20110180 Ver 1_More Info Received_20110413

Environmental Consultants, PA
Road • Raleigh, North Carolina 27614 • Phone: [phone] • Fax: [phone]
April 13, 2011
S&EC Project # 9929.P1
DWQ #: EXP 11-0180
NC Department of Environment and Natural Resources
Division of Water Quality
Wetlands, Buffers, Stormwater, Compliance and Permitting Unit (WebSCaPe)
Attn: Ian McMillan/Lia Gilleski
512 N. Salisbury Street (9th floor)
Raleigh, NC 27604
Re: Request for More Information Response-EXPRESS REVIEW
Generation II Commercial Center
Fuquay-Varina, Wake County, NC
To Mr. McMillan and Mrs. Gilleski:

APR 1 3 2011
DENR - wATER QUkn
WETLANDS ANDSTORMWATERWA W
The purpose of this letter is to respond to your Request for More Information letter dated April 6,
2011. The original questions/requests are copied below as they appear within the letter and are
then responded to by the project engineer within a Memorandum dated April 12, 2011.
Additional Information Requested.
1. Culvert Outlet Plunge Pool. Please provide another design option to reduce the 5-foot
plunge pool depth. In particular, since the design must also meet sediment & erosion control
requirements, we request that you evaluate the outlet plunge pool design using the NC
Division of Land Quality's design guidance in Sections 6.41 and Appendix 8.06 of the Erosion
and Sediment Control Planning and Design Manual, available at:
http://www. dlr. enr. state. nc. us/pages/publica tions. html.
See attached memorandum and letter provided by project engineer.
2. Wet Detention Ponds:
a. Revise the temporary pool elevation and forebay volume on the East Pond Supplement
form.
b. Per our calculation both the 4-inch and 3-inch orifices draw down their respective water
quality volumes in less than 2 days. Please choose appropriate sizes and revise the
supplement forms and the affected plan sheets.
Please see attached memorandum and revised supplemental forms provided by
project engineer.
Charlotte Office: Greensboro Office:
Phone: [phone] Phone: [phone]
Fax: [phone] Fax: [phone]
We anticipate that this answers all of the DWQ's questions in order to complete the final review
process requested for the written concurrence of Water Quality Certification 3821 and Riparian
Buffer Authorization. If you have any further questions or any additional explanation is needed,
please don't hesitate to call.
Sincerely,
SOIL & ENVIRONMENTAL CONSULTANTS, PA
tw
Debbie Edwards
Environmental Specialist
Attachments:
1) Project Memorandum-dated April 12, 2011
2) Stormwater Design Memo-re: Outlet Protection Pad
3) Revised Wet Pond Supplement Forms
4) Revises sheets 5 & 7 of the PCN
5) Revised Site Plan Maps-signed & sealed 04-12-11
6) Data CD
George Finch I Boney and Associates, P.A
309 North Boylan Avenue
Raleigh, NC 27606-1402
Post Office Box 10472
gf lba Raleigh, NC 27605-0472
T 9191833-1212
F 91 9 1 8343203
April 12, 2011
Project Memorandum
Project: Generations II Commercial Center
7416 Sunset Lake Road
Fuquay-Varina, NC
DWQ #: Exp11-0180
Re: Response(s) to DWQ's Request for Additional Information
We are submitting the following in response to the request for more information letter that was
sent out by DWQ on April 6th, 2011.
Letter Item # 1:
Please see the attached letter addressing the different outlet protection options
considered.
Letter Item #2:
A: Please see the attached supplemental forms.
B: The controlled outlet pipes for each pond have been reduced to extend the draw
down time for each pond to meet the 48+ hour requirement. See the revised
supplement forms.
Sincerely,
Don Wiggins and Daniel Woods
0504 1 -Trans-S&EC-DWQ-401 ExpSubl-03231 1 -dw
cc: Julie Zalkind-Generations II-via US Main-CD & 11" x 17" Plan Sets
gf Iba
April 12, 2011
George Finch I Boney and Associates, P.A.
