20051280 Ver 2_More Info Received_20080623

•
Soil & Environmental Consultants, PA
11010 Raven Ridge Road - Raleigh, North Carolina 27614 - Phone: [phone] - Fax: [phone]
www.SandEC.com
June 20, 2008
S&EC Project # 3057.P4
DWQ EXP Project # 05-1280v2
Department of Environment and Natural Resources
Division of Water Quality
Attn: Cyndi Karoly/Lia Myott Gilleski D (, ,
2321 Crabtree Boulevard, Suite 250
Raleigh, NC 27604
Re: Reply to the Division of Water Quality's Request for More Information UEiv1c e'rt,,L UoikL;
EXPRESS REVIEW PROGRAM-Tryon Village Townhomes WETL*USANDSTORM`NATER? G?
Cary, Wake County, NC
To Mrs. Karoly and Mrs. Gilleski:
The purpose of this letter is to respond to your Request for More Information letter dated June
17, 2008. The original questions/requests are copied below as they appear within letter and are
then followed by our response.
Additional Information Requested.
Diffuse Flow.
a. The supplement form for the proposed level spreader lists the wooded
vegetation below (and possibly above) the sewer easement as dense vegetation.
In the picture provided, it appears that the vegetation is wooded and not dense
vegetation. Therefore, using a 50 ft vegetated filter strip (36 ft grass and 14 ft
wooded vegetation), out calculations show that you will need at least a 28 It level
spreader.
Please see attached revised supplemental form and sheet SW-2 and SW-4.
b. Please provide outflow calculations for both the outlet pipes from the wet pond
and provide the rip rap sizing calculations.
Please see attached stormwater BMP-Wet Detention Pond calculations and
velocity dissipaters for both the outlet pipes of the wet pond and the rip rap
sizing calculations.
c. Please provide construction details of the outlet protection for the high flow
bypass pipe.
Please see attached construction details of the outlet protection for the high
flow bypass pipe located on sheet SW-5.
Charlotte Office:
236 LePhillip Court, Suite C
Concord, NC 28025
Phone: [phone]
Fax: [phone]
Greensboro Office:
3817-E Lawndale Drive
Greensboro, NC 27455
Phone: [phone]
Fax: [phone]
d. Please explain the purpose of the trapezoidal area around the bypass pipe
outlet.
This area has been removed from the plans, this was an errant line.
e. Please add a construction note to indicate that the level spreader shall be
installed when the drainage area to the wet pond is stabilized (as requested in
the Required Items Checklist).
Please see sheet SW-5 with construction note is added.
We anticipate that this answers all of the DWQ's questions in order to complete the final review
process requested for the written Riparian Buffer Authorization. If you have any further
questions or any additional explanation is needed, please don't hesitate to call.
Sincerely,
Debbie Edwards
Environmental Specialist
CC:
Mr. Randy King-Pulte Homes-Raleigh
Mr. Ken Jesneck-Withers & Ravenel
Attachments:
1) Supplemental Form for Level Spreader
2) Stormwater BMP Wet Detention Pond Calculations
3) Velocity Dissipater Calculations
4) Sheets SW-2, SW-4 and SW-5
\O?pF WATe9?G
AN" y
O -~C
NCDENR
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
401 CERTIFICATION APPLICATION FORM
LEVEL SPREADER, FILTER STRIP AND RESTORED RIPARIAN BUFFER SUPPLEMENT
This form must be completely filled out, printed and submitted.
DO NOT FORGET TO ATTACH THE REQUIRED ITEMS CHECKLIST AND ALL REQUIRED ITEMS (NEXT WORKSHEET)!
I. PROJECT INFORMATION
Project name Tryon Village Townhomes
Contact name Ken Jesneck, PE
Phone number 919469-3340
Date June 20, 2008
Drainage area number BMP 1
IL DESIGN INFORMATION
For Level Spreaders Receiving Flow From a BMP
Type of BMP Wet Detention Pond
Drawdown flow from the BMP 0.30 cfs
For Level Spreaders Receiving Flow from the Drainage Area
Drainage area
Impervious surface area
Percent impervious
Rational C coefficient
Peak flow from the 1 in/hr storm
Time of concentration
Rainfall intensity, 10-yr storm
Peak flow from the 10-yr storm
Where Does the Level Spreader Discharge?
To a grassed bioretention cell?
To a mulched bioretention cell?
To a wetland?
To a filter strip or riparian buffer?
Other (specify)
Filter Strip or Riparian Buffer Characterization (if applicable)
Width of grass
Width of dense ground cover
Width of wooded vegetation
Total width
Elevation at downslope base of level lip
Elevation at top of bank of the receiving water
Slope (from level lip to to top of bank)
Are any draws present?
Level Spreader Design
Forebay surface area
Feet of level lip needed per cfs
Answer "Y" to one of the following:
Length based on the 1 in/hr storm?
Length based on the 10-yr storm?
Length based on the BMP discharge rate?
Design flow
Is a bypass device provided?
Length of the level lip
Do not complete this section of the worksheet.
ft2 Do not complete this section of the worksheet.
ft2 Do not complete this section of the worksheet.
% Do not complete this section of the worksheet.
Do not complete this section of the worksheet.
cfs Do not complete this section of the worksheet.
min
in/hr Do not complete this section of the worksheet.
cfs Do not complete this section of the worksheet.
(Y or N)
(Y or N)
(Y or N)
y (Y or N) Please complete filter strip characterization below.
36.00 ft
ft
14.00 ft
50.00 ft
427.00 fmsl
423.00 fmsl
8.00 %
N (Y or N)
sq ft
28 ft/cfs
(Y or N)
(Y or N)
Y (Y or N)
0.30 cfs
Y (Y or N)
28.00 ft
Level spreaders must be used in series if vegetation is >50% wooded.
OK
No forebayis needed.
OK
#VALUE!
Form SW401-Level Spreader, Filter Strip, Restored Riparian Buffer-Rev.S Parts I. and H. Design Summary, page 1 of 2
Are level spreaders in series?
Bypass Channel Design (if applicable)
Does the bypass discharge through a wetland?
Does the channel enter the stream at an angle?
Dimensions of the channel (see diagram below):
M
B
W
y
Peak velocity in the channel during the 10-yr storm
Channel lining material

