20081015 Ver 1_More Info Received_20080905

51 Kilmayne Drive
Suite 203
Cary, North Carolina 27511
ADVANCED
C I V I L I) 8 S I G N
SEP
GV1
USNR-VI;R QUA RERAN
WE'tiJ?S?pB ANDS 1646'
Mr. Ian McMillan
Division of Water Quality, Stormwater Department
2321 Crabtree Blvd, Suite 250
Raleigh, North Carolina 27604
ph 919.481.6294
fax [phone]
September 4th, 2008
Re: Glencreek Subdivision, Beasley Branch [030402, 27-43-(8), C, NSW]
Dear Mr. McMillan:
The following are responses to the additional information requested on your letter dated
July 7, 2008.
1. Please locate the project on the most recent bound and published Wake county
soil survey and the USGS 1:24,000 topographic map.
SOIL SURVEYPER 1970 BOUND WAKE COUNTY PUBLICATIONAND USGS
1:24, 000 MAPPING ARE LOCATED ON SHEET 1.
2. Please provide cross section details showing the provisions for aquatic life
passage.
A CROSS SECTION DETAIL HAS BEEN ADDED TO SHEET 2 THAT SHO WS
THE CULVERT BURIED I ' BELOW GRADE FOR AQUATIC LIFE PASSAGE.
3. Please provide building envelopes for all lots with wetlands, streams or buffers
(both Zones 1 and 2 should be defined) on the site plans.
ALL PROPOSED BUILDING ENVELOPES HAVE BEEN ADDED TO SHEET 2
AS WELL AS A TABLE OF PROPOSED IMPER VIO US AREA BY LOT.
() $ - IBIS
4. Per the requirements of the Neuse 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 (see littp://h2o.enr.state.nc.us/su/bmp. foims.htm).
PER OUR MEETING ONAUGUST 5TH THE FLOW IN THE CHANNELS IS
MINIMAL AS IS THE AMO UT OF IMPER VIO US AREA WITHIN THE
DRAINAGE AREAS. IT WAS AGREED MEASURES FOR DIFFUSE FLOW ARE
NOT REQ UIRED FOR THE CHANNELS WITH THE EXCEPTION OF THE
CABANA/POOL AREA WHICH NO W HAS A LEVEL SPREADER. PLEASE SEE
SHEET 4 FOR LOCATION OF THE LEVEL SPREADER.
5. Please provide an inventory of imperviousness surfaces in each drainage area. The
inventory should include all proposed building footprints, roads, driveways,
sidewalks, gravel-surfaced areas, amenity areas, etc.
A TABLE HAS BEEN ADDED TO SHEET 2 THAT PROVIDES AN INVENTORY
OF IMPER VIO US AREAS, AND A STORMWA TER MANAGEMENT PLAN
REPORT IS ATTACHED. TABLE SHO WN INCL UDES PROPOSED
IMPER VIO US AREAS B UT CO ULD BE INCREASED TO THE ALLO WABLE
PER LOT AREA OF 5950 SF.
6. "Buffer Encroachment" area is a parallel impact and mitigation must be provided
for this apparent Zone 2 impact. However, please explain why this impact cannot
be avoided.
THE ROAD HAS BEEN MOVED OUT OF THE BUFFER AND ONLY 8' OF
GRADING AT A 3:1 IS INSIDE THE ZONE 2 BUFFER, SEE SHEET 3 FOR
THE PLAN VIEW.
7. You have stated that stormwater will be addressed via vegetated roadside ditches.
Please show these ditches on your plans along with their corresponding diffuse
flow measures.
ATTACHED IS THE CONSTR UCTION DRA WINGS PRE VIO USL Y SUBMITTED
TO WAKE COUNTY WHICH SHOWS ALL DITCH AND CHANNEL CAL CS
AND ALL PROPOSED CHANNEL LOCATIONS HAVE BEENPLACED ON
SHEET 2.
If there are further comments please contact me at 460-2020 (direct).
Thank you,
Michael J. K , P.E.
Subject Lcae1 `gypm`'?LS
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ADVANCED
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Sheet No.
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Stormwater Management Plan S/DNo.:
WAKE Date: 7/17/2008
COUNTY
Designer: ACD
SUMMARY INFORMATION
Site Data
Total Area: 137.24 acres
Zoning: R-30
Number of Lots: 84
Percent Impervious: 12.87 %
Volume Management Calculations
Target Curve Number: 66
Proposed Curve Number: 65
Total Volume Required: -19345 ft3
Total Volume Provided: ft3
Nitrogen Calculations
TN Loading from Site: 3.56 Ibs/ac/yr
Buy-down (if in NRB):
Peak Flow Management Calculations:
Pre-Development Peak Flow: N/A cfs
Post-Development Peak Flow: N/A cfs
S E P 5 2008
OENR - WATER QOAU C
V?E1lANDS AND STORM`1t'ATER RRAN{;ii
Wake County Stormwater Tool
Version 2.1 9/4/2008 2:45 PM
Stormwater Management Plan
\/%'AKE
COUN"FY
TARGET CURVE NUMBER CALCULATION
Wake County Target Curve Numbers
S/D No.:
Date: 7/17/2008
Desianer: ACD
Zoning District A B C D
R-80W and R-80 37 60 73 79
R-40W and R-40 41 62 75 80
R-30, R-20, R-15, R-5 43 63 76 81
Site Data:
Total Site Area: 137.24 acres "Excludes Area of Exisitng Lakes or Ponds on site
Existing Lake/Pond Area: acres
Area used for Overall Density Calcs: 137.24 acres
Zoning District: R-30
Soil Composition:
Hydrologic Soil Group Site Area
A
B 117.73
C
D 19.51
Target Curve Number:
Runoff (inches) = Q* =
% Target CN
43
86% 63
76
14% 81
100%
66
0.54 inches
Wake County Stormwater Tool
Version 2.1 9/4/2008 2:45 PM
Stormwater Management Plan S/D No.:
WAKE Date: 7/17/2008
COUNTY
Designer: ACD
POST-DEVELOPMENT CALCULATIONS
CURVE NUMBER:
Is Data from Preliminary Plan Still Valid?
Total Area of Lots:
Number of Lots:
Impervious Area per Lot:
% Impervious on Lots:
% Woods on Lots:
% Impervious in R/W:
Percent Impervious for Site*:
'Using total site area plus existing lakes/ponds
Percent of Total Disconnected Impervious:
Yes
96.64 acres
84,
7000 sf
13.97 %
32.3841 %
40.5941 %
12.87 %
50 % (50% is Default. See Table 3.3)
HSG Land-use CN Area acres %
D Woods (C.O.S. or Off-Lot Buffer) 77 13.35 9.70%
B Woods (C.O.S. or Off-Lot Buffer) 55 3.12 2.27%
D Open Space (Grassed C.O.S 80 3.48 2.53%
B Open Space (Grassed C.O.S 61 12.99 9.44%
B R/W w/Ditch Sections 87 10.56 7.68%
B Impervious (not in R/W or Lots) 98 0.27 0.20%
B Lots 64 93.802 68.18%