309 North Boylan Avenue
Raleigh, NC 27606-1402
Post Office Box 10472
Raleigh, NC 27605-0472
T 9191833-1212
F 9 1 9 1 834-3203
Generations II Commercial Center Stormwater Design
North Carolina Department of Natural Resources
Raleigh Regional Office
Raleigh, NC
Attn. Joseph Gyamfi
Ref. Outlet protection at Stream Crossing
Mr. Gyamfi
This letter has been developed to provide the requested narrative relating to the design
and final development of the Outlet Protection Pad as it is currently proposed within our
resubmitted Site Plans, at the Product's Drive Stream Crossing within the center of this
Project's Site. A significant amount of study, design and consideration has been put
into how to properly introduce a Velocity Reduction Pad in this application and we
hope this will provide what is necessary to meet the requests of the North Carolina
Department of Environmental and Natural Resources (NCDENR) where this Project can
receive its Permit.
As an introduction, this Project is required to cross the Site's existing wetlands and
designated stream, with Product's Drive, a 41 ft Thoroughfare Roadway within a 60ft.
ROW. A 60 inch concrete pipe and culvert is proposed at the crossing of this existing
stream. The stoned dissipation pad studied is located at the outlet of this Crossing, to
prevent any potential downstream erosion from the development of the Project's
Roadway Crossing. As requested by NCDENR Staff, the design of the Pad was based
upon a 10 year storm event where the upstream watershed was at a potential full build-
out.
The outlet is an at-grade free discharge pipe with minimum tail water driven by the
stream flow depth. As required by NCDENR, the invert of this pipe has been designed
so it is 12 inches below the top of the stream elevation that was provided in the existing
conditions survey of the Site, at the location of this crossing. The estimated flow depth
below the culvert is less than 12 inches within this relatively shallow stream detailed
within the on-site survey, which is surrounded by a large expanse of designated
wetlands.
gf lba
George Finch I Boney and Associates, P.A.
309 North Boylan Avenue
Raleigh, NC 27606-1402
Post Office Box 10472
Raleigh, NC 27605-0472
T 9191833-1212
F 9 1 9 1 834-3203
NCDENR staff expressed a concern about the large length of Velocity Reduction Pad
proposed in the Project's pre-submittal meeting, so the Pipe and Culvert size was
reduced to the current 60" size, using the existing upstream wetlands as a temporary
storage.
The standard at grade rip-rap pad was incorporated into the Project's original submittal
to NCDENR, producing a permanent stream impact of 40 If. As an alternative, we
submitted in our supplementary data an alternate design of a Pool Type Pad as a
substitute to the standard rip-rap pad. The purpose of the request was an attempt to
reduce the length of the permanent impact to the stream, and requested we provide
additional information and design as how those systems could be applied in this
location.
In response, a number of Velocity Reduction Pad designs have been evaluated,
studied and considered at this stream crossing, for their inclusion into this Project's
Permit Submittal.
They include a typical, at grade, stoned pad and three "pooled" designs, similar a pre-
formed scour hole. The pooled methods include a free discharge outlet protection
derived from the State of Maine's erosion control manual, a submerged pipe outlet
protection derived from NCDENR manual and a submerged outlet design by the
Federal Highway Administration (FHWA). Both NCDENR and FHWA have other pool pad
designs, but they are designed for elevated-cantilever pipe, which did not seem to be
applicable to this project.
The State of Maine's design was considered because it closely mimicked the proposed
conditions, at grade with minimal tail water discharge. Utilizing this method the length
of the pad was reduced from 40 If to 30 If. However, it did generate a 5 ft deep pool at
the outlet. The pool depth was not desirable to NCDENR. As a result the NCDENR and
FHWA methods were considered.
The next method was the NCDENR submerged plunge pool design. The pool depth
includes a logarithmic formula based on the flow, pipe size, tail water and stone size.
Using the excel spread sheet, available on the NCDENR Sedimentation website, with an
8" average diameter stone, a 5' pipe, flow of 105 cfs (estimated flow through the pipe)
and a tail water of I' the calculations provide a dissipation pad length of approx. 30 If.
However, it also required a pool depth of 12.8'.
gf lba
George Finch I Boney and Associates. P.A.
