20061651 Ver 2_More Info Received_20070316

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~ Soil & Environmental Consultants, PA
11010 Raven Ridge Road Raleigh, North Carolina 27614 Phone: [phone] Fax: [phone]
www.SandEC.com
March 15, 2007
S&EC Project #9654.W2
DWQ Project #06-1651
Department of Environment and Natural Resources
Division of Water Quality
Attn: Cyndi Karoly/Annette Lucas
2321 Crabtree Boulevard, Suite 250
Raleigh, NC 27604
Re: Reply to the Division of Water Quality's Request for More Information
West Chatham Townhomes
Cary, Wake County, NC
To Whom It May Concern:
The purpose of this letter is to respond to your Request for More Information email dated March 12, 2007.
The original questions/requests are copied below as they appear within email, a response is provided
below.
Additional Information Requested:
1) Orifice seems oversized, I compute a drawdown of 0.5 day.
2) Please remove cattails from planting plan.
3) Please keep the micropool in a round or oval shape, remove the "finger" which is jutting out close to
the forebay. We want to keep the forebay and micropool as far apart as possible.
4) Make sure there is access for maintenance. It looks like large plant species have been planting
around the entire perimeter of the wetland.
The orifice size has been changed to 2 inches (see worksheet), the cattails have been removed
from the planting plan and replaced with hardstem bulrush, the micropool shape has been
modified and moved farther away from the forebay and the large plant species have been removed
from around the forebay and the north side of the BMP.
We anticipate that this answers all of the DWQ's questions in order to complete the final review process
fora 401 Water Quality Certification. If you have any further questions or any additional explanation is
needed, please don't hesitate to call.
Sincerely,
Debbie Edwards D
Environmental Specialist MAR 1 6 2007
DENR - WgTEtt QUALITY
CC: ~TLMIDSANp ST
Matthew Danielson-Beazer Homes, 5811 Glenwood Ave, Suite 200, Raleigh, NC 27612 ~RMWATER6RANCH
Travis Crissman-BNK, 6310 Chapel Hill Road, Suite250, Raleigh, NC 27607
Attachments:
1) Revised worksheet
2) Revised Constructed Wetlands Detail sheet C3.3
Charlotte Office: Greensboro Office:
236 LePhillip Court, Suite C 3817-E Law ale Drive
Concord, NC 28025 Greensboro, C 27455
Phone: [phone] Phone: [phone]
Fax: [phone] Fax: [phone]

DWQ Project No. ~b - ~ ~S
DIVISION OF WATER QUALITY - 401 EXTENDED DETENTION (and POCKET*) WETLAND WORKSHEET
I. PROJECT INFORMATION (please complete the
Project Name : W ~N CHPTH'AM
Contact Person: T1xv~S CRr55M~-.I
lowing information)'.
~~l~ri~5
Phone Number:
For projects with multiple basins, specify which basin this worksheet applies to:
Permanent Pool Elevation 'i ~•~ •~~ ft. (elevation of the orifice invert out)
Temporary Pool Elevation y' I • (~ ft. (elevation of the outlet structure invert in)

Permanent Pool Surface Area ~ orb ~ ( sq. ft. (water surface area at permanent pool elevation)
Drainage Area 9 • ~3 ac. (on-site and off-site drainage to the basin)
Impervious Area ~{• 02 ac. (on-site and off-site drainage to the basin)
Forebay Surface Area I (oDA sq. ft. (at permanent pool elevation approximately 15%)*
Marsh 0"-9" Surface Area ~ O4Z sq. ft. (at permanent pool elevation approximately 35%)*
Marsh 9"-18" Surface Area ~{, 23 ~ sq. ft. (at permanent pool elevation approximately 35%)*
Micro Pool Surface Area 1 ~ ~ 55 sq. ft. (at permanent pool elevation approximately 15%)*

Temporary Pool Volume ~ y S cu. ft. (volume detained on top of the permanent pool)

