraction(s)
Primary OutFlow Max=16.16 cfs @ 11.99 hrs HW=422.43' (Free Discharge)
L1=Emergency Spillway (Weir Controls 16.16 cfs @ 2.4 fps)

0360 - POST DEVELOPMENT Type 11 24-hr 100-Year Rainfall=7.40"
Prepared by {enter your company name here} Page 9
HydroCAD®7 10 s/n 003899 © 2005 HydroCAD Software Solutions LLC _5/19/2008
Pond 1 P: Bioretention Cell
Hydrograph
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? Inflow
19 17 50 ifs - - -
? Primary
Inflow Ar-ea,1.770 -ac -

16.19 cfs
17

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Peak Elev=422
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Time (hours)

0360 - POST DEVELOPMENT Type 11 24-hr 100-Year Rainfall=7.40"
Prepared by {enter your company name here} Page 10
HydroCADO 7.10 s/n 003899 © 2005 HydroCAD Software Solutions LLC 5/19/2008
' Pond 2P: Wetland
' Inflow Area = 2.470 ac, Inflow Depth= 5.29" for 100-Year event
Inflow 23.04 cfs @ 11.96 hrs, Volume= 1.089 of
Outflow = 10.46 cfs @ 12.05 hrs, Volume= 1.040 af, Atten= 55%, Lag= 5.4 min
Primary = 10.46 cfs @ 12.05 hrs, Volume= 1.040 of
' Routing by Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.01 hrs
Peak Elev= 420.26' @ 12.05 hrs Surf.Area= 7,443 sf Storage= 14,290 cf
Plug-Flow detention time= 215.1 min calculated for 1.039 of (95% of inflow)
Center-of-Mass det. time= 188.8 min ( 985.7 - 796.9 )
Volume Invert Avail.Storage Storage Description
' #1 418.00' 20,082 cf Custom Stage Data (Prismatic) Listed below (Recalc)
Elevation
(feet) Surf.Area Inc.Store Cum.Store
(sq-ft) (cubic-feet) (cubic-feet)
418.00 5,248 0 0
418.50 5,709 2,739 2,739
' 419.00 6,183 2,973 5,712
419.50 6,672 3,214 8,926
420.00 7,174 3,462 12,388
420.50 7,691 3,716 16,104
' 421.00 8,222 3,978 20,082
Device Routing Invert Outlet Devices
' #1 Primary 416.50' 15.0" x 28.0' long OUTLET BARREL
RCP, square edge headwall, Ke= 0.500
Outlet Invert= 416.00' S= 0.0179'P Cc= 0.900
n= 0.013 Concrete pipe, bends & connections
#2 Device 1 419.00' 48.0" Horiz. RISER Limited to weir flow C= 0.600
#3 Device 1 418.00' 1.0" Vert. ORIFICE C= 0.600
Primary OutFlow Max=10.46 cfs @ 12.05 hrs HW=420.26' (Free Discharge)
't-1 =OUTLET BARREL (Inlet Controls 10.46 cfs @ 8.5 fps)
t2=RISER (Passes < 58.10 cfs potential flow)
3=ORIFICE (Passes < 0.04 cfs potential flow)
n
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0360 - POST DEVELOPMENT Type 1124-hr 100-Year Rainfall=7.40"
Prepared by {enter your company name here} Page 11
HydroCAD®7 10 s/n 003899 © 2005 HydroCAD Software Solutions LLC 5/19/2008
Pond 2P: Wetland
Hydrograph

__ I3 Inflow

- - - - -
23.04 cfs
© Primary
24 -470 ac -
lnflow Area=2
.
/ Peak Elev=420.26
20
'

- - -
- - - - - - ?- - -Storage=-14;2--90-cf -
18
16 - - - - - - - r }- -- - - - -
14
-
- -
O 12

LL 10.46 cfs
- - -
10 - - - - - - - - -

/ i
-- - -- - -'
6 - - - - - - - - - - -_ - - -- - -- - - -_ _._ -

41 /"
1'0 11 12 13 14
Time (hours)
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WATER QUALITY CALCULATIONS

