20070193 Ver 1_More Info Received_20070316

Environmental Consultants, PA
Road Raleigh, North Carolina 27614 Phone: [phone] Fax: (919) 84b-9467
wvvw.SandEC.com
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Jrw~ ~ Y'VAi~K l]UALITY
Y~ETU-NDS AND STORA~MATERljfi~PICH
Division of Water Quality
Attn: Cyndi Karoly /Ian McMillan
2321 Crabtree Boulevard
Suite 250
Raleigh, NC 27604
March 15, 2007
S&EC Project # 9629.W2
DWQ No. # 07-0193
Re: Reply to the Division of Water Quality's 02/14/07 request for additional information
Wake Med Apex Health Plex Building
Wake County, North Carolina
Dear Ms. Karoly and Mr. McMillan:
This letter is in response to your letter dated February 14, 2007, which requested
additional information for the proposed Wake Med Apex Health Plex Building. The
following restates your questions/comments and is then followed by our response.
Additional Information Requested
1. The extended detention wetland may not be designed with two
forebays. Please combine all flow into a single forebay and move the
outlet pipe so that it maximizes the flow path between the inlet and
outlet structures.
The engineer has redesigned the extended detention wetland so that there is only one
forebay. Additionally, the grading plan of the wetland has also been modified to allow
for maximum attenuation time of any Stormwater runoff entering the system (please see
attached revised drawings). The outlet pipe, however, cannot be moved as it is a pre-
existing permanent structure that has been retrofitted to meet with NC DENR's current
Stormwater Best Management Practices Manual.
Charlotte Office:
236 LePhillip Court, Suite C
Concord, NC 28025
Phone: [phone]
Fax: [phone]
Greensboro Office:
3817-E Lawndal'e Drive
Greensboro, NC 27455
Phone: [phone]
Fax: [phone]

2. Please provide worksheets for the extended detention wetland and the
wet detention pond.
Please find the attached requested worksheets.
3. Please specify the soils for the extended detention wetland and the
benthic shelf of the wet detention pond.
Please find the soil notes on the attached revised drawings.
Please call if you have any questions or require further explanation.
Sincerely, _
~~~ ~ - /~
Nicole J. omson
Regulatory Specialist
Attachments: 5 copies of Response letter
5 copies of revised drawings
5 copies of worksheets
CC: Mr. Mike Horan, DWQ Raleigh Regional Office

Project No. DWQ ~'~ - ~ l 9 3 (to be provided by DWQ)
DIVISION OF WATER QUALITY - 401 WET DETENTION BASIN WORKSHEET
DWO Stormwater Management Plan Review:
A complete stormwater management plan submittal includes a wet detention basin worksheet for each basin,
design calculations, plans and specifications showing all basin and outlet structure details, 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.
I. PROJECT INFORMATION (please complete the following information):
Project Name : Inl~ke. Mrs ~c ~a ~~ h D IGX
Contact Person: I~; ~,~ i -(~l O W~50p Phone Number: (91q 1846 ' S~ a o
For projects with multiple basins, specify which basin this worksheet applies to: EX i9'~ i nti ~`f' P6~1 d
Basin Bottom Elevation 4~3• oo ft. (average elevation of the floor of the basin)
Permanent Pool Elevation ~! 0 • Do ft. (elevation of the orifice invert out)
Temporary Pool Elevation 41Z . ZS ft. (elevation of the outlet structure invert in)
40, a 1 ~
Permanent Pool Surface Area sq. ft. (water surface area at permanent pool elevation)
Drainage Area 24.5 ac. (on-site and off-site drainage to the basin)
Impervious Area 18.9 7 ac. (on-site and off-site drainage to the basin)
Permanent Pool Volume ~ 1 cu. ft. (combined volume of main basin and forebay)
Temporary Pool Volume I $ 3{ 94 cu. ft. (volume detained on top of the permanent pool)
Forebay Volume ,~(T_ cu. ft.