SA/DA used 1 • $2 ~4'1 • (0701 np. ~ (surface area to drainage area ratio)*
Diameter of Orifice 2.O in. (draw down orifice diameter)
REQUIRED ITEMS CHECKLIST
Initial in the space provided to indicate the following design requirements have been met and supporting documentation is attached. If a
requirement has not been met, attach an explanafion of why. At a minimum, a complete stormwater management plan submittal includes
a worksheet for each BMP, design calculations, plans and specifications showing all BMPs and outlet structure details, a detailed
drainage plan and a fully executed operation and maintenance agreement. An incomplete submittal package will result in a request for
additional information and will substantially delay final review and approval of the project
Applicants Initials
CIt"C The temporary pool controls runoff from the 1 inch rain.
4I ~ The basin side slopes are no steeper than 3:1.
v 1 ~ A planting plan for the marsh areas with plant species and densities is provided.
J(~ Vegetation above the permanent pool elevation is specified.
G(c. An emergency drain is provided to drain the basin.
-~ ~ The temporary pool draws down in 2 to 5 days.
~7(~ Sediment storage is provided in the permanent pool.
~~ A sediment disposal area is provided.
~1(~ Access is provided for maintenance.
~(. A site specific, signed and notarized operation and maintenance agreement is provided.
~(o The drainage area (including any offsite area) is delineated on a site plan.
~(c Access is provided for maintenance.
;R~ Plan details for the wetland are provided.
J(~ Plan details for the inlet and outlet are provided.
Slr, A site specific operation and maintenance agreement, signed and notarized by the responsible party is provided (see
http:i/h2o.ehnr.state. nc.us/ncwetlandsioandm.doc).
* Pocket Wetlands have different design parameters and are only assumed to remove 35% TSS -See pp.19and 20 of the NC DENR
stormwater BMP Manual, April 1999.10% open water, 50% high marsh, 40% low marsh.

Water Quality Retention Calculations
Project Name: West Chatham Street Townhomes
Determine Surface Area Required for Permanent Pool:
Drainage Area (ac): 9.43
Impervious Area (ac): 4 02
Percent Impervious: 42.6%
Perm. Pool Depth (ft): 3
SA/DA @ 40% 1.73 (from Table 1.1 of NCDENR's Starmwater BMP manual)
SA/DA @ 50% 2.06 (from Table 1.1 of NCDENR's Stormwater BMP manual)
Interpolated SA/DA: 1.82
Req. Surface Area (sf): 7463 (at permanent pool elevation)
Perm. Pool Elevation: 440.00
Provided Surtace Area (sf): 11641.00 OK -Surface area requirement met
Provided Storage (cf): 12837..50
Calculate the Volume Required to Treat the First Flush:
Rainfall to Treat: t inch(es)
Runoff Coefficient (Rv) = 0.05 + 0.009*(% Impervious)
Runoff Coefficient (Rv): 0.43 in/in
Runoff Volume (V) =Rainfall " (Rv) * (Drainage Area)
Runoff Volume (V): 14845 CF
Calculate the Death Required for the Temporary Pool:
Perm. Pool Elevation: 440.00
Provided Surface Area (sf): 11641.00 (at permanent pool elevation)
Provided Storage (cf) 12837.50
Volume Req, for Temp. Pool (CF): 14845 (this amount required above Perm. Pool)
Total Volume Req Temp & Perm(CF): 27682
EI. Of Temp. Pool Between: 441.00 and 442.00
EI.Of Temp. Pool: 441.17
Depth of Temp. Pool (ft): 1.17 measured from perm.. Pool elevation
Determine the Orifice Size for 2-5 Dav Drawdown:
Orifice Invert Elevation: 440.00
Elevation of Temp. Pool: 441.17
Orifice Diameter (in) 2.00
Use the orifice equation to determine flow and drawdown time:
Orifice Equation: O = C "A * (2gh)^0.5
Volume to Draw Down (CF): 14845
Flow for 2-Day Drawdown (CFS): 0.086
Flow for 5-Day Drawdown (CFS): 0.034
C: 0.6
g (SF/s): 32.2
h (ft): 0.544 (average driving head to centerline of orifice)
A (sf): 0.0218
Solve Orifice Equation for O (CFS) 0.077
Drawdown Time (Days): 2.22 OK -Drawdown between 2 and 5 days.