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0360 BIORETENTION CELL CALCULATIONS.As
Design Sheet
Underdrain Calculations
Depth of Soil Media, D, = 4 [ft]
Soil Permeability, k = 1 [in/hr)
Flow Area, A = 4623 [sfl
1=(Ds*ht )/Ds
Max. Hydraulic Gradient, I = 1.25 [ft/ft)
Q=(k/(12`3600) "1"A
Maximum Flowrate, Q = 0.134 [cfs]
Safety Factor, SF = 10.0
Final Flowrate, Q = 1.34
Roughness factor, n = 0.011
Pipe slope, s = 0.5%
1.
DP=(16"Q"n/S.5)13/81 1
Diameter of single pipe, Dp = 1.57 [in]
2, 4 inch pipes
Number & Diameter of Pipes to be used: or
2, 6 inch pipes
Summary
The required water treatment surface area is: 4274 [sf]
The provided water treatment surface area is: 4623 [sf]
Therefore, the required depth above normal pool for storm storage is: 0.84 [ft]
Thus, set the crest of the principal spillway at stage: 0.9 [ft]
and at an elevation of: 421.9
Thus, the storage at the spillway crest is: 4309 [cf]
The number and diameter of underdrain pipes shall be: 2, 4 inch pipes
The minimum number of clean-out pipes to be used is: 5
Bill Price
5/19/2008

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0360 BIORETENTION CELL CALCULATIONS XIS
Design Sheet
Bioretention Cell Design Calculations
Drainage Areas
Impervious Area, IA = 1.21 [ac]
Drainage Area, DA = 1.77 [ac]
I,= IA / DA
Impervious Fraction, IA = 0.68
Required Volume by Simple Method
RD = 1 [in]
Rv =0.05+0.9*IA
Rv = 0.67
V = 3630 * RD* Rv* DA
V = 4274 [cf]
Required Surface Area
Ponding Depth, hf= 1 [ft]
A,=V/hf
Req'd Surface Area, Ar = 4274 [5f]
StnnP. Unrnae
ncremen a ccumu a e s ima e
Average Contour Contour Stage w/SS
Contour Stage Contour Area Contour Area Volume Volume Fxn
(feet) (feet) (SF) (SF) (CF) (CF) (feet)
421.0 0.0 4623
421.5 0.5 5082 4853 2426 2426 0.50
422.0 1.0 5554 5318 2659 5085 0.99
422.5 1.5 6041 5798 2899 7984 1.49
423.0 2.0 6542 6292 3146 11130 2.02
Storage vs. Stage

15000

10000 096
Y = 5149x' 3
A Rz = 0.9997
1! 5000
0
0
0.0 0.5 1.0 1.5 2.0 2.5
Stage (feet)
Ks = 5149
b = 1.0963
Rise Resulting from 1" Rainfall Event
Norm. Pool Depth, DN = 0.00 [ft]
VN=KS*DNb
Storage at Norm. Pool, VN = 0 [cf]
Total Storage Required, VT = 4274 [cf]
ST = (VT * Q111bl
Stage Of VT, ST= 0.84 [ft]
Bill Price
5/19/2008
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0360 BIORETENTION CELL CALCULATIONS.As Bill Price
Channel Analysis - Spillway 5/19/2008
Channel Analysis Calculations
Channel Data
Q to = 10.04 [cfs]
Min. Channel Slope, s = 0.5 [ft/ft]
Design Side Slope, M = 5 :1 [H:V]
Channel Bottom Width, B = 4.0 [ft]
Channel Invert Elevation = 421.0 [ft]
Manning's 'n' value = 0.069
Determination of Flow Depth & Velocity (Using 'Solver')
Iteration
# '/2)
Qn/(1.49s Assumed y
, A
Area Wetted
Perimeter, P AR 2/3
Iff] [sq• ft] Iffl
1 0.658 0.308 1.707 7.142 0.658
bummary
10-Year Channel Depth = 0.31 [ft]
10-Year Channel Velocity = 5.88 [fps]
10-Year WSE = 421.31 [ft]
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0360 BIORETENTION CELL CALCULATIONS.As
VELOCITY DISSIPATOR - SPILLWAY
Velocity Dissipator Design Calculations
(From Spillway)
10-Year Outflow, Q (cfs) = 10.04
Slope, S (%) = 0.50
Weir Length (ft)= 13
Manning's n Value = 0.013
Flow Depth (ft.) = 0.31
Velocity, V (ft/s) = 5.88
Average Dia. Stone Thickness
(inches) Class (inches)
>> 4 A 12 <<
8 B 18
10 1 24
14 2 36
FINAL DIMENSIONS:
Length, L (ft.) = 7.5
Width, W (ft.) = 15.0
Depth, D (in.) = 12
Stone Class = A
*This and the channel analysis design sheets show that
Class 'A' riprap will dissipate the velocity resulting from the
10-year storm.
Bill Price
5/19/2008
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0360 BIORETENTION CELL CALCULATION S.xIs
VELOCITY DISSIPATOR -UNDERDRAIN
Velocity Dissipator Design Calculations
(From Underdrain)
Max Outflow, Q (cfs) = 1.34
Slope, S (%) = 0.50
Pipe Diameter, D [ft] = 0.5
Manning's n Value = 0.010
Velocity, V (ft/s) = 6.81
Average Dia. Stone Thickness
(inches) Class (inches)
>> 4 A 12
8 B 18
10 1 24
14 2 36
FINAL DIMENSIONS:
Length, L (ft.) = 2.0
Width, W (ft.) = 1.0
Depth, D (in.) = 12
Stone Class = A