SA/DA used . 7 S ~e (surface area to drainage area ratio)
Diameter of Orifice ,~ in. (draw down orifice diameter)
II. REQUIRED ITEMS CHECKLIST
The following checklist outlines design requirements per the Stormwater Best Management Practices manual
(N.C. Department of Environment, Health and Natural Resources, November 1995) and Administrative Code
Section: 15 A NCAC 2H .1008. 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 explanation of
why.
~~ The temporary pool controls runoff from the 1 inch storm event.
The basin length to width ratio is greater than 3:1.
n The basin side slopes are no steeper than 3:1.
/~ A submerged and vegetated perimeter shelf at less than 6:1 is provided.
ISM Vegetation to the permanent pool elevation is specified.
An emergency drain is provided to drain the basin.
The permanent pool depth is between 3 and 6 feet (required minimum of 3 feet).
The temporary pool draws down in 2 to S days.
~~ yV~ The forebay volume is approximately equal to 20% of the total basin volume.
;~l~w Sediment storage is provided in the permanent pool.
Access is provided for maintenance.
A minimum 30-foot vegetative filter is provided at the outlet.
Il A site specific operation and maintenance (O&M) plan is provided.
A vegetation management/mowing schedule is provided in the O&M plan.
1N~t Semi-annual inspections are specified in the O&M plan.
A debris check is specified in the O&M plan to be performed after every storm event.
A specific sediment clean-out benchmark is listed (elevation or depth) in O&M plan.
_~-~jil ~( A responsible party is designated in the O&M plan.
FORM SWG100 09/97 Page 1 of 1

DWQ Project No. ~ ~ ~ ~ ~ ~ 3
DIVISION OF WATER QUALITY - 401 EXTENDED DETENTION (and POCKET*) WETLAND WORKSHEET
I. PROJECT INFORMATION (lease complete the following info mation):
Project Name : U/ a th ~' i
Contact Person: ~ i kki "(hb rviSo vt Phone' umber: 0
For projects with multiple basins, specify which basin this worksheet applies to: Co ~ - d
Permanent Pool Elevation 3gZ • o o ft. (elevation of the orifice invert out)
Temporary Pool Elevation 3$S. So ft. (elevation of the outlet structure invert in)
Permanent Pool Surface Area
Drainage Area
Impervious Area
Forebay Surface Area
Marsh 0"-9" Surface Area
Marsh 9"-18" Surface Area
Micro Pool Surface Area
Temporary Pool Volume
SA/DA used
Diameter of Orifice
(I .q-$1 sq. ft.
1. Z o ac.
5. Z o ac.
,14 I sq. ft.
2 sq. ft.
0 ! 3 sq. ft.
1' 10 J sq. ft.
19 0~ cu. ft.
3.6` l '
2 in.
II. REQUIRED ITEMS CHECKLIST
(water surface area at permanent pool elevation)
(on-site and off-site drainage to the basin)
(on-site and off-site drainage to the basin)
(at permanent pool elevation approximately 15%)*
(at permanent pool elevation approximately 35%)*
(at permanent pool elevation approximately 35%)*
(at permanent pool elevation approximately 15%)*
(volume detained on top of the permanent pool)
(surface area to drainage area ratio)*
(draw down orifice diameter)
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 explanation 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
The temporary pool controls runoff from the 1 inch rain.
The basin side slopes are no steeper than 3:1.
A planting plan for the marsh areas with plant species and densities is provided.
Vegetation above the permanent pool elevation is specified.
An emergency drain is provided to drain the basin.
The temporary pool draws down in 2.to 5 days.
Sediment storage is provided in the permanent pool.
m ~y_A sediment disposal area is provided.
Access is provided for maintenance.
A site specific, signed and notarized operation and maintenance agreement is provided.
The drainage area (including any offsite area) is delineated on a site plan.
Access is provided for maintenance.
Plan details for the wetland are provided.
Plan details for the inlet and outlet are provided.
A site specific operation and maintenance agreement, signed and notarized by the responsible party is provided (see
http://h2o.ehnr.state. nc.us/ncwetlands/oandm.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.