309 North Boylan Avenue
Raleigh, NC 27606-1402
Post Office Box 10472
Raleigh, NC 27605-0472
T 9191833-1212
F 91 9 1 834-3203
We determined that to use this design where a "shallower" pool was created, the
conditions dictated that the stone diameter must be reduced to 3". By our
calculations, this produced a shallow pool, at the depth of 3.3', but the total length of
the required Pad was 45', which would have been longer than the pad length in our
initial submittal (rejected based upon its length). In addition, we determined in our
study that the use of 3" stone would not provide the appropriate protection in this
application. Therefore, this alternative was not proposed, or submitted for NCDENR
consideration. The limited tail water seemed to provide the extreme results in this
application.
Finally, the FHWA method for a rip-rap basin on a mild slope was considered in our
Study. The design for this Method, as it is applied to the conditions in this Project,
produced a "negative" pool depth, primarily affected by the pipe diameter and
minimal tail water. We determined that this method would not be applicable for this
Project's application.
The results of this Study determined that the Pool type Pads developed by the Methods
studied above, which included the NC-Div. of Land Quality's design guidelines in
Sections 6.41 and Appendix 8.06 of the Erosion and Sediment Control Planning and
Design Manual, did not produce a Pad where the Depth of Pool was less than our
designed 5ft, and/or length of Pad was less than the 40ft submitted in the Project's first
submittal.
The findings of the above studies and designs were submitted and reviewed with
NCDENR Staff after we received the NCDENR April 6th Request for More Information
Letter. Subsequently, and at the direction of NCDENR Staff, the Pool type Pad that is
included within this Project's current submittal is 35ft long and the pool depth is 3ft.
We believe this letter adequately address's the Study that was undertaken to
determine how to best provide a Velocity Reduction Pad in this Project at the Stream
Crossing. Meeting the requests and requirements of NCDENR
We will be available for any additional phone discussion/review on this issue.
Sincerely,
Daniel Woods, PE
George Finch/Boney and Associates
Permit
-WA
A
A
WDEHR
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
401 CERTIFICATION APPLICATION FORM
WET DETENTION BASIN SUPPLEMENT
This form must be fixed out printed and submitted.
The Required Items Checklist (Part Ill) must be printed, fixed out and submitted along with aN of the required information,
(to be provided by DWQ)
o1a0F?W?AT?c9 pG
77
kP lqii? <
I. PROJECT INFORMATION
Project name Generations II Carolina, LLC Space Parcells
Contact person Don wiggins
Phone number 9194311212
Date 3121/2011
Drainage area number 2
U, DESIGN INFORMATION
Site Characteristics
Drainage area 287,496 its
Impervious area, post-development 233,046 ft
% impervious 81.06 %
Design rainfall depth 1.0 in
Storage Volume: Non-SA Waters
Minimum volume required 18,680 ft3 OK
Volume provided 19,307 ft3
OK, volume provided is equal to or in excess of volume required.
Storage Volume: SA Waters
1.5" runoff volume ft3
Pre-development 1-yr, 24-hr runoff ft3
Post-development 1-yr, 24-hr runoff ft1
Minimum volume required ft3
Volume provided tt3
Peak Flow Calculations
Is the prelpost control of the 1yr 24hr storm peak flow required? Y (Y or N)
1-yr, 24-hr rainfall depth 3.0 in
Rational C, pre-development (unitless)
Rational C, post-development (unitless)
Rainfall intensity: 1-yr, 24-hr storm irVhr
Pre-development 1-yr, 24-hr peak flow 1292 ft3/yam
Post-development 1-yr, 24-hr peak flow 18.33 lf/sec
Pre/Post 1-yr, 24-hr peak flow control 5.41 ft3/sec
Elevations
Temporary pool elevation 384.75 fmsl
Permanent pool elevation 383.50 find
SHWT elevation (approx. at the perm. pool elevation) AVG=83.88 frnsl
Top of 10ft vegetated shelf elevation 384,00 imsl
Bottom of 1 Oft vegetated shelf elevation 383,00 b d
Sediment deanDut, top elevation (bottom of pond) 378.50 hd
Sed rnent cleanout, bottom elevation 377.50 fmsl
Sediment storage provided 1.00 ft
Is there additional volume stored above the state-required temp. pool? Y (Y or N)
Elevation of the top of the additional volume 384.8 fmsl OK
Form SW401-Wet Detention Basin-Rev.8-9/17/09 Parts I. & II. Design Summary, Page 1 of 2
Permit No.