Bill Price
5/19/2008
0360 WETLAND #2 DESIGN CALCULATIONS.xis
RAINFALL & VOLUME
EXTENDED DETENTION WETLAND
RAINFALL & WATER QUALITY VOLUME CALCULATIONS
Bill Price
5/15/2008
WATER QUALITY VOLUME CALCULATIONS
Precipitation (P) [in] 1
Drainage Area (A) [ac] 2.47
Impervious Area (Almp) [ac] 1.43
Runoff Coefficient (Rv) [in/in] 0.57
Water Quality Volume (WQv) [cf] 5120
VOLUMES CALCULATIONS
FOREBAY MAIN POOL
NORMAL POOL ELEV [ft] 418.00 418.00
VOLUME BELOW NORMAL POOL [cf] 1366.91 2482.22
SURFACE AREA AT NORMAL POOL [sf] 662.00 5248.00
AVERAGE DEPTH [ft] - -
TOTAL
4393.05
6418.00
0.68
FOREBAY PORTION OF TOTAL VOLUME
31.1%

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0360 WETLAND #2 DESIGN CALCULATIONS.As
1-INCH RAINFALL
EXTENDED DETENTION WETLAND
I-INCH RAINFALL CALCULATIONS
VOLUME REQUIRED TO TREAT THE RUNOFF FROM THE 1-INCH RAINFALL EVENT
DRAINAGE AREA [ac] 2.47
IMPERVIOUS AREA [ac] 1.43
IA (IMPERVIOUS FRACTION) 0.58
RAINFALL DEPTH [in] 1.00
RV 0.57
REQUIRED VOLUME [cf] 5120
erAC_F_srnaAr,F CAL CULATIONS

SURFACE AVERAGE
INCREMENTAL
CUMULATIVE
TEST STAGE
ELEV [ff] STAGE [ff] AREA [sf] SURFA
CE VOL [cf] VOLUME [ff] [ft]
REA
A
[Sfj
418.00 0.0 5248 0.0 0.0 0.0 0.0
418.50 0.5 5709 5479 2739 2739 0.5
419.00 1.0 6183 5946 2973 5712 1.0
419.50 1.5 6672 6428 3214 8926 1.5
420.00 2.0 7174 6923 3462 12388 2.0
420.50 2.5 7961 7568 3784 16171 2.5
421.00 3.0 8222 8092 4046 20217 3.1
STAGE-STORAGE FUNCTION y = 5804.6x1113
Rz = 0.9993

25000

20000

W 15000
Q?
a
O 10000
W

5000

0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
STAGE [ft]
0- STAGE-STORAGE FUNCTION -Power (STAGE-STORAGE FUNCTION)
Ks = 5804.6
B= 1.113
SUMMARY FOR 1" RAINFALL EVENT
Stage Required [ft] 0.89
Actual Riser Crest Stage [ft] 1.0
Actual Riser Crest Elev [ft] 419.0
Volume Provided 5805
Temporary Pool Surface Area [sf] 6183
Bill Price
5/19/2008

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0360 WETLAND #2 DESIGN CALCULATIONS.xis
FOREBAY VOL. BELOW NORMAL POOL
EXTENDED DETENTION WETLAND
FOREBAY VOLUME BELOW NORMAL POOL
Bill Price
5/15/2008
cra .F_sT0RacE CALCULATIONS

SURFACE AVERAGE
INCREMENTAL
CUMULATIVE
TEST STAGE
ELEV [ft] STAGE [ft] AREA [sq SURFACE VOL [cq VOLUME [ft] [ft]
A
REA fl
415.0 0.0 242.0 0.0 0.0 0.0 0.0
415.5 0.5 302.0 272.0 136.0 136.0 0.5
416.0 1.0 389.0 345.5 172.8 308.8 1.0
416.5 1.5 466.0 427.5 213.8 522.5 1.4
417.0 2.0 569.0 517.5 258.8 781.3 2.0
417.5 2.5 662.0 615.5 307.8 1089.0 2.5
418.0 3.0 762.0 712.0 356.0 1445.0 3.1
STAGE-STORAGE FUNCTION
y = 322.1 x1.31 57
R2 = 0.9972

1600.0

1400.0

1200.0

a 1000.0
W
800.0
O
0 600.0

400.0

200.0

0.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
STAGE [ft]
-H-STAGE-STORAGE FUNCTION Power (STAGE-STORAGE FUNCTION)
Ks = 322.1
B = 1.3157
VOLUME OF FOREBAY BELOW NORMAL POOL
1367 [cf]
' 0360 WETLAND #2 DESIGN CALCULATIONS.As Bill Price
TOTAL VOL. BELOW NORMAL POOL 5/15/2008