t i---------
M
N (Y or N)
(Y or N)
(Y or N)
ft
ft
ft
ft
cfs

Y
M
n
Form SW401-Level Spreader, Filter Strip, Restored Riparian Buffer-Rev.5 Parts I. and H. Design Summary, page 2 of 2
Type.... Pond E-V-Q Table
Name.... WET POND
File.... K:\08\08-0130\080134-Tryon VIllage Page 5.01

Townhomes\H-H\Wet Pond.ppw

I LEVEL POOL ROUTING DATA
HYG Dir = K:\08\08-0130\080134-Tryon VIllage Townhomes\H-H\
Inflow HYG file = work_pad.hyg - WET POND IN 10
Outflow HYG file = work_pad.hyg - WET POND OUT 10
I Pond Node Data = WET POND
Pond Volume Data = WET POND
Pond Outlet Data = Outlet 1
No Infiltration
I
INITIAL CONDITIONS
-
--
---
-------

-----------

-----
--
-
-
-
Starting WS Elev = 431.00 ft
Starting Volume = .000 ac-ft
Starting Outflow = .00 cfs
Starting Infiltr. _ .00 cfs
Starting Total Qout= .00 cfs
Time Increment = .0500 hrs
Elevation Outflow Storage Area Infilt. Q Total 2S/t + O
ft cfs ac-ft sq.ft cfs
-- cfs
------------- cfs
--------
----------------------
431.00 .00 -----------
.000 -------------
17014 ---------
.00 .00 .00
431.10 .00 .039 17165 .00 .00 18.99
431.20 .03 .079 17317 .00 .03 38.18
I 431.30 .04 .119 17469 .00 .04 57.51
431.40 .05 .159 17622 .00 .05 77.02
431.50 .06 .200 17776 .00 .06 96.69
431.60 .07 .241 17930 .00 .07 116.54
431.70 .08 .282 18085 .00 .08 136.55
431.80 .08 .324 18241 .00 .08 156.74
431.90 .09 .366 18397 .00 .09 177.10
I 432.00 .09 .408 18554 .00 .09 197.63
432.10 .10 .451 18678 .00 .10 218.32
432.20 .10 .494 18802 .00 .10 239.15
432.30 .11 .537 18926 .00 .11 260.11
432.40 .11 .581 19051 .00 .11 281.21
432.50 1.88 .625 19177 .00 1.88 304.23
432.60 5.13 .669 19303 .00 5.13 328.85
432.70 9.32 .713 19429 .00 9.32 354.56
432.80 14.29 .758 19555 .00 14.29 381.18
I 432.90 19.94
I
I
1
1
I
I
I
I .803 19683 .00 19.94 408.63
SIN: DOYXYWH3NLBE Withers & Ravenel
PondPack (10.00.015
I
I .00) 2:03 AM 5/8/2008
Project Name: Tryon Village Townhomes
City/State: Cary, NC
STORMWATER BMP - Wet Detention Pond
Orifice Calculator
Q =Cd*A*(2gh)"(1/2)
Variables
WQ Volume: 0.452 Acre-ft 19689.12 cf
Head: 1.5 ft 0.75 ft
Draw down time: 72 hrs 259200 s
Orifice Area = 0.018217 sq. ft 2.623185 sq. in
Orifice Diameter = 1.827552 in
USE 2 In DIAMETER ORIFICE
Actual Diameter = 0.021817 sq ft
Crest Elevation = 432.40 msl
Orifice Elevation = 427.00 msl
Head = 5.48 ft
Flow = 0.25 cfs
Project #: 2080134
Date: 8-May-08
Constants
9 = 32.2 ft/sz
Cd= 0.6
Velocity Dissipaters
FES 1
FES IA
NRCD Land Quality Section
NYDOT Dissipater Design Results
Pipe diameter (ft) 3
Outlet velocity (fps) 20.61 cfs
Apron length (ft) 36
Apron Width (ft) 17.4 (W = Dia. + 0.4xLength)
AVG DIAM STONE THICKNESS
(inches) CLASS (inches)
3 A 9
6 B 22
13 B or 1 22
» 23 2 27
NRCD Land Quality Section
NYDOT Dissipater Design Results
Pipe diameter (ft) 2.5
Outlet velocity (fps) 9.78
Apron length (ft) 15
Apron Width (ft) 17.5 (W = Dia. + Length)
AVG DIAM STONE THICKNESS
(inches) CLASS (inches)
3 A 9
» 6 B 22
13 B or 1 22
23 2 27