(to be provided by DWQ)
U. DESIGN INFORMATION
Surface Areas
Area, temporary pool
Area REQUIRED, permanent pool
SAIDA ratio
Area PROVIDED, permanent pool, Av„y,,,
Area, bottom of 1 Oft vegetated shell, Abe dw
Area, sediment deancut, top elevation (bottom of pond), Abaw,d
17,250 ft
11,787 ft2
4.10 (unitless)
12,276 a OK
8,774 ft2
3,093 ft2
Volumes
Volume, temporary pool 19,307 fe
Volume, permanent pool, Vp,,,,,_.,, 30,584 f?
Volume, foreIM (sum of forebays if more than one forebay) 5,552 fe
Forebay % of permanent pool volume 18.2% %
SAIDA Table Data
Design TSS removal
Coastal SAIDA Table Used?
Mountain/Piedmont SAIDA Table Used?
SAIDA ratio
Average depth (used in SAIDA table):
Calculation option 1 used? (See Figure 10-2b)
Volume, permanent pool, Vp,._,,,,
Area provided, permanent pool, A,,,,,
Average depth calculated
Average depth used in SAIDA, da, (Round to nearest 0.5ft)
Calculation option 2 used? (See Figure 10-2b)
Area provided, permanent pool, Ap._ ,,,
Area, bottom of 1 Oft vegetated shelf, Abm ,tw
Area, sediment cieanout, top elevation (bottom of pond), Abo,yo,d
'Depth' (distance b/w bottom of 1 Oft shelf and top of sediment)
Average depth calculated
Average depth used in SAIDA, d,,(Round to nearest 0.5ft)
Drawdown Calculations
Drawdown through orifice?
Diameter of orifice (if circular)
Area of orifice (if-non-circular)
Coefficient of discharge (Cc)
Driving head (H,)
Drawdown through weir?
Weir type
Coeffkient of discharge (C j
Length of weir (L)
Driving head (H)
PreAevelcpment 1-yr, 24-hr peak flow
Post-development 1-yr, 24-hr peak flow
Storage volume discharge rate (through discharge orifice or weir)
Storage volume drawdown time
Additional Information
Vegetated side slopes
Vegetated shelf slope
Vegetated shelf width
Length of flowpath to width ratio
Length to width ratio
Trash rack for overflow & orifice?
Freeboard provided
Vegetated filter provided?
Recorded drainage easement provided?
Capures all runoff at ultimate build-out?
Drain mechanism for maintenance or emergencies is:
OK
OK
90 %
n (Y or N)
y (Y or N)
4.10 (unitless)
n (Y or N)
30,584 fe
12,276 fe
ft Need 3 ft min.
ft
y (Y or N)
12,276 fe
8,774 ft2
3,093 ft
4.50 it
3.47 ft OK
3.5 ft OK
y (Y or N)
2.50 in
in2
0.60 (uni(less
0.38 ft
(Y or N)
_ (unitless)
_ (uritless)
ft
_ft
12.92 fetsec
18.33 ft3lsec
0.10 f
2.20 days
OK, draws down in 2-5 dirs.
3 :1 OK
10 :1 OK
10.0 ft OK
5 :1 OK
5.0 :1 OK
y (Y or N) OK
1.0 ft OK
y (Y or N) OK
y (Y or N) OK
y (Y or N) OK
Pump
Forth SW401-Wet Detention Basin-Rev.8-9/17/09 Parts I. & It. Design Summary, Page 2 of 2
Permit No
H=NR
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
401 CERTIFICATION APPLICATION FORM
WET DETENTION BASIN SUPPLEMENT
This form must be filed out, pirated and submitted.
The Required Items Check id (Part I//) must be printed, filed out and submitted along with all of ft required information.
(to be provided by DWQ)
O-?F?W A?T?c9oG
a lqiiii? s
I. PRMCI 11MROTION
Project name Generations II Carolina, LLC Space Pwwlls
Contact person Don Waggins
Phone number 919-833-1212
Date 30/2011
Drainage area number 1
Ill. DEEM INFORMATION
Site Characteristics
Drainage area 664,333 fe
Impervious area, post-development 545,414 f?