1

k

EXTENDED DETENTION WETLAND
TOTAL VOLUME BELOW NORMAL POOL
QTAl3C_4ZTnDArF rAlrill AT?nNS
FOREBAY MICROPOOL TOTAL AVERAGE
INCREMENTAL
CUMULATIVE TEST
ELEV [ft] STAGE [FT] SURFACE SURFACE SURFACE SURFACE AREA
cf]
VOL [
VOLUME [ft] STAGE
AREA [sf] AREA AREA [sf] [sfl [ft]
415.0 0.0 242 0 242 242 0 0 0.0
415.5 0.5 302 0 302 272 136 136 0.5
416.0 1.0 389 319 708 505 253 389 1.0
416.5 1.5 466 411 877 793 396 785 1.5
417.0 2.0 569 508 1077 977 489 1273 2.0
417.0 2.0 662 0 662 870 0 1273 2.0
417.5 2.5 762 0 3197 1930 965 2238 2.8
418.0 0.0 0 0 0 0 0 0 0.0
0.0 0.0 0 0 0 0 0 0 0.0
STAGESTORAGE FUNCTION
y = 413.08x1 121
R2 = 0.9935

2500.0

2000.0
W
1500.0
ga
O 1000.0
y

500.0

0.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0
STAGE [ft]
STAGE-STORAGE FUNCTION -Power (STAGE-STORAGE FUNCTION)
Ks = 421.47
B = 1.614
TOTAL VOLUME BELOW NORMAL POOL
2482 [Cf]
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0360 WETLAND #2 DESIGN CALCULATIONS.As
INV SIPHON SIZING
EXTENDED DETENTION WETLAND
INVERTED SIPHON SIZING
DIAMETER [in] 1
# OF SIPHONS 1
ks 5804.6
b 1.113
CD 0.6
SIPHON INVERT [ft] 418
VOL AT NORM POOL [cf] 0
BASIN INVERT [ft] 418

WSE [ff] VOLUME
STORED [cf] [NCR
SIPHONE
FLOW [cfs] AVG FLOW
[cfs] INCR
VOLUME
[cf] INCR TIME
[sec]
419.00 5805 0.03
418.91 5243 0.02 0.03 562 22401
418.83 4688 0.02 0.02 556 23302
418.74 4139 0.02 0.02 549 24348
418.65 3597 0.02 0.02 542 25584
418.56 3064 0.02 0.02 533 27081
418.48 2539 0.02 0.02 524 28948
418.39 2026 0.02 0.02 513 31378
418.30 1526 0.01 0.01 500 34750
418.21 1042 0.01 0.01 484 39947
418.13 580 0.01 0.01 461 49879
STEP INCREMENT 0.08737
END GOAL 580.46
DRAWDOWN TIME [days] 3.56
By comparison, if calculated by the average head over the orifice
(assuming average head is half the total depth), the result would be:
AVG DRIVING HEAD ON ORIFICE [ft] 0.48
ORIFICE COMPOSITE LOSS COEFFICEINT 0.60
X-SECTIONAL AREA OF 1-4# SIPHON [sf] 0.01
FLOWRATE THROUGH ORIFICE [cfs] 0.02
DRAWDOWN TIME = VOLUME/FLOWRATE/86400 (sec/day)
DRAWDOWN TIME [days] 3.70
Summary
Use one- 1 inch diameter PVC inverted
siphon to draw down the accumulated volume from the 1.0"
storm runoff, with a required time of about 3.6 days.
Bill Price
5/15/2008
' 0360 WETLAND #2 DESIGN CALCULATIONSAS
L TO W

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EXTENDED DETENTION WETLAND
LENGTH TO WIDTH ANALYSIS
Without Baffle Wall
Flowpath Length = 67 [ft]
Station #
(10 ft intervals) Width [ft]
1 36
2 41
3 86
4 87
5 86
6 84
7 58
Avg. Width = 68.29
L : W = 0.98 :1
With Baffle Wall
Flowpath Length = 147 [ft]
Station #
(20 ff intervals) Width [ft]
1 35
2 34
3 28
4 52
5 80
6 58
7 33
8 42
9 46
Avg. Width = 45.33
L : W = 3.24 :1
Bill Price
5/15/2008
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0360 WETLAND #2 DESIGN CALCULATIONS.As
PREFORMED SCOUR HOLE
EXTENDED DETENTION WETLAND
PREFORMED SCOUR HOLE
INPUT DATA
PIPE DIAMETER [in] 15
SCOUR HOLE DEPTH [ftj 1
SIDE SLOPES 2 :1
SCOUR HOLE BASE SIZE
SCOUR HOLE WIDTH [ft] 3.75
SCOUR HOLE LENGTH [ft] 3.75
SCOUR HOLE OUTER PERIMETER SIZE
OUTER WIDTH [ft] 7.75
OUTER LENGTH [ft] 7.75
CLASS'B' RIPRAP IS TO BE USED
Bill Price
5/15/2008
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401 CERTIFICATION APPLICATION FORMS
' Permit Number:
(to be provided bV DWQ)
Red triangles at the upper right hand corner Indicate design comments
Please complete the yellow shaded items.
o? ?ryw??a r??Fgoc
NCDENR
' STORMWATER MANAGEMENT PERMIT APPLICATION FORM
401 CERTIFICATION APPLICATION FORM
BIORETENTION CELL 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 of the required information.