Totals: 137.572 100.00%
Post-Development CN = 65
lWarnings/Notes:
Runoff (inches) = Q* = 0.51 inches
Percent woods on lots exceeds allowable. Please show the wooded area to be preserved on the construction drawing.
Total Area does not match the Total Site Area given on Target Worksheetil
Wake County Stormwater Tool
Version 2.1
9/4/2008 2:45 PM

WAKE
COUN FY Stormwater Management Plan S/D No.:
Date: 7/17/2008

Designer: ACD
PRE-DEVELOPMENT CALCULATIONS
CURVE NUMBER:

User Defined
User Defined
User Defined
User Defined
Totals: 137.24
Pre-development CN = 59
Runoff (inches) = Q* = 0.30 inches
TIME OF CONCENTRATION:

Sheet Flow: 100 Woods 0.17
Sheet Flow:
Shallow Flow:
Shallow Flow:

Channel Flow:
Channel Flow: 5178 0.01 0.015 16.0 22.0 0.18
Pre-development Tc = 0.47 hrs (Minimum 5minutes)
HSG Land-use CN Area acres
98
D Woods, Good Cond. 77 14.66 10.68%
B Woods, Good Cond. 55 102.43 74.64%
B Pasture or Open Space, Good Cond. 61 16.67 12.15%
D Pasture or Open Space, Good Cond. 80 3.48 2.54%
98
98
98
98
98
98
98

1 00 .00%

Length (ft)
Slope (ft/ft)
n-value Flow
Area (ft)
Wetted Perimeter (ft)
Tt (hrs)
2405 0.025 0.03 7.9 10.9 0.11

Length (ft) Slope (ft/ft) Surface Cover Tt (hrs)
0.11

230 0.109 Unpaved 0.01

Wake County Stormwater Tool
Version 2.1 9/4/2008 2:45 PM

"AKE
COUNTY Stormwater Management Plan S/D No.:
Date: 7/17/2008

Designer: ACD
POST-DEVELOPMENT CALCULATIONS
TIME OF CONCENTRATION:

Sheet Flow: 55 0.073 Woods 0.12
Sheet Flow:
Shallow Flow: 410 0.088 Unpaved 0.02
Shallow Flow:

(ft) Wetted Perimeter (ft) Tt (hrs)
Flow:
E
Channel Flow: 51
78 0
.01 22.0
0 1
5
1
6.0
-o. 0.18
Post-
development T
? = (Minimum 5mi
nutes)
0.
43
hrs
Notes:
Proposed Tc is shorter than Pre-development. Increasing proposed Tc will lower peak flow