% impervious 82.10 %
Design rainfall depth 1.0 in
Storage Volume: Non-SA Waters
Minimum volume required 43,680 ft3 OK
Volume provided 43,916 ft3
OK, volume provided is equal to or in excess of volume required.
Storage Volume: SA Waters
1.5' runoff volume ft
Pre-development 1-yr, 24-hr runoff ft3
Post-development 1-yr, 24-hr runoff ft3
Minimum volume required ft3
Volume provided ft3
Peak Flow Cakulatfons
Is the pre/post control of the 1yr 24hr storm peak flow required? y (Y or N)
1-yr, 24-hr rainfall depth 3.0 in
Rational C, pre-development (unitless)
Rational C, post- development (unitless)
Rainfall intensity: )-yr, 24-hr storm in/hr
Pre-development 1-yr, 24-hr peak flow 31.64 ft3/sec
Post-development 1-yr, 24-hr peak flow 27.80 ft3/ceo
Pre/Post 1-yr, 24-hr peak flow control -384 ft3/sec
Elevations
Temporary pool elevation 384.63 fmsl
Permanent pod elevation 383.00 fmsl
SHWT elevation (approx. at the perm. pool elevation) AVG=82.84 imsl
Top of 1 Oft vegetated shelf elevation 383.50 imsl
Bottom of 1 Oft vegetated shelf elevation 382.50 frrasl
Sediment deariout, top elevation (bottom of pond) 378.00 fmsf
Sediment cleanout, bottom elevation 377.00 fmsl
Sediment storage provided 1.00 ft
Is there additional volume stored above the state-required temp. pool? y (Y or N)
Elevation of the top of the additional volume 384.6 fmsl OK
Form SW401-Wet Detention Basin-Rev.8-9/17109
Parts I. & 11. Design Summary, Page 1 of 2
Permit
(to be provided by DINO)
11. DESIGN INFORMATION
Surface Areas
Area, temporary pool
Area REQUIRED, permanent pool
SAIDA ratio
Area PROVIDED, permanent pool, A,,,,,_pw
Area, bottom of 10ft vegetated shelf, AW ,1,
Area, sediment deanout, top elevation (bottom of pond), Abdo
23,732 fe
23,252 If
3.50 (unitess)
23,712 ff OK
20,731 ff
14,205 ff
Volumes
Volume, temporary pool 43,916 113
Volume, permanent pool, V,,m_pw 86,833 ft
Volume, forebay (sum of forebays if more than one forebay) 16,025 ft3
Forebay % of permanent pool volume 18.5% %
SAIDA Table Data
Design TSS removal
Coastal SAIDA Table Used?
Mountain/Piedmont SAIDA Table Used?
SAIDA rata
Average depth (used in SAIDA table):
Calculation option 1 used? (See Figure 10-2b)
Volume, permanent pool, V?,,,,_md
Area provided, permanent pool, Ap,,,,_,,W
Average depth calculated
Average depth used in SAIDA, dam„ (Round to nearest 0.5ft)
Calculation option 2 used? (See Figure 10-2b)
Area provided, permanent pod, Ap.._,w
Area, bottom of 1 Oft vegetated shelf, Ab,t , w
90 %
n (Y or N)
y (Y or N)
3.50 (unit ess)
n (Y or N)
86,833 ff3
23,712 ff
It
ft
y (Y or N)
23,712 ff
20,731 ff
Area, sediment deanout, top elevation (bottom of pond), Aem-11d 14,205 fe
'Depth` (distance b/w bottom of 1 Oft shelf and top of sediment)
Average depth calculated
Average depth used in SAIDA, d.„ (Round to nearest 0.5ft)
Drawdown Calculations
Drawdown through orifice?
Diameter of orifice ('If circular)
Area of orifice (uf-non-circular)
Coefficient of discharge (Cc)
Driving head (HQ)
Drawdown through weir?
Weir type
Coefficient of discharge (C j
Length of weir (L)
Driving head (H)
PreAevelopment 1-yr, 24-hr peak flow
Post-development 1-yr, 24-hr peak flow
Storage volume discharge rate (through discharge orifice or weir)
Storage volume drawdown time
Additional Information
Vegetated side slopes
Vegetated shelf dope
Vegetated shelf width
Length of flowpath to width ratio
Length to width ratio
Trash rack for overflow & orifice?