' I. PROJECT INFORMATION
Project name Chatham Pointe
' Contact name
Phone number John Schrum
(919) 4904990
Date May 19, 2008
Drainage area number 1S

N
II. DESIGN INFORMATIO
Site Characteristics
Drainage area 77,101.20 ft2
' Impervious area 52,707.60 ft2
Percent impervious 68.4% %
Design rainfall depth 1.00 inch
Peak Flow Calculations
1-yr, 24-hr runoff depth 12.00 in
1-yr, 24-hr intensity 0.50 in/hr
' Pre-development 1-yr, 24-hr peak flow 1.79 ft3/sec
Post-development 1-yr, 24-hr peak flow 1.37 ft3/sec
Pre/Post 1-yr, 24-hr peak control -0.42 ft3/sec
Storage Volume: Non-SR Waters
Design volume 5,093.00 ft3
Storage Volume: SR Waters
' Pre-development 1-yr, 24-hr runoff ft 3
Post-development 1-yr, 24-hr runoff ft 3
Minimum volume required 0.00 ft 3
' Volume provided ft 3
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 5093.00 ft2 OK
' Length:
Width: 41.00 ft
119.00 ft OK
OK
or Radius ft
Soils Report Summary
' Drawdown time, ponded volume 12.00 hr OK
Drawdown time, to 24 inches below surface 24.00 hr OK
Drawdown time, total: 36.00 hr
' In-situ soil:
Soil permeability in/hr
Planting media soil:
Soil permeability 1.00 in/hr OK
Soil composition
% Sand (by weight) 85% OK
% Fines (by weight) 12% OK
Form SW401-Bioretention-Rev.3 Parts I and II. Design Summary, Page 1 of 3
% Organic (by weight)
Form SW401-Bioretention-Rev.3
3%
Total: 100%
OK
Permit Number:
(to be provided by DWQ)
Parts I and 11. Design Summary, Page 2 of 3
-W -
1 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?
(unitless)
422.00 fmsl
421.00 fmsl
417.00 fmsl
4.00 ft
4.00 inches
fmsl
OK
OK
y (Y or N)
8 OK
How many clean out pipes are being installed?
What factor of safety is used for sizing the underdrains? (See
10.00 OK
BMP Manual Section 12.3.6)
Additional distance between the bottom of the planting media and 1 ft
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 localed 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 ft of grass)
Grassed Swale
Forebay
1
416.00 fmsl
416.00 ft OK
(Y or N)
y (Y or N) OK media depth
13 OK
24 OK
264 OK
y (Y or N) OK
y (Y or N) OK
Permit Number:
,,to be provided by DWQ)
30 tt
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
Insufficient inlet velocity unless energy dissipating devices are
5.88 ft/sec being used.
n (Y or N) OK
n (Y or N) OK
y (Y or N) OK
X
OK
I Form SW401-Bioretention-Rev.3 Parts I and 11. Design Summary, Page 3 of 3
Permit No:
(to be assigned by DWQ)
III. REQUIRED ITEMS 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.
Pagel Plan
Initials Sheet No.
1. Plans (1" - 50' or larger) of the entire site showing:
Design at ultimate build-out,
Off-site drainage (if applicable),
Delineated drainage basins (include Rational C coefficient per basin),
Cell dimensions,
Pretreatment system,
High flow bypass system,
Maintenance access,
Proposed drainage easement and public right of way (ROW),
Clean out pipe locations,
Overflow device, and
Boundaries of drainage easement.
2. Plan details (1" = 30' or larger) for the bioretention cell showing:
' Cell dimensions
Pretreatment system,
High flow bypass system,
Maintenance access,
Recorded drainage easement and public right of way (ROW),
Design at ultimate build-out,
Off-site drainage (if applicable),
Clean out pipe locations,
Overflow device, and
- Boundaries of drainage easement.
3. Section view of the bioretention cell (1" = 20' or larger) showing:
Side slopes, 3:1 or lower
Underdrain system (if applicable), and
Bioretention cell layers [ground level and slope, pre-treatment, ponding depth, mulch depth, fill media
depth, washed sand, filter fabric (or choking stone K applicable), #57 stone, underdrains (if applicable),
SHWT level(s), and overflow structure]
4. A soils report that is based upon an actual field investigation, soil borings, and infiltration tests. The
' results of the soils report must be verified in the field by DWQ, by completing & submitting the soils
investigation request form. County soil maps are not an acceptable source of soils information. All
elevations shall be in feet mean sea level (fmsl). Results of soils tests of both the planting soil and the in
situ soil must include:
Soil permeability,
Soil composition (% sand, % fines, % organic), and
P-index.
5. A detailed planting plan (1" = 20' or larger) prepared by a qualified individual showing:
A variety of suitable species,
Sizes, spacing and locations of plantings,
Total quantity of each type of plant specified,
A planting detail,
The source nursery for the plants, and
Fertilizer and watering requirements to establish vegetation.
6. A construction sequence that shows how the bioretention cell will be protected from sediment until the
entire drainage area is stabilized.
7. The supporting calculations (including underdrain calculations, if applicable).
' 8. A copy of the signed and notarized operation and maintenance (0&M) agreement.
9. A copy of the deed restrictions (if required).
' Form SW401-Bioretention-Rev.3 Part III Page 1 of 1