Length (ft)
Slope (ft/ft)
n-value Flow
Area (ft)
2405 0.025 0.03 7.9 10.9 0.11

Length (ft) Slope (ft/ft) Surface Cover Tt (h rs)

Wake County Stormwater Tool
Version 2.1 9/4/2008 2:45 PM
NOW Stormwater Management Plan S/D No.:
WAKE Date: 7/17/2008
COUNTY
Designer: ACD
I PEAK FLOW CALCULATIONS I
CURVE NUMBER:
Pre-development CN = 59
Post-Development CNadj = 65
TIME OF CONCENTRATION:
Pre-development T, = 0.47 hrs
Post-development T, = 0.43 hrs
PEAK FLOW:
Method: TR-55 Graphical Peak Discharge Method for Tvoe II Distribution
Qp = quAmQ*
Where:
QP = Peak Discharge (cfs)
q„ = Unit peak discharge (csm/in) TR-55 Appendix F
Am = Drainage Area (Mi2)
Q* = runoff (inches)
Pre-development
q„ = 302.50 csm/in
Am = 0.21 mil
Q* = 0.30 inches
Q1-year = N/A cfs
Post-development
q„ = 440.32 csm/in
Am = 0.21 mil
Q* = 0.51 inches
Q1-year = N/A cfs
Wake County Stormwater Tool
Version 2.0 9/4/2008 2:45 PM
Stormwater Management Plan S/D No.:
WAKE Date: 7/17/2008
COUNTY
Designer: ACD
PROPOSED STORAGE DEVICES
Enter only runoff volume below that will be infiltrated or drawn down over 2 to 5 days. Additional
volume provided in devices should not be entered in this worksheet.
Storage Volume
Name/Location Type of Device Provided (ft) Additional Comments
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Total Volume Provided: ft
Volume Required by Wake
County Ordinance: -19345 ft3
Minimum Volume Required to Meet Peak
Flows for Neuse Rules: ft3
Total Volume Required: -19345 ft
Post-Development Curve Number Adjustment based on Volume Provided
Source: "Modeling Infiltration Practices Using TR-20", October, 1983, Maryland Department of the Environment
200
CNadj _
2
1i2
)
(P+2Q+2) - (5PQ+4Q
Where:
P = Rainfall (inches) = 3 inches
Q = Runoff Depth for Proposed CN (Q*) - Volume Provided (inches)
Volume Provided (Inches) = inches
Q* = 0.51 inches
Q = 0.51 inches
Post-Development CNadj = 65
Wake County Stormwater Tool
Version 2.1 9/4/2008 2:45 PM
Stormwater Management Plan SID No.:
YVAKE Date: 7/17/2008
COUNTY
Designer: ACD
NITROGEN CALCULATIONS
TN export TN export
coefficient from use
Type of Land Cover Area (acres) (Ibs/ac/yr) (Ibs/ r
Permanently protected undisturbed open
space (forest, unmown meadow 46.85 0.60 28.11
Permanently protected managed open
space (grass, landscaping, etc. 73.07 1.20 87.68
Impervious surfaces (roads, parking lots,
driveways, roofs, etc.) 17.66 21.20 374.37
TOTAL 137.57 490.16
Nitrogen Loading w/out BMP Reductions: 3.56 Ibs/ac/yr
Neuse Buy-down w/out BMP Reductions:
Nitrogen Loading with BMP Reductions
See Wake County Stormwater Design Manual Chapter 4 for Details
IDrainaae Area 1:

Type of Land Cover
Area (acres) TN coeff.
(Ibs/ac/yr) TN export
Ibs/ r
Permanently protected open space 0.60
Managed open space 1.20
Impervious surfaces 21.20
TOTAL
Nitrogen Removal Efficiency of BMP(s) %
Nitrogen Loading for DA 1: Ibs/ac/yr
IDrainaae Area 2:

Type of Land Cover
Area (acres) TN coeff.
(Ibs/ac/yr) TN export
Ibs/ r
Permanently protected open space 0.60
Managed open space 1.20
Impervious surfaces 21.20
TOTAL
Nitrogen Removal Efficiency of BMP(s) %
Nitrogen Loading for DA 2: Ibs/ac/yr
IDrainaae Area 3:

Type of Land Cover
Area (acres) TN coeff.
(Ibs/ac/yr) TN export
Ibs/ r
Permanently protected open space 0.60
Managed open space 1.20
Impervious surfaces 21.20
TOTAL
Nitrogen Removal Efficiency of BMP(s) %
Nitrogen Loading for DA 3: Ibs/ac/yr
Final Nitrogen Loading from Site: 3.56 Ibs/ac/yr
Buy-down (Neuse Only):
Wake County Stormwater Tool
Version 2.1 9/4/2008 2:45 PM