Freeboard provided
Vegetated filter provided?
Recorded drainage easement provided?
Capures all runoff at ultimate build-out?
Drain mechanism for maintenance or emergencies is:
4.50 ft
4.28 ft
4.5 It
y (Y or N)
3.00 in
in2
0.60 (unitless)
0.50 ft
(Y or N)
(unidess)
(unitless)
ft
ft
31.64 felsec
27.80 fetsec
0.17 ft3/sec
3.00 days
OK
OK
Need 3 It min.
OK
OK
OK, draws down in 2-5 days.
3 :1 OK
10 :1 OK
10.0 ft OK
2 :1 Insufficient flow path to width ratio. Must not shat-circuit pond.
2.0 :1 OK
y (Y or N) OK
y ft OK
y (Y or N) OK
y (Y or N) OK
y (Y or N) OK
Pump
Form SW401Met Detention Basin-Rev.8-W17/09
Parts I. & II. Design Summary, Page 2 of 2
C. Proposed Impacts Inventory
1. Impacts Summary
1a. Which sections were completed below for your project (check all that apply):
® Wetlands ® Streams - tributaries ® Buffers
? Open Waters ? Pond Construction
2. Wetland Impacts
If there are wetland impacts proposed on the site, then complete this question for each wetland area impacted.
2a. 2b. 2c. 2d. 2e. 2f.
Wetland impact number - Type of jurisdiction
Permanent (P) or Type of Type of wetland Forested (Corps - 404, 10 Area of impact
Temporary T impact if known DWQ - non-404, other acres
W1 ®P ? T Fill-Culvert & Bottomland ® Yes ® Corps 0.38
Dissipater Hardwood ? No ? DWQ
W2 ? P ? T ? Yes ? Corps
? No ? DWQ
W3 ? P ? T ? Yes ? Corps
? No ? DWQ
W4 ? P ? T ? Yes ? Corps
? No ? DWQ
W5 ? P ? T ? Yes ? Corps
? No ? DWQ
2g. Total wetland impacts 0.38
2h. Comments:
3. Stream Impacts
If there are perennial or intermittent stream impacts (including temporary impacts) proposed on the site, then complete this
question for all stream sites impacted.
3a. 3b. 3c. 3d. 3e. 3f. 3g.
Stream impact number - Type of Stream name Perennial Type of jurisdiction Average Impact
Permanent (P) or impact (PER) or (Corps - 404, 10 stream length
Temporary (T) intermittent DWQ - non-404, width (linear
(INT)? other) (feet) feet)
S1 ®P ? T Culvert & UT to Terrible ® PER ® Corps 3' 143
Dissipater Creek ? INT ? DWQ
S2 ? P ® T Construction UT to Terrible ® PER ® Corps 3' 20
Corridor Creek ? INT ? DWQ
S3 ? P ? T ? PER ? Corps
? INT ? DWQ
S4 ? P ? T ? PER ? Corps
? INT ? DWQ
3h. Total stream and tributary impacts 163
3i. Comments:
Page 5 of 12
PCN Form - Version 1.3 December 10, 2008 Version
6. Buffer Impacts (for DWQ)
If project will impact a protected riparian buffer, then complete the chart below. If yes, then individually list all buffer impacts
below. If an impacts require mitigation, then you MUST fill out Section D of this form.
6a.
® Neuse ? Tar-Pamlico ? Other:
Project is in which protected basin? ? Catawba ? Randleman
6b. 6c. 6d. 6e. 6f. 6g.
Buffer impact
number - Reason for impact Buffer Zone 1 impact Zone 2 impact
Permanent (P) or Stream name mitigation (square feet) (square feet)
Temporary T required?
131 ®P ? T Road Crossing UT to Terrible
Creek ®Nos 8,401 5,147
B2 ?P?T ?Yes
? No
B3 ?P?T ?Yes
? No
B4 ?P?T ?Yes
? No
6h. Total buffer impacts 8,401 5,147
6i. Comments:
Page 7 of 12