L
1M 40A HCDEHR
t
Permit Number
(to be provided by DWQ)
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 lll) must be printed, filled out and submitted along with all the required information.
o??F W A tF9QG
r
o
' I. PROJECT INFORMATION
Project name Chatham Pointe
Contact name John Schrum
Phone number [phone]
Date May 13, 2008
Drainage area number 2S
' II. DESIGN INFORMATION
Site Characteristics
Drainage area 107,593 ft2
1 Impervious area 62,291 ft2
_
Percent impervious 57.9%
%
Design rainfall depth 1.0 inch
' Peak Flow Calculations
Does this project require pre/post control of the 1-yr 24-hr peak
flow?
1-yr, 24-hr runoff depth
' 1-yr, 24-hr intensity
Pre-development 1-yr, 24-hr runoff
Post-development 1-yr, 24-hr runoff
Pre/Post 1-yr, 24-hr peak control
Storage Volume: Non-SR Waters
' Design volume (temporary pool volume)
Depth of temporary poollponding depth (DP,anM)
Drawdown time
Diameter of orifice
Coefficient of discharge (CD) used in orifice diameter
calculation
Driving head (Ho) used in the orifice diameter calculation
Storage Volume: SR Waters Parameters
1-yr, 24-hr depth
Pre-development 1-yr, 24-hr runoff
Post-development 1-yr, 24-hr runoff
Minimum volume required
Volume provided
1
Form SW401-Wetland-Rev.1
Y (Y or N)
1.38 in
0.0575 in/hr
6.76 ft 3/sec
6.34 ft 3/sec
-0.4 ft3/sec
6,183 ft 3 OK
12 in OK
3.63 days OK
1.00 in OK
0.60 (unitless)
0.479 ft
in
ft3
ft 3
ft 3
ft3
OK
Parts I and II. Project Design Summary, Page 1 of 3

Permit Number
(to be provided by DWQ)
Surface Areas of Wetland Zones
' Surface Area of Entire Wetland 6,183 ft2 OK
Shallow Land 2,345 ft 2 OK
The shallow land percentage is: 38%
' Shallow Water 2,463 ft2 OK
The shallow water percentage is: 40%
Deep Pool
Forebay portion of deep pool (pretreatment) 762 ft2 OK
The forebay surface area percentage is: 12%
Non-forebay portion of deep pool 613 ft2 OK
' The non-forebay deep pool surface area percentage is: 10%
Total of wetland zone areas 6,183 ft2 OK
Add or subtract the following area from the zones
Topographic Zone Elevations 0.00 ft2
Temporary Pool
Shallow Land (top) 419.00 fmsl
' Permanent Pool
Shallow Water (top) 418.00 fmsl
Deep Pool (top) 417.50 fmsl
' Most shallow point of deep pool's bottom 416.00 fmsl
Deepest point of deep pool's bottom 415.00 fmsl
Design must meet one of the following two options:
This design meets Option #1,

'
n (Y or N)
inches below SLWT, If yes:
Deep pool is 6
SLWT (Seasonally Low Water Table) fmsl
This design meets Option #2,
Has a clay liner y
If yes:
Depth of topsoil above clay liner 4 in
Topographic Zone Depths
Temporary Pool
' Shallow Land 12 in OK
Permanent Pool
Shallow Water 6 in OK
Deep Pool (shallowest) 18 in OK
Deep Pool (deepest) 30 in OK
Planting Plan
' Are cattails included in the planting plan? N (Y or N) OK
Number of Plants in planting plan recommended:
Herbacious (flinch diameter) 186
Shrubs/small trees (1 gallon or larger) 124
Trees (1.5" dbh) 31
Number of Plants in planting plan provided (several species of
each plant type are recommended):
Herbacious (41inch diameter) 186 OK
Shrubs/small trees (1 gallon or larger) 124 OK
' Trees (1.5" dbh) 31 OK
Form SW401-Wetland-Rev.1 Parts I and II. Project Design Summary, Page 2 of 3
M
Permit Number
DWQ)
rovided b
(to be
y
p
Additional Information
Can the design volume be contained?
y
(Y or N)
OK
Does volume in excess of the design volume flow evenly y (Y or N) OK
distributed through a vegetated filter?
What is the length of the vegetated filter? 30 ft
' Does the design use a level spreader to evenly distribute flow? N (Y or N) Show how flow is evenly distributed.
Are calculations for supporting the design volume provided in the y (Y or N) OK
application?
Is BMP sized to handle all runoff from ultimate build-out? y (Y or N) OK
Is the BMP located in a recorded drainage easement with a Y (Y or N) OK
recorded access easement to a public Right of Way (ROW)?
' The length to width ratio is: 3.2 :1 OK
Approximate wetland length 147.0 ft
Approximate wetland width 45.3 ft

id
id
h
d
664 ft 2
6 approx. surface area is within this number of square
This
' prov
e
t
Approximate surface area using length and w , feet of the entire wetland surface area reported above:
Will the wetland be stabilized within 14 days of construction? y (Y or N) OK

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1
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' Form SW401-Wetland-Rev.1 Parts I and II. Project Design Summary, Page 3 of 3

III. REQUIRED ITEMS 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 Pagel Plan
' Sheet No.
1. Plans (1" 50' or larger) of the entire site showing:
Design at ultimate build-out,
' Off-site drainage (if applicable),
Delineated drainage basins (include Rational C coefficient per basin),
Wetland dimensions (and length to width ratio),
Pretreatment system,
' Maintenance access,
Recorded drainage easement and public right of way (ROW),
Overflow device, and
Boundaries of drainage easement.
2. Plan details (1" = 50' or larger) for the wetland showing:
Wetland dimensions (and length to width ratio)
Pretreatment system,
Maintenance access,
Recorded drainage easement and public right of way (ROW),
Design at ultimate build-out,
Off-site drainage (if applicable),
Overflow device, and
Boundaries of drainage easement.
3. Section view of the wetland (1" = 20' or larger) showing:
Side slopes, 3:1 or lower
Wetland layers
All 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
4. A detailed planting plan (1" = 20' or larger) prepared by a qualified individual showing:
A variety of suitable species (not including cattails),
Sizes, spacing and locations of plantings,
Total quantity of each type of plant specified,
' A planting detail,
The source nursery for the plants, and
Fertilizer 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 inspection and maintenance agreement.
8. A copy of the deed restriction.
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u

HORVATH
ASSOCIATE S
CIVIL ENGINEERS PLANNERS LANDSCAPE ARCHITECTS
Chatham Pointe
Stormwater Management
Plan Addendum:
Nitrogen Loading
August 5, 2008
Job 03 60
North Carolina iennessee
16 Consultant Place, Suite 201 537 Market Street Suite LL20
Durham, NC 27707 Chattanooga, TN 37402
p 919.490.4990 / f 919.490.8953 p 423.266.4990 / f 423.266.5700
k1m@[ROW[Ep
AUG 6 2008
DENR - WATER QUALITY
WETLANDS AND STORMWATER BRANCH

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CHATHAM POINTE
STORM WATER MANAGEMENT PLAN ADDENDUM
NITROGEN LOADING
CHATHAM POINTE
West Chatham Street
Cary, North Carolina
Horvath Associates Project Number: 0360
MAY 28, 2008
Addendum: June 25, 2008
.-VIOUMNAIJAW
Prepared for: T.O.W. INC.
105 West Main Street
Durham, North Carolina 27701
[phone]
Prepared by: Horvath Associates, P.A.
Engineers - Planners - Landscape Architects
P.O. Box 51806
Durham, North Carolina 27717
[phone]

L'
CHATHAM POINTE
' S70RMWATER MANAGEMENT PLAN ADDENDUM
NITROGEN LOADING
1

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1

1
Addendum
This Report is an addendum to the Stormwater Management Plan for Chatham
Pointe. The narrative and accompanying calculations describe the nitrogen
loading and required Ecosystem Enhancement Fund Payment for the project.
Nitrogen Loading
The composite post-development nitrogen loading for this project exceeds the
3.6 lb/acre/year limitation. Physical treatment of the nitrogen in the stormwater
runoff will be accomplished using the wetlands as discussed above. The
wetland will provide removal of 40% and the bioretention cell will provide
removal of 35% of the nitrogen in the runoff that drains to them. The portion of
impervious area that does not drain to either of the BMP's along with managed
and permanently protected open space is accounted for with separate
nitrogen loading calculations. The total nitrogen loading for the site is then
summed to provide the post-development nitrogen loading with treatment. The
post-development nitrogen loading rate is then based upon this loading rate
divided by the total land area. Payment to the Ecosystem Enhancement Fund is
required to reduce the effective nitrogen loading rate to 3.6 Ibs/acre/year. The
nitrogen loading and required payment are provided in the Summary of Results.
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TOWN OF CARY NITROGEN EXPORT.xIs
' CHATHAM POINTE - POST-DEV

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John E. Schrum, PE
6/24/2008
(1) (2) (3) (4)
TN export coeff. TN export from
Type of Land Cover Area (acres) Ib acre r use Ib r
Permanently protected
undisturbed open space
(forest, un-mown meadow; 4.27 0.6 2.56
does not include areas to be
graded)
Permanently protected
managed open space (grass, 1.60 1.2 1.92
landscaping, etc.)

Impervious Surfaces (roads,
parking lots, driveways, roofs, 2.64 21.2 55.97
paved storage areas, etc.)
TOTAL 8.51 -- 60.45
TOTAL EXPORT (lbs/ac/yr) = 7.10
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TOWN OF CARY NITROGEN EXPORT.xIs
CHAT PNTE - POST-DEVE TREATMENT
John E. Schrum, PE
6/24/2008
IV YIV. V.Y....V.• v
(1)
(2)
(3)
(4)
TN export coeff. TN export from
Type of Land Cover Area (acres) Ib acre r use Ib r
Permanently protected
undisturbed open space
(forest, un-mown meadow; 0.00 0.6 0.00
does not include areas to be
graded)
Permanently protected
managed open space (grass, 0.56 1.2 0.67
landscaping, etc.)

Impervious Surfaces (roads,
parking lots, driveways, roofs, 1.21 21.2 25.65
paved storage areas, etc.)
TOTAL 1.77 -- 26.32
TOTAL EX PORT (Ibs/ac/yr) = 14.87
Treatment Efficiency =
NITROGEN EXPORT AFTER TREATMENT =
T.. \A?..il..r.A 40)
35%
17.11
(1) (2) (3) (4)
Type of Land Cover Area (acres) TN export coeff.
Ib acre r TN export from
use Ib r
Permanently protected
undisturbed open space
(forest, un-mown meadow; 0.00 0.6 0.00
does not include areas to be
graded)
Permanently protected
managed open space (grass, 1.04 1.2 1.25
landscaping, etc.)

Impervious Surfaces (roads,
parking lots, driveways, roofs, 1.43 21.2 30.32
paved storage areas, etc.)
TOTAL 2.47 -- 31.56
TOTAL EX PORT (Ibs/ac/yr) = 12.78
Wetland Treatment Efficiency =
NITROGEN EXPORT AFTER TREATMENT =
40%
18.94
lb/year
Ib/year
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1
1
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TOWN OF CARY NITROGEN EXPORT.As
CHAT PNTE - POST-DEVE TREATMENT
W-61-4 12 -
John E. Schrum, PE
6/24/2008
(1) (2) (3) (4)
Type of Land Cover Area (acres) TN export coeff.
Ib acre r TN export from
use Ib r
Permanently protected
undisturbed open space
(forest, un-mown meadow; 4.27 0.6 2.56
does not include areas to be
graded)
Permanently protected
managed open space (grass, 0.00 1.2 0.00
landscaping, etc.)

Impervious Surfaces (roads,
parking lots, driveways, roofs, 0.00 21.2 0.00
paved storage areas, etc.)
TOTAL 4.27 -- 2.56
TOTAL EX PORT (lbs/ac/yr) = 0.60
TOTAL NITROGEN LOADING AFTER TREATMENT = 38.61
NITROGEN LOADING RATE AFTER TREATMENT = 4.56
Amount of Nitrogen to Treat for 3.6 lb/acre/year = 0.96
Nutrient Offset Payment Rate = $ 28.35
# Years to Offset Nitrogen Loading = 30
Total Area to Treat = 8.51
REQUIRED PAYMENT TO ECOSYSTEM ENHANCEMENT FUND = $ 6,918.35
lb/year
lb/acre/year
lb/acre/year
years